GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyzer) is a detection system installed at the focal plane of the SHELS (Separator for Heavy Elements Spectroscopy) recoil ...separator for gamma and internal conversion electron spectroscopy of heavy and superheavy nuclei. GABRIELA has recently been upgraded. The characteristics of the new setup are presented using the
Geant4
Monte Carlo simulation toolkit and validated against experimental results. The impact of summing on the gamma-ray and electron detection efficiencies is discussed.
The analysis of fission events following the implantation of evaporation residues produced in the fusion reaction of 50Ti and 209Bi at different bombarding energies has revealed 5 millisecond decays, ...which are attributed to the spontaneous fission of proton-evaporation channels. The average cross sections for proton evaporation are found to be ∼100 and 10 times smaller than the largest neutron-evaporation channel cross section at the same excitation energy. These results suggest that the proton evaporation channel, albeit weak, may represent a realistic alternative to synthesize new, more neutron rich super heavy nuclei.
The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in ...groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of 283112 through the alpha decay of the short-lived 287114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of 283112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.
The new neutron-deficient isotope
249
No was synthesized for the first time in the fusion-evaporation reaction
204
Pb(
48
Ca,3n)
249
No. After separation, using the kinematic separator SHELS, the new ...isotope was identified with the GABRIELA detection system through genetic correlations with the known daughter and granddaughter nuclei
245
Fm and
241
Cf. The alpha-decay activity of
249
No has an energy of 9129(22) keV and half-life 38.3(2.8) ms. An upper limit of 0.2% was measured for the fission branch of
249
No. Based on the present data and recent information on the decay properties of
253
Rf and aided by Geant4 simulations, the ground state of
249
No is assigned the 5/2
+
622 neutron configuration and a partial decay scheme from
253
Rf to
245
Fm could be established. The production cross-section was found to be
σ
(3n)=0.47(4) nb at a mid-target beam energy of 225.4 MeV, which corresponds to the maximum of the calculated excitation function. Correlations of the
249
No alpha activity with subsequent alpha decays of energy 7728(20) keV and half-life
1
.
2
-
0.4
+
1.0
min provided a firm measurement of the electron-capture or
β
+
branch of
245
Fm to
245
Es. The excitation function for the 1n, 2n and 3n evaporation channels was measured. In the case of the 2n-evaporation channel
250
No, a strong variation of the ground state and isomeric state populations as a function of bombarding energy could be evidenced.
An experimental study of 256Rf spontaneous fission following the fusion reaction of 50Ti+208Pb was performed using the velocity filter SHELS of the Flerov laboratory at JINR. The average number of ...neutrons of ν‾=4.30±0.17 and variance of σν2=3.2 from the prompt neutron multiplicity distribution were obtained. The alpha decay branching ratio of bα=0.003−0.003+0.005 and the half-life of T1/2=(6.7±0.2) ms of the isotope were determined. For the first time, our neutron detector system allowed us to extend investigation of the prompt neutron multiplicity study to the superheavy element region.
The SHELS velocity filter originated upon reconstruction of the VASSILISSA electrostatic separator used for investigations of heavy nuclei produced in complete fusion reactions. The goals of this ...modernization were to increase the transmission of products of asymmetric reactions and to extend the region of reactions to be investigated up to symmetric combinations. The first tests of the set-up were performed with the beams of accelerated 22Ne, 40Ar, 48Ca, and 50Ti ions.
The current work discusses the experimental evaluation technique for the prompt neutron multiplicity distribution (PNMD) emitted is the spontaneous fission (SF). The restoring technique for the ...detector efficiency correction is shown as well as the comparison of two regularization parameter choice methods. The shape of the PNMD helps to achieve the information according the dynamic of the SF. The work also compiles all currently published PNMDs in the transfermium (Z > 100) region and discusses their shapes, providing a physical interpretation of the distortion of these distributions.
Alpha-decay spectroscopy of $$^{257}$$Rf Hauschild, K.; Lopez-Martens, A.; Chakma, R. ...
The European physical journal. A, Hadrons and nuclei,
01/2022, Letnik:
58, Številka:
1
Journal Article
The structure of the 102254No152 nucleus has been studied for more than 20 years: the last publications on its decay spectroscopy are from LBNL 1, GSI 2, JYFL 3 and ANL 4. Four decay schemes ...featuring two isomers have been published and are interpreted differently in terms of excitation energy and decay scheme of the 2nd isomer and configuration assignments of both K-isomers. These discrepancies have triggered new experiments including this one, performed with the GABRIELA 5, 6 array, at the focal plane of the SHELS 7 separator at the FLNR, Dubna. The first part of this proceeding will present the experimental setup and the analysis techniques used to reveal the electromagnetic decay of the known isomers in 254No. The second part will focus on the new results obtained with more than 1 million 254No nuclei implanted in the focal plane detector. In particular, the internal conversion electron spectrum observed in the decay of the 8− K-isomer has revealed the presence of a strong transition, most likely E0, suggesting low-lying shape coexistence in this nucleus as predicted in 8, 9. The γ-ray spectrum obtained from the decay of the short-lived 170 μs isomer has revealed new γ-ray lines putting in doubt the previous interpretations about this isomer decay.
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