The isotope au-197 is irradiated in a thermal neutron flux of 1018 neutrons/(m²s). the cross section for neutron capture is 99 barn (1 barn= 10-28 m²), and the half- life of the radioactive au-198 produced is 2.7 days. (a) how long does the sample have to be irradiation for 0.1 percent of the target atoms to be destroyed? (b) what is the irradiation time necessary to produce 95% of saturation activity?