Binary character of highly dissipativeBi209+136<

Abstract

Exclusive measurements of neutrons and charged products have been performed using a combination of 4/r neutron and 4n charged-particle detectors. The maximum observed energy dissipation corresponds to only approximately one-half of the available kinetic energy. For any degree of dissipation, the velocity distributions of charged particles are characteristic of sequential emission following binary collisions. The data imply that central collisions also lead to bimodal emission patterns or that they are not sufficiently well isolated by the requirement of high particle multiplicities. PACS numbers: 25.70.Lm During the last few years, considerable effort [1] has been devoted to the search for novel reaction mechanisms and nuclear decay modes that have been postulated for the Fermi energy domain [2-5]. Such novel reaction scenarios include the formation of inherently unstable, hot, and possibly compressed mononuclei that are predicted either to expand and eventually disintegrate into multiple fragments of intermediate mass (IMFs) or to vaporize into a multitude of light particles. Features similar to those expected for such processes have been observed in heavy-ion reactions at intermediate bombarding energies [6-11], but their interpretation is subject to considerable ambiguities. In order to resolve some of these ambiguities, the strategy adopted in the present work was to explore how the binary reaction dynamics characteristic of weakly dissipative, peripheral heavy-ion collisions evolves with increasing energy dissipation for the very heavy system 209 Bi+ ,36 Xe at 28.2 MeV per nucleon, i.e., at the lower boundary of the Fermi energy domain. As suggested by systematics established at lower bombarding energies [12], such a heavy system is likely to exhibit a gradual evolution of a rather uniform dissipative reaction mechanism over a significant range of impact parameters, which would simplify the detection of the onset of a new, competing process.The present paper reports on the first experiment of its kind in which almost full solid-angle coverage for both neutrons and charged particles was achieved. The experiment was performed at the National Superconducting Cyclotron Laboratory of the Michigan State University. A beam of 28.2 MeV per nucleon l36 Xe ions from the K1200 cyclotron was focused on a self-supporting 209 Bi target (1.5 mg/cm 2 ) placed in the center of the internal scattering chamber of the Rochester neutron multiplicity meter (NMM). The NMM, providing information on multiplicity and summed neutron energy, has an outer

Deep inelastic collision followed by disassembly in the reactionXe136+Bondorf1, Dasso2, Donangelo3 et al. 1993Phys. Rev. C2010View full textAdd to dashboardCite

“…This reaction scenario has been confirmed recently by exclusive measurements performed by Lott et al with a combination of 4m neutron and 4~charged-particle detectors [4]. The data suggest that even rather central collisions may be dominated by events in which the identity of a projectilelike and a targetlike fragment is well preserved.…”

Short timescale behavior of colliding heavy nuclei at intermediate energies

“…The multiplicity of neutrons saturates for mid-central collisions, making neutron multiplicity a poor selector of central collisions. The geometric crosssection combined together with the saturation of excitation energy for mid-peripheral collisions may explain the observed persistence of binary collisions at intermediate energies even when the largest neutron multiplicities are selected [47].…”

Possibility of production of neutron-rich isotopes in transfer-type reactions at intermediate energies

“…Indeed, the value of B Z,N,J Z,N contains the corresponding Q value. As known from the experimental study of deep inelastic collisions, the isotopic distribution follows the Q gg systematics [12,14,22].…”

“…[22,23], in the 209 Bi + 136 Xe and 197 Au + 208 Pb reactions at the lower boundary of the Fermi energy domain the total reaction cross section is almost entirely accounted for by binary collisions irrespective of a possible further disassembly of the two highly excited primary partners. The dissipative binary dynamics at these bombarding energies have been also observed in Refs.…”