Correlations between fission fragments for 172 MeV20Ne+197Au: A case study for incomplete fusion

Abstract

These data have been analyzed to test for fission after incomplete fusion and its admixture with fission generally attributed to the relatively pure compound-nucleus mechanism. A Monte Carlo kinematic simulation program has been written to provide a basis for detailed comparisons of the experimental data to the calculations that employ various mechanistic assumptions. We conclude that incomplete fusion is indeed a prominent precursor to fission even for incident energies of less than 10 MeV/u. Similar data from earlier studies have been reanalyzed and shown to be consistent with this conclusion.Nuclear Reactions: 197An (2~ fission), E=172MeV, measured energy and angular correlations for fission-fragment pairs. Analysis made of these and other similar studies by a Monte Carlo reaction-simulation program.

Ternary fission involving4He emission in the16O (144 MeV)+232Th and12C (108 MeV)+197Au reactions

“…The mean and FWHM values of the TKEI~AB and M F distributions presented in Fig. 2 are in agreement with the values obtained for similar systems in [22][23][24][25][26]. The comparison between the calculated curves and experimental points suggests that the fusion-fission reaction with the full momentum transfer is the main process in our case.…”

“…where temperature T=(8 U/A) -~ [22] and the coulomb barrier C=0.187Z+1.4 (MeV) [32]. Here U, A and Z are the excitation energy, mass and charge of the emitter, respectively.…”

Fission accompanied by alpha particle emission in the12C(85MeV)+232Th reaction

“…The LMT distribution for the fragment-fragment correlation measurement is centered around a value which constitutes 93% of Pbe,m" This high value is a proof of the dominant role of compound nucleus formation in the given reaction. According to the analysis performed in [13] for similar reactions, one may presume that the reduction below 100% is due to light particle emission prior to fission.…”

“…This conclusion is based on a Monte Carlo calculation (code ELPHIC) which for the (fl,f2) case under the assumption of the emission of n, p and alpha particles from the direct processes, compound nucleus and fission fragments gives FWHM of the LMT equal to 27.8% of LMT. For this simulation light particle emission probabilities were taken the same as for the 2~ + 197AH reaction in [13] (last row of Table 2 of this reference). The error of LMT determination is ~ 5% due to the errors of angle and energy measurements for the fission fragments.…”

“…system), which in the given case almost coincide with the energy corresponding to the beam velocity (28 MeV). The observed e particles may originate from a number of sources and as a result of different reaction mechanisms [1,2,12,13], e.g. evaporation from the compound nucleus, evaporation from the excited fission fragments; ternary fission, projectile break-up or break-up fusion, e activity of the different nuclei produced in fusion of the projectile (or part of it) with the target followed by neutron or charged-particle evaporation, preequilibrium emission, and others.…”