Nuclear Theory·nucl-th

Tuesday·July 12, 2016

12 papers—8 primary·4 cross-listed

01
Production of Energetic Light Fragments in CEM, LAQGSM, and MCNP6
Stepan G. Mashnik · Leslie M. Kerby · Konstantin K. Gudima · Arnold J. Sierk · Jeffrey S. Bull · Michael R. James
We extend the cascade-exciton model (CEM), and the Los Alamos version of the quark-gluon string model (LAQGSM), event generators of the Monte-Carlo N-particle transport code version 6 (MCNP6), to describe production of energetic light fragments (LF) heavier than 4He from various nuclear reactions induced by particles and nuclei at energies up to about 1 TeV/nucleon. In these models, energetic LF can be produced via Fermi break-up, preequilibrium emission, and coalescence of cascade particles. Initially, we study several variations of the Fermi break-up model and choose the best option for these models. Then, we extend the modified exciton model (MEM) used by these codes to account for a possibility of multiple emission of up to 66 types of particles and LF (up to 28Mg) at the preequilibrium stage of reactions. Then, we expand the coalescence model to allow coalescence of LF from nucleons emitted at the intranuclear cascade stage of reactions and from lighter clusters, up to fragments with mass numbers A < 8, in the case of CEM, and A < 13, in the case of LAQGSM. Next, we modify MCNP6 to allow calculating and outputting spectra of LF and heavier products with arbitrary mass and charge numbers. The improved version of CEM is implemented into MCNP6. Finally, we test the improved versions of CEM, LAQGSM, and MCNP6 on a variety of measured nuclear reactions. The modified codes give an improved description of energetic LF from particle- and nucleus-induced reactions; showing a good agreement with a variety of available experimental data. They have an improved predictive power compared to the previous versions and can be used as reliable tools in simulating applications involving such types of reactions.
nucl-thPRC(2017)·13 citations
02
Charmonium dissociation in collision with phi meson in hadronic matter
Shi-Tao Ji🇨🇳 · Xiao-Ming Xu🇨🇳
The phi-charmonium dissociation reactions in hadronic matter are studied. Unpolarised cross sections for 12 reactions are calculated in the Born approximation, in the quark-interchange mechanism and with a temperature-dependent quark potential. The potential leads to remarkable temperature dependence of the cross sections. With the cross sections and the phi distribution function we calculate the dissociation rates of the charmonia in the interactions with the phi meson in hadronic matter. The dependence of the rates on temperature and charmonium momentum is meaningful to the influence of phi mesons on charmonium suppression.
nucl-thCPC(2017)·0 citations
03
Remarks on the Woods-Saxon Potential
M Capak · B Gonul
More recently, comprehensive application results of approximate analytical solutions of the Woods-Saxon potential in closed form for the 5-dimensional Bohr Hamiltonian have been appeared [14] and its comparison to the data for many different nuclei has clearly revealed the domains for the sucsess and failure in case of using such potential forms to analyse the data concerning with the nuclear structure of deformed nuclei within the frame of the collective model. Gaining confidence from this work, exact solvability of the Woods-Saxon type potentials in lower dimensions for the bound states having zero angular momentum is carefully reviewed to finalize an ongoing discussion in the related literature and clearly shown that such kind of potentials have no analytical solutions even for l=0 case.
nucl-thmath-phmath.MPquant-phMod.Phys.Lett.A(2016)·10 citations
04
Large-scale shell-model calculations on the spectroscopy of $N < 126$ Pb isotopes
Chong Qi🇸🇪 · L.Y. Jia🇨🇳 · G.J. Fu🇨🇳
Large-scale shell-model calculations are carried out in the model space including neutron-hole orbitals $2 p_{1/2}$ , $1 f_{5/2}$ , $2 p_{3/2}$ , $0 i_{13/2}$ , $1 f_{7/2}$ and $0 h_{9/2}$ to study the structure and electromagnetic properties of neutron deficient Pb isotopes. An optimized effective interaction is used. Good agreement between full shell-model calculations and experimental data is obtained for the spherical states in isotopes $^{194 - 206}$ Pb. The lighter isotopes are calculated with an importance-truncation approach constructed based on the monopole Hamiltonian. The full shell-model results also agree well with our generalized seniority and nucleon-pair-approximation truncation calculations. The deviations between theory and experiment concerning the excitation energies and electromagnetic properties of low-lying $0^{+}$ and $2^{+}$ excited states and isomeric states may provide a constraint on our understanding of nuclear deformation and intruder configuration in this region.
nucl-thnucl-exPRC(2016)·25 citations
05
Large-scale configuration interaction description of the structure of nuclei around $^{100}$ Sn and $^{208}$ Pb
