A gold foil of mass `m= 0.20 g` was irradiated during `t=6.0` hours by a thermal neutron flux falling normally on its suface. Following `tau=12 hours` after the completion of irradiation the activity of the foil became equal to `A= 1.9.10^(7)dis//s`. Find the neutron flux density if the effective cross-section of formation of a radioactive nucleus is `sigma= 96b`, and the half-life is equal to `T=2.7 days`

Explanation

We apply the formula of the previous problem except that have `N=no`. Of radio nuclide and no. of host nuclei originally.
Here `n=(0.2)/(197)xx6.023xx10^(23)=6.115xx10^(20)`
Then after time `t N=(n.J.sigma.T)/(In 2)(1-e^(-(tIn 2)/(T)))`
T= half life of the radionuclide
After the source of neutrons is cut off the acitivity after time `T` will be `A=(n.J.sigma.T)/(In 2)(1-e^(-tIn2//T))e^(tauIn2//Txx(In 2)/(T))=n.J.sigma(1-e^(-tIn2//T))e^(-tauIn2//T)`
Thus `J=Ae^(tau In 2//T)//n sigma(1-e^(-tIn 2//T))= 5.92xx10^(9)part//cm^(2).s`