Radioactivity Nuclear Chemistry

Chapter objectives Different types of nuclear radiation Biological effect of nuclear radiation Half-life and nuclear stability Application of nuclear radiation in food, health, and medical fields Application of nuclear energy

Facts About the Nucleus: What are in there? Very small volume compared to volume of the atom but Essentially entire mass of atom Composed of Protons (+ charge) and Neutrons (0 charge) that are tightly held together nucleons

Nucleus & Isotope Every atom of an element has the same number of protons (+ charge) atomic number (Z) Atoms of the same elements can have different numbers of neutrons Isotopes. Carbon-12 (6 neutrons), Carbon-13 (7-neutrons) different atomic masses Isotopes are identified by their mass number (A) mass number = number of protons + neutrons

Facts About the Nucleus: Symbol #neutrons = mass number - atomic number The nucleus of an isotope is called a nuclide less than 10% of the known nuclides are non- radioactive, most are Radio-nuclides Symbol of Nuclide Element -Mass Number = X-A Cl 35 17

The Curies Marie Curie discovered new elements by detecting their rays Radium Polonium (named for her homeland) Since these rays were no longer just a property of uranium, she renamed it radioactivity

What is Radioactivity? Release of tiny, high energy particles from the Nucleus

Radioactivity Radioactive nuclei spontaneously decompose into smaller nuclei Unstable Parent Nuclide (Reactant)  Radioactive Decay  Daughter Nuclide (Product) Radioactivity: Nuclide emitting a particle and/or energy All nuclides with 84 or more protons are radioactive

Detecting Radioactivity 1)Radioactive rays can expose light- protected photographic film Application: Film badges 2)Radioactive rays cause air to become ionized Geiger-Müller Counter: counting electrons generated when Ar gas atoms are ionized by radioactive rays

Radiation passing through a Geiger counter ionizes one or more gas atoms, producing ion pairs.

Properties of Radioactive Rays have high energy ionize matter cause uncharged matter to become charged Design of Geiger Counter penetrate matter cause phosphorescent chemicals to glow basis of scintillation counter

Types of Radioactive Rays Rutherford discovered there were three types of radioactivity Alpha rays (  ) have a charge of +2 c.u. and a mass of 4 amu now known as Helium nucleus Beta rays (  ) have a charge of -1 c.u. and negligible mass electron-like Gamma rays (  form of light energy (not particle like  )

Alpha emission an  particle contains 2 protons + 2 neutrons helium nucleus loss of an alpha particle means atomic number decreases by 2 mass number decreases by 4

 decay

Beta emission a  -particle is like an electron moving much faster produced from the nucleus when an atom loses a  particle its atomic number increases by 1 mass number remains the same in beta decay, a Neutron changes into a Proton

 decay

Gamma emission High energy photons of light No loss of particles from the nucleus No change in the composition of the nucleus Same atomic number and mass number Generally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrange

Positron emission Positron has a charge of +1 c.u. and negligible mass anti-electron : a kind of anti-matter! when an atom loses a positron from the nucleus, its Mass number remains the same Atomic number decreases by 1 positrons appear to result from a proton changing into a neutron

Important Atomic Symbols ParticleSymbolNuclear Symbol protonp+p+ neutronn0n0 electrone-e- alpha  beta   positron  

Half-Life Each radioactive isotope decays at a unique rate some fast, some slow not all the atoms of an isotope change simultaneously rate is a measure of how many of them change in a given period of time measured in counts per minute, or grams per time Length of time it takes for half of the parent nuclides in a sample to undergo radioactive decay is called the half-life

Radiocarbon Dating % C-14 (compared to living organism) Object’s Age (in years) 100%0 90%870 80% % % % %11,500 10%19,000 5%24,800 1%38,100

Half-Lives of Various Nuclides NuclideHalf-LifeType of Decay Th x yralpha U x 10 9 yralpha C yrbeta Rn secalpha Th x 10 –6 secalpha

Object Dating (Radiometric Dating) Mineral (geological) compare the amount of U-238 to Pb-206 compare amount of K-40 to Ar-40 Archeological (once living materials) compare the amount of C-14 to C-12 C-14 radioactive with half-life = 5730 yrs. while substance living, C-14/C-12 fairly constant  CO 2 in air ultimate source of all C in body  C-14 in living organism maintained at the same level once dies C-14/C-12 ratio decreases limit up to 50,000 years

Example: Radiometric Dating A sample of ancient human blood stain was examined, showing C-14 level is 1/8 of present C-14 level. How old is the sample? C- 14 radioactive with half-life = 5730 yrs. Every ONE half-life, C-14 level decrease to ½ of previous level. 1/8 3 half-lives = 17,200 yrs

Tro's Introductory Chemistry, Chapter Ionizing Radiation: Ion pair formation.

