Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics.

Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics of alpha, beta, and gamma radiation. • To be able to balance a nuclear reaction • To be able to interpret a radioactive decay series • To know the differences between ionizing and nonionizing radiation and their effects on matter • To be able to identify natural and artificial sources of radiation • To be able to calculate a mass-energy balance and a nuclear binding energy • To understand the differences between nuclear fission and fusion • To understand how nuclear reactors operate • To understand how nuclear transmutation reactions led to the formation of the elements in the stars and how they can be used to synthesize transuranium elements

Guiding Questions Is radiation dangerous?
Is nuclear power a good choice? What is nuclear energy? Are nuclear energy and nuclear bombs both dangerous? More Specifically...: Give a brief history of radioactivity Define nuclear chemistry State that energy can be converted into matter List factors that determine stability of a nucleus Balance nuclear equations Distinguish between various forms of radiation in terms of penetration depth and energy Determine the half-life of a radioactive substance. Define nuclear fusion and fission Describe a chain reaction List applications of radioisotopes

The Power of the Nucleus
Nuclear Energy Adapted from Chemcases.com Energy and Matter: Nuclear science began with Albert Einstein who recognized that matter and energy were equivalent. We have all heard the equation: E=mc2 This was Einstein's understanding at the beginning of the last century. Energy - the ability to provide heat or do work, had an equivalency with matter - the mass of the physical universe. The relationship was astonishing in that the amount of energy equivalent to a given amount of matter was related by the square of the speed of light. The equation predicted that IF matter could be converted to energy in a practical manner, a very small amount of matter would generate enormous amounts of energy. How many grams of matter does it take to produce enough energy to light a 100 W light bulb for 1 year? The amount of energy that would take is: 3.15 x 107 Joules. Using E=mc2, find the mass needed to give 3.15 x 107 Joules. The speed of light is 3.0 x 108 m/s. Did you get a very small number? One neutron weighs, x g, how many neutrons would that be? Let’s do the reverse calculation, if you have 1 gram of sugar, how many 100 W light bulbs could you light for one year? Find amount of energy using E= mc2 Divide by 3.15 x 107 Joules Converting small amounts of matter to energy could provide huge sources of energy, but is it possible? All year we have talked about chemical reactions that would either give off energy or absorb energy, in all cases matter was conserved and energy was conserved. (Remember, the mass on both sides of a chemical equation must be equal). Also, in all the reactions we’ve studied so far, electrons move from atom to atom but the nucleus (protons and nucleus) stays put. Soon after the discovery of the neutron by James Chadwick in 1932, scientists began to use neutrons as chemical bullets - firing them at atoms of other elements. When neutrons are fired at Uranium, an unusual thing happened that was named nuclear fission: U neutron  other elements + 3 neutrons + energy (a neutron can be written using isotope notation as well: 1n0 where 1 is the mass and zero gives the number of protons and electrons) U n0  other elements + 3 n0 + energy Careful observation of the products - a mixture of smaller atoms and neutrons, showed that the mass of the products was LESS than the mass of the reactants! Einstein's proposal that mass and energy are convertible was confirmed. The loss of mass in the products resulted in the production of energy - energy that perhaps was useful. Nuclear Energy for Power and Weapons: The energy released by fission excited the European scientists who discovered the phenomenon. And it troubled others who recognized from the simple equation, above, that a powerful and rapid conversion of matter to energy could result from the fission phenomenon. Look at the equation. Every neutron produces about 3 neutrons by reaction with U-235 in addition to the energy. If those 3 neutrons go on to cause 3 more U-235 to split which then produces energy and 9 more neutrons which go on to cause 9 more U-235 to split producing more energy and 27 more neutrons …. Theoretically, this could be a huge source of energy. U n0n0n0n0n0n0n0n0n0n0n0n0n0U U U n0U neutronUranium atomChain Reaction A controllable chain reaction was first demonstrated in 1942 at the University of Chicago by the Italian scientist, Enrico Fermi. The uranium "fuel" was moderated in the chain reaction by neutron absorbers that could be added and removed to make certain the reaction didn't "run away" and release huge amounts of energy from fission caused by too many neutrons. The Hungarian scientist, Leo Szilard, a Hungarian expatriate in the United States, alerted Albert Einstein just prior to World War II that the fission chemistry held the possibility of weapons of mass destruction, far beyond anything imagined before. Under some conditions, the chain reaction might be condensed into a millisecond burst of fission, unleashing enormous energy. Einstein's communications with President Franklin Roosevelt led to the "Manhattan Project" that resulted in the first atomic bombs which were used on Japan in WWII. The science was critical. Only the U-235 is fissionable at the rates necessary for a weapon- the vastly more common U-238 is not. So complicated separation plants were built to make the separation. (In the 21st century, it is the presence of these uranium "gas separation" plants that is one mark of the presence of nuclear capabilities.) What does it mean to be fissionable? Still, U-238 plays a role in the fission process. Although it does not itself fission, the isotope reacts with neutrons and undergoes a series of nuclear transformations that occur rapidly resulting in the production of a new element, plutonium (Pu). In the equations below , ß-1 is an electron, or in the language of the nuclear scientists, a "beta" particle: U-238 + 1n0  U-239 U-239  Np-239 + ß-1 Np-239  Pu-239+ ß-1 The plutonium thus produced, is itself fissionable and the scientists of the Manhattan Project isolated Pu from the neutron bombardment of U-238 and demonstrated it as a source for nuclear weapons. In the decades since World War II, plutonium has been the source for most fissionable nuclear devices. Spent Fuel and Nuclear Weapons: The nations of the world use nuclear power derived from uranium enriched to about 4% U-235 . In the "fuel rods", as the uranium is fissioned and the energy is drawn from the fission reaction, some neutrons react with the bulk of the uranium, the nonfissionable U This process produces a small amount of Pu in the spent fuel rods. These rods, then, become a potential source for scavenging the minute amounts of Pu produced in an attempt to make weapons. Control of spent fuel rods and their safe disposable thus becomes a worldwide concern in the efforts to limit the proliferation of nuclear weapons. Bravo – 15,000 kilotons

Development of the Atom

Nuclear Review Background Nuclear Radiation Fission
Nuclear Power Plants Half-Life Decay Series Fusion

Key Terms alpha decay moderator alpha particles natural radioactivity
artificial transmutation background radiation beta decay beta particle chain reaction control rods critical mass curie disintegrations per second gamma decay Geiger counter half-life ionizing radiation irradiate isotope moderator natural radioactivity nuclear equation nuclear fission nuclear fusion nuclide plasma positrons rad radioisotope rem roentgen tracers transmutation X-rays

Radioactivity Much of our understanding of atomic structure
came from studies of radioactive elements. Radioactivity The process by which atoms spontaneously emit high energy particles or rays from their nucleus. First observed by Henri Becquerel in 1896

History: On The Human Side
Michael Faraday - electrolysis experiments suggested electrical nature of matter Wilhelm Roentgen - discovered X-rays when cathode rays strike anode Henri Becquerel - discovered "uranic rays" and radioactivity Marie (Marya Sklodowska) and Pierre Curie - discovered that radiation is a property of the atom, and not due to chemical reaction. (Marie named this property radiactivity.) Joseph J. Thomson - discovered the electron through Crookes tube experiments Marie and Piere Curie - discovered the radioactive elements polonium and radium Ernest Rutherford - discovered alpha and beta particles Paul Villard - discovered gamma rays Ernest Rutherford and Frederick Soddy - established laws of radioactive decay and transformation Frederick Soddy - proposed the isosope concept to explain the existence of more than one atomic weight of radioelements Ernest Rutherford - used alpha particles to explore gold foil; discovered the nucleus and the proton; proposed the nuclear theory of the atom Ernest Rutherford - announced the first artificial transmutation of atoms James Chadwick - discovered the neutron by alpha particle bombardment of Beryllium Frederick Joliet and Irene Joliet Curie - produced the first artificial radioisotope Otto Hahn, Fritz Strassmann, Lise Meitner, and Otto Frisch - discovered nuclear fission of uranium-235 by neutron bombardment Edwin M McMillan and Philip Abelson - discovered the first transuranium element, neptunium, by neutron irradiation of uranium in a cyclotron Glenn T. Seaborg, Edwin M. McMillan, Joseph W. Kennedy and Arthur C. Wahl - announced discovery of plutonium from beta particle emission of neptunium Enrico Fermi - produced the first nuclear fission chain-reaction Glenn T. Seaborg- proposed a new format for the periodic table to show that a new actinide series of 14 elements would fall below and be analagous to the 14 lanthanide-series elements. Murray Gell-Mann hypothesized that quarks are the fundamental particles that make up all known subatomic particles except leptons.

Lithium Li = 1s22s1 H He Li C N Al Ar F Fe La Energy Level Diagram
6s p d f Bohr Model 5s p d 4s p d Arbitrary Energy Scale 3s p N 2s p 1s Electron Configuration NUCLEUS Li = 1s22s1 H He Li C N Al Ar F Fe La CLICK ON ELEMENT TO FILL IN CHARTS

An Excited Lithium Atom
Excited Li atom Energy Photon of red light emitted Li atom in lower energy state Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326

Waves Low frequency High frequency long wavelength l
Amplitude Low frequency short wavelength l Amplitude High frequency

A Cathode Ray Tube Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58

particles (electrons)
A Cathode Ray Tube Source of Electrical Potential Metal Plate Gas-filled glass tube Metal plate Stream of negative particles (electrons) Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 58 PAPER

Interpreting the Observed Deflections
. gold foil . beam of alpha particles undeflected particles . . deflected particle Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120

Rutherford’s Apparatus
beam of alpha particles radioactive substance MODERN ALCHEMY Ernest Rutherford ( ) was the first person to bombard atoms artificially to produce transmutated elements. The physicist from New Zealand described atoms as having a central nucleus with electrons revolving around it. He showed that radium atoms emitted “rays” and were transformed into radon atoms. Nuclear reactions like this can be regarded as transmutations – one element changing into another, the process alchemists sought in vain to achieve by chemical means. Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 35 fluorescent screen circular - ZnS coated gold foil Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120

Photon In 1905, Einstein postulated that light was made up of particles of discrete energy E = hf He called these particles PHOTONS He also suggested that in the photoelectric effect each single photon gives up all its energy to a single electron He suggested that the electron was ejected immediately Increasing the intensity of the light increases the number of the electrons but not the energy of the electrons

Photoelectric Effect Light photons Electrons ejected from the surface
cathode anode Symbolic representation of a photoelectric cell evacuated glass envelope Light photons Photoelectric Cell Electrons ejected from the surface Sodium metal

When light strikes a metal surface, electrons are ejected.
Photoelectric Effect Light Electron Nucleus Metal When light strikes a metal surface, electrons are ejected.

