Angular anisotropy of fragments in fission of 226Ra by neutrons in energy region 4-9 MeV

The authors measured the angular distributions of fission fragments from 4-9 MeV neutron-induced fission of 226Ra. The shape of the distributions in all cases agrees with the predictions of the Halpern-Strutinsky statistical theory. It is interesting that when En is between 4.7 and 7.1 MeV the anisotropy is constant and has a very high value (A = 1. 5). Calculations of the dispersion (K02) of the projection of the angular momentum on the approximate symmetry axis of the nucleus gives a K02 value of between 8 and 10 when En is between 6.2 and 7.1 MeV. This is approximately half the K02 values for heavier nuclei at a corresponding excitation energy above the threshold, and corresponds exactly to Griffin's value for dispersion determined solely by the momentum of the unpaired particle. These results seem to point to a considerable increase in the pairing energy at the saddle point of 227Ra. (author)