G. G. Chubarian

Bio: G. G. Chubarian is an academic researcher from Texas A&M University. The author has contributed to research in topics: Neutron & Fission. The author has an hindex of 12, co-authored 40 publications receiving 437 citations. Previous affiliations of G. G. Chubarian include Joint Institute for Nuclear Research.

Isotopic scaling of heavy projectile residues from the collisions of 25 MeV/nucleon 86 Kr with 124 Sn, 112 Sn and 64 Ni, 58 Ni

Abstract: The scaling of the yields of heavy projectile residues from the reactions of $25\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}{ }^{86}\mathrm{Kr}$ projectiles with ${}^{124}\mathrm{Sn},$ ${}^{112}\mathrm{Sn}$ and ${}^{64}\mathrm{Ni},$ ${}^{58}\mathrm{Ni}$ targets is studied. Isotopically resolved yield distributions of projectile fragments in the range $Z=10--36$ from these reaction pairs were measured with the MARS recoil separator in the angular range $2.7\ifmmode^\circ\else\textdegree\fi{}--5.4\ifmmode^\circ\else\textdegree\fi{}.$ For these deep inelastic collisions, the velocities of the residues, monotonically decreasing with Z down to $Z\ensuremath{\simeq}26--28,$ are employed to characterize the excitation energy. The ratios ${R}_{21}(N,Z)$ of the yields of a given fragment $(N,Z)$ from each pair of systems are found to exhibit isotopic scaling (isoscaling), namely, an exponential dependence on the fragment atomic number Z and neutron number N. The isoscaling is found to occur in the residue Z range corresponding to the maximum observed excitation energies. The corresponding isoscaling parameters are $\ensuremath{\alpha}=0.43$ and $\ensuremath{\beta}=\ensuremath{-}0.50$ for the $\mathrm{Kr}+\mathrm{Sn}$ system and $\ensuremath{\alpha}=0.27$ and $\ensuremath{\beta}=\ensuremath{-}0.34$ for the $\mathrm{Kr}+\mathrm{Ni}$ system. For the $\mathrm{Kr}+\mathrm{Sn}$ system, for which the experimental angular acceptance range lies inside the grazing angle, isoscaling was found to occur for $Zl~26$ and $Nl~34.$ For heavier fragments from $\mathrm{Kr}+\mathrm{Sn},$ the parameters vary monotonically, $\ensuremath{\alpha}$ decreasing with Z and $\ensuremath{\beta}$ increasing with N. This variation is found to be related to the evolution towards isospin equilibration and, as such, it can serve as a tracer of the $N/Z$ equilibration process. The present heavy-residue data extend the observation of isotopic scaling from the intermediate mass fragment region to the heavy-residue region. Interestingly, such high-resolution mass spectrometric data can provide important information on the role of isospin and isospin equilibration in peripheral and midperipheral collisions, complementary to that accessible from modern large-acceptance multidetector devices.

Fusion-fission and quasifission of superheavy systems with Z = 110 – 116 formed in Ca 48 -induced reactions

Abstract: Background: In heavy-ion-induced reactions the mechanism leading to the formation of the compound nucleus and the role of quasifission is still not clear.Purpose: Investigation of the quasifission process of superheavy composite systems with $Z=110\text{\ensuremath{-}}116$ and comparison with properties of fusion-fission and quasifission of lighter composite systems.Method: Mass and energy distributions of fissionlike fragments formed in the reactions $^{48}\mathrm{Ca}+^{232}\mathrm{Th}$, ${}^{238}\mathrm{U}$, ${}^{244}\mathrm{Pu}$, and ${}^{248}\mathrm{Cm}$ at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the U-400 cyclotron of the FLNR JINR.Results: The most probable fragment masses as well as total kinetic energies and their dispersions in dependence on the interaction energies and ion-target combinations have been studied for asymmetric and symmetric fragments formed in the reactions. The capture cross sections were obtained for the reactions $^{48}\mathrm{Ca}+^{244}\mathrm{Pu}$ and ${}^{248}\mathrm{Cm}$. The lower limits for fission barriers of ${}^{283\ensuremath{-}286}\mathrm{Cn}$, ${}^{289\ensuremath{-}292}\mathrm{Fl}$, and ${}^{293\ensuremath{-}296}\mathrm{Lv}$ compound nuclei were estimated.Conclusions: Analysis of the properties of symmetric fragments has shown that a significant part of these fragments may be attributed to fusion-fission process for the reactions ${}^{48}\mathrm{Ca}{+}^{238}\mathrm{U}$, ${}^{244}\mathrm{Pu}$, and ${}^{248}\mathrm{Cm}$.

