The β decay of 82 Ge was re-investigated using the newly commissioned tape station BEDO at the el... more The β decay of 82 Ge was re-investigated using the newly commissioned tape station BEDO at the electron-driven ISOL facility ALTO operated by the Institut de Physique Nucléaire, Orsay. The original motivation of this work was focused on the sudden occurrence in the light N = 49 odd-odd isotonic chain of a large number of J ≤ 1 states (positive or negative parity) in 80 Ga by providing a reliable intermediate example viz. 82 As. The extension of the 82 As level scheme towards higher energies from the present work has revealed three potential 1 + states above the already known one at 1092 keV. In addition our data allow ruling out the hypothesis that the 843 keV level could be a 1 + state. A detailed analysis of the level scheme using both an empirical core-particle coupling model and a fully microscopic treatment within a Skyrme-QRPA approach using the finite-rank separable approximation was performed. From this analysis two conclusions can be drawn : i-the presence of a large number low lying low spin negative parity states is due to intruder states stemming from above the N = 50 shell closure and ii-the sudden increase, from 82 As to 80 Ga, of the number of low-lying 1 + states and the corresponding Gamow-Teller fragmentation are naturally reproduced by the inclusion of tensor correlations and couplings to 2p-2h excitations.
Bulletin of the Russian Academy of Sciences: Physics, 2007
The excitation functions for the fusion reactions with subsequent neutron evaporation, 197 Au( 6 ... more The excitation functions for the fusion reactions with subsequent neutron evaporation, 197 Au( 6 He, x n) 203x n Tl ( x = 2-7), and the neutron transfer reactions with production of the 196 Au and 198 Au isotopes have been measured. Unusually high cross section of the 198 Au isotope production at energies below the Coulomb barrier has been observed. Possible mechanisms of production and decay of the transfer reaction products are considered.
New results from a series of experiments dedicated to the study of the 12 C exotic state (the so ... more New results from a series of experiments dedicated to the study of the 12 C exotic state (the so called Hoyle state) are presented. In spite of the many investigations that have been carried out, the structure of this state (which lies above the threshold for breaking up into three alpha particles) is still unknown. The different models assume that the nucleus has an abnormally large size in this excited state. However, until recently, methods for measuring the radii of unbound states have not been suggested. The best way to solve this problem seems to be by measuring the angular distributions of elastic and inelastic scattering of 12 C on different target nuclei, and the determination of the radii is based on the fact that, at small scattering angles, the cross sections for direct reactions at high enough energies behave like Frauenhofer diffraction on a black ball. Accordingly, an experiment was performed aimed at measuring the elastic and inelastic angular distri butions of 12 C with an energy of (121.5 ± 0.5) MeV on a 12 C target. The elastic scattering was measured in the angular range from 18° to 50° in the c.m. system with uncertainty in the angle of measurement equal to Δθ = ± 0.6°. The inelastic cross section was measured for the 12 C excited state 2 + (4.44 MeV) and 0 + (7.65 MeV). Estimates were made for the diffraction radii for the ground and excited states. An increase was observed in the radius of the state at 7.65 MeV compared to those of the ground and first excited states.
Obtaining monochromatic beams of accelerated 6He ions with a near-Coulomb-barrier energy on the DRIB accelerator complex at the JINR
Instruments and Experimental Techniques, 2009
Two methods for obtaining monochromatic beams of accelerated 6He ions with energies around the Co... more Two methods for obtaining monochromatic beams of accelerated 6He ions with energies around the Coulomb barrier on the DRIB accelerator complex at the Joint Institute for Nuclear Research (JINR) is described. In the first method, the MSP-144 magnetic spectrometer is used as a monochromator of low-energy 6He beam after its passing through an energy absorber. The energy resolution of the
Bulletin of the Russian Academy of Sciences: Physics, 2010
Two methods for obtaining monochromatic beams of radioactive nuclei with energies near the Coulom... more Two methods for obtaining monochromatic beams of radioactive nuclei with energies near the Coulomb barrier on Joint Institute of Nuclear Research accelerator complex DRIBs are described. In the first method, an MSP 144 magnetic spectrometer was used as the monochromator of low energy 6 He beam obtained after passing through an energy degrader. In the second method, a specially developed probe was used for experiments with the internal beam of the DRIBs complex post accelerator (the U 400 cyclotron).
A technique for measuring the quadrupole deformation parameter of transuranium nuclei
Instruments and Experimental Techniques, 2008
ABSTRACT A method for determining the quadrupole deformation parameter of transuranium nuclei is ... more ABSTRACT A method for determining the quadrupole deformation parameter of transuranium nuclei is presented. This method is based on giant dipole resonance splitting in the photofission cross section. The experimental setup containing an avalanche counter of fission fragments, as well as a method for reconstructing the cross section from the measured dependence of the photofission reaction yield on the endpoint energy of the bremsstrahlung spectrum, are described. The setup was tested on the bremsstrahlung beam of the MT-25 microtron at the Flerov Laboratory for Nuclear Reactions of the Joint Institute for Nuclear Research. The test results—in particular, the measured excitation function of the uranium photofission reaction—are presented.
