New Insights into the ^{243}Am+^{48}Ca Reaction Products Previously Observed in the Experiments on Elements 113, 115, and 117 (original) (raw)
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Physical Review C, 2013
Results from the production and decay properties of element 115 nuclei observed using the reaction 243 Am+ 48 Ca at various beam energies between November 1-st, 2010 and February 26-th, 2012 at the Dubna Gas Filled Recoil Separator are presented. This long-running experiment with a total beam dose of 3.3•10 19 and carried out in the excitation energy range E * =31-47 MeV of the 291 115 compound nucleus resulted in observation of three isotopes of element 115 with masses 287, 288 and 289. The 28 detected decay chains of 288 115 show that this isotope is produced with the maximum probability at E * =34.0-38.3 MeV with a corresponding cross section of σ3n=8.5 +6.4 −3.7 pb. The four events attributed to the isotope 289 115 that decays via a short α→α→SF chain could be detected only at the lowest excitation energy E * =31-36 MeV in accordance with what could be expected for the 2n-evaporation channel of the reaction. The decay characteristics of this nuclide were established earlier (2010) and more recently (2012) in the reaction 249 Bk(48 Ca,4n) 293 117 and following α decay to 289 115. At the energy E * =44.8±2.3 MeV we observed only a single long chain of the isotope 287 115. The decay properties of nuclei starting at 288 115 and 287 115 isotopes obtained in the present work reproduce in full the results of the first experiment of 2003 that reported the discovery of elements 115 and 113. The excitation functions of the production of the isotopes of element 115 and observation of the isotope 289 115 in cross-bombardment reactions with the targets of 243 Am and 249 Bk provide additional evidence of the identification of the nuclei of elements 115 and 113. The experiments were carried out using the 48 Ca beam of the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions, JINR.
Study of the decay of 291 115* formed in 48 Ca+ 243 Am reaction
EPJ Web of Conferences, 2014
The decay of 291 115* formed in 243 Am+ 48 Ca reaction is studied using the dynamical cluster-decay model (DCM), including the possible effect of deformations. A comparative study of spherical and β 2 -static deformed choices of fragmentation is made for the 2n evaporation residue (ER) of the compound nucleus (CN) 291 115*. The heavier neutron clusters 3n and 4n could be fitted only after the inclusion of deformation effect in DCM. Symmetric fission is observed for the spherical approach, which changes to asymmetric one with inclusion of deformation effect. Also, a comparative analysis between spherical and deformed (β 2 ) cases of observed α-decay chains shows that the magnitude of penetration probability gets enhanced whereas preformation factor decreases due to decreased ΔR, when the α-daughter product is taken as spherical rather than deformed.
Synthesis of elements 115 and 113 in the reaction Am243+Ca48
Physical Review C, 2005
The results of two experiments designed to synthesize element 115 isotopes in the 243 Am + 48 Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV 48 Ca projectiles, we observed three similar decay chains consisting of five consecutive α decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV 48 Ca projectiles, we registered a different decay chain of consecutive α decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new αand SF-decaying nuclei are consistent with expectations for consecutive α decays originating from the parent isotopes 288 115 and 287 115, produced in the 3n-and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the 288 115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, 268 Db (15 events), was found to be chemically consistent with the fifth group of the periodic table. The odd-odd isotope 288 115 was observed with largest cross section of about 4 pb. In the SF decay of 268 Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z = 105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov
Decay of excited nuclei produced in ^{78,82}Kr+^{40}Ca reactions at 5.5 MeV/nucleon
Physical Review C, 2011
Decay modes of excited nuclei are investigated in 78,82 Kr + 40 Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the 4π INDRA array. Kinetic-energy spectra and angular distributions of fragments with atomic number 3 ≤ Z ≤ 28 indicate a high degree of relaxation and are compatible with a fission-like phenomenon. Persistence of structure effects is evidenced from elemental cross-sections (σZ) as well as a strong odd-even-staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross-section of the 78 Kr + 40 Ca reaction is slightly higher than the one measured in 82 Kr + 40 Ca reaction. The fission-like component is larger by ∼ 25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to Z = 14 in their ground states as well as excited states does not account for the main features of σZ. For both reactions, the transition-state formalism reasonably reproduces the Z-distribution of the fragments with charge 12 ≤ Z ≤ 28. However, this model strongly overestimates the light-fragment cross-sections and does not explain the o-e-s of the yields for 6 ≤ Z ≤ 10. The shape of the whole Z-distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition between evaporation, fusion-fission and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 ≤ Z ≤ 22 could signal a mechanism in addition to the capture process. PACS numbers: 24.60.Dr, 24.10.Pa, 25.70.Gh Z a) 78 Kr+ 40 Ca J max = 73 J max = 65 2 6 10 14 18 22 26 b) 82 Kr+ 40 Ca J max = 75 J max = 70 FIG. 13: (Color online) Comparison between measured and calculated cross-sections. The calculated results with Jmax = 65 (Jmax = 73) for the 78 Kr + 40 Ca reaction and Jmax = 70 (Jmax = 75) for the 82 Kr + 40 Ca reaction are shown by dashed (solid) lines in panel a (b), respectively. Full (open) squares are data from the 78 Kr + 40 Ca ( 82 Kr + 40 Ca) reaction, respectively.
