1. Health, Safety and Environment www.hse.ubc.ca

2. The rate of radioactive decay is referred to as the activity: measure of the number of radionuclide decays per unit of time Radioactive Decay

3. UNITS OF ACTIVITY Becquerel (Bq) = 1 disintegration per second (dps) 1 Bq = 27 picoCuries 1 kiloBq (kBq) = 27 nanoCuries 1 MegaBq (MBq) = 27 microCuries (µCi) 1 GigaBq (GBq) = 27 milliCuries (mCi) 1 TeraBq (TBq) = 27 Curies

4. *The rate of decay of a radionuclide is exponential with time. At time T, activity A is given by: A = A o e –λT A o =initial activity λ = decay constant

5. The difference is related to a unique property of all radionuclides called the half-life. Activity of 1 mg of U-238 is 10 Bq Activity of 1 mg of Am-241 is 1 x 10 8 Bq ?????

6. *The half-life of a radionuclide is the time required for it to lose 50% of its activity by radioactive decay. *Each radionuclide has its own unique half-life regardless of the quantity or form – solid,gas,liquid. * The half-life is an unalterable property of the radioisotope. Half-Life

7. After 7 half-lives the activity decreases to about 1% of its original value. * Half-lives of radioisotopes vary: Uranium-238 4.5 x 10 9 years Americium-241 4.32 x10 2 years Polonium-212 0.3 microseconds After 10 half-lives the activity reduces to one thousandth of its original value.

8. Mathematically the concept of half-life Can be defined by : A = A o ____ 2 n The decay constant and half life are related : t 1/2 = ln(2) = 0.693 λ n= #half-lives

9. A = A o e -0.693 t / T 1/2 A = A o e –λT Combine to form: t 1/2 = 0.693 λ

10. A researcher has 500 MBq of 32 P but cannot use it for 35 days. What is the activity when she wants to use the material? A = A o 2 n After 2 half-lives (n=2) A = 500 4 = 125 MBq After 3 half-lives (n=3) A = 500 8 = 62.5 MBq For 32 P T ½ = 14.3 days After 1 half-life (n=1) A = 500 2 = 250 MBq

11. A = 91.7 MBq A = A o e -0.693 t / T 1/2

12. *History *Radiation : types alpha, beta, positron, gamma, x-rays neutron activation *Energy levels: ionizing radiation. *Radioactive decay

13. For EXAM! Learn characteristics of two isotopes Type of radiation : alpha, beta, gamma Energy of radiation: eV Shielding required: material and thickness Half-life (Tables 1, 4 of manual)