Nuclear Chemistry

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Nuclear Decay Nuclear Decay Why nuclides decay… Why nuclides decay… need stable ratio of neutrons to protons need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

Radiation Radiation-it’s the transfer of energy Radiation-it’s the transfer of energy Radioactivity-The spontaneous emission of radiation by an unstable nucleus. Radioactivity-The spontaneous emission of radiation by an unstable nucleus.

Good vs. Bad Ionizing Ionizing Has enough energy to kick off an ion. Has enough energy to kick off an ion. Very high energy Very high energy Non ionizing Non ionizing Does not have enough energy to kick off an ion Does not have enough energy to kick off an ion Low energy Low energy

Types of Radiation Alpha particle (  ) Alpha particle (  ) helium nucleus helium nucleus paper 2+ Beta particle (  -) Beta particle (  -) electron electron 1- lead Gamma (  ) Gamma (  ) high-energy photon high-energy photon 0 concrete

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

Nuclear Decay Nuclear Decay Beta Emission Beta Emission electron

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

Half-life Half-life (t ½ ) Half-life (t ½ ) Time required for half the atoms of a radioactive nuclide to decay. Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. Shorter half-life = less stable.

Half-life m f :final mass m i :initial mass n:# of half-lives

Half-lifeHalf-life n:# of half lives t 1/2 : half life

Half-lifeHalf-life m f :final mass m i :initial mass n:# of half-lives

Half-life 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? 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: t ½ = 5.0 s m i = 25 g m f = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK : m f = m i (½) n m f = (25 g)(0.5) 12 m f = g

Half-lifeHalf-life A sample of a radioactive isotope that was initially 5000 g decayed for 10,000 years. If 625 g remains after this time, what is the half-life of the isotope? A sample of a radioactive isotope that was initially 5000 g decayed for 10,000 years. If 625 g remains after this time, what is the half-life of the isotope? GIVEN: t ½ = ? m i = 5000 g m f = 625 g total time=10000yrs n = ? WORK : n=n =3 n= total time ÷ t 1/2 t 1/2 = total time/n t 1/2 = ÷ 3 t 1/2 = yrs.

Or plug into the equation Or plug into the equation and solve: and solve: Half-life Half-life GIVEN: t ½ = ? m i = 5000 g m f = 625 g total time=10000yrs n = ? WORK : m f =m i (1/2) n 625g = (5000) (1/2) n.125=(1/2) n ln(.125)÷ln(1/2) =n n=3 then plug into n=total time ÷ t 1/2

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

F ission F ission chain reaction - self-propagating reaction chain reaction - self-propagating reaction critical mass - the minimum critical mass - the minimum amount of fissionable material needed to sustain a chain reaction

Fission Uranium-235 is the only naturally occurring element that undergoes fission. Uranium-235 is the only naturally occurring element that undergoes fission. Uranium - 235

Fission Why does fission produce so much energy? Why does fission produce so much energy? Small quantities of mass are converted into appreciable quantities of energy. Small quantities of mass are converted into appreciable quantities of energy. E = mc 2

Fission 1 gram matter Energy 700,000 Gallons of high octane gasoline

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

Fission vs. Fusion 235 U is limited 235 U is limited danger of meltdown danger of meltdown toxic waste toxic waste thermal pollution thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable FISSIONFISSION FUSIONFUSION

Nuclear Power Nuclear Power Fission Reactors Fission Reactors Cooling Tower

Nuclear Power Fission Reactors Fission Reactors

Nuclear Power Fusion Reactors (not yet sustainable) Fusion Reactors (not yet sustainable)

Nuclear Power Fusion Reactors (not yet sustainable) Fusion Reactors (not yet sustainable) Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment

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

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

Nuclear Medicine Nuclear Medicine Radioisotope Tracers Radioisotope Tracers absorbed by specific organs and used to diagnose diseases absorbed by specific organs and used to diagnose diseases Radiation Treatment Radiation Treatment larger doses are used to kill cancerous cells in targeted organs larger doses are used to kill cancerous cells in targeted organs internal or external radiation source internal or external radiation source Radiation treatment using  -rays from cobalt-60.

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

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