Photoelectric Effect More Light Electron Electron Nucleus Metal If the threshold frequency has been reached, increasing the intensity only increases the number of the electrons ejected.

Photoelectric Effect Higher frequency light Faster electron Nucleus Metal If the frequency is increased, the ejected electrons will travel faster.

Strong vs. Weak Force Weak force: electrostatic attractions between protons and electrons in atoms e.g. covalent bonding, ionic bonding, hydrogen bonding Strong force: force that holds the nucleus together. i.e. The nucleus contains protons that naturally repel each other. The strong force holds the nucleus together. When the nucleus is split, the energy released is the energy of the strong force. The nucleus of an atom occupies a tiny fraction of the volume of the atom and contains the number of protons and neutrons that is characteristic of a given isotope • Electrostatic repulsions would cause the positively charged protons to repel each other, but the nucleus does not fly apart because of the strong nuclear force, an extremely powerful but very short-range attractive force between nucleons • All stable nuclei except the hydrogen-1 nucleus contain at least one neutron to overcome the electrostatic repulsion between protons

Absorption of Radiation
g Nuclear reactions do not cause chemical reactions directly. The particles and photons emitted during nuclear decay are very energetic, and they can indirectly produce chemical changes in the matter surrounding the nucleus that has decayed. Effects of radiation on matter are determined by the energy of the radiation, which depends on the nuclear decay reaction that produced it. Nonionizing radiation Low in energy; when it collides with an atom in a molecule or ion, most of its energy can be absorbed without causing a structural or chemical change The kinetic energy of the radiation is transferred to the atom or molecule with which it collides, causing it to rotate, vibrate, or move more rapidly This energy can be transferred to adjacent molecules or ions in the form of heat, so many radioactive substances are warm to the touch Ionizing radiation Higher in energy and some of its energy can be transferred to one or more atoms with which it collides as it passes through matter If enough energy is transferred, electrons can be excited to very high energy levels, resulting in the formation of positively charged ions Molecules ionized in this way are highly reactive and can decompose or undergo other chemical changes that create a cascade of reactive molecules that can damage biological tissues and other materials Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 625

Absorption of Radiation
We are continuously exposed to measurable background radiation from a variety of natural sources, which is equal to about 150–600 mrem/yr Cosmic rays, high-energy particles, and  rays emitted by the sun and other stars that bombard Earth continuously Cosmogenic radiation, produced by the interaction of cosmic rays with gases in the upper atmosphere Terrestrial radiation, due to the remnants of radioactive elements that were present on the primordial Earth and their decay products Tissues also absorb radiation (40 mrem/yr) from naturally occurring radioactive elements present in our bodies Radon is the most important source of background radiation The heaviest of the noble gases and tends to accumulate in enclosed spaces Radon exposure can cause lung damage or cancer In addition to naturally occurring background radiation, humans are exposed to small amounts of radiation from a variety of artificial sources X-rays used for diagnostic purposes in medicine and dentistry; X-rays are photons with much lower energy than  rays Television screens and computer monitors with cathode-ray tubes that produce X-rays Luminescent dials Residual fallout from atmospheric nuclear-weapons testing Nuclear power industry A large dose of radiation spread over time is less harmful than the same total amount of radiation administered over a short time • Tissues most affected by large, whole-body exposures are bone marrow, intestinal tissue, hair follicles, and reproductive organs Timberlake, Chemistry 7th Edition, page 84

Typical Radiation Exposure per Person per Year in the United States
Source Radiation atmosphere at sea level* 26 mrem dental X-ray 1 mrem ground 30 mrem chest X-ray 6 mrem foods 20 mrem X-ray of hip 65 mrem air travel above 1,800 m 4 mrem CAT scan 110 mrem construction site 7 mrem nuclear power plant nearby 0.02 mrem X-ray of arm or leg TV and computer use 2 mrem *Add 3 mrem for every 300 m of elevation Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 341

Geiger Counter (-) (+) e- + e- + e- + + e- Ionization of fill gas
takes place along track of radiation (-) Speaker gives “click” for each particle (+) Metal tube (negatively charged) e- + e- Window + e- + + e- Radiation cannot be seen, heard, felt, or smelled. Thus warning signs and radiation detection instruments must be used to alert people to the presence of radiation and to monitor its level. The Geiger counter is one such instrument that is widely used. Other devices used to detect and measure ionizing radiation: scintillation counter, film badge Free e- are attracted to (+) electrode, completing the circuit and generating a current. The Geiger counter then translates the current reading into a measure of radioactivity. Ionizing radiation path Free e- are attracted to (+) electrode, completing the circuit and generating a current. The Geiger counter then translates the current reading into a measure of radioactivity. Atoms or molecules of fill gas Central wire electrode (positively charged) Wilbraham, Staley, Matta, Waterman, Chemistry, 2002, page 857

Geiger-Muller Counter
Radiation cannot be seen, heard, felt, or smelled. Thus warning signs and radiation detection instruments must be used to alert people to the presence of radiation and to monitor its level. The Geiger counter is one such instrument that is widely used. Other devices used to detect and measure ionizing radiation: scintillation counter, film badge Free e- are attracted to (+) electrode, completing the circuit and generating a current. The Geiger counter then translates the current reading into a measure of radioactivity. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 614

Animation by Raymond Chang
Alpha, Beta, Gamma Rays Lead block (+) (-) b rays (negative charge) Aligning slot (no charge) g rays a rays Radioactive substance (positive charge) Three kinds of radiation – α particles, β particles and γ rays 1. Distinguished by the way they are deflected by an electric field and by the degree to which they penetrate matter 2. α particles and β particles are deflected in opposite directions; α particles are deflected to a much lesser extent because of their higher mass-to-charge ratio. 3. γ rays have no charge and are not deflected by electric or magnetic fields. 4. α particles have the least penetrating power, and γ rays are able to penetrate matter readily. Photographic plate Electrically charged plates (detecting screen) Animation by Raymond Chang All rights reserved

Types of Radiation Type Symbol Charge Mass (amu) Alpha particle 2+
Beta particle 1- Positron 1+ Gamma ray Three kinds of radiation – α particles, β particles and γ rays 1. Distinguished by the way they are deflected by an electric field and by the degree to which they penetrate matter 2. α particles and β particles are deflected in opposite directions; α particles are deflected to a much lesser extent because of their higher mass-to-charge ratio. 3. γ rays have no charge and are not deflected by electric or magnetic fields. 4. α particles have the least penetrating power, and γ rays are able to penetrate matter readily.

Characteristics of Some Ionizing Radiation
Characteristics of Some Ionizing Radiations Property Alpha radiation Beta radiation Gamma radiation Composition Alpha particle (helium nucleus) Beta particle (electron) High-energy electromagnetic radiation Symbol a, He-4 b, e g Charge 2+ 1- Mass (amu) 4 1/1837 Common source Radium-226 Carbon-14 Cobalt-60 Approximate energy 5 MeV* 0.05 to 1 MeV 1 MeV Penetrating power Low (0.05 mm body tissue) Moderate (4 mm body tissue) Very high (penetrates body easily) Shielding Paper, clothing Metal foil Lead, concrete (incomplete shields) *(1 MeV = x J)

Nuclear reactions Nuclear equations show how atoms decay.
Similar to chemical equations. - must still balance mass and charge. Differ from chemical equations because Nuclear Chemistry - An Introduction by Anthony Carpi, Ph.D Traditional chemical reactions occur as a result of the interaction between valence electrons around an atom's nucleus. In 1896, Henri Becquerel expanded the field of chemistry to include nuclear changes when he discovered that uranium emitted radiation. Soon after Becquerel's discovery, Marie Sklodowska Curie began studying radioactivity and completed much of the pioneering work on nuclear changes. Curie found that radiation was proportional to the amount of radioactive element present, and she proposed that radiation was a property of atoms (as opposed to a chemical property of a compound). Marie Curie was the first woman to win a Nobel Prize and the first person to win two (the first, shared with her husband Pierre and Becquerel for discovering radioactivity; the second for discovering the radioactive elements radium and polonium). Radiation and Nuclear Reactions In 1902, Frederick Soddy proposed the theory that "radioactivity is the result of a natural change of an isotope of one element into an isotope of a different element." Nuclear reactions involve changes in particles in an atom's nucleus and thus cause a change in the atom itself. All elements heavier than bismuth (Bi) (and some lighter) exhibit natural radioactivity and thus can "decay" into lighter elements. Unlike normal chemical reactions that form molecules, nuclear reactions result in the transmutation of one element into a different isotope or a different element altogether (remember that the number of protons in an atom defines the element, so a change in protons results in a change in the atom). There are three common types of radiation and nuclear changes: Alpha Radiation (α) is the emission of an alpha particle from an atom's nucleus. An α particle contains two protons and two neutrons (and is similar to a He nucleus: ). When an atom emits an a particle, the atom's atomic mass will decrease by four units (because two protons and two neutrons are lost) and the atomic number (Z) will decrease by two units. The element is said to "transmute" into another element that is two Z units smaller. An example of an a transmutation takes place when uranium decays into the element thorium (Th) by emitting an alpha particle, as depicted in the following equation: (Note: in nuclear chemistry, element symbols are traditionally preceded by their atomic weight (upper left) and atomic number (lower left). Beta Radiation (β) is the transmutation of a neutron into a proton and a electron (followed by the emission of the electron from the atom's nucleus: ). When an atom emits a β particle, the atom's mass will not change (since there is no change in the total number of nuclear particles), however the atomic number will increase by one (because the neutron transmutated into an additional proton). An example of this is the decay of the isotope of carbon named carbon-14 into the element nitrogen: Gamma Radiation (γ) involves the emission of electromagnetic energy (similar to light energy) from an atom's nucleus. No particles are emitted during gamma radiation, and thus gamma radiation does not itself cause the transmutation of atoms, however γ radiation is often emitted during, and simultaneous to, α or β radioactive decay. X-rays, emitted during the beta decay of cobalt-60, are a common example of gamma radiation. - we can change the elements. …transmutation - the type of isotope is important.

