Near-barrier fission of the system12C+232Th

Abstract

Abstract. The fission fragment angular distributions for the system 12C + 232Th have been measured in the energy range 0.97 < Ec.m./VB < 1.22. The measured anisotropies have been compared with the predictions of the standard saddle point statistical model, using the second moment of the compound nucleus spin distribution (I 2) deduced from a Wong model fit to the fission excitation function. While the measured anisotropies agree with the standard saddle point statistical model for E .... /VB > 1.05, they are abnormally large at lower energies. This is also true for the existing measurements of 160 and 19F -+-232Th systems. Since for this system pre-equilibrium fission contributions are not expected, this anomaly indicates strong channel coupling effects leading to an increase in (/2) at sub-barrier energies.

Measuring Barriers to Fusion

“…The fission anisotropies (Figure 15b, d ) show the same qualitative features determined in other measurements (108,112,113,115,116,118), although quantitative differences occur. The expected energy dependence of the anisotropy based on TSM calculations is indicated by the dot-dashed curves, and no reasonable variation of parameters could reproduce the data.…”

“…For reactions with actinide targets at near-barrier energies, a different and puzzling behavior was persistently observed. The anisotropies increased (108,(112)(113)(114)(115)(116) to values much larger than TSM predictions as the beam energy dropped through the fusion barrier region. A method developed (79) to isolate fission following capture in the fusion potential pocket from fission of target-like nuclei, using the deduced velocity vector of the fissioning nucleus, resulted in more reliable data and helped to clarify this anomaly.…”

“…S + 110 Pd (87),40 Ca +116,124 Sn (88), and40 Ca +90,96 Zr(52,53), and barrier distributions have been extracted to investigate the effects of two-or more neutron transfer channels with positive Q values. The 32,36 S + 110 Pd and40 Ca +90,96 Zr measurements are discussed, since they show typical effects of two-neutron and possibly multineutron transfer on fusion cross sections and barrier distributions.…”

Evidence of Complete Fusion in the Sub-BarrierO16+U238Reaction

“…Recently, there has been much interest in the fission fragment angular distribution in sub-barrier heavy-ion reactions using actinide targets [1][2][3][4][5][6][7][8]. This is because of the observation that the angular anisotropies [A W180 =W90 ] in the sub-barrier region show much larger values than the prediction of the standard transition state model (TSM) [9].…”