The main goal of creation of a Superheavy Element Factory at the Flerov Laboratory of Nuclear Reactions (FLNR) is to sufficiently improve the efficiency of studies on heavy and superheavy nuclei. The ...factory will be based on a high-current DC-280 cyclotron. The use of beams with the intensity up to 6×1013s−1 (10pμA) requires effective separators providing high suppression of unwanted reaction products. Following the analysis of the kinematic characteristics of several hundreds of reactions, a conclusion was drawn that it is necessary to construct three separators optimized for specific tasks: a universal gas-filled separator for synthesis and study of the properties of heavy isotopes, a velocity filter for spectroscopic investigations, and a pre-separator for further chemical separation and precise mass measurements.
We present new results on multi-nucleon transfer reactions in low-energy collisions of
48
Ca
+
238
U
measured at the velocity filter SHIP of GSI Helmholtz Centre, where we observed around 90 ...different nuclides from Tl to Am (
Z
=
81–95). We followed the idea to use uranium targets for the synthesis of neutron-rich MNT products, particularly in the region below lead, which was triggered by model calculations. The
γ
,
α
and spontaneous fission activities of the populated nuclides have been analyzed for their identification. The cross-sections of the observed isotopes for elements
Z
=
81–93 as a function of their mass number have been investigated. Excitation energy, total kinetic energy and the influence of nuclear shell effects on the production cross-sections of the observed transfer products have been studied. Also we present a compact review and comparative analysis of various multi-nucleon transfer and fragmentation reactions which are aimed at the synthesis of neutron-rich nuclides along the
N
=
126
shell closure in heavy nuclei.
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 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.
In deep inelastic multinucleon transfer reactions of 48Ca + 248Cm we observed about 100 residual nuclei with proton numbers between Z=82 and Z=100. Among them, there are five new neutron-deficient ...isotopes: 216U, 219Np, 223Am, 229Am and 233Bk. As separator for the transfer products we used the velocity filter SHIP of GSI while the isotope identification was performed via the α decay chains of the nuclei. These first results reveal that multinucleon transfer reactions together with here applied fast and sensitive separation and detection techniques are promising for the synthesis of new isotopes in the region of heaviest nuclei.
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.
.
The reaction
54
Cr$ + $
248
Cm
was investigated at the velocity filter SHIP at GSI, Darmstadt, with the intention to study production and decay properties of isotopes of element 120. Three ...correlated signals were measured, which occurred within a period of 279ms. The heights of the signals correspond with the expectations for a decay sequence starting with an isotope of element 120. However, a complete decay chain cannot be established, since a signal from the implantation of the evaporation residue cannot be identified unambiguously. Measured properties of the event chain are discussed in detail. The result is compared with theoretical predictions. Previously measured decay properties of even element super-heavy nuclei were compiled in order to find arguments for an assignment from the systematics of experimental data. In the course of this review, a few tentatively assigned data could be corrected. New interpretations are given for results which could not be assigned definitely in previous studies. The discussion revealed that the cross-section for production of element 120 could be high enough so that a successful experiment seems possible with presently available techniques. However, a continuation of the experiment at SHIP for a necessary confirmation of the results obtained in a relatively short irradiation of five weeks is not possible at GSI presently. Therefore, we decided to publish the results of the measurement and of the review as they exist now. In the summary and outlook section we also present concepts for the continuation of research in the field of super-heavy nuclei.
The standard reaction methods, such as fragmentation, fission or fusion used to synthesis exotic nuclei have reached their experimental limits. Multi-nucleon transfer (MNT) reactions are discussed as ...the potential method to reach the still unknown region of exotic proton/neutron rich heavy and superheavy nuclei. Studies of MNT reactions to follow this goal are presently a hot topic in diverse laboratories worldwide. At the velocity filter SHIP of GSI Darmstadt, our high sensitivity lead for the first time in collisions of
48
Ca +
248
Cm to the discovery of five new isotopes with
Z
92 produced in MNT reactions. As well, it enabled the observation of three nuclei of the quite heavy and neutron-rich isotope
260
No. These results are very promising for further studies of MNT reactions for the synthesis of new heavy and superheavy nuclei. The implementation of improved detection efficiency, a faster data acquisition system, the use of various actinide targets, a longer irradiation time along with optimal field settings will be beneficial. This additionally allows to suppress high background and to observe new neutron-deficient nuclides in the
Z
92 region of interest with a half-life of up to microseconds, also several above target nuclides located close to the border in the present nuclear chart are possible to reach. In this context, first experimental tests for separation of the transfer products with the use of velocity filter SHELS at Flerov Laboratory of Nuclear Reactions, Joint Institute for Nucler Research, Dubna was performed. The applied fast detection systems assured its best possible performance similar to SHIP, for the future investigation of deep inelastic transfer collisions. In this review article, our results are discussed together with previous measurements, and perspectives will be given for the application of multi-nucleon transfer reactions to produce new heavy and superheavy isotopes. The project of new kinematic separator dedicated for the MNT reactions studies is also discussed. We plan to implement a project together with modernization of U400 cyclotron (U400R).
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