A patient is given radioactive iodine to test thyroid function.
What happens to the iodine? I 131 53 Xe 54 b- -1 + g Thyroid gland Is this equation balanced? You must see if the mass and charge are the same on both sides. 53 protons protons 78 neutrons neutrons 131 total mass 131 total mass Mass +53, protons , protons -1 charge from b- +53 total charge total charge Charge Yes – it’s balanced

Discovery of the Neutron
+ + Chadwick is credited with the discovery of the neutron as a result of this transmutation experiment. James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted. Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764

New Radioactive Isotope
= neutrons = protons + 4 2 He 10 5 B 13 7 N 1 n bombarding particle stable isotope new radioactive isotope neutron Timberlake, Chemistry 7th Edition, page 92

Alpha Decay radioactive isotope 4 He radiation new isotope U neutron
alpha particle radioactive isotope 4 2 He radiation new isotope 238 92 U Alpha decay Nuclei with mass numbers greater than 200 undergo alpha decay, which results in the emission of a helium-4 nucleus as an  particle, 4 The daughter nuclide contains two fewer protons and two fewer neutrons than the parent, thus -particle emission produces a daughter nucleus with a mass number A that is lower by 4 and a nuclear charge Z that is lower by 2 than the parent nucleus AX A-4X′  parent daughter αparticle neutron proton 234 90 Th Timberlake, Chemistry 7th Edition, page 87

Measuring Circuit in Detection Chamber
Terminal screw Reference chamber Radioactive source Detection chamber cover Control unit or processor Plastic cover Contact Alarm indicator Metal Plates Ionization Chamber Screen Alpha Particles Americium Source + a BATTERY - Measuring Circuit in Detection Chamber material + - High current value Ionized particles Radioactive Clean air Current 1 2 + Low current value Smoke to particles Radioactive 1 2 - material attached Smoke detectors sense the early stages of fire and sound a warning so that the occupants of a building may safely escape. They detect smoke and sometimes heat in a variety of ways, in this case by using a detection chamber filled with ionized air. Rays from a radioactive source ionize the atoms of air in the chamber. The charged particles carry current between the top and bottom plates of the detection chamber, which act as electrodes. Smoke entering the chamber attracts the charged particles so that the amount of current passing between the electrodes is reduced (shown on right). When a drop in current is recorded, a message is sent to the control unit, which activates the alarm. Ionization Smoke Detectors An Ionization Smoke Detector has two key parts: the ionization chamber, and a source of radiation. This source of radiation consists of a very minute concentration of Americium-241, which produce alpha particles. The Ionization Chamber contains two plates: one plate is negatively charged, and the other is positively charged. The alpha particles created by the Americium-241 move at very high speeds and bump into oxygen and nitrogen molecules within the ionization chamber. The force exerted by this collision causes electrons to fall off from each molecule, creating an ion. The now positively charged ions are attracted to the negatively charged plate while the electrons attracted to the positively charged plate. This attraction causes a consistent electrical current within the chamber itself. When smoke travels into the chamber, its particles attach to the ionized molecules to neutralize them and pull them away from the plate. This disrupts the electrical current and triggers the alarm. The ion chamber also contains a small amount of synthetic element, americium This element produces alpha particles. Alpha particles have a positive charge, which attracts electrons from the gases in the air inside the chamber. This causes some gas particles to become ionized, or charged. Ionized air is a good conductor of electricity. The electric circuits apply a voltage between the chamber walls and the metal piece. These circuits constantly measure the current flowing through the air. Smoke particles entering the chamber interact with some of the alpha particles. This interaction reduced the number of ions inside the chamber. With fewer ions, the electric current is reduced. The electronic circuits detect this change in current and sound the alarm. 1. Alpha particles do not last a long time. Why? (Think about what happens when alpha particles attract electrons.) 2. Some elements produce beta particles instead of alpha particles. A beta particle is a high-speed electron. Would a smoke detector work if beta particles replaced alpha particles? Explain. 3. Why is it important to periodically replace smoke detectors? Pg 321 Chemistry by Packard, Jacobs and Marshall Pearson AGS Globe ISBN Copyright 2007

Beta Decay radioactive carbon isotope e radiation new isotope C
beta particle -1 e radiation new isotope 14 6 C Beta decay Nuclei that contain too many neutrons undergo beta decay, in which a neutron is converted to a proton and a high-energy electron that is ejected from the nucleus as a  particle n p β unstable neutron proton retained beta particle emitted in nucleus by nucleus by nucleus Beta decay does not change the mass number of the nucleus but results in an increase of +1 in the atomic number due to the addition of a proton in the daughter nucleus; beta decay decreases the neutron-to-proton ratio, moving the nucleus toward the band of stable nuclei AX A X′ β parent daughter  particle neutron 14 7 N proton Timberlake, Chemistry 7th Edition, page 90

Bombardment of aluminum-27 by alpha particles produces phosphorous-30
and one other particle. Write the nuclear equation and identify the other particle. a 27 Al 4 He 30 P 1 n + + 13 2 15 Plutonium-239 can be produced by bombarding uranium-238 with alpha particles. How many neutrons will be produced as a by product of each reaction. Write the nuclear equation for this reaction. 238 U 4 He 239 Pu 4 ? 1 n + + 92 2 94

Unstable Isotopes + and or Excited nucleus Stable nucleus Energy
Particles Radiation Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 439

Unstable Nucleus Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 620

Fissionable U-235

Fission Process Nucleus Two neutrons Neutron from fission
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 620

Stages of Fission First stage: 1 fission Second stage: 2 fissions Third stage: 4 fissions Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 454

Nuclear Power Plants map: Nuclear Energy Institute

Energy Sources in the United States
100 80 60 40 20 91 1900 21 71 5 3 1980 20 70 10 1990 26 58 16 1940 10 50 40 2005 50 21 26 Percent 9 Source: US Energy Information Administration (2005 Electricity Generation) 49.9% Coal 3.1% Renewable (biomass, geothermal, solar, wind) 6.6% Hydroelectric 2.5% Petroleum 18.8% Natural gas 19.3% Nuclear 1850 Wood Coal Petroleum / natural gas Hydro and nuclear Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 307

Energy Sources in the United States
100 80 60 40 20 91 50 Percent 19 19 9 7 3 3 Source: US Energy Information Administration (2005 Electricity Generation) 49.9% Coal 3.1% Renewable (biomass, geothermal, solar, wind) 6.6% Hydroelectric 2.5% Petroleum 18.8% Natural gas 19.3% Nuclear 1850 2005 Coal Petroleum Nuclear Hydroelectric natural gas Renewable (biomass, geothermal, solar, wind) Source: US Energy Information Administration (2005 Electricity Generation)

Coal Burning Power Plant
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Nuclear Power Plant When a critical mass of a fissile isotope has been achieved, the resulting flux of neutrons can lead to a self-sustaining reaction; a variety of techniques can be used to control the flow of neutrons, which allows nuclear fission reactions to be maintained at safe levels Many levels of control are required, along with a fail-safe design; otherwise, the chain reaction can accelerate so rapidly that it releases enough heat to melt or vaporize the fuel and the container, causing the release of enough radiation to contaminate the surrounding area If the neutron flow in a reactor is carefully regulated so that only enough heat is released to boil water, then the resulting steam can be used to produce electricity Light-water reactors Used to produce electricity Fuel rods containing a fissile isotope in a structurally stabilized form (uranium oxide pellets encased in a corrosion-resistant zirconium alloy) are suspended in a cooling bath that transfers the heat generated by the fission reaction to a secondary cooling system Heat is used to generate steam for the production of electricity Control rods are utilized to absorb neutrons and control the rate of the nuclear chain reaction Pulling the control rods out increases the neutron flow, allowing the reactor to generate more heat; inserting the rods completely stops the reaction Heavy-water reactors Deuterium (2H) absorbs neutrons less effectively than does hydrogen (1H), but it is about twice as effective at scattering neutrons A nuclear reactor that uses D2O instead of H2O as the moderator is so efficient that it can use unenriched uranium as fuel, which reduces the operating costs and eliminates the need for plants that produce enriched uranium Breeder reactors A nuclear fission reactor that produces more fissionable fuel than it consumes; the fuel produced is not the same as the fuel consumed Overall reaction is the conversion of nonfissile 238U to fissile 239Pu, which can be isolated chemically and used to fuel a new reactor Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 621

Reactor Core Hot coolant Control rods of neutron-absorbing substance
Uranium in fuel cylinders Incoming coolant Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 622

Nuclear Power Plant Production of heat Production of electricity
Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.

Chant of the Radioactive Workers
We're not afraid of the alpha ray. A sheet of paper will keep it away! A beta ray needs much more care, Place sheets of metal here and there. And as for the powerful gamma ray (Pay careful heed to what we say) Unless you wish to spend weeks in bed Take cover behind thick slabs of lead! Fast neutrons pass through everything. Wax slabs remove their nasty sting. These slow them down, and even a moron Knows they can be absorbed by boron. Remember, remember all that we've said, Because it's no use remembering when you're dead.

Inside a nuclear power plant.

Nuclear Waste Disposal
Shaft Repository Waste package Surface deposits Nuclear Waste Disposal River Aquifier Interbed rock layer Host rock formation Waste form Interbed rock layer Aquifier Bedrock Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 626

Half-Life 20 g 10 g 5 g 2.5 g after 1 half-life after 2 half-lives
Start Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 757

Half-Life g I Xe b- 1.00 mg 0.875 mg 0.500 mg 0.750 mg Xe 0.500 mg I I
b emissions g emissions 89.9% 7.3% 131 53 I 54 Xe Xe* Half-Life 1.00 mg 0.875 mg 0.500 mg 0.750 mg 131 54 Xe 131 53 0.500 mg I 131 53 I 0.250 mg 0.125 mg 8.02 days 16.04 days 24.06 days 0.00 days I 131 53 Xe 54 b- -1 + g Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 757

Half-life of Radiation
Initial amount of radioisotope Number of half-lives Radioisotope remaining (%) 100 50 25 12.5 After 1 half-life After 2 half-lives After 3 half-lives t1/2 t1/2 t1/2

Half-Life Plot Half-life of iodine-131 is 8 days
20 Half-life of iodine-131 is 8 days 15 1 half-life Amount of Iodine-131 (g) 10 16 2 half-lives 5 24 3 half-lives 32 4 half-lives etc… 40 48 56 8 Time (days) Timberlake, Chemistry 7th Edition, page 104

Half-Life of Isotopes Half-Life and Radiation of Some Naturally Occurring Radioisotopes Isotope Half-Live Radiation emitted Carbon-14 5.73 x 103 years b Potassium-40 1.25 x 109 years b, g Radon-222 3.8 days a Radium-226 1.6 x 103 years a, g Thorium-230 7.54 x 104 years a, g Thorium-234 24.1 days b, g Uranium-235 7.0 x 108 years a, g Uranium-238 4.46 x 109 years a

Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. 1/2 1/4 1/8 1/16 1/1 1/2 1/4 1/8 1/16 Ratio of Remaining Potassium-40 Atoms to Original Potassium-40 Atoms 1 half-life 1.3 2 half-lives 2.6 3 half-lives 3.9 4 half-lives 5.2 Time (billions of years) Newly formed rock Potassium Argon Calcium

Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. 1/1 Newly formed rock Potassium Argon Calcium Ratio of Remaining Potassium-40 Atoms to Original Potassium-40 Atoms 1/2 1/4 1/8 1/16 1 half-life 1.3 2 half-lives 2.6 3 half-lives 3.9 4 half-lives 5.2 Time (billions of years)

How Much Remains? After one half-life, of the original atoms remain.
1 2 After two half-lives, ½ x ½ = 1/(22) = of the original atoms remain. 1 4 After three half-life, ½ x ½ x ½ = 1/(23) = of the original atoms remain. 1 8 After four half-life, ½ x ½ x ½ x ½ = 1/(24) = of the original atoms remain. 1 16 After five half-life, ½ x ½ x ½ x ½ x ½ = 1/(25) = of the original atoms remain. 1 32 After six half-life, ½ x ½ x ½ x ½ x ½ x ½ = 1/(26) = of the original atoms remain. 1 64 Accumulating “daughter” isotopes 1 2 1 4 Surviving “parent” isotopes 1 8 1 16 1 32 1 64 1 128 Beginning 1 half-life 2 half-lives 3 half-lives 4 half-lives 5 half-lives 6 half-lives 7 half-lives

2. The burning creates carbon dioxide gas comprised of carbon-12
1. A small piece of fossil is burned in a special furnace. 2. The burning creates carbon dioxide gas comprised of carbon-12 isotopes and carbon-14 isotopes. Stable C-12 isotope Nitrogen Decaying C-14 isotope 3. As the carbon- 14 decays into nitrogen-14, it emits an electron. Electron All organisms absorb, use and accumulate the element carbon during life. There are several types or isotopes, depending upon the number of neutrons in the carbon atom. It is the difference in the behavior of these isotopes that permits researchers to estimate age. While alive, organisms accumulate both carbon-12 and carbon-14 isotopes at a steady ratio of about 12 trillion C-12 isotopes to each C-14 isotope. Carbon-12 is a stable isotope. It doesn't change or decay. A fossil or piece of parchment contains as much C-12 as the original living dinosaur or goat. In contrast, C-14 is radioactive. It is always in a process of decay, with a half-life of 5,730 years. That means that after 5,730 years, only half of the original C-14 in an organic sample will remain, the rest having decayed into another element, specifically nitrogen-14. By measuring the ratio of C-12 to remaining C-14 atoms in a sample and comparing it to the known rate of C-14 decay, researchers can estimate the age of almost any organic object. 4. A radiation counter records the number of electrons emitted. Note: Not to scale. SOURCE: Collaboration for NDT Education MATT PERRY / Union-Tribune

The iodine-131 nuclide has a half-life of 8 days
The iodine-131 nuclide has a half-life of 8 days. If you originally have a 625-g sample, after 2 months you will have approximately? 40 g 20 g 10 g 5 g less than 1 g Data Table: Half-life Decay ~ Amount Time # Half-Life 625 g 312 g 156 g 78 g 39 g 20 g 10 g 5 g 2.5 g 1.25 g 0 d 8 d 16 d 24 d 32 d 40 d 48 d 56 d 64 d 72 d 1 2 3 4 5 6 7 8 9 N = No(1/2)n N = amount remaining No = original amount n = # of half-lives N = (625 g)(1/2)7.5 Assume 30 days = 1 month N = g 60 days = 7.5 half-lives 8 days

N ln = - k t No 0.693 ln 2 t1/2 = k 0.693 k 1.5 g k = 1.209 x 10-4
Given that the half-life of carbon-14 is 5730 years, consider a sample of fossilized wood that, when alive, would have contained 24 g of carbon-14. It now contains 1.5 g of carbon-14. How old is the sample? Data Table: Half-life Decay ln = - k t N No Amount Time # Half-Life 24 g 12 g 6 g 3 g 1.5 g 0 y 5,730 y 11,460 y 17,190 y 22,920 y 1 2 3 4 0.693 ln 2 t1/2 = k 0.693 Petrified wood is a type of fossil: it exists of fossil wood where all the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. 5730 y = k ln = - (1.209x10-4) t 1.5 g 24 g k = x 10-4 t = 22,933 years

Half-Life Practice Calculations
The half-life of carbon-14 is 5730 years. If a sample originally contained 3.36 g of C-14, how much is present after 22,920 years? Gold-191 has a half-life of 12.4 hours. After one day and 13.2 hours, 10.6 g of gold-19 remains in a sample. How much gold-191 was originally present in the sample? There are 3.29 g of iodine-126 remaining in a sample originally containing 26.3 g of iodine The half-life of iodine-126 is 13 days. How old is the sample? A sample that originally contained 2.5 g of rubidium-87 now contains 1.25 g. The half-life of rubidium-87 is 6 x 1010 years. How old is the sample? Is this possible? Why or why not? 0.21 g C-14 84.8 g Au-191 39 days old 6 x 1010 years (60,000,000,000 billions years old) What is the age of Earth??? Demo: Try to cut a string in half seven times (if it begins your arm’s length).

3.36 g of C-14, how much is present after 22,920 years?
The half-life of carbon-14 is 5730 years. If a sample originally contained 3.36 g of C-14, how much is present after 22,920 years? Data Table: Half-life Decay t1/2 = years Amount Time # Half-Life 3.36 g 1.68 g 0.84 g 0.42 g 0.21 g 0 y 5,730 y 11,460 y 17,190 y 22,920 y 1 2 3 4 22,920 years n = 5,730 years n = 4 half-lives Australian scientists have found a new species of hobbit-sized humans who lived about 18,000 years ago on an Indonesian island. The discovery adds another piece to the complex puzzle of human evolution. The partial skeleton of Homo floresiensis, found in a cave on the island of Flores, is of an adult female that was a meter tall, had a chimpanzee-sized brain and was substantially different from modern humans. It shared the isolated island to the east of Java with miniature elephants and Komodo dragons. The hominins walked upright and probably evolved into their dwarf size because of environmental conditions and coexisted with modern humans in the region for thousands of years. (# of half-lives)(half-life) = age of sample (4 half-lives)(5730 years) = age of sample 22,920 years

Uranium Radioactive Decay
238 4.5 x 109 y 24 d 1.2 m 2.5 x 105 y 8.0 x 104 y 1600 y 3.8 d 3.0 m 27 m 160 ms 5.0 d 138 d stable U-238 Th-234 a 234 Pa-234 b U-234 b Th-230 a 230 Ra-226 a 226 Rn-222 a 222 Mass number Po-218 a 218 Pb-214 a Impossible for any nuclide with Z > 85 to decay to a stable daughter nuclide in a single step, except via nuclear fission • Radioactive isotopes with Z > 85 usually decay to a daughter nucleus that is radioactive, which in turn decays to a second radioactive daughter nucleus, and so forth, until a stable nucleus finally results • This series of sequential alpha- and beta-decay reactions is called a radioactive decay series Some nuclei spontaneously transform into nuclei with a different number of protons, producing a different element These naturally occurring radioactive isotopes decay by emitting subatomic particles Should be possible to carry out the reverse reaction, converting a stable nucleus to another more massive nucleus by bombarding it with subatomic particles in a nuclear transmutation reaction Po-214 b 214 Bi-214 b Pb-210 a Bi-210 b Po-210 b 210 Pb-206 a 206 81 82 83 84 85 86 87 88 89 90 91 92 Atomic number

140 130 120 110 100 90 80 70 60 50 40 30 20 10 Nuclear Stability Decay will occur in such a way as to return a nucleus to the band (line) of stability. Neutrons (N) As the number of protons in the nucleus increases, the number of neutrons needed for a stable nucleus increases even more rapidly; too many protons (or too few neutrons) in the nucleus result in an imbalance between forces, which leads to nuclear instability Relationship between the numbers of protons and neutrons in stable nuclei is shown in the following figure The stable isotopes form a “peninsula of stability” in a “sea of instability” Only three stable isotopes, 1H, 3He, and 4He, have a neutron-to-proton ratio less than or equal to 1; all other stable nuclei have a higher neutron-to-proton ratio, which increases steadily to about 1.5 for the heaviest nuclei All elements with Z > 83 are unstable and radioactive More than half of the stable nuclei have even numbers of both neutrons and protons; only 6 of the 279 stable nuclei do not have odd numbers of both • Certain numbers of neutrons or protons result in especially stable nuclei; these are the so-called magic numbers 2, 8, 20, 50, 82, and 126 • Nuclei with magic numbers of both protons and neutrons are said to be “doubly magic” and are even more stable In addition to the “peninsula of stability,” the preceding figure shows a small “island of stability” that exists in the upper right corner • The island corresponds to the superheavy elements, with atomic numbers near the magic number of 126, and may be stable enough to exist in nature Protons (Z)

All elements with Z > 83 are unstable and radioactive
As the number of protons in the nucleus increases, the number of neutrons needed for a stable nucleus increases even more rapidly; too many protons (or too few neutrons) in the nucleus result in an imbalance between forces, which leads to nuclear instability Relationship between the numbers of protons and neutrons in stable nuclei is shown in the following figure The stable isotopes form a “peninsula of stability” in a “sea of instability” Only three stable isotopes, 1H, 3He, and 4He, have a neutron-to-proton ratio less than or equal to 1; all other stable nuclei have a higher neutron-to-proton ratio, which increases steadily to about 1.5 for the heaviest nuclei All elements with Z > 83 are unstable and radioactive More than half of the stable nuclei have even numbers of both neutrons and protons; only 6 of the 279 stable nuclei do not have odd numbers of both • Certain numbers of neutrons or protons result in especially stable nuclei; these are the so-called magic numbers 2, 8, 20, 50, 82, and 126 • Nuclei with magic numbers of both protons and neutrons are said to be “doubly magic” and are even more stable In addition to the “peninsula of stability,” the preceding figure shows a small “island of stability” that exists in the upper right corner • The island corresponds to the superheavy elements, with atomic numbers near the magic number of 126, and may be stable enough to exist in nature Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Band of Stability n = p Number of neutrons Number of protons 160 150
140 130 120 110 100 90 80 70 60 50 40 30 20 10 Band of Stability n = p Number of neutrons The band of black squares, which shows the stable nuclides, is known as the band of stability. In general, the further a nuclide is from the band of stability, the shorter the half-life of the nuclide. No stable isotopes are known for elements with atomic numbers higher than 83 (bismuth). Stable nuclides Naturally occurring radioactive nuclides Other known nuclides Number of protons

positron emission and/or
140 209 83 Bi a decay 130 120 184 74 W 110 100 90 b decay 80 107 47 Ag Neutrons (N) 70 60 50 56 26 Fe 40 30 positron emission and/or electron capture 20 20 10 Ne 10 10 20 30 40 50 60 70 80 90 Protons (Z)

positron emission and/or
140 209 83 Bi a decay Nuclear Stability 130 120 184 74 W 110 100 90 Decay will occur in such a way as to return a nucleus to the band (line) of stability. b decay 80 107 47 Ag Neutrons (N) 70 60 50 56 26 Fe 40 30 positron emission and/or electron capture 20 20 10 Ne 10 10 20 30 40 50 60 70 80 90 Protons (Z)

