Binary fragmentations of excited nuclear systems in the 372 MeVFe56+Th232reaction

Abstract

The binary fragmentation of the excited superheavy system of Z = 116 formed in the reaction 372 MeV 56 Fe + 232 Th has been investigated. The fragment masses and kinetic energies were determined through measurement of the fragment velocities by the time-of-flight method. Neutron spectra were measured in coincidence with the fragments at several angles with respect to the fragment direction, which were analyzed to deduce the total as well as the pre-scission neutron multiplicities. We analyzed the correlations between fragment mass and kinetic energy, gated and nongated by the coincidence with neutrons, to learn about the dynamics of the reaction with respect to the two-body exit channels. The events in the near-mass-symmetric valley region appear to receive a significant contribution from the asymmetric mode of fission of the superheavy compound nucleus Z = 116, which can be due to the influence of the closed proton and neutron shells of Z = 50 and N = 82 in the light fragments. From the observed number of pre-scission neutrons, it is inferred that the time scales of the fissionlike reactions leading to near-mass-symmetric splits are rather large, of the order of several times 10 −20 s. The average number of prompt neutrons emitted in the spontaneous fission of such a superheavy nucleus is ν = (12 ± 1), as deduced from the neutron measurements.

Mass, total kinetic energy, and neutron multiplicity correlations in the binary fragmentation of Ti50+Pb208 at 294 MeV bombarding energy

“…Q eff is the effective Q value for fission defined as Q eff = Q Fiss − TKE and represents the available energy for fission when the CN is populated in its ground state. The value ν sf = 4.7 ± 1.4 is consistent with systematics of spontaneous and neutroninduced fission on heavy nuclei [25,26] and with the findings of previous works [9,10] for the superheavy nuclei Z = 116 and Z = 124.…”

“…Neutron-γ discrimination was achieved by using the zerocrossing method [16]. Intrinsic neutron detection efficiency was calculated by Monte Carlo simulations as a function of the experimental neutron detection threshold [9,10,15]. The energy detection threshold was determined by calibrating the energy deposited in the scintillators with 60 Co, 137 Cs, and 54 Mn γ sources.…”

“…The energy balance of the reaction process for the different mass cuts can be derived by using the experimental neutron multiplicity along with the measured total kinetic energy [9,10].…”

“…In the past [9,10], fragment-fragment-neutron correlations have been studied for the binary fragmentation of the 56 Fe + 232 Th, 80 Se + 208 Pb, and 80 Se + 232 Th at center-ofmass energies from 300 to 470 MeV. The excitation energies of the equilibrated CN (Z = 116 and 124) range from 50 to 180 MeV.…”

Nuclear tracks in PADC induced by neutron, heavy ion and energetic fragments formed in the reaction 54Cr+208Pb, at 320MeV

“…Dynamics of binary fragmentation and fusionfission of nuclear systems produced through reactions in the frontiers of nuclear physics has been studied in the past with active detectors. Sahu et al (2005) give an interesting results for the fragment mass distribution for the 372 MeV 56 Fe þ 232 Th reaction meanwhile Thomas et al (2007) investigated the mass distribution of fission and binary fragmentation of the excited nuclear system with Z ¼ 116 in the 80 Se þ 208 Pb reaction (470-630 MeV). Togo et al (2007) give experimental evidence that passive PADC detector's are useful in studies of Fe, Si and C ion interactions with CR-39 (C 12 H 18 O 7 ) and Al targets due to their sensitivity for a wide range of charges above Z ¼ 6e in the relativistic energy region.…”