You want to find out how many atoms of the isotope 65Cu are in a small sample of material. You bombard the sample with neutrons to ensure that on the order of 1% of these copper nuclei absorb a neutron. After activation, you turn off the neutron flux and then use a highly efficient detector to monitor the gamma radiation that comes out of the sample. Assume half of the 66Cu nuclei emit a 1.04-MeV gamma ray in their decay. (The other half of the activated nuclei decay directly to the ground state of 66Ni.) (Enter your answer using one of the following formats: 1.2e-3 for 0.0012 and 1.20e 2 for 120.) Required:
a. If after 10 min (two half-lives) you have detected 10000 MeV of photon energy at 1.04 MeV, approximately how many 65Cu atoms are in the sample?
b. Assume the sample contains natural copper. Refer to the isotopic abundances listed in your text (Chemical and Nuclear Information for Selected Isotopes) and estimate the total mass of copper in the sample.