Half-Lives of Some Isotopes of Carbon
Nuclide Half-Life Carbon s Carbon s Carbon m Carbon Stable Carbon Stable Carbon y Carbon s Carbon s Isotopes of oxygen can be represented in any of these ways: A X: O O O Z AX: O O O Element-A: Oxygen Oxygen Oxygen-18 • Isotopes of naturally occurring elements on Earth are present in nearly fixed proportions with each proportion constituting an isotope’s natural abundance Any nucleus that is unstable and decays spontaneously is said to be radioactive, emitting subatomic particles and electromagnetic radiation • The emissions are collectively called radioactivity and can be measured • Isotopes that emit radiation are called radioisotopes • The rate at which radioactive decay occurs is characteristic of the isotope and is reported as a half-life (t½), the amount of time required for half the initial number of nuclei present to decay in a first-order reaction

Enlargement of part of band of stability around Neon
moves into band of stability by beta decay. moves into band of stability by positron emission. Electron capture would also move into the band of stability. Umland and Bellama, General Chemistry 2nd Edition, page 773

Effects of Radioactive Emissions on Proton and Neutrons
Loss of Loss of Number of protons Chemistry: The Central Science, Eighth Edition by Brown, LeMay, Bursten Figure 21.3 T-193 Two general kinds of nuclear reactions 1. Nuclear decay reaction (or radioactive decay) An unstable nucleus emits radiation and is transformed into the nucleus of one or more other elements Resulting daughter nuclei have a lower mass and are lower in energy (more stable) than the parent nucleus that decayed Occur spontaneously under all conditions 2. Nuclear transmutation reaction A nucleus reacts with a subatomic particle or another nucleus to form a product nucleus that is more massive than the starting material Occur spontaneously only under special conditions Each of the three general classes of radioactive nuclei is characterized by a different decay process or set of processes Neutron-rich nuclei Have too many neutrons and have a neutron-to-proton ratio that is too high to give a stable nucleus These nuclei decay by a process that converts a neutron to a proton, thereby decreasing the neutron-to-proton ratio Neutron-poor nuclei Have too few neutrons and have a neutron-to-proton ratio that is too low to give a stable nucleus These nuclei decay by processes that convert a proton to a neutron, thereby increasing the neutron-to-proton ratio 3. Heavy nuclei Heavy nuclei (with A  200) are intrinsically unstable, regardless of the neutron-to-proton ratio All nuclei with Z > 83 are unstable Decay by emitting an  particle, which decreases the number of protons and neutrons in the original nucleus by 2 Since the neutron-to-proton ratio in an  particle is 1, the net result of alpha emission is an increase in the neutron-to-proton ratio Loss of or electron capture Number of protons

Nuclear Decay “absorption”, “bombardment” vs. “production”, “emission”
223 4 a 2+ 219 2 Ra + Rn H 3 4 + H He + 1 n 88 2 86 1 1 2 4 2+ a 14 17 1 + N O + H 2 H + 2 H 4 He 2 7 8 1 1 1 2 87 b 87 Rb + Sr 14 17 37 -1 38 C b + N 6 -1 7 Can use the number and type of nucleons present to write a balanced equation for a nuclear decay reaction Procedure allows us to predict the identity of either the parent or daughter nucleus if the identity of only one is known Regardless of the mode of decay, the total number of nucleons is conserved in all nuclear reactions, as is the total positive charge • To describe nuclear decay reactions, the AX notation for nuclides has been extended to include radioactive emissions The following table lists the name and symbol for each type of emitted radiation The left superscript in the symbol for a particle gives the mass number, which is the total number of protons and neutrons For a proton or a neutron, A = 1 Because neither an electron nor a positron contains protons or neutrons, its mass number is 0 The left subscript gives the charge of the particle Protons carry a positive charge, so Z = +1 for a proton A neutron contains no protons and is electrically neutral, so Z = 0 For an electron, Z = –1, and for a positron, Z = +1 Because  rays are high-energy photons, both A and Z are 0 In some cases, two different symbols are used for particles that are identical but produced in different ways Symbol 0e, simplified to e– represents a free electron or an electron associated with an atom Symbol 0, simplified to – denotes an electron that originates from within the nucleus, which is a  particle 4He refers to the nucleus of a helium atom, and 4 is an identical particle ejected from a heavier nucleus There are six fundamentally different kinds of nuclear decay reactions, each of which releases a different kind of particle or energy (see table) Alpha Beta Positron Gamma neutron proton 4 a 2+ b b g 2 -1 +1 1 1 n H 1+ 1

Units Used in Measurement of Radioactivity
Units Measurements Curie (C) radioactive decay Becquerel (Bq) radioactive decay Roentgens (R) exposure to ionizing radiation 1.  radiation Reacts strongly with matter because of its high charge and mass Does not penetrate deeply into an object and can be stopped by clothing or skin Alpha particles most damaging if their source is inside the body because their energy is absorbed by internal tissues 2.  radiation  rays, with no charge and no mass, do not interact strongly with matter and penetrate deeply into most objects, including the human body Lead or concrete needed to completely stop  rays The most dangerous type when they come from a source outside the body 3.  radiation Intermediate in mass and charge between  particles and  rays, so interaction with matter is intermediate Beta particles penetrate paper or skin but can be stopped by wood or a thin sheet of metal There are many ways to measure radiation exposure, or the dose The roentgen (R) is used to measure the amount of energy absorbed by dry air and is used to describe exposure quantitatively Damage to biological tissues is proportional to the amount of energy absorbed by tissues, not air The most common unit to measure the effects of radiation on biological tissue is the rad (radiation absorbed dose); S unit is the gray (Gy) Rad is defined as the amount of radiation that causes 0.01 J of energy to be absorbed by 1 kg of matter, and the gray is defined as the amount of radiation that causes 1 J of energy to be absorbed per kilogram 1 rad = J/kg Gy = 1J/kg The amount of tissue damage caused by 1 rad of  particles is much greater than the damage caused by 1 rad of  particles or  rays because  particles have higher masses and charge A unit called the rem (roentgen equivalent in man) describes the actual amount of tissue damage caused by a given amount of radiation The number of rems of radiation is equal to the number of rads multiplied by the RBE (relative biological effectiveness) factor, which is 1 for  particles,  rays, and X-rays, and 20 for  particles Most measurements are reported in millirems Rad (rad) energy absorption caused by ionizing radiation Rem (rem) biological effect of the absorbed dose in humans

Effects of Instantaneous Whole-Body Radiation Doses on People
Dose, Sv (rem) Effect >10 (1000) Death within 24 h from destruction of the neurological system. Alexander Litvinenko 7.5 (750) Death within 4-30 d from gastrointestinal bleeding. 1.5 – 7.5 (150 – 750) Intensive hospital care required for survival. At the higher end of range, death through infection resulting from destruction of white-blood cell-forming organs usually takes place 4 – 8 weeks after accident. Those surviving this period usually recover. < 0.5 (50) Only proven effect is decrease in white blood cell count. The effects of ionizing radiation depend on four factors The type of radiation, which dictates how far it can penetrate into matter The energy of the individual particles or photons The number of particles or photons that strike a given area per unit time The chemical nature of the substance exposed to the radiation The relative abilities of the various forms of ionizing radiation to penetrate tissues are: The dose of ionizing radiation is the quantity of ionizing radiation absorbed by a unit mass of matter. Dose is measured in grays or rads. The gray, Gy, is the SI unit of radiation dose and is defined as joules of energy absorbed per kilogram of target material: 1 Gy = 1 J/kg The traditional unit for radiation dosage is the rad (radiation absorbed dose); 1Gy = 100 rad. A dose in terms of absorbed energy is not enough. Different kinds and energies of radiation affect tissues differently. Before doses can be compared, they must be multiplied by a quality factor, Q. The quality factor is sometimes referred to as the relative biological effectiveness or RBE value. Q-Values for Various Kinds of Radiation Radiation Q (RBE) X-rays, beta, gamma 1 Slow neutrons 3 Fast neutrons 10 Alpha The traditional unit that takes the type of radiation into account is called the rem (roentgen equivalent man): Rem = rad x RBE

The intensity of radiation is proportional to 1/d2, where d is the distance from the source.

