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.
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.
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 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.
This report describes a series of experiments aimed on investigating characteristics of spontaneous fission of nuclei in the exotic region of short-lived neutron-deficient isotopes with Z ≥ 100. ...Unique data on the decay properties of neutron-deficient isotopes 244,246Fm, 250No, 252No, 254Rf and 256Rf produced in the complete fusion reactions with accelerated heavy ions 40Ar + 206,208Pb → 246,248Fm*, 48Ca + 204,206Pb → 252,254No*, 50Ti + 206,208Pb →256,258Rf* were obtained in experiments at the VASSILISSA (SHELS) separator combined with a neutron detector.
Alpha-decay spectroscopy of 257Rf Hauschild, K.; Lopez-Martens, A.; Chakma, R. ...
The European physical journal. A, Hadrons and nuclei,
2022/1, Letnik:
58, Številka:
1
Journal Article
Recenzirano
The decay properties of states in
257
Rf have been investigated with the detector array GABRIELA at the FLNR, Dubna. The electromagnetic decay of a new excited state in
253
No has been observed. The ...state lies 750 keV above the ground state and is favourably populated in the alpha decay from a low-lying isomeric state in
257
Rf. It decays to the 9/2
-
ground state by an M1 transition and is assigned the 11/2
-
725 Nilsson configuration. The presence of this state suggests a possible reinterpretation of the decay of the high-K isomer in
253
No. Due to the favoured nature of the
α
-decay the 11/2
-
725 Nilsson configuration is also assigned to the first excited state of
257
Rf, lying at 74 keV.
The GRAND universal gas-filled separator, located at the Factory of Super-Heavy Elements in the Flerov Laboratory of Nuclear Reactions (FLNR), Joint Institute for Nuclear Research, has been created ...and put into operation. The separator can be used both in experiments on α, β, and γ spectroscopy of isotopes of heavy and superheavy elements and in experiments on the chemical properties of superheavy elements as a preseparator. The results of the first experimental tests of the GRAND separator are presented. The possibility of effectively carrying out experiments both on a “physical” detection system and on a “chemical” installation has been demonstrated.
A great many experimental studies devoted to exploring in detail the properties of radioactive decay of the isotopes of transfermium elements by means of alpha, beta, and gamma spectroscopy have been ...performed over the past fifteen years at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research, Dubna). High-intensity accelerated heavy-ion beams of
Ne,
Ca,
Ti, and
Cr from the U-400 cyclotron were used in experiments with the SHELS kinematic separator. An upgrade of the separator and detector system is planned in the future with the aim of improving the transportation efficiency for the nuclei under study and the detection efficiency for gamma rays.
The SFiNx Detector System Isaev, A. V.; Yeremin, A. V.; Zamyatin, N. I. ...
Physics of particles and nuclei letters,
02/2022, Letnik:
19, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A new detector system for investigating the properties of spontaneous fission of short-lived transuranium nuclei has been created. This system consists of an assembly of double-sided silicon strip ...detectors surrounded by 116 proportional neutrons counters filled with
3
He. The neutron registration efficiency is 54.7 ± 0.1%. The detector system is tested in an experiment investigating the characteristics of spontaneous fission of the
252
No isotope. The experimental data on neutron yields are compared with previously published results. The average number of neutrons per fission act (
= 4.25
0.09) and the multiplicity distribution of prompt neutrons are obtained. The true form of the neutron distribution is reconstructed via a statistical regularization.
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