Actinide production from the interactions ofCa40andCa44withCm248and a comparison with theCa48+248Cm system (original) (raw)
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Physical Review Letters, 2012
Results of a new series of experiments on the study of production cross sections and decay properties of the isotopes of element 115 in the reaction 243 Am þ 48 Ca are presented. Twenty-one new decay chains originating from 288 115 were established as the product of the 3n-evaporation channel by measuring the excitation function at three excitation energies of the compound nucleus 291 115. The decay properties of all newly observed nuclei are in full agreement with those we measured in 2003. At the lowest excitation energy E Ã ¼ 33 MeV, for the first time we registered the product of the 2n-evaporation channel, 289 115, which was also observed previously in the reaction 249 Bk þ 48 Ca as the daughter nucleus of the decay of 293 117. The maximum cross section for the production of 288 115 is found to be 8.5 pb at E Ã % 36 MeV.
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.
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 Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.
Study of Properties for Ca (a, n)Ti Reactions and n-Yield for Ca Isotopes (A=41-50)
Advances in Physics Theories and Applications, 2014
In this study, (44 Ti-53 Ti) isotopes for one of intermediate elements (A>40) from Ca (α, n)Ti reactions with alpha energy from (10 to 50) MeV are used according to the available data of reaction cross sections obtained from Lab (TENDL-2012). The more recent cross sections data of Ca (α, n)Ti reaction is reproduced in fine steps of (0.5MeV), by using (MATLAB R2008b) program. These cross sections together with the stopping powers which calculated from the Zeigler formula by using SRIM-2013 have been used to calculate the n-yield for reaction by depend on Ca isotopes (41 Ca-50 Ca) as targets, and then clarify the behavior between the energies which corresponding to these cross sections and neutron yield for isotopes, and then we drowned the relationship between the n-yield for these reactions and symmetry at these energies. Was obtained on mathematical formulas and find constants those equations and these equations were calculated yield neutron and comparing with theoretical values also studying the properties of these isotopes, calculated binding energy and reduced mass and also were calculated Q-value and threshold energy for each reaction and the relative abundance of the isotopes of entering and leaving for alpha reactions. And then drawing scheduled and discusses the results.
Physical Review C, 2013
Recent theoretical work has renewed interest in radiochemically determined isotope distributions in reactions of 238 U projectiles with heavy targets that had previously been published only in parts. These data are being reexamined. The cross sections σ (Z) below the uranium target have been determined as a function of incident energy in thick-target bombardments. These are compared to predictions by a diffusion model whereby consistency with the experimental data is found in the energy intervals 7.65-8.30 MeV/u and 6.06-7.50 MeV/u. In the energy interval 6.06-6.49 MeV/u, the experimental data are lower by a factor of 5 compared to the diffusion model prediction indicating a threshold behavior for massive charge and mass transfer close to the barrier. For the intermediate energy interval, the missing mass between the primary fragment masses deduced from the generalized Q gg systematics including neutron pair-breaking corrections and the centroid of the experimental isotope distributions as a function of Z have been used to determine the average excitation energy as a function of Z. From this, the Z dependence of the average total kinetic-energy loss (TKEL) has been determined. This is compared to that measured in a thintarget counter experiment at 7.42 MeV/u. For small charge transfers, the values of TKEL of this work are typically about 30 MeV lower than in the thin-target experiment. This difference is decreasing with increasing charge transfer developing into even slightly larger values in the thick-target experiment for the largest charge transfers. This is the expected behavior which is also found in a comparison of the partial cross sections for quasielastic and deep-inelastic reactions in both experiments. The cross sections for surviving heavy actinides, e.g., 98 Cf, 99 Es, and 100 Fm indicate that these are produced in the low-energy tails of the dissipated energy distributions, however, with a low-energy cutoff at about 35 MeV. Excitation functions show that identical isotope distributions are populated independent of the bombarding energy indicating that the same bins of excitation energy are responsible for the production of these fissile isotopes. A comparison of the survival probabilities of the residues of equal charge and neutron transfers in the reactions of 238 U projectiles with either 238 U or 248 Cm targets is consistent with such a cutoff as evaporation calculations assign the surviving heavy actinides to the 3n and/or 4n evaporation channels.
