2 Remember the easy stuff!! nucleusElectronsWe don’t care about the electrons right now…
3 What particles make up the nucleus? Both protons and neutrons are called NUCLEONSprotonsneutrons
4 238U 92 Recall some stuff about the nucleus: Mass number Notation: elementAtomic numberIsotopes: nuclei with the same number of protons, but not necessarily the same number of neutrons
5 IsotopesIsotopes have the same number of protons, different number of neutronsAnother way to show an isotope is to have the mass number follow the name of the element (Carbon-14)
6 (c) number of electrons in orbit around the nucleus. 12C and 13C differ in their(a) number of neutrons.(b) number of protons.(c) number of electrons in orbit around the nucleus.(d) chemical behavior.(e) all of the above.
7 What is the charge on a proton? The neutron? What is the nature of the force between the nucleons?How does the nucleus hold itself together??!!
8 The Nucleus is a delicate balance between  The attractive nuclear strong force between all of the nucleons, and The repulsive electromagnetic force between all of the protons
9 It turns out that our delicate balance of forces tends to break down when nuclei get large: The electromagnetic forces eventually overcome the nuclear ones and the nucleus spontaneously breaks apart
10 This “instability” is called radioactivity: All nuclei having atomic number larger than 83 (bismuth) are radioactive.
11 RadioactivityRadioactivity is the process in which an unstable atomic nucleus emits charged particles and energyAny atom containing an unstable nucleus is called a radioactive isotope or radioisotope for short
12 As more protons are added (the nucleus gets heavier) the proton-proton repulsion gets larger. The heavier the nucleus, the more neutrons are required for stability.The belt of stability deviates from a 1:1 neutron to proton ratio for high atomic mass.
13 Ratio of neutrons to protons in nucleus determines if nuclei are stable Too many neutronsToo few neutronsnuclei with >than 83 protons all unstable
14 Radioactive decay is how nuclei get to belt of stability
15 sometimes an unstable nucleus goes through a series of nuclear reactions before it gains stability. This sequence is called aradioactive series
16 3 Types of Spontaneous Decay: 1. Alpha particle emission 2. Beta particle emission3. Gamma ray emissionHigh energy photon (light)
21 No study on radiation is complete without giving credit to the Curies (Marie, Pierre and Irene)- Their discoveries include radium, polonium and positron.Marie-died fromOverexposureTo radiation
22 Types of Nuclear Radiation Alpha 2.Beta 3. Gamma
23 alpha particles and alpha decay alpha particles and alpha decay
24 What is an alpha-particle? It has two protons and two neutrons4He2
25 What is alpha-decay?It is when a nucleus emits an alpha particle4He2Alpha Decay = Alpha Particle Emission
26 Nuclear Equations -represent nuclear decay to become stable - they must balance. 1) mass #2)atomic #The total number of p+and n0 before a nuclear reaction must be the same as the total number of nucleons after reaction.
27 1. Alpha emissionNuclides that undergo alpha decay have too many protons for stability( >83 protons and mass > 209 )
29 Alpha Particles (a)- They have a mass of 4 and charge of +2 Remember: This is the mass number, which is the number of protons plus neutronsAlpha Particles (a)- They have a mass of 4 and charge of +2RadiumRa22688RadonRn22286+pnnpa (4He)88 protons138 neutrons86 protons136 neutrons2 protons2 neutronsThe alpha-particle (a) is a Helium nucleus.It’s the same as the element Helium, with the electrons stripped off !The alpha particles go in the air collide with air molecules and become Helium – not dangerous.
30 Example: Write the nuclear equation for the alpha decay of uranium 238: 92234X90+Now look at the chart to find this one:THORIUM
31 Nuclear Equation Practice: Alpha Decay How would alpha decay equations be written for these atoms:U Po
32 beta particles and beta decay beta particlesandbeta decay
36 Beta Particles (b)- are electrons, “no” mass and charge of –1 Beta Particles (b)- are electrons, “no” mass and charge of –1. The decay of Carbon 14CarbonC146NitrogenN147e-+0Electron-1(beta-particle)6 protons8 neutrons7 protons7 neutronsWe see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus.In symbolic notation, the following process occurred:n p + e
37 Write out the nuclear equations in each case and identify the daughter nuclei: Alpha decay of Rn:Beta decay of 3H:Beta decay of 90Sr86138
38 A beta particle is an electron emitted by an unstable nucleus Beta DecayA beta particle is an electron emitted by an unstable nucleusBeta particles can be stopped by a thin sheet of metal such as aluminum
39 Nuclear Reaction Equation Practice: Beta Decay A beta particle is written 0-1 e or During beta decay, the mass remains the same and the atomic number increases by onePb Po
40 3890Sr is a radioactive isotope that decays by beta-decay 3890Sr is a radioactive isotope that decays by beta-decay. Its daughter nucleus is(a) 3686Kr.(b) 3788Rb.(c) 3789Rb.(d) 3989Y.(e) 3990Y.
