Suppose that the scattering angle for an elastic collision of a neutron with an atomic nucleus in a nuclear fuel rod is observed to be 45°. What was the atomic mass A of the nucleus that the neutron...

Suppose that the scattering angle for an elastic collision of a neutron with an atomic nucleus in a nuclear fuel rod is observed to be 45°. What was the atomic mass A of the nucleus that the neutron hits if the scattering angle was 90° in the COM system? From your knowledge of nuclear materials, what element did the neutron collide with in the fuel rod?