How many years are required for the amount of krypton-85 (8536Kr) in a spent nuc
ID: 1485555 • Letter: H
Question
How many years are required for the amount of krypton-85 (8536Kr) in a spent nuclear reactor fuel rod to be reduced by a factor of 1/8? The half-life of krypton-85 is 10.8 years.
Express your answer using three significant figures.
How many years are required for the amount of krypton-85 (8536Kr) in a spent nuclear reactor fuel rod to be reduced by a factor of 1/32?
Express your answer using three significant figures.
How many years are required for the amount of krypton-85 (8536Kr) in a spent nuclear reactor fuel rod to be reduced by a factor of 1/128?
Express your answer using three significant figures.
Explanation / Answer
Half life of krypton =10.8 years
Initial number of Krypton= No
Krypton reduced to a factor of 1/8, so the number of krypton,N=No/8
So,N=Noexp(-0.693*t/th)
No/8=Noexp(-0.693*t/th)
1/8=exp(-0.693*t/th)
ln(1/8)=(-0.693*t/10.8)
t=32.40 years
b)N=Noexp(-0.693*t/th)
No/32=Noexp(-0.693*t/th)
1/32=exp(-0.693*t/th)
ln(1/32)=(-0.693*t/10.8)
t=54.01 years
c)N=Noexp(-0.693*t/th)
No/128=Noexp(-0.693*t/th)
1/128=exp(-0.693*t/th)
ln(1/128)=(-0.693*t/10.8)
t=75.6 years
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