Coincidence studies of heavy fragment pairs in the reaction 343 MeV40Ar+197Au

Abstract

Nuclear Reactions: 197Au (~~ fission-like reactions), E=343MeV, measured energy and angular correlations for heavy-fragment pairs. Evolution shown from fission-like to projectile-target-like products. Analysis made of the fission-like reactions in terms of complete vs. incomplete fusion.Measurements are reported for correlated energies and angles of heavy fragments from reactions of 343 MeV ~~ with 197Au. The results show a continuous evolution of the mass distributions from fission-like products at angle pairs of ~60 and 300 degrees to deeply inelastic projectile-like products at ~45 ~ and 300 ~ Certain difficulties are emphasized for the use of the "symmetric fragmentation" cross sections in the context of current theoretical models (e.g. the "extra push" theory). The fission-like reactions have been studied in some detail and the results have been compared to a Monte Carlo kinematic simulation. To account for the experimental results forward-peaked light particle emission (n, H, He) must occur in a large fraction of the fission-like reactions.

Correlations between fission fragments and light charged-particles in the reaction20Ne+197Au at 13 MeV/nucleon

“…Therefore, it can be deduced that the fission cross section measured here is the sum of the cross section for fission of a totally equilibrated compound nucleus and of that for fast fission [15]; in the latter process, the characteristics of the symmetric fragmentation are determined at the turning point rather than at the equilibrium saddlepoint. The cross section value measured here is slightly lower than the one obtained at 172 MeV on the same system by Duek et al [16] (1,570 mb). Although the error bars are large, this could be an indication of a limitation of the fusion cross section when the energy grows up.…”

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

“…These and other studies of fission angular correlations have implied that this phenomenon requires incident energies of > 10MeV/u [11][12][13][14][15][16][17][18]. The results reported here and in [8,23,[29][30][31] show that extensive incomplete fusion occurs at lower energies as well. It is possible to make a rough estimate of the importance of incomplete fusion for the particular reaction studied here, 172MeV 2~…”

“…Also fission after incomplete momentum transfer has been clearly identified for beams of >15MeV/u 4He, and strongly suggested for 12MeV/u ZONe [16][17][18]. Reactions induced by 6.5 -12 MeV/u 32S and 4~ have been extensively studied by various methods as discussed in the following paper [23]. We chose for this study the reaction 172 MeV Z~ +197Au.…”

Violence of Heavy-Ion Reactions from Neutron Multiplicity: (11 to 20)A-MeVNe20+Jahnke1, Ingold2, Hilscher3 et al. 1986Phys. Rev. Lett.16130View full textAdd to dashboardCite

“…The recent availability of medium-energy heavy-ion beams in the range of 20 to 50 MeV/nucleon, where the transition from mean-field to nucleon-nucleon dominated collisions is expected to occur, has promoted a veritable renaissance 1 -2 of this 25-year-old folding-angle technique 3 and also considerable refinements: Energy and velocity of the fission fragments have been measured 4 and coincidence experiments have been performed on both fragments and outgoing projectile remainders. 5 Neither type of experiment, however, allows a complete reconstruction of the reaction kinematics and thus a reliable access to the excitation energies involved, either because of preceding light-particle evaporation or because of sequential breakup of the projectile residues, which is by no means negligible 6 even in the lower-energy domain.…”

“…A smaller part of the discrepancies might also be due to the neglect of the dispersion of the fission fragments in mass and energy, as well as the defocusing effect of the light-particle evaporation. These effects could be incorporated in a kinematic reaction simulation similar to the one performed only recently by Duek et al 4 Furthermore, in these simulations the implicit assumption made above that the uncaptured projectile residues proceed undeflected and with the beam velocity could be relaxed in favor of the experimental observation of a rather broad distribution in energy and angle (see for instance Awes et al n for the precompound charged-particle emission).…”