Penetrating Ability of Radioactive Rays    0.01 mm 1 mm 100 mm Pieces of Lead

Natural Radioactivity Everyday, small amounts of radioactive minerals in the air, ground and water even in the food you eat! the radiation you are exposed to from natural sources is called background radiation High radiation level at very high altitude and outer space

Radiation Exposure (even travelling in airplane)

Biological Effects of Radiation Radiation is high energy, energy enough to knock electrons from molecules and break bonds: Ionizing radiation: M +   M + + e - Energy transferred to cells can damage biological molecules and cause malfunction of the cell and genetic mutation.

Acute Effects of Radiation High levels of radiation over a short period of time kill large numbers of cells From a nuclear blast or exposed reactor core Causes weakened immune system and lower ability to absorb nutrients from food May result in death, usually from infection

Chronic Effects of Radiation Low doses of radiation over a period of time show an increased risk for the development of cancer Radiation damages DNA that may not get repaired properly Low doses over time may damage reproductive organs, which may lead to sterilization Damage to reproductive cells may lead to a genetic defect in offspring

A commercially available kit to test for radon gas in the home. Detection of Radon Gas

→ Food irradiation utilizes the effect of ionizing radiation to damage DNA in microorganisms. Food Preservation: Irridated and nonradiated mushrooms © Peticolas/Megna/Fundamental Photographs, NYC

Medical Uses of Radioisotopes, Diagnosis PET scan positron emission tomography C-11 in glucose brain scan and function

Medical Uses of Radioisotopes, Diagnosis Radiotracers certain organs absorb most or all of a particular element can measure the amount absorbed by using tagged isotopes of the element and a Geiger counter use radioisotope with short half- life use radioisotope low ionizing  beta or gamma

Brain scans are obtained using radioactive technetium-99, a laboratory-produced radionuclide. Radioactive Imaging Science Photo/Custom Medical Stock Photo

Medical Uses of Radioisotopes, Treatment - Radiotherapy Cancer treatment cancer cells more sensitive to radiation than healthy cells 1.brachytherapy  place radioisotope directly at site of cancer 2.teletherapy  use gamma radiation from Co-60 outside to penetrate inside 3.radiopharmaceutical therapy  use radioisotopes that concentrate in one area of the body

Cobalt-60 is used as a source of gamma radiation in radiation therapy. Radiation Therapy Yoav Levy/Phototake

Fission Fission Fission: Heavy nucleus split by neutron into smaller nuclei + Energy!!

Fission Chain Reaction Online video: Chain reaction: A reactant in the process is also a product of the process in the fission process it is the neutrons so you only need a small amount of neutrons to start the chain Many of the neutrons produced in the fission causes splitting of other heavy nuclei, multiplying the amount of energy released in the reaction. Critical mass: minimum amount of fissionable isotope needed to sustain the chain reaction

Nuclear Power Nuclear reactors use fission to generate electricity About 20% of US electricity, even higher percentage in France, Germany, etc. The fission of U-235 produces heat How does Nuclear power work? The heat boils water, turning it to steam The steam turns a turbine, generating electricity

Nuclear Power Plants vs. Coal-Burning Power Plants Use about 50 kg of fuel to generate enough electricity for 1 million people No air pollution Use about 2 million kg of fuel to generate enough electricity for 1 million people Produces NO 2 and SO x that add to acid rain Produces CO 2 that adds to the greenhouse effect

A fission chain reaction is caused by further reaction of the neutrons produced during fission. Nuclear Fission: Nuclear Power and Atomic weapon

Nuclear Fission Applied © Bettmann/CORBIS

Nuclear Fusion Fusion: combining of light nuclei to make a heavier one The sun uses the fusion of hydrogen isotopes to make helium as a power source Requires high input of energy to initiate the process Because need to overcome repulsion of positive nuclei Produces 10x the energy per gram as fission No radioactive byproducts Unfortunately, the only currently working application is the H-bomb

Fusion: H-bomb and Solar Energy H1H 3 1H1H 4 2 He 1 0n0n deuterium + tritiumhelium-4 + neutron The process of nuclear fusion maintains the interior of the sun at the temperature of approximately 15 million degrees.