Alpha, Beta, Positron Emission
Examples of Nuclear Decay Processes a emission (alpha) b- emission (beta) b+ emission (positron) Positron emission A positron has the same mass as an electron but opposite charge Positron emission is the opposite of beta decay and is characteristic of neutron-poor nuclei which decay by the transformation of a proton to a neutron and a high-energy positron that is emitted 1p  1n  Positron emission does not change the mass number of the nucleus, however the atomic number of the daughter nucleus is lower by 1 than that of the parent. The neutron-to-proton ratio increases, moving nucleus closer to the band of stable nuclei AX  A X′  parent daughter positron Electron capture A neutron-poor nucleus can decay by either positron emission or electron capture (EC), in which an electron in an inner shell reacts with a proton to produce a neutron p e  1 n When a second electron moves from an outer shell to take the place of the lower-energy electron that was absorbed by the nucleus, an X-ray is emitted. The overall reaction for electron capture is AX e  A X’ X-ray parent electron daughter The mass number does not change, but the atomic number of the daughter nucleus is lower by 1 than that of the parent; neutron-to-proton ratio increases, moving the nucleus toward the band of stable nuclei Gamma emission Many nuclear decay reactions produce daughter nuclei that are in a nuclear excited state A nucleus in an excited state releases energy in the form of a photon when it returns to the ground state These high-energy photons are  rays Gamma emission can occur instantaneously or after a significant delay General formula AX*  AX  Because  rays are energy, their emission does not affect either the mass number or the atomic number of the daughter nuclide; gamma-ray emission is the only kind of radiation that does not involve the conversion of one element to another but is observed in conjunction with some other nuclear decay reaction Spontaneous fission Only very massive nuclei with high neutron-to-proton ratios can undergo spontaneous fission, in which the nucleus breaks into two pieces that have different atomic numbers and atomic masses Process most important for trans-actinide elements with Z  104 Spontaneous fission is accompanied by the release of large amounts of energy and is accompanied by the emission of several neutrons The number of nucleons is conserved; the sum of the mass numbers of the products equals the mass number of the reactant; the sum of the atomic numbers of the products is the same as the atomic number of the parent nuclide Although beta emission involves electrons, those electrons come from the nucleus. Within the nucleus, a neutron decays into a proton and an electron. The electron is emitted, leaving behind a proton to replace the neutron, thus transforming the element. (A neutrino is also produced and emitted in the process.) Herron, Frank, Sarquis, Sarquis, Schrader, Kulka, Chemistry, Heath Publishing,1996, page 275

Nuclear Reactions First recognized natural transmutation of an element (Rutherford and Soddy, 1902) First artificial transmutation of an element (Rutherford, 1919) ? Discovery of the neutron (Chadwick, 1932) ? Discovery of nuclear fission (Otto Hahn and Fritz Strassman, 1939) Bailar, Chemistry, pg 361

Preparation of Transuranium Elements
Atomic Number Year Discovered Name Symbol Reaction Neptunium Np Plutonium Pu Americium Am Curium Cm Berkelium Bk Californium Cf Ralph A. Burns, Fundamentals of Chemistry 1999, page 553

Additional Transuranium Elements
99 Einsteinium Es 100 Fermium Fm 101 Mendelevium Md 102 Nobelium Nb 103 Lawrencium Lr 104 Rutherfordium Rf 105 Dubnium Db 106 Seaborgium Sg 107 Bohrium Bh 108 Hassium Hs Meitnerium Mt Darmstadtium Ds Unununium Uun 1994 Ununbium Uub 1996 114 Uuq (Russia) (Russia)

CHAPTER 22 Nuclear Chemistry
I. The Nucleus (p ) II III IV Courtesy Christy Johannesson

Nuclear Binding Energy
10x108 9x108 Fe-56 He-4 U-238 8x108 7x108 B-10 Binding energy per nucleon (kJ/mol) 6x108 5x108 Li-6 4x108 3x108 2x108 H-2 1x108 20 40 60 80 100 120 140 160 180 200 220 240 Mass number Unstable nuclides are radioactive and undergo radioactive decay.

Average binding energy per nucleon (MeV) Unstable nuclides are radioactive and undergo radioactive decay.

II. Radioactive Decay (p ) I II III IV Courtesy Christy Johannesson

Types of Radiation Alpha particle () helium nucleus 2+
paper Beta particle (-) electron 1- lead Positron (+) positron 1+ concrete Gamma () high-energy photon Courtesy Christy Johannesson

Nuclear Decay Numbers must balance!! Alpha Emission parent nuclide
daughter nuclide alpha particle Numbers must balance!! Courtesy Christy Johannesson

Nuclear Decay Beta Emission electron Positron Emission positron
Courtesy Christy Johannesson

Nuclear Decay Electron Capture electron Gamma Emission
Usually follows other types of decay. Transmutation One element becomes another. Courtesy Christy Johannesson

Nuclear Decay Why nuclides decay…
need stable ratio of neutrons to protons 120 100 80 60 40 20 Neutrons (A-Z) Protons (Z) P = N b stable nuclei a e-capture or e+ emission Courtesy Christy Johannesson DECAY SERIES TRANSPARENCY

Nuclear Decay Why nuclides decay… b a
need stable ratio of neutrons to protons stable nuclei P = N b stable nuclei a P = N 120 120 e-capture or e+ emission 100 100 80 80 60 60 Neutrons (A-Z) Neutrons (A-Z) 40 40 20 20 20 40 60 80 100 120 20 40 60 80 100 120 Protons (Z) Protons (Z)

Time (billions of years)
Half-life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. 1/1 Newly formed rock Potassium Argon Calcium Ratio of Remaining Potassium-40 Atoms to Original Potassium-40 Atoms 1/2 1/4 1/8 1/16 1 half-life 1.3 2 half-lives 2.6 3 half-lives 3.9 4 half-lives 5.2 Time (billions of years)

Half-life mf: final mass mi: initial mass n: # of half-lives

Half-life GIVEN: WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g
Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = g Courtesy Christy Johannesson

III. Fission & Fusion (p ) II III IV Courtesy Christy Johannesson

F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal Courtesy Christy Johannesson

F ission chain reaction - self-propagating reaction
critical mass - mass required to sustain a chain reaction Courtesy Christy Johannesson

Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal occurs naturally in stars Courtesy Christy Johannesson

Fission vs. Fusion FISSION FUSION 235U is limited danger of meltdown
Courtesy Christy Johannesson FISSION FUSION Nuclear fission The splitting of a heavy nucleus into two lighter ones Nucleus usually divides asymmetrically rather than into equal parts, and the fission of a given nuclide does not give the same products every time In a typical nuclear fission reaction, more than one neutron is released by each dividing nucleus; when these neutrons collide with and induce fission in other neighboring nuclei, a self-sustaining series of nuclear fission reactions known as a nuclear chain reaction can result Each series of events is called a generation The minimum mass capable of supporting sustained fission is called the critical mass If the mass of the fissile isotope is greater than the critical mass, then under the right conditions, the resulting supercritical mass can release energy explosively • Nuclear fusion Two light nuclei combine to produce a heavier, more stable nucleus and is the opposite of a nuclear fission reaction The positive charge on both nuclei results in a large electrostatic energy barrier to fusion; barrier can be overcome if one or both particles have sufficient kinetic energy to overcome the electrostatic repulsions, allowing the two nuclei to approach close enough for a fusion reaction to occur 235U is limited danger of meltdown toxic waste thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable

IV. Applications (p ) II III IV Courtesy Christy Johannesson

Nuclear Power Fission Reactors Cooling Tower

Nuclear Power Fission Reactors

Nuclear Power Fusion Reactors (not yet sustainable) ITER TOROIDAL
(International Thermonuclear Experimental Reactor) TOROIDAL FIELD COILS (produces the magnetic field which confines the plasma) BLANKET (provides neutron shielding and converts fusion energy into hot, high pressure fluid) FUSION PLASMA CHAMBER (where the fusion reactions occur) Height 100 feet Diameter 100 feet Fusion power 1100 Megawatts Courtesy Christy Johannesson

Nuclear Power Fusion Reactors (not yet sustainable)
National Spherical Torus Experiment A Tokamak Fusion Test Reactor (TFTR) was constructed at MIT and Princeton University. These reactors use a doughnut-shaped magnetic field to confine the plasma so it does not come in contact with any material. A temperature of 410 million oC has been attained at the Princeton reactor but for only a few seconds. -Fundamentals of Chemistry (3rd edition) by Ralph Burns pg 572 Tokamak Fusion Test Reactor Princeton University Courtesy Christy Johannesson

Synthetic Elements Transuranium Elements
elements with atomic #s above 92 synthetically produced in nuclear reactors and accelerators most decay very rapidly Courtesy Christy Johannesson

Natural and artificial radioactivity
Natural radioactivity Isotopes that have been here since the earth formed. Example - Uranium Produced by cosmic rays from the sun. Example – carbon-14 Man-made Radioisotopes Made in nuclear reactors when we split atoms (fission). Produced using cyclotrons, linear accelerators,…

Positive particle source Alternating voltage Particle beam Vacuum
Target Uranium (Z = 92) is the heaviest naturally occurring element; all the elements with Z > 92, the transuranium elements, are artificial and have been prepared by bombardment of suitable target nuclei with smaller particles • Bombarding the target with more massive nuclei creates elements that have atomic numbers greater than that of the target nucleus • Accelerating positively charged particles to the speeds needed to overcome the electrostatic repulsions between them and the target nuclei requires a device called a particle accelerator, which uses electrical and magnetic fields to accelerate the particles Types of particle accelerators The linear accelerator is the simplest particle accelerator in which a beam of particles is injected at one end of a long evacuated tube; rapid alternation of the polarity of the electrodes along the tube causes the particles to be alternately accelerated toward a region of opposite charge and repelled by a region with the same charge, resulting in a tremendous acceleration as the particle travels down the tube. A cyclotron achieves the same outcome in less space and forces the charged particles to travel in a circular path; particles are injected into the center of a ring and accelerated by rapidly alternating the polarity of two large D-shaped electrodes above and below the ring, which accelerates the particles outward along a spiral path toward the target. The synchrotron is a hybrid of the previous two designs and contains an evacuated tube similar to that of the linear accelerator, but the tube is circular and can be more than a mile in diameter; charged particles are accelerated around the circle by a series of magnets whose polarities rapidly alternate. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Radioactive Dating half-life measurements of radioactive elements are used to determine the age of an object decay rate indicates amount of radioactive material EX: 14C - up to 40,000 years 238U and 40K - over 300,000 years Courtesy Christy Johannesson

Radiation treatment using
Nuclear Medicine Radioisotope Tracers absorbed by specific organs and used to diagnose diseases Radiation Treatment larger doses are used to kill cancerous cells in targeted organs internal or external radiation source Radiation treatment using -rays from cobalt-60. Radiation is destructive to rapidly dividing cells such as tumor cells and bacteria, so it has been used medically to treat cancer; many radioisotopes are available for medical use, and each has specific advantages for certain applications Radiation therapy Radiation is delivered by a source planted inside the body, or in some cases, physicians take advantage of the body’s own chemistry to deliver a radioisotope to the desired location In cases where a tumor is surgically inaccessible, an external radiation source is used to aim a tightly focused beam of  rays at it Medical imaging A radioisotope is temporarily localized in a particular tissue or organ where its emissions provide a map of the tissue or organ Positron emission tomography (PET) is an imaging technique that produces remarkably detailed three-dimensional images; biological molecules that have been tagged with a positron-emitting isotope can be used to probe the functions of organs Ionizing radiation is used in the irradiation of food to kill bacteria Courtesy Christy Johannesson

