Nuclear Radiation NC Essential Standard Types of Radiation, Penetrating Ability of Radiation, Nuclear Equations, Nuclear Decay, Half-Life, Fission vs. Fusion

Radioactivity Radiation is emitted during radioactive decay There are three main types of radiation: – Alpha radiation – Beta Radiation – Gamma radiation

Alpha Particles Alpha particles are helium nuclei emitted from a radioactive source Each consist of two Protons and two neutrons and have a +2 charge He

Beta Particlese If neutron:proton is too high, a neutron will decay, emitting a beta particle What is left is all the mass of the neutron, and a positive charge So a neutron  proton and a beta particle is ejected Same properties as an electron – No mass, -1 charge 0

γ Gamma Ray Gamma Rays are high energy photons emitted by radioactive isotopes – Similar to x-rays – No mass – No charge Most powerful form of radiation Gamma Rays are usually emitted along with alpha or beta particles during radioactive decay

Penetration ability

Nuclear Decay Equations These nuclear reactions must be balanced, but not for atoms, for MASS and CHARGE K-42 undergoes BETA DECAY 42 K  o e + ____ What undergoes ALPHA EMISSION / Decay to form U-235? ____  4 He U Atomic # for K is 19 Mass has to be 42 Charge must be 20 So it is Ca 42 Ca Atomic # for He is 2 and U is 92 Mass = = 239 Charge = = Pu 94

Half Life Amount of time it takes for half a radioisotope to decay – Vary from fractions of a second to millions of years Radioisotopes decay into atoms of other elements Transmutation-The changing of one element into another through the decay process  A very useful half life equation is A = A0 (1/2) n  where n = T/t  A = the amount of sample remaining  N= number of half lives past

Half Life Calculations  A very useful half life equation is  A = A 0 (1/2) n  where n = T/t  A = the amount of sample remaining  n = number of half lives past  A 0 = original mass  n can be calculated by taking the total time (T) divided by the length of the half life (t) A 50.0 g sample of N-16 decays to 12.5 g in 14.4 seconds. What is its half life? A = 12.5 g A 0 = 50 g T = 14.4 sec. 12.5g = 50 g (1/2) 14.4/t t= 3.6 seconds

Alternate Calculations A 50.0 g sample of N-16 decays to 12.5 g in 14.4 seconds. What is its half life? How many half-lives has it gone through? 50/2 = 25 1st half life 25/2 = nd half life It goes through 2 half life periods. Each half life is the same length 14.4/2 = 7.2 seconds The half life of K-42 is 12.4 hours. How much of a 750 g sample is left after 62 hours? How many half lives is 62 hours? 62/12.4 = 5 half life periods Now, divide 750 in half 5 times 750/2/2/2/2/2 = 23.4 g OR 750/2 5 = 23.4 g

Nuclear Fission Splitting of a nucleus into smaller parts Initiated by hitting fissionable isotopes with neutrons Uranium-235 and Plutonium-239 are the only fissionable isotopes Used for nuclear power and nuclear weapons (Bombs)‏ The fission of 1 Kg U-235 = 20,000 tons of dynamite

Representation of a fission process.

Nuclear Fusion  Occurs when nuclei combine to form a nucleus of greater mass  In solar fusion hydrogen nuclei fuse to form helium nuclei  Fusion occurs at temperatures in excess of 40 million degrees Celsius

Being studied as energy source 2 H + 3 H  4 He + 1 n +ENERGY Solar Fusion 4 1 H e  4 He + ENERGY 0

Diagram of a nuclear power plant.

Schematic of the reactor core.

Nuclear waste  Main source of waste is spent fuel rods from nuclear power plants  Made up of Uranium-235 or Plutonium-239  Fuel rods are about 3 meters long and 1/2cm in diameter  300 fuel rods bundled together are an assembly  A reactor core is 100 assemblies

Existing radioactive waste disposal and proposed alternatives for storage

Fission Pros: Very controllable process High Energy output Abundant sources (naturally occurring, enriched, and from breeder reactors) Clean burning Cons: produces radioactive waste No long term storage solutions for waste Risk of countries attaining capability to enrich fuel for weapons Fusion Pros: Extremely high energy output VERY abundant sources (deuterium from normal water and tritium produced from lithium) Very little radioactive waste Cons: technology to contain process has not been fully developed Requires extremely high temperatures and pressures Current technology is impractical and EXPENSIVE