Chong Qi
In this contribution I would like to discuss briefly the recent developments of the nuclear configuration interaction shell model approach. As examples, we apply the model to calculate the structure and decay properties of low-lying states in neutron-deficient nuclei around $^{100}$ Sn and $^{208}$ Pb that are of great experimental and theoretical interests.
nucl-thJ.Phys.Conf.Ser.(2016)·4 citations
06
The anomalous quadrupole collectivity in Te isotopes
Chong Qi
We present systematic calculations on the spectroscopy and transition properties of even-even Te isotopes by using the large-scale configuration interaction shell model approach with a realistic interaction. These nuclei are of particular interest since their yrast spectra show a vibrational-like equally-spaced pattern but the few known E2 transitions show anomalous rotational-like behavior, which cannot be reproduced by collective models. Our calculations reproduce well the equally-spaced spectra of those isotopes as well as the constant behavior of the $B (E 2)$ values in $^{114}$ Te. The calculated $B (E 2)$ values for neutron-deficient and heavier Te isotopes show contrasting different behaviors along the yrast line. The $B (E 2)$ of light isotopes can exhibit a nearly constant bevavior upto high spins. We show that this is related to the enhanced neutron-proton correlation when approaching $N = 50$ .
nucl-thnucl-exPRC(2016)·33 citations
07
Monopole excitation of the Hoyle state and linear-chain state in 12C
Yasuro Funaki
Background: Two new $J^{π} = 0^{+}$ states are recently observed around a few MeV above the Hoyle state (the second $0^{+}$ state in 12C). The characters of them are only poorly discussed in theory and are still mysterious. Purpose: I give for the first time a comprehensive understanding of the structures of the $0^{+}$ states by analyzing their wave functions, and discuss relationship with the Hoyle state, similarities, and differences between the states. Method: I extend a microscopic $α$ -cluster model called Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function so as to incorporate $2 α + α$ asymmetric configuration explicitly. The so-called $r^{2}$ -constraint method to effectively eliminate spurious continuum components is also used. Results: The $0_{3}^{+}$ state is shown to have a very large squared overlap with a single configuration of the extended THSR wave function in an orthogonal space to the Hoyle state as well as to the ground state. The $0_{4}^{+}$ state has a maximal squared overlap with a single extended THSR wave function with an extremely prolately-deformed shape. Conclusions: The $0_{3}^{+}$ state appears as a family of the Hoyle state to have a higher nodal structure in the internal motions of the $3 α$ clusters, due to the orthogonalization to the Hoyle state. The $0_{4}^{+}$ state dominantly has a linear-chain structure, where the $3 α$ clusters move freely in a non-localized way, like a one-dimensional gas of the $3 α$ clusters.
nucl-thnucl-exPRC(2016)·29 citations
08
Effects of an induced electric field on \pi^{-}/\pi^{+} ratio in heavy-ion collisions
Gao-Feng Wei🇨🇳 · Shi-Hai Dong🇲🇽 · Xin-Wei Cao🇨🇳 · Yun-Liang Zhang🇨🇳
Using an isospin- and momentum-dependent transport model, we examine the effects of an electric field induced by a variable magnetic field on the \pi^{-}/\pi^{+} ratio in central to peripheral heavy-ion collisions at beam energies of 400 and 1500MeV/nucleon. It is shown that while the induced electric field does not affect the total multiplicities of both $π^{-}$ and $π^{+}$ mesons at both the lower beam energy of 400MeV/nucleon and the higher beam energy of 1500MeV/nucleon, it reduces (enhances) the emission of $π^{-}$ ( $π^{+}$ ) mesons in midrapidity, but enhances (reduces) the emission of $π^{-}$ ( $π^{+}$ ) mesons in forward and backward rapidities especially for the more peripheral collisions at the lower beam energy because of the rapidly transient variable magnetic field at more peripheral collisions and longer reaction duration time at the lower beam energy. These findings indicate that the total \pi^{-}/\pi^{+} ratio is still a precisely reliable probe of symmetry energy at both the lower and higher beam energies, but one should consider the induced electric field when using the differential \pi^{-}/\pi^{+} ratio to probe the symmetry energy especially for the lower beam energy and more peripheral collisions. Finally, the relative suppression factor based on the ratio of \pi^{-}/\pi^{+} in different rapidities is proposed to be an effective probe of the induced electric field generated in heavy-ion collisions due to its maximizing effects of induced electric fields on the differential \pi^{-}/\pi^{+} ratio but minimizing effects of some uncertainty factors in heavy-ion collisions.
nucl-thPRC(2016)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE