Angular Momentum Effects on Mass Division in Actinide Fission

Abstract

Angular momentum (/) effects on mass yield curves were studied for the fission from the same compound nucleus (CN) 239 Np of the same excitation energy but with different angular momenta, produced by the 7 Li+ 232 Th and p+ 2M U reactions. The effects were examined only for the complete fusion-fission events after careful estimation of the contribution of incomplete fusion-fission. It is found that the width of the whole mass yield curve is larger while the peak-to-valley ratio is smaller for the 7 Li+ 232 Th fission at the same excitation energy (E x ) of the CN, the former value increases while the latter ratio decreases with Ex. Statistical model calculations incorporating angular momentum dependent fission barriers were made to reproduce the observed cross section data of evaporation residues and fission. The observations can well be explained if the angular momentum dependence of fission barriers is taken into account in the competition process of fission and neutron evaporation in the decay of a compound nucleus except the observed trend of the width of the mass yield curve which could not be explained straightforwardly.

Charge and mass distribution in7Li induced fission of232Th

“…This analysis indicates that the magnitude of transfer induced fission may be small. This is consistent with the observation of Zhao et al [9]. PACE2 code was also used to calculate the complete fusion fission cross section (CFF) and cross sections of evaporation residues formed following complete fusion.…”

“…The mass distribution is asymmetric, which is typical of low energy fission of actinides. Zhao et al [9] have also reported the asymmetric mass distribution in 7 Li induced fission of 232 Th at similar excitation energies. In order to extract the total fission cross section, the cumulative yields of various mass chains were fitted as sum of two Gaussians.…”

“…7 Li is a weakly bound projectile like 11 B and therefore, it is expected to have significant transfer reaction cross section. But, recent work of Zhao et al [9] indicates negligible transfer induced fission cross section in 7 Li + 232 Th system. In the *Author for correspondence (E-mail: avreddy@magnum.barc.ernet.in).…”

“…Cross sections of evaporation residues formed following complete fusion as well as transfer reaction have also been measured. The measured data in the present work have been compared with the results of Zhao et al [9]. The evaporation residue cross sections were used to obtain an estimate of transfer induced fission cross section with the statistical model calculations using PACE2 code [10].…”

Production of235Np,236Pu and237Puvianuclear reactions on235,236,238U and237Np targets

“…6. Cross sections of the following reactions: a) 238 U( p, 3n) 236m Np (1), 238 U( p, n) 238 Np β − −→ 238 Pu (2) and 238 U( p, 3n) 236m Npβ − −→ 236 Pu (3)[7,8]; solid and dashed lines are polynomial fits of the experimental cross sections; crosses and triangles are from[25], diamonds -from[33]; b) 236 U( p, n) 236m Np (1), 236 U( p, 2n) 235 Np (2) and 236 U( p, 3n) 234 Np (3)[4,5]; solid lines are results of the theoretical calculations from[4]; c) 237 Np( p, 2n) 236 Pu (1) and 237 Np( p, pn + d) 236m Np (2); circular and rombic points were derived in work[9], E p = 10.9-17.5 MeV; squared and triangular points are from[10], E p = 15.9-39.6 MeV; solid lines are spline fits of experimentally determined cross sections; d)237 Np( p, n) 237 Pu (1) and 237 Np( p, 2n + pnβ − + dβ − ) 236 Pu (2); circular and rombic points were derived in work[9], E p = 10.9-17.5 MeV; squared and triangular points are from[10], E p = 15.9-39.6 MeV; solid lines are spline fits of experimentally determined cross sections; e) 237 Np( 3 He, 4nε + p3n + 2 p2nβ − ) 236 Pu (1), 237 Np( 3 He, 3nε + p2n) 237 Pu (2) and 237 Np( 3 He, 2nε + pn + 2 pβ − ) 238 Pu (3)[4,5,11,12]; solid lines are polynomial fits of the experimental cross sections; f) 236 U( 3 He, t) 236m Np (1), 236 U( 3 He, p3n) 235 Np (2) and 236 U( 3 He, p4n) 234 Np (3) [6, 14 and this work]; solid lines are polynomial fits of the experimental cross sections; g) 236 U( 3 He, n + pβ − ) 238 Pu (1) and 236 U( 3 He, p2nβ − ) 236 Pu (2)[6,14]; solid lines are polynomial fits of the experimental cross sections; h) 236 U( 3 He, 2n) 237 Pu; solid line is polynomial fit of the experimental cross sections[6,14].…”