Nuclear Weapons Atomic Bomb chemical explosion is used to form a critical mass of 235U or 239Pu fission develops into an uncontrolled chain reaction Hydrogen Bomb chemical explosion  fission  fusion fusion increases the fission rate more powerful than the atomic bomb Courtesy Christy Johannesson

Others Food Irradiation  radiation is used to kill bacteria
Radioactive Tracers explore chemical pathways trace water flow study plant growth, photosynthesis Consumer Products ionizing smoke detectors - 241Am Courtesy Christy Johannesson

Simplified diagram of fission bomb
Chemical Explosive A conventional explosive is used to drive two sections of U-235 together. This creates a supercritical mass. Subcritical masses Critical mass

All the elements originally present on Earth were synthesized from hydrogen and helium nuclei in the interiors of the stars that have long since exploded and disappeared • Six of the most abundant elements in the universe (carbon, oxygen, neon, magnesium, silicon, and iron) have nuclei that are integral multiples of the helium-4 nucleus, which suggests that helium-4 is the primary building block for heavier nuclei Elements are synthesized in discrete stages during the lifetime of a star, and some steps occur only in the most massive stars known All stars are formed by the aggregation of interstellar dust, which is mostly hydrogen As the cloud of dust slowly contracts due to gravitational attraction, its density reaches 100g/cm3 and the temperature increases to 1.5 x 107 K, forming a dense plasma of ionized hydrogen nuclei Self-sustaining nuclear reactions begin and the star ignites, creating a yellow star In the first stages of life, the star is powered by a series of nuclear fusion reactions that convert hydrogen to helium Overall reaction is the conversion of four hydrogen nuclei to a helium-4 nucleus, accompanied by the release of two positrons, two  rays, and a great deal of energy When large amounts of helium-4 have been formed, they become concentrated in the core of the star, which slowly becomes denser and hotter At a temperature of 2 x 108 K, the helium-4 nuclei begin to fuse, producing beryllium-8, which is unstable and decomposes in 10–16 s, long enough for it to react with a third helium-4 nucleus to form the stable carbon-12 Sequential reactions of carbon-12 with helium-4 produce the elements with even numbers of protons and neutrons up to magnesium-24 So much energy is released by these reactions that it causes the surrounding mass of hydrogen to expand, producing a red giant that is 100 times larger than the original yellow star As the star expands, the heavier nuclei accumulate in its core, which contracts to a density of 50,000 g/cm3 and becomes hotter At a temperature of 7 x 108 K, carbon and oxygen nuclei undergo nuclear fusion reactions to produce sodium and silicon nuclei At these temperatures, carbon-12 reacts with helium-4 to initiate a series of reactions that produce more oxygen-16, neon-20, magnesium-24, and silicon-28, as well as heavier nuclides such as sulfur-32, argon-36, and calcium-40 Energy released by these reactions causes a further expansion of the star to form a red supergiant Core temperature increases steadily, at a temperature of 3 x 109 K, the nuclei that have been formed exchange protons and neutrons freely This equilibration process forms heavier elements up to iron-56 and nickel-58, which have the most stable nuclei known All naturally occurring elements heavier than nickel are formed in the rare but spectacular cataclysmic explosions called supernovas Fuel in the core of a massive star is consumed, so its gravity causes it to collapse in about 1 s As the core is compressed, the iron and nickel nuclei within it disintegrate to protons and neutrons, and many of the protons capture electrons to form neutrons The resulting neutron star is so dense that atoms no longer exist The energy released by the collapse of the core causes the supernova to explode in a violent event Force of the explosion blows the star’s matter into space, creating a gigantic and rapidly expanding dust cloud called a nebula The concentration of neutrons is so great that multiple neutron-capture events occur, leading to the production of the heaviest elements and many of the less-stable nuclides Force of the explosion distributes these elements throughout the galaxy surrounding the supernova and are eventually captured in the dust that condenses to form new stars

Nuclear Fusion + + + Sun Energy Four hydrogen nuclei (protons)
Two beta particles (electrons) One helium nucleus

Conservation of Mass …mass is converted into energy
Hydrogen (H2) H = amu Helium (He) He = amu FUSION 2 H  He ENERGY 1.008 amu x 4 amu = amu amu This relationship was discovered by Albert Einstein E = mc2 Energy= (mass) (speed of light)2

Nuclear Fusion Nuclear Fusion (Positron)

Cold Fusion Fraud? Experiments must be repeatable to be valid
Stanley Pons and Martin Fleischman

Tokamak Reactor Fusion reactor 10,000,000 o Celsius
Russian for torroidial (doughnut shaped) ring Magnetic field contains plasma central solenoid magnet Poloidall field magnet The giant donut-shaped Tokamak Fusion Test Reactor at Princeton University is a 50-foot-high, 40-foot-diameter facility that uses a magnetic field to confine a hot ionized gas (a plasma). The reactor achieved a temperature of 410 million oC and generated a record of 9 MW (9 million watts) in 1994. This record is impressive, but the reactor delivered less energy than it consumed, and it can operate only a few seconds at a time. Commercial fusion power is estimated to be ~40 years away! The Princeton Tokamak reactor was shut down in 1997 after Congress, under strong pressure to balance the federal budget and seeing no immediate need for fusion energy, cut 1996 funding by 35%. Torroidal field magnet

Fission vs. Fusion Different Alike Different Topic Topic Fusion
Change Nucleus of Atoms Split large atoms U-235 Fuse small atoms 2H2 He Topic Topic Radioactive waste (long half-life) Create Large Amounts of Energy E = mc2 NO Radioactive waste Fusion Fission Nuclear Power Plants Transmutation of Elements Occurs Very High Temperatures ~5,000,000 oC (SUN)

Atomic Structure ATOMS IONS ISOTOPES Differ by number of protons
Differ by number of electrons ISOTOPES Differ by number of neutrons carbon vs. oxygen 6 protons protons C C C4- 6 e e e- 6 p p p+ Most of the known elements have at least one isotope whose atomic nucleus is stable indefinitely A great majority of elements also have isotopes that are unstable and disintegrate, or decay, at measurable rates by emitting radiation Some elements have no stable isotopes and eventually decay to other elements The process of nuclear decay is a nuclear reaction that results in changes inside the atomic nucleus Each element can be represented by the notation Z X A is the mass number, the sum of the numbers of protons and neutrons Z is the atomic number, the number of protons The protons and neutrons that make up the nucleus of an atom are called nucleons An atom with a particular number of protons and neutrons is called a nuclide Nuclides that have the same number of protons but different numbers of neutrons are called isotopes The number of neutrons is equal to A – Z C vs. C-14 6 e e- 6 p p+ 6 n n0

Mass Defect Difference between the mass of an atom and the mass of its individual particles. amu amu Courtesy Christy Johannesson

Energy released when a nucleus is formed from nucleons. High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s) Courtesy Christy Johannesson

10x108 9x108 Fe-56 He-4 U-238 8x108 7x108 B-10 Binding energy per nucleon (kJ/mol) 6x108 5x108 Li-6 4x108 3x108 2x108 H-2 1x108 20 40 60 80 100 120 140 160 180 200 220 240 Mass number Unstable nuclides are radioactive and undergo radioactive decay.

Mass Defect and Nuclear Stability
2 protons: (2 x amu) = amu 2 neutrons: (2 x amu) = amu 2 electrons: (2 x amu) = amu Total combined mass: amu = amu The atomic mass of He atom is amu. This is amu less than the combined mass. This difference between the mass of an atom and the sum of the masses of its protons, neurons, and electrons is called the mass defect.

What causes the loss in mass? According to Einstein’s equation E = mc2 Convert mass defect to energy units amu x kg 1 amu = x kg The energy equivalent can now be calculated Nuclear reactions are accompanied by changes in energy Energy changes in nuclear reactions are enormous compared with those of even the most energetic chemical reactions Energy changes in a typical nuclear reaction are so large that they result in a measurable change of mass Nuclear reactions are accompanied by large changes in energy, which result in detectable changes in mass. The relationship between mass, m, and energy, E, is expressed in the equation E = mc2, where c is the speed of light (2.998 x 108 m/s), and energy and mass are expressed in units of joules and kilograms, respectively. Every mass has an associated energy, and any reaction that involves a change in energy must be accompanied by a change in mass. Large changes in energy in nuclear reactions are reported in units of keV or MeV; a change in energy that accompanies a nuclear reaction can be calculated from the change in mass (1 amu = 931 MeV). Chemical reactions are accompanied by changes in mass, but these changes are too small to be detected E = m c2 E = ( x kg) (3.00 x 108 m/s)2 E = (4.54 x kg m2/s2) = 4.54 x J This is the NUCLEAR BINDING ENERGY, the energy released when a nucleus is formed from nucleons.

Binding Energy per Nucleon
mass number (# of protons + neutrons) 1) Calculate mass defect 7 Li protons: amu neutrons: amu 3 atomic number (# of protons) electrons: amu Li - 7 2) Convert amu kg 1 amu ________ amu x kg = _______ kg The mass of an atom is always less than the sum of the masses of its component particles; the only exception is hydrogen-1. The difference between the sum of the masses of the components and the measured atomic mass is called the mass defect of the nucleus. The amount of energy released when a nucleus forms from its component nucleons is the nuclear binding energy. The magnitude of the mass defect is proportional to the nuclear binding energy, so both values indicate the stability of the nucleus. Not all nuclei are equally stable; the relative stability of different nuclei are described by comparing the binding energy per nucleon, which is obtained by dividing the nuclear binding energy by the mass number A of the nucleus. The binding energy per nucleon increases rapidly with increasing atomic number until Z = 26, where it levels off and then decreases slowly. 3) E = mc2 speed of light (c) x108 m/s 4) Divide binding energy by number of nucleons

The Energy of Fusion The fusion reaction releases an enormous amount of energy relative to the mass of the nuclei that are joined in the reaction. Such an enormous amount of energy is released because some of the mass of the original nuclei is converted to energy. The amount of energy that is released by this conversion can be calculated using Einstein's relativity equation E = mc2. Suppose that, at some point in the future, controlled nuclear fusion becomes possible. You are a scientist experimenting with fusion and you want to determine the energy yield in joules produced by the fusion of one mole of deuterium (H-2) with one mole of tritium (H-3), as shown in the following equation:

amu amu amu amu amu amu amu amu First, you must calculate the mass that is "lost" in the fusion reaction. The atomic masses of the reactants and products are as follows: deuterium ( amu), tritium ( amu), helium-4 ( amu), and a neutron ( amu). Mass defect: - amu

According to Einstein’s equation E = mc2
Mass defect = amu According to Einstein’s equation E = mc2 Convert mass defect to energy units amu x kg 1 amu = x kg The energy equivalent can now be calculated E = m c2 E = ( x kg) (3.00 x 108 m/s)2 E = (2.81 x kg m2/s2) = 2.81 x J This is the NUCLEAR BINDING ENERGY, for the formation of a single Helium atom from a deuterium and tritium atom.

