Thermal-neutron fission of gives the compound nucleus
PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Fission, fusion and nuclear energy · Fission, fusion and nuclear energy
The Nucleus Resolved, Ch Fission: the double-humped barrier and the shells the drop cannot see
Problem
Thermal-neutron fission of 241Pu gives the compound nucleus 242Pu, with mean neutron multiplicity νˉ=2.90. Take the peak-to-valley ratio at the thermal excitation to be about 600, a typical value for similar actinides, and take the rule of thumb that the ratio falls by about one order of magnitude for every 10MeV rise in excitation energy above the thermal value, as the shell correction of the forming fragments is progressively washed out.
((a)) Using mass conservation with the heavy peak pinned at AH=139, predict the light peak's mass number.
((b)) Estimate the peak-to-valley ratio if the same compound nucleus is instead formed by absorption of a 20MeV neutron, so that the excitation is about 20MeV above the thermal value.