Excitation functions are measured for the fusion reactions 197 Au( 4 He, xn) 201−xn Tl that are i... more Excitation functions are measured for the fusion reactions 197 Au( 4 He, xn) 201−xn Tl that are induced by alpha-particle interaction with gold nuclei in the energy range 14-36 MeV and in which x neutrons (0 ≤ x ≤ 3) are evaporated. The stack-activation technique was used to record and separate reaction products. Experimental data on the fusion reactions followed by evaporation of one to three neutrons agree with results of previous studies. For the radiative-capture reaction 197 Au( 4 He,γ) 201 Tl, the upper limit on the cross section proved to be much lower. The excitation functions for the reactions subjected to measurements are compared with the results of calculations based on the statistical model and with the results of an experiment performed previously in a 6 He beam.
The decay of 84 Ga has been reinvestigated at the PARRNe online mass separator of the electron-dr... more The decay of 84 Ga has been reinvestigated at the PARRNe online mass separator of the electron-driven installation ALTO at IPN Orsay. The nominal primary electron beam of 10 μA (50 MeV) on a 238 UC x target in combination with resonant laser ionization were used for the first time at ALTO. Improved level schemes of the neutron-rich 83,84 Ge (Z = 32) isotopes were obtained. The experimental results are compared with the state-of-the-art shell model calculations and discussed in terms of collectivity development in the natural valence space outside the 78 Ni core.
Excitation functions for evaporation residues in the reactions 197 Au( 6 He, x n) 203−x n Tl, x =... more Excitation functions for evaporation residues in the reactions 197 Au( 6 He, x n) 203−x n Tl, x = 2-7, and 206 Pb( 6 He, 2n) 210 Po, as well as for neutron transfer reactions for the production of 196 Au and 198 Au in the interaction of 6 He with 197 Au were measured. The 6 He beam was obtained from the accelerator complex for radioactive beams DRIBs (JINR). The maximum energy of the beam was about 10 AMeV and the intensity reached 2 × 10 7 pps. The stacked-foil activation technique was used directly in the beam extracted from the cyclotron or in the focal plane of the magnetic spectrometer MSP-144. The identification of the reaction products was done by their radioactive γ-or α-decay. The fusion reaction with the evaporation of two neutrons was characterized by an increase in the cross-section compared to statistical model calculations. The analysis of the data in the framework of the statistical model for the decay of excited nuclei, which took into account the sequential fusion of 6 He has shown good agreement between the experimental and the calculated values of the cross-sections in the case of sub-Coulomb-barrier fusion in the 206 Pb + 6 He reaction. An unusually large cross-section was observed below the Coulomb barrier for the production of 198 Au in the interaction of 6 He with 197 Au. Possible mechanisms of formation and decay of transfer reaction products are discussed.
Excitation Functions for Complete Fusion and Transfer Reactions in the Interaction of 4He Nuclei with 197Au
Excitation functions have been measured for the fusion reaction 197Au(alphaxn)201-xnTl with the e... more Excitation functions have been measured for the fusion reaction 197Au(alphaxn)201-xnTl with the evaporation of x neutrons (0<=x<=3) in the energy range 14-36 MeV. The induced-activation method was used for registration and identification of the reaction products. The experimental cross sections for the (1-3)-neutron evaporation residues are in good agreement with the results known from literature. For the radiation capture reaction
The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich... more The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238 U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208 Hg to 218 Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the beta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in r-process model calculations. Further measurements around N ∼ 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.
Forthcoming experiments aimed at studying the mechanism of collinear cluster tripartition are pla... more Forthcoming experiments aimed at studying the mechanism of collinear cluster tripartition are planning to be performed with the new facility. Charged products will be registered with the double arm time-of-flight spectrometer composed of mosaics of PIN-diodes and MCP (micro channel plates) based timing detectors. Several tens of 3 He-filled counters will be gathered round the 252 Cf source. In order to choose an optimal configuration of the neutron detector and other parameters of the experiment special modeling has performed using both "neutron barrel" and known MCNP code. The first test run of the new facility is in progress also its "neutron skin" in under construction.
First Delayed Neutron Emission Measurements at Alto With the Neutron Detector Tetra
Exotic Nuclei, 2013
ABSTRACT Beta decay properties are among the easiest and therefore, the first ones to be measured... more ABSTRACT Beta decay properties are among the easiest and therefore, the first ones to be measured to study new neutron rich isotopes. Eventually it could be sufficient just a few number of nuclei to estimate its lifetime and neutron emission probability. With the new radioactive beam facilities which have been commissioned recently (or will have been constructed shortly) new areas of neutron rich isotopes are becoming reachable. To study beta decay properties of such nuclei at IPN Orsay in the frame of collaboration with JINR, Dubna a new experimental setup including the neutron detector TETRA of high efficiency was developed and commissioned.
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