Fission modes in the reaction 208 Pb( 18 O, f)

Abstract: Results of fission fragment mass-energy distributions of the compound ${}^{226}\mathrm{Th}$ nucleus formed in the sub-barrier fusion reaction ${}^{18}\mathrm{O}{+}^{208}\mathrm{Pb}$ at an energy of ${}^{18}\mathrm{O}$ ions ${E}_{\mathrm{lab}}=78$ MeV are reported. The reaction has been studied twice using two different accelerators, and both sets of experimental data agree quite well. Performed analysis of the experimental data with the use of a new multicomponent method has shown that alongside the well-known modes, i.e., the symmetric (S) and two asymmetric modes standard-one and standard-two, a high-energy mode standard-three has manifested itself. The last named mode appears due to the influence of the close-to-sphere neutron shell with $N\ensuremath{\approx}50$ in the light fission fragment group. Theoretical calculations of the prescission shapes of the fissioning nuclei ${}^{224,226}\mathrm{Th}$ confirm this conclusion.

Production cross sections from 82 Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line

Abstract: Production cross sections for neutron-rich nuclei from the fragmentation of a ${}^{82}$Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements $11\ensuremath{\le}Z\ensuremath{\le}32$ were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements $22\ensuremath{\le}Z\ensuremath{\le}25$ (${}^{64}$Ti, ${}^{67}$V, ${}^{69}$Cr, and ${}^{72}$Mn). One event was registered consistent with ${}^{70}$Cr and another one with ${}^{75}$Fe. The production cross sections are correlated with ${Q}_{g}$ systematics to reveal trends in the data. The results presented here confirm our previous results from a similar measurement using a ${}^{76}$Ge beam and can be explained with a shell model that predicts a subshell closure at $N=34$ around $Z=20$. This is demonstrated by systematic trends and calculations with the abrasion-ablation model that are sensitive to separation energies.

Enhanced Production of Neutron-Rich Rare Isotopes in the Reaction of 25 MeV/nucleon Kr-86 on Ni-64

Abstract: The cross sections and velocity distributions of projectile-like fragments from the reaction of 25 MeV/nucleon 86Kr + 64Ni have been measured using the MARS recoil separator at Texas A&M, with special emphasis on the neutron rich isotopes. Proton-removal and neutron pick-up isotopes have been observed with large cross sections. A model of deep-inelastic transfer (DIT) for the primary interaction stage and the statistical evaporation code GEMINI for the deexcitation stage have been used to describe the properties of the product distributions. The results have also been compared with the EPAX parametrization of high-energy fragmentation yields. The experimental data show an enhancement in the production of neutron-rich isotopes close to the projectile, relative to the predictions of DIT/GEMINI and the expectations of EPAX. We attribute this enhancement mainly to the effect of the extended neutron distribution (neutron ``skin'') of the 64Ni target in peripheral interactions of 86Kr with 64Ni. The large cross sections of such reactions near the Fermi energy, involving peripheral nucleon exchange, suggest that, not only the N/Z of the projectile and the target, but also the N/Z distribution at the nuclear surface may properly be exploited in the production of neutron-rich rare isotopes. This synthesis approach may offer a fruitful pathway to extremely neutron-rich nuclei, towards the neutron-drip line.

The jina reaclib database: its recent updates and impact on type-i x-ray bursts

Abstract: We present results from the JINA REACLIB project, an ongoing effort to maintain a current and accurate library of thermonuclear reaction rates for astrophysical applications. Ongoing updates are transparently documented and version tracked, and any set of rates is publicly available and can be downloaded via a Web interface at http://groups.nscl.msu.edu/jina/reaclib/db/. We discuss here our library V1.0, a snapshot of recommended rates for stable and explosive hydrogen and helium burning. We show that the updated reaction rates lead to modest but significant changes in full network, one-dimensional X-ray burst model calculations, compared with calculations with previously used reaction rate sets. The late time behavior of X-ray burst light curves shows significant changes, suggesting that the previously found small discrepancies between model calculations and observations may be solved with a better understanding of the nuclear input. Our X-ray burst model calculations are intended to serve as a benchmark for future model comparisons and sensitivity studies, as the complete underlying nuclear physics is fully documented and publicly available.

Heaviest nuclei from 48Ca-induced reactions

Abstract: After a brief introduction of the role of shell effects in determining the limiting nuclear masses, the experimental investigation of the decay properties of the heaviest nuclei is presented. For the production of superheavy nuclides fusion, reactions of heavy actinide nuclei with 48Ca-projectiles have been used. The properties of the new nuclei, the isotopes of elements 112–118, as well as of their decay products, together with the known data for the light isotopes with Z ≤ 113, give evidence of the significant increase of the stability with the neutron number of the heavy nucleus. The obtained results are discussed in the context of the theoretical predictions about the 'island of stability' of the hypothetical superheavy elements.

The dynamics of nuclear coalescence or reseparation

Abstract: LBL-1 0911 c La renee Berkeley Laboratory UNIVERSITY OF CALIFORNIA Presented at the Nobel Symposium on High-Spin States, Orenas, Sweden, June 22-25, 1980; and submitted to Physica Scripta THE DYNAMICS OF NUCLEAR COALESCENCE OR RESEPARATION W. J. Swiatecki June 1980 TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diu is ion, Ext. 6782 o i \ !(:·(··, t.:· 1 ·v -~::; Y ) • •• u .... LAWF