Radiation
Atomic Anatomy Atoms –electrons (e-) –protons (p+) –neutrons (n)
Atoms are electrically neutral with no net charge. Ions are atoms that have been stripped of one or more of their electrons and have a net charge.
Isotopes Identical Chemical Properties, Different Atomic Weight Difference = presence of # of neutrons in the nucleus Hydrogen = amu
ISOTOPEConstituents Atomic Mass Occurrence H1 proton 1 electron amu % Deuterium1 proton 1 electron amu % 1 neutron Tritium1 proton 1 electron amu % 2 neutrons
A Z X X = Element Symbol Z = Atomic Number (periodic table, # protons) A = Isotope Number (# neutrons)
Hydrogen 1 1 H 1 proton, 0 neutrons Helium He2 protons, 2 neutrons Uranium U92 protons, 143 neutrons Isotope Designations
Radioactive Particles Alpha Ejection of 2 protons and 2 neutrons from an unstable nucleus. 4 2 He = Beta Ejection of an electron from an unstable nucleus as part of the decay of a neutron e = Gamma Atomic nucleus transition, yielding high energy photons.
Nuclear Reactions Ra Rn He Note that the numbers all add-up (conservation of particles). A Z X A=Protons + neutrons (Total particles in nucleus) 226 = ZprotonsNumber of protons 88 =
Alpha Decay Alpha = 4 2 He Parent Ra Radium Daughter Rn Radon Radiation 4 2 He Ra Rn He Most of the energy is with the lighter particle, in this case the alpha particle.
Beta Decay Beta = 0 -1 e 1 0 n 1 1 p e The decay of a neutron into a proton and electron.
Beta Decay Beta = 0 -1 e 1 0 n 1 1 p e The decay of a neutron into a proton and electron C 14 7 N e(Radioactive Carbon) Sr Y +
Gamma Radiation Gamma Very high energy photons are emitted from the nucleus. Excess radiation emitted from an excited nucleus… Sr* Sr +
Fission The splitting of an unstable atomic nucleus into two or more nuclei. Fission occurs spontaneously, generally when a nucleus has an excess of neutrons, resulting in the inability of the strong force to bind the protons and neutrons together. The fission reaction used in many nuclear reactors and bombs involves the absorption of neutrons by uranium-235 nuclei, which immediately undergo fission, releasing energy and fast neutrons.
Shielding We can detect the radiation from a radioactive source. Say we get X counts/minute (cpm). Geiger Counter
Shielding We can shield the source with various materials to test their usefulness in protecting against the radiation. Geiger Counter
Shielding Efficiency Cotton FabricWoodLead ’s are the most penetrating type of radiation.
Half Life The amount of time required for exactly 1/2 of the original (N o ) sample of parent atoms to decay into daughter products. After one half life, you have 1/2 N o parent atoms, and 1/2 N o daughter atoms.
Half Life After two half lives, you have 1/4 N o parent atoms, and 3/4 N o daughter atoms. After three half lives, you have 1/8 N o parent atoms, and 7/8 N o daughter atoms.
Radioactive Decay If you start out with a sample of parent atoms (N o ), after some time there will be fewer because of radioactive decay into the daughter atoms.
Radioactive Carbon Dating 14 6 C 14 7 N + Radioactive Carbon Half-life = 5730 years There is a certain amount of 14 6 C occurring naturally. Living things continually replenish this by ingesting plants or drinking water with some 14 6 C in them. When death occurs, no replenishment takes place and the 14 6 C decays into 14 7 N.
By measuring the ratios of 14 6 C and 14 7 N, with the half- life value of 14 6 C an accurate estimate of the age is obtained.
Fusion The joining together of atomic nuclei, especially hydrogen or other light nuclei, to form a heavier nucleus, especially a helium nucleus. Fusion occurs when plasmas are heated to extremely high temperatures, forcing the nuclei to collide at great speed. The resulting unstable nucleus emits one or more neutrons at very high speeds, releasing more energy than was required to fuse the nuclei, thereby making chain-reactions possible, since the reaction is exothermic. Fusion reactions are the source of the energy in the Sun and in other stars, and in hydrogen bombs.