Production and Decay of Element 114: High Cross Sections and the New Nucleus ^{277}Hs
Physical Review Letters, 2010
The fusion-evaporation reaction 244 Pu( 48 Ca,3-4n) [288][289] 114 was studied at the new gasfilled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of 288-289 114. At a compound nucleus excitation energy of E*=39.8-43.9 MeV, the 4n evaporation channel cross section was
Physical Review C, 2012
The study of the 48 Ca+ 249,250,251,252 Cf reactions in a wide energy interval around the external barrier has been achieved with the aim of investigating the dynamical effects of the entrance channel via the 48 Ca induced reactions on the 249−252 Cf targets and to analyze the influence of odd and even neutron composition in target on the capture, quasifission and fusion cross sections. Moreover, we also present the results of the individual evaporation residue excitation functions obtained from the de-excitation cascade of the various even-odd and even-even 297−300 118 superheavy compound nuclei reached in the studied reactions, and we compare our results of the 294 118 evaporation residue yields obtained in the synthesis process of the 48 Ca+ 249,250 Cf reactions with the experimental data obtained in the 48 Ca+ 249 Cf experiment carried out at the Flerov Laboratory of Nuclear Reactions of Dubna.
Production and Decay of Element 114: High Cross Sections and the New NucleusHs277
Physical Review Letters, 2010
The fusion-evaporation reaction 244 Pu(48 Ca,3-4n) 288-289 114 was studied at the new gasfilled recoil separator TASCA. Thirteen correlated decay chains were observed and assigned to the production and decay of 288-289 114. At a compound nucleus excitation energy of E*=39.8-43.9 MeV, the 4n evaporation channel cross section was
Recoil-α-fission and recoil-α–α-fission events observed in the reaction 48Ca + 243Am
Nuclear Physics A, 2016
Products of the fusion-evaporation reaction 48 Ca + 243 Am were studied with the TASISpec setup at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung. Amongst the detected thirty correlated α-decay chains associated with the production of element Z = 115, two recoil-α-fission and five recoil-α-α-fission events were observed. The latter are similar to four such events reported from experiments performed at the Dubna gas-filled separator. Contrary to their interpretation, we propose an alternative view, namely to assign eight of these eleven decay chains of recoil-α(-α)-fission type to start from the 3n-evaporation channel 288 115. The other three decay chains remain viable candidates for the 2n-evaporation channel 289 115.
Synthesis of the isotope 282113 in the 237Np+48Ca fusion reaction
The decay properties of the new isotope 282 113 and its daughter nuclei have been measured in the 237 Np( 48 Ca, 3n) 282 113 reaction. During an irradiation with a beam dose of 1.1 × 10 19 244-MeV 48 Ca projectiles, two decay chains originating from the odd-odd isotope 282 113 (E α = 10.63 ± 0.08 MeV, T α = 73 +134 −29 ms) were produced in the complete fusion reaction with a cross section of 0.9 +1.6 −0.6 pb; these properties are all in agreement with expectations based on the results of previous experiments.