How many curies of $238$Np will there be present in $1$ mole $237$Np after exposure to a thermal neutron flux of $1$x$10\mathrm{¹}\mathrm{¹}$ sec$-1$ cm$-2$ for $10$ min, $10$h$,30$h$,60$h$,100$h$,300$h$?$ Graph these values and estimate the time to reach half the limiting value.