In this respect, nitrogen was characterized by somewhat lower anisotropies than the other ions. There was no distinct evidence for a monotonic relationship between the anisotropy and the mass of the projectile. For a given heavy more » ion, this anisotropy was found to increase with bombarding energy and decrease with the value of Z/sup 2//A of the compound nucleus. It was observed that the ratio of 0 to 90 deg differential cross sections is much larger for heavy ions than for lighter projectiles. ![]() Both targets were also studied with /sub 5/B/ sup 1//sup 1/ at the maximum energy. Targets of /sub 7//sub 9/Au/sup 1//sup 9//sup 7/ and / sub 8//sub 3/Bi/sup 2//sup 0//sup 9/ were bombarded wit h /sub 6/C/sup 1//sup 2/ / sub 7/N/sup 1//sup 4/ and /sub 8/O/sup 1//sup 6/ ions at energies of plus or minus 5.5to 10.4 Mev per nucleon. « lessĪngular distributions of fission fragments from heavyion-induced nuclear reactions were studied. At all bombarding energies, the variation of laboratory-system kinetic energy of the fragments with laboratory-system angle indicates full momentum transfer by the bombarding particle to the fissioning system. The experimental fission cross sections agree well with the cross sections for compound-nucleus formation calculated by use of a squarewell nuclear potential with a radius parameter r/sub 0/ = 1.5 x 10/sup -13/ cm. The fission cross section increases from a value of 40 mb at 63 Mev to 2.4b at 124 Mev. By correspondence this suggests that the fissioning nuclei are californium more » isotopes. ![]() Over the entire range of bombarding energies, the most probable total kinetic energy release is 186 plus or minus 6 Mev. The contribution from this kind of reaction is estimated to be of the order of 30% at 95 and 124 Mev. A possible explanation for these discrepancies is that before the fission event there is competition from reactions in which particles are emitted in the forward direction. The mean linear momentum of the fissioning nucleus appears to be less than that of the heavy ion. At the highest bombarding energies, the observed angular distributions were found to be more nearly isotropic than predicted. The percent fission from each isotope in the evaporation chain was calculated and the over-all angular distribution estimated with the use of the theoretical curves of Halpern and Strutinski. The distributions were analyzed in terms of the formation of a compound nucleus and subsequent decay by evaporation of neutrons in competition with fission. ![]() Angular distributions and kinetic-energy spectra of fragments, and cross sections for fission of U/sup 238/ with 63- to 124-Mev C/sup 12/ ions, were measured with the use of a silicon p-n junction detector.
0 Comments
Leave a Reply. |