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4.17 During nuclear explosion, one of the products is 90Sr with half-life of 28.1 years. If 1µg of 90Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 years and 60 years if it is not lost metabolically.


K=0.693t1/2=0.69328.1y-1
Here, 
It is known that, 
t=2.303Klog[R]0[R]
10=2.3030.693log1[R]
2.3030.693(-log[R])
        28.1
log [R]=-10×0.6932.303×28.1
[R]=antilog)-0.1071)
=antilog(1.8929)
=0.7814μg

Therefore, 0.7814 µg of S90r will remain after 10 years.
Again,

t=2.303Klog[R]0[R]
60=2.3030.693log1[R]
log[R]=-60×0.6932.303×28.1
[R]=antilog(-0.6425)
=antilog (1.3575)
=0.2278μg

Therefore, 0.2278 µg of  90Sr will remain after 60 years.