need help with (b) (a) A sample of cesium-137 has an activity of 5.60 µCi and a
ID: 1556948 • Letter: N
Question
need help with (b)
(a) A sample of cesium-137 has an activity of 5.60 µCi and a half-life of 30.2 years. How many cesium-137 nuclei are present in the original sample?
Correct, computer gets: 2.85e+14
(b) The sample of cesium-137 emits gamma rays that have an energy of 656 keV each. Assume that you enclose the entire sample in your hand and that your hand represents 0.740 kg of tissue. If your hand absorbs 26% of the radiation emitted, calculate the equivalent dose absorbed by your hand tissue if you hold the cesium-137 sample for 36 minutes. (Compare your answer with the average dose your whole body receives in a year due to natural events, which is around 300 mrem.)
Explanation / Answer
a. Half life 30.2 yrs
Activity means here the number of decays taking place each second or disintegrations per second.
since dacay constant =0.693/30.2= 0.0229 yr-1 or 7.2764*10-10 s-1
Present activity= 5.60 micro Ci
The total number of nuclei, N, can be determined from the known half-life and activity of cesium-137 (30.2 y)
N= (activity *half life)/0.693
convert to becquerels and years to seconds
N= (activity*(3.7*10^10) *half life*(3.16*10^7))/0.693=(5.6*10^-6*(3.7*10^10) *30.2*(3.16*10^7))/0.693
N= 2.8533e+014 CORRECT
B) ENergy = 656 keV and absorb 26 % THUS ABSORBED ENERGY= 170.5600
ENERGY ABSORBED PER GRAM=170.560/740= 0.230 MeV/g
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