1.

The half life of ._92^238U undergoing alpha-decay is 4.5xx10^9 years. The activity of 1 g sample of ._92^238U is

Answer»

`1.23xx10^4` Bq
`1.23xx10^5` Bq
`1.23xx10^3` Bq
`1.23xx10^6` Bq

Solution :`T_(1//2)=4.5xx10^9` years
`=4.5xx10^9xx3.16xx10^7=1.42xx10^17` s
One kmol of any isotope CONTAINS Avogadro's NUMBER of ATOMS, so 1G of `._92^238U` contains
`=1/(238xx10^(-3))"kmol"xx6.025xx10^26` atoms per kmol
`=25.3xx10^20` atoms
Activity, R=`lambdaN`
`=0.693/T_(1//2) N =(0.693xx25.3xx10^20)/(1.42xx10^17)s^(-1)`
`=1.23xx10^(4) s^(-1) =1.23xx10^4` Bq


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