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204 ATOMLAB 500 DOSE CALIBRATOR
Alternate Decay Calculation Method
If You Are Using A Calculator With The Y
x
Function, Perform The Following:
1. Measure the current activity of the radioisotope (A
0
), which can be compared to the decayed
calculated activity.
2. Look up half life (T
1/2
) of the radioisotope in APPENDIX E. Note the time units.
3. T
1/2
= half life of the isotope
t = Elapsed Time
a = Current Activity
a
0
= Activity at the time of calibration
n = elapsed time / half life
4. Calculate A = A
0
/ 2
n
5. Calculate the elapsed time (t) in the same units as the (T
1/2
) that will elapse between when
the calculated activity measurement was made and when you wish to know what the decayed
activity of your radioisotope will be.
Sample Calculation
6. A
0
= 43 mCi.
7. For Tc-99m, T
1/2
= 6.007 h.
8. Elapsed t = 53 min x 1 hr = 0.8833 hr
60 min
9. Replace equation with following:
A = A
0
/2
n
A = 43 mCi / 2
(0.8833/6.007)
A = 43 mCi / 2
(0.1470451)
A = 43 mCi / 1.1072992
A = 38.83 mCi
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