Therefore, one mole of helium formed by the fusion of one mole of deuterium
and one mole of hydrogen would be 6.02 x 1023 times greater energy. 2.81 x J x 6.02 x 1023 1.69 x J of energy released per mole of helium formed 1,690,000,000,000 J The combustion of one mole of propane (C3H8), which has a mass of 44 g, releases x 106 J. How does this compare to the energy released by the fusion of deuterium and tritium, which you calculated? C3H8 + O H2O + CO x 106 J (unbalanced) 44 g 4 g He 1,690,000,000,000 J Fusion produces ~1,000,000 x more energy/mole 44 g C3H8 2,043,000 J

Lise Meitner and Otto Hahn
Meitner, Lise Image: AUSTRIAN PHYSICIST 1878–1968 On any list of scientists who should have won a Nobel Prize but did not, Lise Meitner's name would be near the top. She was the physicist who first realized that the atomic nucleus could be split to form pairs of other atomic nuclei—the process of nuclear fission. Although she received many honors for her work, the greatest of all was to elude her because of the unprofessional conduct of her colleague Otto Hahn. Born in Vienna, Meitner decided early on that she had a passion for physics. At that time, education for female children in the Austro-Hungarian Empire terminated at fourteen, as it was argued that girls did not need any more education than that to become a proper wife and mother. Willing to support his daughter's aspirations, her father paid for private tutoring so she could cover in two years the eight years of education normally needed for university entrance. In 1901 Meitner was one of only four women admitted to the University of Vienna, and in 1905 she graduated with a Ph.D. in physics. As a student, Meitner had become fascinated with the new science of radioactivity, but she realized that she would have to travel to a foreign country to pursue her dream of working in this field. She applied for work with Marie Curie, but was rejected. However, she did eventually receive an offer from the University of Berlin, which had just hired a young scientist by Austrian physicist Lise Meitner standing with Otto Hahn (l.). Meitner discovered nuclear fission, but was never honored as such. the name of Otto Hahn. Having a chemical background, Hahn was looking for a collaborator with a theoretical physics background. Unfortunately, the chemistry institute at the university was run by Emil Fischer who had banned women from the institute's premises. Reluctantly, Fischer agreed to let Meitner work in a small basement room. During this time, she received no salary and relied on her family for enough money to cover her living expenses. Meitner and Hahn's research during this time period resulted in the discovery of the element protactinium. The post–World War I government in Germany was much more favorable to women, and Meitner became the first woman to serve as a physics professor in that country. By the 1930s scientists were bombarding heavy elements with neutrons and it was claimed that new superheavy elements formed as a result of this process. Using such a procedure, Meitner and Hahn thought they had discovered nine new elements. Meitner was puzzled by all the new elements for which claims were made. Unfortunately, the Nazi Party's rise to power changed everything for Meitner. Because she was a Jew by birth, although a later convert to Christianity, Meitner's situation became increasingly precarious. With help from a Dutch scientist, Dirk Coster, she escaped across the German border into Holland and then made her way to Stockholm, where the director of the Nobel Institute for Experimental Physics reluctantly offered her a position. Stockholm had one advantage for Meitner, an overnight mail service to Germany so she could keep in regular contact with Hahn. On December 19, 1938, Hahn sent Meitner a letter describing how one of the new elements had chemical properties strongly resembling those of barium and asking if she could provide an explanation. The physicist Otto Frisch visited Meitner, his aunt, for Christmas to help dispel her loneliness. While there, the two went for the now famous "walk in the snow." During an extended conversation in the woods, they came to realize that if the nucleus was considered a liquid drop, the impact of a subatomic particle could cause the atom to fission. If so, it was possible that the barium-like element was actually barium itself. Meitner immediately contacted Hahn and his colleague Fritz Strassmann. Through experiment they confirmed that the so-called new element was indeed barium. They reported their discovery of nuclear fission to the world's scientific press, barely mentioning the names of Meitner and Frisch. In fact, Hahn never admitted that it was Meitner who had made the critical conceptual breakthrough. In 1944 Hahn was awarded the Nobel Prize in chemistry for his contribution to the discovery of nuclear fission. Although nominated several times, Meitner never did receive the Nobel Prize for physics that many scientists considered her due. Only now, with element 109 having been named Meitnerium (symbol Mt) has she finally received some recognition for her crucial work. Meitner retired to England where she died at the age of eighty-nine. Source:

Atoms for Peace Eisenhower Food irradiation Cancer treatment
Show nuclear science is not evil Has good uses, too. Food irradiation Cancer treatment PET & CAT scan Destroy ANTHRAX bacteria Bombing of Japan in WW II Radiation is destructive to rapidly dividing cells such as tumor cells and bacteria, so it has been used medically to treat cancer; many radioisotopes are available for medical use, and each has specific advantages for certain applications Radiation therapy Radiation is delivered by a source planted inside the body, or in some cases, physicians take advantage of the body’s own chemistry to deliver a radioisotope to the desired location In cases where a tumor is surgically inaccessible, an external radiation source is used to aim a tightly focused beam of  rays at it Medical imaging A radioisotope is temporarily localized in a particular tissue or organ where its emissions provide a map of the tissue or organ Positron emission tomography (PET) is an imaging technique that produces remarkably detailed three-dimensional images; biological molecules that have been tagged with a positron-emitting isotope can be used to probe the functions of organs Ionizing radiation is used in the irradiation of food to kill bacteria • In addition to the medical uses of radioisotopes, radioisotopes have hundreds of other uses: smoke alarms, dentistry, detectors, and gauges

X-rays Chest X-ray showing scoliosis corrected with steel rod

Radioisotopes Radioactive isotopes Many uses Medical diagnostics
Optimal composition of fertilizers Abrasion studies in engines and tires Radioisotope is injected into the bloodstream to observe circulation.

Isotopes of Three Common Elements
Symbol Fractional Abundance Average Atomic Mass Carbon Chlorine Silicon Si 28 29 30 27.977 28.976 29.974 92.21% 4.70% 3.09% Mass Number Mass (amu) 12 6 C 12 12 (exactly) 99.89% 12.01 13 6 C 13.003 1.11% 13 35 17 Cl 35 34.969 75.53% 35.45 37 17 Cl 37 36.966 24.47% 28 14 29 14 28.09 30 14 LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 110

Radioactivity and Nuclear Energy Practice Quiz
1. Which of the following is not an example of spontaneous radioactive process? alpha-decay beta-decay positron production autoionization electron capture 2. If a nucleus captures an electron, describe how the atomic number will change. It will increase by one It will decrease by one It will not change because the electron has such a small mass It will increase by two It will decrease by two mass number 14 N + b 14 C 7 -1 6 atomic number

Radioactivity and Nuclear Energy
Polonium is a naturally radioactive element decaying with the loss of an alpha particle 210 4 Po He ? What is the second product of this decay? 84 2 Rn-214 Pb-206 At-206 Hg-208 none of these 210 Po a Rn 4 214 alpha absorption 84 2 86 210 Po a Pb 4 206 alpha emission 84 2 82 4. Thorium-234 undergoes beta particle production. What is the other product? Pa Ac Th none of these 234 91 89 233 90 234 Th b Pa 234 90 -1 91

The element curium (Z = 242, A = 96) can be produced by positive-ion bombardment when an alpha particle collides with which of the following nuclei? Recall that a neutron is also a product of this bombardment. 249 Cf Pu Am U 98 241 94 239 4 a 2+ 242 1 Pu + Cm + n 241 94 2 96 95 239 92 239 94 When N is bombarded by (and absorbs) a proton, a new nuclide is produced plus an alpha particle. The nuclide produced is ______? 14 7 14 1 11 4 N + p C-11 C + a 7 1 6 2

When the uranium-235 nucleus is struck with a neutron, the cesium-144 and strontium-90 nuclei are produced with some neutrons and electrons. a) How many neutrons are produced? b) How many electrons are produced? 2 3 4 5 6 1 2 3 4 5 235 U n Cs Sr n b 1 144 90 1 92 55 38 -1 When the palladium-106 nucleus is struck with an alpha particle, a proton is produced along with a new element. What is the new element? cadmium-112 cadmium-109 silver-108 silver-109 none of these 106 Pd a p Ag 4 1 109 46 2 1 47

Strontium-90 from radioactive fallout is a health threat because, like _________, it is incorporated into bone. iodine cesium iron calcium uranium Strontium (Sr) and calcium (Ca) are alkaline earth metals. Strontium is chemically more reactive than calcium. 10. Nuclear fusion uses heavy nuclides such as U as fuel. True / False 235 92 FALSE, Nuclear fission splits heavy nuclides such as U-235 for fuel in nuclear reactors. Nuclear fusion joins light nuclides such as H-1 into He-4 (on the Sun).

Textbook Problems Modern Chemistry
Chapter 22 Pg 704 #1-4 Section Review Pg 712 #1-5 Section Review Pg 715 #1-4 Pg 719 #1-4 End of Chapter #25-47 (pg ) The mass of a Ne-20 atom is amu. Calculate its mass defect. The mass of Li-7 is amu. Calculate the nuclear binding energy of one lithium-6 atom. The measured atomic mass of lithium-6 is amu. Teacher Notes: Lesson Planning Day 1) Video “Back to Chernobyl Day 2) Complete video (~10 minutes) and show National Geographic issue of Chernobyl Show website on Nuclear Chemistry and give background information about radiation Day 3) Show website and links – Begin PowerPoint of nuclear history Day 4) PowerPoint all day – emphasis on nuclear fission vs. nuclear fusion Day 5) PowerPoint on half-life concept Day 6) Assign textbook problems (give all day to work in class) Day 7) Nuclear Equations practice and additional time to complete textbook questions Day 8) Look at old author made test and practice together in class. End PowerPoint with bombing in WW II and Atoms for Peace program Pass out vocabulary Day 9) Quiz – vocabulary, binding energy, half-life, nuclear equations

Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics.

Similar presentations

Presentation on theme: "Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics.

Similar presentations

Presentation on theme: "Nuclear Objectives: • To understand the factors that affect nuclear stability • To know the different kinds of radioactive decay • Give characteristics."— Presentation transcript:

Similar presentations

About project

Feedback