Calculate the mass of `.^(140)La` in a sample whose activity is `3.7xx10^(10)Bq` (`1` Becquerel, `Bq= 1` disintegration per second) given that is `t_(1//2)` is 40 hour.

Answer

`1.82xx10^(-6)g`

Explanation

`(dN)/(dt)=KN`
`3.7xx10^(10)Bq=KxxN`
`3.7xx10^(10)dps=(0.69)/(t_(1//2))xxN( :'1 Bq=1dps)`
`(3.7xx10^(10)dpsxxt_(1//2))/(0.69)=(N_(A)xx "Mass of La"^(140))/(140)`
Mass `La=(3.7xx10^(10)dpsxx40hxx60mxx60sxx140)/(0.69xx6xx10^(23))`
`=1.82xx10^(-6)g`