Effects of finite ground-state spin on fission fragment angular distributions following collisions with spherical or deformed nuclei

Abstract

The influence of the ground-state spin of fusing nuclei on the subsequent fission fragment angular distributions has been investigated through realistic quantum-mechanical calculations. The domain of applicability of an approximate formula is found for spherical nuclei. For deformed nuclei, a generalization of the standard transition state model expression for the fission fragment angular distribution is presented. This predicts dramatic changes in the shape and anisotropy of the distribution, for reactions of deformed nuclei with large ground-state spin.

Review of metastable states in heavy nuclei

“…Furthermore, Butt et al [345] have demonstrated that fission angular distributions following fusion are very sensitive to the input angular momentum, providing another probe of the reaction mechanism. These predictions could be tested equally well with other isomers such as the K = 15 state in 184 Hf identified in storage-ring measurements [82,83].…”

“…Significant cross-section differences will arise using a projectile (or target) of something like the 178 Hf isomer, whose large angular momentum of = π + K 16 would dramatically skew the input l-distributions compared to normal beams. Furthermore, Butt et al [343] have demonstrated that fission angular distributions following fusion are very sensitive to the input angular momentum, providing another probe of the reaction mechanism. These predictions could be tested equally well with other isomers such as the K = 15 state in 184 Hf identified in storage-ring measurements [82,83].…”

Experimental studies of the competition between fusion and quasifission in the formation of heavy and superheavy nuclei

“…One type of fission-like events was seen in interactions of heavy projectiles (e.g. 84 Kr), where the yield of (mass-symmetric) fusion-fission was found to be much lower than expected, and there was a large yield of fully damped events with some mass evolution towards symmetry [17]. This process was initially described as [17] "the deepest inelastic collisions", or alternatively "quasifission" [69].…”

“…This process was initially described as [17] "the deepest inelastic collisions", or alternatively "quasifission" [69]. Figure 1(a) shows the fragment mass vs. Total Kinetic Energy distribution, for binary reaction products in the 84 Kr + 186 W reaction forming Ds (Z=110). The spectrum was determined from the two fragment kinetic energies recorded using Si detectors at 40 degrees.…”

“…This is called the anisotropy. To a reasonably good approximation, when M is small [84], the anisotropy can be written…”