ANALYSIS OF YIELDS OF FUSION-FISSION AND QUASIFISSION FRAGMENTS IN HEAVY ION COLLISIONS
The decrease of the evaporation residues yield in reactions with massive nuclei is explained by increase of the competition between quasifission and complete fusion processes and by the decrease of the survival probability of the heated and rotating compound nucleus against fission. The experimental data on the yields of evaporation residues, fusion-fission and quasifission fragments in the 48 Ca + 154 Sm reaction are analyzed simultaneously in the framework of the theoretical method based on the DNS concept and advanced statistical model. The measured yields of evaporation residues and fission fragments for the 48 Ca + 154 Sm reaction have been well reproduced by using the partial fusion and quasifission cross sections obtained in the DNS model. Such way of calculation is used to find optimal conditions for the synthesis of the new element Z = 120 (A = 302).We compare the excitation functions of evaporation residues of the three reactions 54 Cr + 248 Cm, 58 Fe + 244 Pu, and 64 Ni + 238 U. Our estimations show that the 54 Cr+ 248 Cm reaction is preferable in comparison with the two others because the excitation function of the evaporation residues is some orders of magnitude higher and the optimal energy for the synthesis is lower than that for the 58 Fe + 244 Pu and 64 Ni + 238 U reactions.
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.
Fusion hindrance and quasi-fission in 48Ca induced reactions
The European Physical Journal A, 2005
Fusion-fission and fusion-evaporation cross sections have been measured in a large energy range for the 48 Ca+ 168 Er, 154 Sm reactions. The comparison of the reduced evaporation data for such reactions and for collisions induced by light projectiles leading to the same compound nuclei 216 Ra* and 202 Pb* puts in evidence a fusion hindrance, which is particularly large for the first composite system. This fusion suppression is consistent with a noticeable contribution coming from quasi-fission events observed in the mass-energy distribution of fission fragments. The asymmetric shape of the quasi-fission component has been explained in terms of shell effects in the exit channel, favouring the population of closed shell fission fragments. The comparison of 48 Ca+ 154 Sm with preliminary data on 48 Ca+ 144 Sm seems to suggest that the target deformation plays a role in the onset of the quasi-fission mechanism.
Fusion-fission of superheavy compound nuclei produced in reactions with heavy ions beyond Ca
EPJ Web of Conferences, 2011
Total Kinetic Energy -Mass distributions of fission-like fragments for the reactions of 22 Ne, 26 Mg, 36 S, 48 Ca, 58 Fe and 64 Ni ions with actinides leading to the formation of superheavy compound systems with Z=108-120 at energies near the Coulomb barrier have been measured. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability drops by three orders of magnitude for the formation of the compound nucleus with Z=120 obtained in the reaction 64 Ni+ 238 U compared to the formation of the compound nucleus with Z=112 obtained in the reaction 48 Ca+ 238 U at the excitation energy of the compound nucleus of about 45 MeV. From our analysis it turns out that the reaction 64 Ni+ 238 U is not suitable for the synthesis of element Z=120.
Physical Review C, 1990
Excitation functions have been'measured for isotopes of Bk, Cf, Es, and Fmproduced from the interactions of 207-to 286-MeV 40Ar ions with 248Cm. The measured isotopic distributions were fouhd to be essentially symmetric with full-widths-at-halfmaximum between 2.0 and 3.5 mass units.. These results are comparable to those obtained in previous studies using 40,44,48Ca with 248Cm. The maxima of the isotopic distributions from the 40Ar-248 Cm system show shifts, to both heavier and lighter mass numbers, of 0 to 2 mass units relative to the corresponding maxima of the isotopic distributions from the 40,44,48Ca-248 Cm. NUCLEAR REACTIONS 248Cm(40Ar,X), E(40Ar) = 207, 225, 245, 266 and 286 MeV; Excitation functions and isotopic distributions were measured for Z = 97-100.