biodex ATOMLAB 500, Operation And Service Manual, Page: 173 / 212

𝐴 = 𝐴
!
× 2
! !
!
! / !
𝐴 = 43 𝑚𝐶𝑖 × 2
! ! . !!""
! . !!"
𝐴 = 43 𝑚𝐶𝑖 × 2
! ! . !"#$"%
𝐴 = 43 𝑚𝐶𝑖 × 0 . 903
𝐴 = 38 . 83 𝑚𝐶𝑖
Alternate Decay Calculation Method
When using a calculator with a Y
x
function:
1. Measure the current activity of the radioisotope A
0
, which can be compared to the decayed
calculated activity.
2. Using the Decay Factor Chart below, look up the half live of T
1/2
for the radioisotope. 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
4. Calculate
𝐴 = 𝐴
!
≠ 2
!
5. Calculate the elapsed time (t) in the same units as the (T
1/2
) that will elapse between the
time the calibrated activity measurement was made and the time at which the decayed
activity of the radioisotope must be known.
Example:
The following is a calculation of the decayed activity of Tc-99m with an initial activity of 43 mCi
after 53 minutes:
A
0
= 43 mCi.
For Tc-99m, T
1/2
= 6.007 h.
Elapsed
𝑡 = 53 𝑚𝑖𝑛 ×
! ! !
!" !"#
= 0 . 8833 ℎ