1) Americium-241 is used in some smoke detectors. It is an alpha emitter with a
ID: 525281 • Letter: 1
Question
1)
Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 33.0 % of an Am-241 sample to decay?
Express your answer with the appropriate units.
2)Fill in the missing particles in each of the following nuclear equations.
135/60Nd_____+(0/+1e)
Express your answer in isotopic notation.
3)A mammoth skeleton has a carbon-14 decay rate of 0.46 disintegrations per minute per gram of carbon (0.46 dis/mingC ).
When did the mammoth live? (Assume that living organisms have a carbon-14 decay rate of 15.3 dis/mingC and that carbon-14 has a half-life of 5715 yr.)
Express your answer using two significant figures.
Explanation / Answer
1) We use the formula
A=Pe^(-rt)
and r=ln2/halflife
r=ln2/432=0.0016
Let P(the starting amount) be equal to 100
If 33% will be decayed the remainig will be 67
Substituting it in the expression
67=100e^(-0.0016t)
ln (67/100)=ln e^(-0.0016t)
ln (67/100)=-0.0016t
t=ln (67/100)/-0.0016
t=250.29 years
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