41 gamma rays and gamma decay gamma raysandgamma decay
42 Gamma decay occurs because the nucleus is at too high an energy Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. Here's a diagram of gamma decay with helium-3:Gamma decay is only energy emission, not particle emission.
43 Gamma particles (g)In much the same way that electrons in atoms can be in an excited state, so can a nucleus.NeonNe20NeonNe20+10 protons10 neutrons (in excited state)10 protons10 neutrons (lowest energy state)gammaA gamma is a high energy light particle.It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum. It has neitherCharge nor mass. They are highly penetrating.
44 Gamma decayA gamma ray is a penetrating ray of energy emitted by an unstable nucleusGamma rays are energy waves that travel through space at the speed of light
45 Gamma decayDuring gamma decay, the atomic number and mass remain the same, but the energy of the nucleus decreasesGamma rays can be stopped by several centimeters of lead or by several meters of concrete
46 There are other types of radioactive decay we will not go into: - positron emission- neutron emission
48 The unit of radiation exposure is called the REM (Radiation Equivalent in Man)This is a direct measure of the number of damaged cells.The average dose for one year is about 0.3 RemSudden dose of 1000 rems causes death in 30 days!!
49 Exposure to ionizing radiation: All of these are IONIZING RADIATIONalphabetagammaIonizing radiation causes cell damage that can lead to DNA damage that can lead to CANCER.
50 Radiation Doses Normal 1 XRay (medical) 0.04 rem = 40 mrem CAT Scan 3 remPortland New York 1 mrem (4 hr flight) (0.001 rem)Cosmic Rays 30 – 50 mrem/yearFood (40K, Ra) ~40 mrem/year
51 Bad News (acute radiation exposures) 1 rem25-50 remrem450 rem1000 rem5000 remMore cancer ~ 100 extra cases per 106 people ( chance)Lose white blood cells (+ above)Sick, low white blood cell count, Get Leukemia in years, Genetic mutations in progeny.50% death in 30 days (with “heroic” medical intervention)Death, 100%Can’t shoot back
52 Detecting RadiationDevices used to detect radiation include Geiger counters and film badges
53 Penetrating Radiation The penetrating power of radiation is really a function of mass.-radiation (zero mass) penetrates much further than -radiation, which penetrates much further than -radiation.When radiation penetrates the body most of its energy is absorbed by water molecules. Alpha, beta and gamma rays are all forms of ionizing radiation that can ionize water. Alpha rays are stopped by skin and beta rays can penetrate about 1 cm beyond the surface of the skin. Gamma rays are the most penetrating of the three types of radiation. Inside the body, alpha rays are the most dangerous form of radiation.
55 “Background” Radiation Background radiation is nuclear radiation that occurs naturally in the environmentRadioisotopes in the air, water, rocks, plants, and animals all contribute to background radiationCosmic rays (streams of charged particles) from outer space that collide with the Earth’s atmosphere also contributeBackground radiation levels are low enough to be safe
57 RATES OF NUCLEAR DECAYA half-life is the time required for one half of a sample of radioactive sample of a radioisotope to decayUnlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area
58 A very important concept in nuclear chemistry and its applications is the idea of HALF-LIFEHalf-Life: the TIME it takes for half of a given amount of a specific isotope to decayThis depends on the relative stability of the the isotope in question: semi-stable nuclei last longer than very unstable ones.
59 1 KgExample: 14C (half-life 6,000 years).How much is left after 6,000 years?12,000 years?18,000 years?24,000 years?30,000 years?36,000 years?
60 1 KgExample: 14C (half-life 6,000 years).There must be an easier way!How much is left after 6,000 years?12,000 years?18,000 years?We divided by 2 six times24,000 years?30,000 years?36,000 years?
64 Let’s meet some of the unstable isotopes in our neighborhood: Radon -222Forms as part of the Uranium SeriesDecomposition of Uranium in many rocks-graniteMigrates into basement cracksDense and collects in lower part of houseReadily inhaledIts decomposition product is polonium, if it decays in the lung it emits an alpha particleThe polonium solid decays resulting in lung disease
65 Radium 2261st radioactive element associated with biological damageSome are phosphorescent (glow)Believed to cause the reaction that caused leukemia that killed Marie CurrieUranium-238Used to estimate age of earthWe use its half life to estimated how long it has been since the rock solidified.
66 Potassium 40Light element (one of the few)Emits positron to form Ar-40Most of argon in atmosphere is Ar-40
67 Artificial Radioactive isotopes-Transmutation Artificial radioactive Isotopes are produced by bombarding a target element with nuclei of other elementsCarried out in cyclotronMany new and usefulIsotopes have beencreated.
