A. A. Bogachev

The CORSET time-of-flight spectrometer for measuring binary products of nuclear reactions

The CORSET time-of-flight spectrometer has been developed at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna, Russia) for investigating binary products of nuclear reactions. The spectrometer has been used to study the dynamics of fusion-fission and quasi-fission of superheavy elements. The design and the main characteristics of the spectrometer, as well as the algorithms for deducing the mass-energy distributions of fragments and the cross sections of nuclear reactions, are presented. The spectrometer contains two time-of-flight arms based on microchannel-plate detectors and three telescopes, each of which is composed of two microchannel-plate detectors and one semiconductor detector. A system of four semiconductor detectors is used to obtain the absolute value of a cross section. The time resolution of the time-of-flight arms is 150 ps, which allows the time-of-flight distances to be set at 10–20 cm, thus providing a mass resolution of 3 amu and an angular resolution of 0.3°. Owing to these characteristics, the spectrometer can be used as a trigger in multidetector setups for measuring light charged particles, neutrons, and γ rays in coincidence with reaction fragments.

The Peculiarities of the Production and Decay of Superheavy Nuclei

The interest in the study of the fission process of superheavy nuclei mainly deals with the opportunity to obtain information about the cross‐section of the compound nucleus (CN) formation at excitation energies E*≈15–30 MeV. It allows one to estimate the survival probability of the superheavy composite system after evaporation of 1–3 neutrons, i.e. in “cold” or “warm” fusion reactions. However, in order to solve this problem deeper understanding of the coalescence processes between colliding nuclei, the competition between fusion‐fission and quasi‐fission processes is needed. The characteristics of both processes, their manifestation in the experimental observables and the relative contribution to the capture cross‐section in dependence on the excitation energies, reaction entrance channel etc were investigated for a wide range of target‐projectile combinations. Results of the experiments devoted to the study of the fusion‐fission and quasi‐fission processes in the reactions of the formation of the super...

Fission dynamics in the proton induced fission of actinide nuclei at intermediate energies

A multi‐parameter correlation study of the reactions 232Th(p,f), 238U(p,f) and 242Pu(p,f) at Ep=13, 20, 40 and 55 MeV has been conducted. The fission fragment mass, total kinetic energy distributions, double differential neutron spectra and γ‐ray spectra have been measured. The three humped shape of mass distributions has been observed up to higher proton energy. Pre‐equilibrium, pre‐scission and post‐scission neutron and γ‐ray multiplicities measured in coincidence with primary fission fragments provided access to fission dynamics. Shell structure effects were observed in fission fragment mass distributions even at high excitation energy. Manifestation of the nuclear shell Z = 28 near fragment mass Afr = 78 has been detected.

Proton induced fission of 232Th at intermediate energies

The mass-energy distributions and cross sections of proton-induced fission of 232Th have been measured at the proton energies of 7, 10, 13, 20, 40, and 55 MeV. Experiments were carried out at the proton beam of the K-130 cyclotron of the JYFL Accelerator Laboratory of the University of Jyväskylä and U-150m cyclotron of the Institute of Nuclear Physics, Ministry of Energy of the Republic of Kazakhstan. The yields of fission fragments in the mass range A = 60–170 a.m.u. have been measured up to the level of 10−4%. The three humped shape of the mass distribution up has been observed at higher proton energies. The contribution of the symmetric component grows up with increasing proton incident energy; although even at 55 MeV of proton energy the shoulders in the mass energy distribution clearly indicate the asymmetric fission peaks. Evolution of shell structure was observed in the fission fragment mass distributions even at high excitation energy.

Fission and Quasifission in the 'Warm' Fusion Reactions

Mass‐energy distributions, as well as capture cross‐section of fission‐like fragments for the reactions of 48Ca, 58Fe and 64Ni ions with actinides leading to the formation of superheavy compound system with Z = 112–120 at energies near the Coulomb barrier have been measured. Fusion‐fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability is approximately the same for the reactions with 48Ca ions and drops three orders of magnitude at the transition to 64Ni ions.

Fusion Probability in the Reactions {sup 58}Fe+{sup 244}Pu and {sup 64}Ni+{sup 238}U

Mass-energy distributions, as well as capture cross-section of fission-like fragments for the reactions {sup 64}Ni+{sup 238}U and {sup 58}Fe+{sup 244}Pu leading to the formation of superheavy compound system with Z = 120 and N 182 at energies near the Coulomb barrier have been measured. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability is about one order of magnitude higher for the reaction {sup 58}Fe+{sup 244}Pu than that for the reaction with {sup 64}Ni-ions.

Fragment mass distribution in 238U(d,pf)reaction at Ed = 124 MeV

Mass‐energy distributions of fission fragments in the deuteron induced fission of 238U at deuteron energy 124 MeV have been measured. For better understanding of the reaction mechanism, the inclusive proton spectra and proton spectra in coincidence with fission fragments were measured in the experiment.