Naturally occurring manganese is 100% 55Mn. This
nuclide has a thermal neutron capture cross section of 13.3 10-24
cm2 . The product of neutron capture is 56Mn, which is a
beta and gamma emitter with a 2.50-h half-life. When Figure 32-9 was produced,
it was assumed that the sample was irradiated for 1 h at a neutron flux of 1.8 1012
neutrons/(cm2 s) and that 10 cpm above background could be detected.
(a) Calculate the minimum mass of manganese that could be
(b) Suggest why the calculated value is lower than the