All Problems Nuclear Reactions
Problem 6.287
A gold foil of mass \(m=0.20 \mathrm{~g}\) was irradiated during \(t=6.0\) hours by a thermal neutron flux falling normally on its surface. Following \(\tau=12\) hours after the completion of irradiation the activity of the foil became equal to \(A=1.9 \cdot 10^{7}\) dis/s. Find the neutron flux density if the effective cross-section of formation of a radioactive nucleus is \(\sigma=96 \mathrm{~b},\) and the half-life is equal to \(T=2.7\) days.
\[ \text { 6.287. } J=\dot{A} \mathrm{e}^{\lambda t} / \sigma N_{0}\left(1-\mathrm{e}^{-\lambda t}\right)=6 \cdot 10^{9} \text { part. } /\left(\mathrm{cm}^{2} \cdot \mathrm{s}\right), \text { where } \lambda \] is the decay constant, \(N_{0}\) is the number of Au nuclei in the foil.