2 RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.
3 Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleusThe nucleus opens, and protons and neutrons are rearrangedThe opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy“Normal” Chemical Reactions involve electrons, not protons and neutrons
4 Types of Radiation Beta (β) – an electron Alpha (ά) – a positively charged (+2) helium isotope - we usually ignore the charge because it involves electrons, not protons and neutronsBeta (β) – an electronGamma (γ) – pure energy; called a ray rather than a particle
5 Other Nuclear Particles NeutronPositron – a positive electronProton – usually referred to as hydrogen-1Any other elemental isotope
8 Geiger CounterUsed to detect radioactive substances
9 X Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons= atomic number (Z) + number of neutronsMass NumberXAZElement SymbolAtomic Number1p11Horproton1nneutron0e-10borelectron0e+10borpositron4He24aora particleA114Z1-1+1223.1
10 Balancing Nuclear Equations Conserve mass number (A).The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.1nU23592+Cs13855Rb9637+ 2= x1Conserve atomic number (Z) or nuclear charge.The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.1nU23592+Cs13855Rb9637+ 2= x023.1
11 212Po decays by alpha emission 212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.4He24aoralpha particle -212Po He + AX842Z212 = 4 + AA = 20884 = 2 + ZZ = 82212Po He + 208Pb8428223.1
12 Nuclear Stability and Radioactive Decay Beta decay14C N + 0b + n67-1Decrease # of neutrons by 140K Ca + 0b + n1920-1Increase # of protons by 11n p + 0b + n1-1Positron decay11C B + 0b + n65+1Increase # of neutrons by 138K Ar + 0b + n1918+1Decrease # of protons by 11p n + 0b + n1+1n and n have A = 0 and Z = 023.2
13 Nuclear Stability and Radioactive Decay Electron capture decay37Ar + 0e Cl + n1817-1Increase # of neutrons by 155Fe + 0e Mn + n2625-1Decrease # of protons by 11p + 0e n + n1-1Alpha decayDecrease # of neutrons by 2212Po He + 208Pb84282Decrease # of protons by 2Spontaneous fission252Cf In + 21n984923.2
14 Learning CheckWhat radioactive isotope is produced in the following bombardment of boron?10B He ? n
15 Learning CheckWhat radioactive isotope is produced in the following bombardment of boron?10B He N n
16 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60.60Co 0e + 60Ni
17 Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B.Reactions using neutrons are called g reactions because a g ray is usually emitted.Radioisotopes used in medicine are often made by g reactions.
18 Artificial Nuclear Reactions Example of a g reaction is production of radioactive 31P for use in studies of P uptake in the body.3115P n ---> 3215P + g
19 Transuranium Elements Elements beyond 92 (transuranium) made starting with an g reaction23892U n ---> U + g23992U > Np b23993Np ---> Pu b
20 Nuclear StabilityCertain numbers of neutrons and protons are extra stablen or p = 2, 8, 20, 50, 82 and 126Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protonsAll isotopes of the elements with atomic numbers higher than 83 are radioactiveAll isotopes of Tc and Pm are radioactive23.2
22 Half-LifeHALF-LIFE is the time that it takes for 1/2 a sample to decompose.The rate of a nuclear transformation depends only on the “reactant” concentration.
23 Half-LifeDecay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?
24 Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes.For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234After 3.6 days > 25 gramsAfter 7.2 days > 12.5 gramsAfter 10.8 days > 6.25 grams
25 A = A0e(-kt) lnA = lnA0 - kt Kinetics of Radioactive Decay A daughter rate = -DADtA = A0e(-kt)lnA = lnA0 - ktA = the amount of atoms at time tA0 = the amount of atoms at time t = 0k is the decay constant (sometimes called l)Ln 2=k0.693t½t½=k23.3
26 Radiocarbon Dating 14N + 1n 14C + 1H 14C 14N + 0b + n t½ = 5730 years 614C N + 0b + n67-1t½ = 5730 yearsUranium-238 Dating238U Pb + 8 4a + 6 0b92-1822t½ = 4.51 x 109 years23.3
27 Learning Check!The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?
28 Biological Effects of Radiation Radiation absorbed dose (rad)1 rad = 1 x 10-5 J/g of materialRoentgen equivalent for man (rem)1 rem = 1 rad x QQuality Factorg-ray = 1b = 1a = 2023.8
30 Nuclear Fission Fission is the splitting of atoms These are usually very large, so that they are not as stableFission chain has three general steps:1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron)2. Propagation. 236U fission releases neutrons that initiate other fissions3. Termination.
32 Nuclear Fission 235U + 1n 90Sr + 143Xe + 31n + Energy 925438Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2Energy = 3.3 x 10-11J per 235U= 2.0 x 1013 J per mole 235UCombustion of 1 ton of coal = 5 x 107 J23.5
34 Mass Defect Some of the mass can be converted into energy Shown by a very famous equation!E=mc2EnergyMassSpeed of light
35 BE = 9 x (p mass) + 10 x (n mass) – 19F mass Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.BE + 19F p + 101n91E = mc2BE = 9 x (p mass) + 10 x (n mass) – 19F massBE (amu) = 9 x x –BE = amu1 amu = 1.49 x JConverts amu to kg and multiplies by c2BE = 2.37 x 10-11Jbinding energy per nucleon =binding energynumber of nucleons=2.37 x J19 nucleons= 1.25 x J23.2
36 Nuclear binding energy per nucleon vs Mass number nuclear stability23.2
37 Nuclear FissionNuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.Non-criticalCritical23.5
38 Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.17% of the world’s energy comes from nuclear.
40 Annual Waste Production Nuclear Fission35,000 tons SO24.5 x 106 tons CO21,000 MW coal-firedpower plant3.5 x 106ft3 ashAnnual Waste Production1,000 MW nuclearpower plant70 ft3 vitrified waste23.5
41 Fusion Nuclear Fusion small nuclei combine 2H + 3H 4He + 1n + 1 1 2 0 Occurs in the sun and other starsEnergy
42 Nuclear FusionFusionExcessive heat can not be containedAttempts at “cold” fusion have FAILED.“Hot” fusion is difficult to contain
43 Radioisotopes in Medicine 1 out of every 3 hospital patients will undergo a nuclear medicine procedure24Na, t½ = 14.8 hr, b emitter, blood-flow tracer131I, t½ = 14.8 hr, b emitter, thyroid gland activity123I, t½ = 13.3 hr, g-ray emitter, brain imaging18F, t½ = 1.8 hr, b+ emitter, positron emission tomography99mTc, t½ = 6 hr, g-ray emitter, imaging agentBrain images with 123I-labeled compound23.7
44 Chemistry In Action: Food Irradiation DosageEffectUp to 100 kiloradInhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables.100 – 1000 kiloradsDelays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit.1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.