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The rate of radioactive decay is referred to as the activity :

Radioactive Decay. The rate of radioactive decay is referred to as the activity : measure of the number of radionuclide decays per unit of time. UNITS OF ACTIVITY. Becquerel (Bq) = 1 disintegration per second (dps). 1 Bq = 27 picoCuries

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The rate of radioactive decay is referred to as the activity :

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

  2. 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

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

  4. Activity of 1 mg of U-238 is 10 Bq Activity of 1 mg of Am-241 is 1 x 108 Bq ????? The difference is related to a unique property of all radionuclides called the half-life.

  5. Half-Life *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.

  6. * Half-lives of radioisotopes vary: Uranium-238 4.5 x 109 years Americium-241 4.32 x102 years Polonium-212 0.3 microseconds • After 7 half-lives the activity decreases to • about 1% of its original value. • After 10 half-lives the activity reduces • to one thousandth of its original value.

  7. Mathematically the concept of half-life Can be defined by : A = Ao ____ 2n n= #half-lives The decay constant and half life are related : t1/2 = ln(2) = 0.693 λλ

  8. t1/2 = 0.693 λ A = Aoe –λT Combine to form: A = Aoe-0.693 t /T1/2

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

  10. A = Aoe-0.693 t /T1/2 A = 91.7 MBq

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

  12. 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)

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