4. A sample of Pr-147 is prepared and put in a scintillation counter. The initia

Question

4. A sample of Pr-147 is prepared and put in a scintillation counter. The initial counting rate is 600. counts/min. After 31.0 minutes, the rate is 119 counts/min. What is the half-life of Pr-147? 5. Calculate the binding energy per nucleon in MeV ofan atom ofPb-208 which has a mass of 208.060 amu. The masses of the proton, neutron, and electron are 1.007277 amu, 1.008665 amu, and 0.0005486 amu respectively. 6. A Se-75 source is producing 300 rem distance of2.0 is needed to decrease the intensity ofexposure to below 25 rem? (optional for some instructors)

Explanation / Answer

Q4.

Initial count = 600 c/min

t = 31 min

Rate = 119 c/min

then

assume:

ln(A) = ln(A0) - k*t

ln(119) = ln(600) - k*31

k = (ln(119) -ln(600) ) /(-31)

K = 0.052187 1/min

now

t 1/2 = ln(2)/k

t 1/2 = ln(2)/(0.052187 = 13.2819 mins

half life = 13.2819 minutes

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