Nuclear Reactions Artificial Radioactivity In 1934 Irene and

Nuclear Reactions

Artificial Radioactivity ] In 1934 Irene and Jean Joliot- Curie transmuted aluminum to phosphorus. • Alpha bombardment • Unstable state of P-31 ] The remaining sample continued to emit positrons. • P-30 is radioactive • Half-life 2. 5 min • Artificial radioisotope

Conservation Laws ] Nuclear reactions follow conservation laws. • Conservation of energy, linear momentum, angular momentum • Conservation of charge • Conservation of mass number ] Conservation of charge is equivalent to proton count plus electrons and positrons. • Za + ZX = ZY + Zb ] Conservation of mass number is equivalent to a count of protons plus neutrons. • Aa + AX = AY + Ab ] Conservation of energy uses relativistic mass energy.

Reaction Energy ] The conservation of energy requires a table of mass energies for individual isotopes. • Not elemental mass ] Use atomic mass units and convert to Me. V to get energy. • 1 u = 931. 5 Me. V/c 2 • Add kinetic energy as needed • Q value is mass difference

Exothermic ] A reaction with a positive Q releases energy. ] Production of carbon-14 is exothermic. • No additional kinetic energy for input ] The energy released becomes kinetic energy for the daughters. • • Mn = 1. 008665 MN 14 =14. 003074 Mp = 1. 007825 MC 14 =14. 003242 ] The mass difference gives Q. • Q = 0. 627 Me. V

Endothermic ] A reaction with a negative Q requires energy. ] Production of carbon-14 is exothermic. • Must come from initial kinetic energy ] There is a threshold kinetic energy for production. • • Mp = 1. 007825 MO 18 =17. 999160 Mp = 1. 008665 Mn 18 =18. 000938 ] The mass difference gives Q. • Q = -2. 453 Me. V

Medical Isotopes ] Radioisotopes are important medical tools. ] Isotopes can be used for imaging internal organs. • Scintigraphs • SPECT • PET ] Energy deposition can be used for treatment. • Tumor treatment next