biodex ATOMLAB 100 - Decay Factor Method for Decay; Sample Calculation (Decay Factor)

3) Elapsed t = 53 min x 1 hr = 0.8833 hr
60 min
4) A = A
0
x 2
(-t/T
1/2
)
A = 43 mCi x 2
(-0.8833/6.007)
A = 43 mCi x 2
(-0.147045)
A = 43 mCi x 0.903
A = 38.83 mCi
DECAY FACTOR METHOD
The following method is used to perform radioisotope decay
calculations using a calculator without the e
x
function:
1) Measure the current activity A
i
of the radioisotope.
2) Look up the half life T
1/2
of the radioisotope in Appendix
D. Note the time units.
3) Calculate the time t, in the same units as T
1/2
, that will
elapse between when the activity measurement was
made and when you wish to know what the decayed
activity of your radioisotope will be.
4) Calculate t / T
1/2
in terms of N + R, where N is an
integer (0, 1, 2, etc.) and R is less than 1.
5) Look up X
n
(N) in Table 1.
6) Look up X
r
(R) in the Decay Factor Chart.
7) Calculate A
f
= A
i
x X
n
(N) x X
r
(R).
The following is a calculation of the decayed activity of Tc-
99m, with an initial activity of 43 mCi, after 32.5 hours:
1) A
i
= 43 mCi.
2) For Tc-99m, T
1/2
= 6.007 h.
3) t = 32.5 h.
4) t / T
1/2
= 32.5 h / 6.007 = 5.410. N = 5, R = 0.410.
ATOMLAB Dose Calibrator Operation Manual Appendix C
Biodex Medical Systems C-2 Release 2.0
Sample
Calculation