E. A. Sokol

Chemical procedure applied for the identification of Rf/Db produced in the 48Ca +243Am reaction

Summary A chemical separation procedure for Rf/Db is described which was applied to a long-lived decay product from the nuclear fusion reaction 48Ca+ 243Am. A 1.2 mg thick 243Am target was bombarded by 247 MeV 48Ca particles. The recoiling products were collected in a thick Cu catcher for about one day and then subjected to a chemical separation procedure that included an ion exchange from dilute HF solutions. Final samples were prepared on 30 μg/cm2 thick polyethylene (PE) foils and counted in 4π-geometry for α-particles and spontaneous fission (SF) coincidences. The detector arrays were surrounded by 3He detectors to also assay prompt neutrons. Decontamination factors from actinides of about 105 were achieved. Group 6 (W) to 14 (Pb) elements as models for their heavier homologues were shown to be separated from the Rf/Db fraction with more than 90%. In eight final samples, representing a total beam dose of 3.4 × 1018 particles, 15 SF events were detected. The decay pattern points to a single component with a half-life of ≈32h, which shows a chemical behavior similar to the lighter homologues of group 4 and 5 elements.

DRIPLINE NUCLEI PRODUCED BY QUASI-FRAGMENTATION OF THE 32,34,36S PRIMARY BEAMS

Some regularities in the production of isotopes with are investigated in reactions induced by beams at on targets , and . A search for using a beam of the neutron-rich has been performed. Evidence for particle instability of was obtained. In the same experiment, the half lives of the very neutron-rich isotopes and were measured for the first time.

Experimental Tests of the Modernized VASSILISSA Separator (SHELS) with the Use of Accelerated 50 Ti Ions

A high intensity ion beam of 50Ti ions was obtained using the ECR ion source on the U400 cyclotron. The experimental tests using accelerated 50Ti ions were performed with a modernized VASSILISSA separator (SHELS). Data has been obtained on the transmission coefficients of recoil nuclei synthesized in complete fusion reactions. Estimates from ion optical calculations performed in the design phase of the project of modernizing the separator are completely confirmed.

First Experimental Tests of the Modernized VASSILISSA Separator

The results of the first experimental tests of the modernized VASSILISSA separator with the use of accelerated 22Ne ions are presented. Data has been obtained on the transmission coefficients of recoil nuclei synthesized in asymmetric combinations of the incident ion and target nuclei. Estimates from ion optical calculations performed in the design phase of the project of modernizing the separator are completely confirmed.

Applications of 3He neutron detectors

Neutron detectors with 3He-filled proportional counters are described. The use of these detectors in measuring the probability of neutron emission (in particular, multiparticle neutron emission) after the β decay of neutron-rich nuclei and in studying rare events of spontaneous fission of superheavy nuclei is considered.

A detector for studying the characteristics of spontaneous fission of short-lived heavy nuclei

The detector system of the VASSILISSA separator has been complemented with an array of 54 3He neutron counters to study the multiplicity of prompt spontaneous-fission neutrons. The detection efficiency of the new neutron detector is 39%. The description of the detector system and the characteristics of 252No spontaneous fission, obtained in the test experiment in July of 2010, are presented.

THE MODIFIED MINI-FOBOS SETUP

The 4π spectrometer FOBOS was proved to be a high-efficiency tool for investigation of the characteristics of multi-body decays of hot heavy nuclei produced in nuclear reactions induced by heavy ions. The time-offlight measurements of charged fragments employing the radio-frequency (RF) signal of the cyclotron U400-M to deduce the START signal require no special START detectors and, hence, the big fraction of the total solid angle is available for particle detection. The lack of the RF signal in experiments aimed at search for the exotic decay modes in spontaneous fission enforces to use an additional START detector. The complicated target station equipped by a START detector shadows a large portion of detector modules making thus no sense to use the whole powerful detection system in such experiments. Therefore, it has been decided to build a simplified facility consisting of several standard FOBOS modules only. The miniFOBOS setup, a prototype of the FOBOS spectrometer, has been chosen for that purpose. It was exploited mainly to solve various method tasks related to the construction of the FOBOS spectrometer. The general idea of the modified miniFOBOS setup (MMF) consists in using a small reaction chamber which can be then unique for each experiment and the basic universal system maintaining the detectors. The special mounting cones are used to joint detectors with the reaction chamber (Fig. 1, 2). Such cones can be used, in particular, to build the high efficiency system joining six modules in the form of 3Dcross.

Spontaneous fission of 256 Rf, new data

Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in the complete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR, JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The average number of neutrons per spontaneous fission of 256Rf (\(\bar v = \;4.47 \pm \;0.09\)) is determined for the first time.

Characteristics of spontaneous fission of 250 No

This study describes an experiment on investigating the properties of spontaneous fission of shortlived neutron-deficient nuclei synthesized in the reaction of complete fusion 48Ca + 204Pb = 252No*. The experiment is performed using the SHELS separator and the beam of multicharged ions at U-400 accelerator (LNR, JINR). Two activities undergoing spontaneous fission, which can be related to the ground and isomeric states of 250No nucleus, are registered. The half-lives, total kinetic energies of fission fragments, and neutron multiplicities are measured for the short-lived nuclei. The average number of neutrons per fission for the activity with t 1/2 = 5.1 ± 0.3 μs is = 4.38 ± 0.13 μs, and for nuclei with the half-life t 1/2 = 36 ± 3 μs it is xxxxx.

Pygmy Gamow-teller Resonance in the

We report on the Pn measurements of the 82,83,84Ga (N = 51, 52, 53) precursors performed in one single experiment using the 3He neutron-counter TETRA at the ALTO facility in Orsay. Altogether our results for the three A = 82, 83 and 84 Ga isotopes point towards a sizable Pn staggering in the N = 50 region, similar to the one already known in the N = 28 region, hinting at a similar mechanism. We will discuss the possible microscopic origin of this behavior i.e. the existence in the N = 50 region of a low-lying component of the so called Pygmy Gamow-Teller Resonance, already well established at Z = 36, and persisting towards 78Ni.