69 Practical uses of Radioisotopes H-3 Tritium Archaeological datingAm Americium Smoke detectorsCo Cobalt Cancer treatmentCr Chromium Determination ofblood volumeU Uranium Nuclear reactors andweaponsU Uranium Archaeological dating
70 Artificial Radioactive isotopes may be used as tracer materials. Example: We might like to know how phosphorus in fertilizers is used by plants. By incorporating a small amount of radioactive Phosphorus in the fertilizer, chemists can measure the time it takes for plants to utilize the Phosphorus. They also can track where the P goes.
72 Dating Archeological samples Example:U-238 decays slowly through the uranium disintegration series to lead The half-life of this conversion is 4.5 X 109 years. To determine the age of a rock, we need to determine the amount of uranium present when the rock solidified, No and the amount of uranium in the rock today, Nf
73 The amount of U-238 present in the rock today can be measured The amount of U-238 present in the rock today can be measured. However, we can’t calculate the original. The solution lies in the fact that each atom of uranium ends up as an atom of lead. Therefore, if we take a rock sample and determine the number of atoms of U-238 and the number of atoms of Pb-206, we can say thatNo = atoms U atoms Pb-206Nt = atoms 238-U**Errors will exist, the original rock may have contained some Pb-206 and some of the original U-238 may not end up as Pb-206
75 FISSION AND FUSIONFission is the splitting of an atomic nucleus into two smaller partsFusion is a process in which the nuclei of two atoms combine to form a larger nucleus
76 FissionA chain reaction is a chain of fission reactions triggered by neutrons released during the fission of a nucleusAbout 20% of the electricity in the US comes from fission reactions
77 FissionA tremendous amount of energy is produced during a fission reaction
78 FissionAdvantages to using fission reactions is the lack of air pollution.Disadvantages include the risk of exposure and radioactive waste
79 Nuclear Power Plant FG21_020.JPG Enriched uranium pellets encased in Zr or stainless steel tubes are used for fuel in nuclear power plants. Control rods made of Cd or B control the fission process by absorbing neutrons. A moderator slows down the neutrons so they are more likely to be captured by the fuel. A cooling liquid circulates through the reactor and its heat is used to produce steam which generates electricity by driving a steam turbine.
80 2 subcritical masses come together when detonated FG21_017.JPGAtomic Bomb2 subcritical masses come together when detonatedChemical explosives are used to bring two subcritical masses of uranium-235 together to form a supercritical mass. A rapid, uncontrolled nuclear reaction results ultimately causing a nuclear explosion.
81 FusionFusion reactions can release huge amounts of energyFusion reactions occur in the sun and stars
82 Nuclear Fission-the process that yields two nuclei of almost equivalent mass. It does not occur spontaneouslyIt is a chain reactionIt is usually used to generate electricity. Heat is generated in fission reactions.
83 Nuclear Fusion- The combination of two nuclei into a larger atom is called nuclear fusion. The reactions within the sun are fusion reactions that combine Hydrogen nuclei to form a helium atomIt takes simple, nonradioactive materials and produces helium, so it should be a clean and inexpensive source of energy.Several designs for fusion reactors are being tested. Some success, it will be some time before this cheap, nonpolluting energy source will become a reality.
85 Tokamak- uses magnetic fields to contain fusion rxn
86 Fusion of tritium and deuterium requires about 40,000,000K: 21H + 31H 42He + 10nThese temperatures can be achieved in a nuclear bomb or a tokamak.A tokamak is a magnetic bottle: strong magnetic fields contained a high temperature plasma so the plasma does not come into contact with the walls. (No known material can survive the temperatures for fusion.)To date, about 3,000,000 K has been achieved in a tokamak.
87 Fusion reaction in sun provides all our energy makes smaller elements fusion in supernova made elements larger than Fe
88 No attack involving nuclear weapons has occurred since. Fat ManProduced this cloud after its detonation at Nagasaki on August 15th, 1945, killing at least80,000 civilians instantly.140,000 civilians perished in Hiroshima when Little Boy was dropped just two weeks earlier.No attack involving nuclear weapons has occurred since.
89 In 1961, when the USSR tested the Hydrogen Bomb “Tsar Bomba”, it was 4000 times more powerful than Little Boy. Its energy yield was ten times greater then all of the munitions exploded during all of World War 2.“A 50-mile radius of ground surface has been completely leveled, swept and licked so that it looks like a skating rink ... The same goes for rocks. There is not a trace of unevenness in the ground.... Everything in this area has been swept clean, scoured, melted and blown away."The shockwave destroyed buildings and tore roofs off of homes hundreds of miles from ground zero, and windows in Norway and Finland were shattered.FromThe USSR concluded that Tsar could not be safely deployed against Western European targets, since the radiation that would have been caused by the blast would spread to the Soviet border. The only cities that would be practical targets for such a device were the New York, Chicago, and Los Angeles metropolitan areas; the use of Tsar was considered overkill for any other target.