T. Materna

Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam

An environmentally safe liquid/solid tritium target suitable for beams of radioactive nuclei was created and used in the study of t+d and t+t transfer reactions with putting emphasis on the observation of 4H and 5H resonance states. A state of 4H with Eres=3.22±0.15u2009MeV and Γobs=3.33±0.25u2009MeV was obtained in t+d reaction from the spectra of protons leaving the target at θlab=18°–32° and detected in coincidence with tritons. A valuable fraction of protons detected in t+t reaction at θlab=18°–32° in ptn coincidence events was attributed to the states of 5H nucleus. At ∼2.5 MeV above the tnn decay threshold the 5H spectrum shows up a narrow maximum followed by a wide structure at 4–7 MeV. One can not exclude that interference effects could modify the observed 5H resonance maximum resulting in its energy shift and width reduction.

SHELL EFFECT MANIFESTATION IN MASS-ENERGY DISTRIBUTIONS OF FISSION AND QUASI-FISSION FRAGMENTS OF NUCLEI WITH Z=102-122

The mass-energy distributions of the fragments, fusion-fission (OFF) and capture (oCap) cross-sections in the reactions 26Mg+248Cm; 48Ca+2RPb, 232Th, 238U , 2 4 4 ~ u , 2 4 8 ~ m ; 244Pu, 248Cm were measured at the U400 accelerator of Flerov Laboratory of Nuclear Reactions (JINR, Russia) with use of double-ann time-of-flight spectrometer CORSET. The influence of reaction entrance channel on the competition between fusion-fission and quasi-fission processes was studied. Strong manifestation of the shell effects in mass distributions of fusion-fission and quasi-fission fragments was observed. The multimodal fission phenomena were found for 2 7 4 H ~ and 256N0 nuclei at low excitation energies. % ~ ~ 2 0 8 p b , 232~h,

Dynamics of fusion‐fission process in superheavy mass region

The fusion‐fission process for the synthesis of superheavy elements is discussed on the basis of the fluctuation‐dissipation model. Recently the experiments at Dubna on fission of superheavy nuclei were carried out, and the mass and total kinetic energy distributions of fission fragments were measured. By analyzing the mass distribution of fission fragments, we can distinguish between fusion‐fission process and quasi‐fission process. We employ three‐dimensional Langevin equation. We find almost all of the mass symmetric fission events come from the quasi‐fission process in the superheavy mass region. In order to classify the fusion‐fission paths and compare with the experimental data directly, we analyze the pre‐scission neutron emission in the correlation with fission fragments. The neutron multiplicity depends on the travelling time of the trajectory. It is useful to investigate the fusion‐fission process.

FUSION-FISSION DYNAMICS OF SUPERHEAVY NUCLEI BY THE FLUCTUATION-DISSIPATION MODEL

We discuss the fusion-fission process in superheavy mass region. By analyzing the mass distribution of fission fragments, we can distinguish between fusion-fission process and quasi-fission process. We investigate the process using the fluctuation-dissipation model and employ the three-dimensional Langevin equation. We find a lot of mass symmetric fission events come from the quasi-fission process in the superheavy mass region. In order to classify the fusion-fission paths and compare with the experimental data directly, we analyze the pre-scission neutron emission in the correlation with the fission fragments. The neutron multiplicity depends on the travelling time of the trajectory. It is useful to investigate the fusion-fission process.

COMPETITION BETWEEN FUSION-FISSION AND QUASIFISSION IN HEAVY-ION REACTIONS LEADING TO SUPERHEAVY ELEMENTS

Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna, Russia I Universite Libre de Bruxelles, Bruxelles, Belgique 21nstitut de Recherches Subatomiques, CNRS-IN2P3, Strasbourg, France Department of Physics, University of Messina and INFN, Italy Institute of Nuclear Physics of the National Nuclear Center of Kazakhstan 480082 Almaty, Kazakhstan Institute of Physics SASc, 84228 Bratislava, Slovakia

STUDY OF SUPER HEAVY HYDROGEN NUCLEI OBTAINED IN TRANSFER REACTIONS WITH EXOTIC BEAMS AND TARGETS

Experimental study of super heavy hydrogen nuclei has been carried out using upgraded ACCULINA facility. New results about 5H and 4H resonance states were obtained with the use of primary triton beam (E=19 AMeV) or 6He secondary beam (E=25 AMeV) and liquid tritium or gas deuterium targets. As a result of investigation of the two-neutron transfer reaction 3H(t,p)5H two resonance states situated at 1.8+0.1 and 2.7 k 0.1 MeV above the t+n+n decay threshold were obtained in the missing mass energy spectrum of the 5H. In the case of 2H(6He,3He)5H reaction only one peak close to E 5 ~ = 1 . 8 MeV was clearly seen. The position and width of the 4H resonance state, &=3.3 MeV and

Investigation of t + t collisions using the ACCULINNA beam line

=2.3 MeV, were deduced from the study of t + t and t+d reactions. Negative result of H observation in stable state or having life time >3*10-9 s was obtained when thick liquid deuterium target was bombarded by *He beam (E=Z9.9 AMe V).

Shell effects in fission and quasi-fission of heavy and superheavy nuclei

Recently, an environmentally safe liquid-tritium target [1] was installed at the radioactive beam line of the ACCULINNA [2] separator working with primary beams of the U-400M cyclotron. The target cell has a material thickness of 0.4 mm for tritium, a beam opening of 10 mm diameter and the entrance and exit windows closed with two pairs of 12-μm stainless steel foils. The first experiment with the target was perfomed on a primary beam of 58 MeV tritons from the U-400M cyclotron. The separator ion optics was used to select a beam having energy and angulardistribution widths of > 0.5% and > 0.5°, respectively. Being delivered to the target the triton beam with an intensity of 1 x 107 s−1 was focused in a 4-mm spot. The detection system consisted of two large-area position-sensitive Si telescopes for charged particles and a neutron wall based on 41 DEMON [3] modules. The parameters of the experiment were optimized in such a way that the target thickness, beam energy spread and angular resolution made comparable contributions to the overall energy resolution. As an example, the resolution of the two-neutron transfer reaction which leads to 5H formation should be about 300 keV in the scale of excitation energy of the resonance.