Therefore: A₀, the activity of arsenic-76,
= 8 × 10¹⁵ × 10¹³ × 4.2 × 10-24 × (1 - e-0.026 × 12)
(Note: e is a physical constant, 2.71+)
= 9 × 10⁴ disintegrations per second per microgram
2. Determination of activity of arsenic measured in the sample and corrected back to the time of removal from the reactor.
We use the equation:
A₁ =
| R |
| E × F |
where R is the measured count rate. (In this case, R is the number of counts per second observed in the 0.559-MeV gamma-ray peak, which is 5300 counts in 20 minutes or 4.4 counts per second.)
E is the efficiency of the detector. (In this case, it is the number of counts observed in the 0.559 peak for each 0.559-MeV gamma ray emitted by a radioactive material at the sample distance. This is known for the detector being used by making other measurements and, for the set-up used here, is 0.010.)
F is the average number of 0.559-MeV gamma rays emitted in each disintegration of arsenic-76. (This can be deduced from the decay scheme of arsenic-76. See the [decay scheme for manganese-56 on page 13]. In the decay of arsenic-76 the number of 0.559-MeV gamma rays emitted per disintegration is approximately 0.41.)
λ is the disintegration constant for arsenic-76. (0.026, see [page 49].)