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Covalent isomeric state in ${}^{12}{Be}$ induced by two-neutron transfers

M. Ito and N. Itagaki

Phys. Rev. C 78, 011602(R) (2008) - Published 18 July, 2008

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The $α +$ ${}^{8}{He}$ low-energy reactions and the exotic structures of ${}^{12}{Be}$ are studied using the generalized two-center cluster ( $α + α + 4 N$ ) model. In the two-neutron transfer reactions, $α +$ ${}^{8}{He}_{g . s .}$ $\to$ ${}^{6}{He}_{g . s .}$ $+$ ${}^{6}{He}_{g . s .}$ , a resonant peak with $J^{π} = 0^{+}$ appears around $E ~$ 1.3 MeV above the ${}^{6}{He}_{g . s .}$ $+$ ${}^{6}{He}_{g . s .}$ threshold as the result of the formation of the covalent superdeformation, which has a hybrid structure of covalent and ionic configurations for the valence neutrons. The covalent superdeformation gives rise to an isomeric state with a sharp width of $Γ ~ 400$ keV, which is smaller by about one order of magnitude than the typical width observed in molecular resonances above the Coulomb barrier. The energy-spin systematics for the two-neutron transfer reactions is investigated, and our calculation predicts a sequence of resonant structures in the range of 3–14 MeV in the center-of-mass energy with spins $0 ℏ − 8 ℏ$ .

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Dynamical simulation of bound antiproton-nuclear systems and observable signals of cold nuclear compression

A. B. Larionov, I. N. Mishustin, L. M. Satarov, and W. Greiner

Phys. Rev. C 78, 014604 (2008) - Published 16 July, 2008

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On the basis of the kinetic equation with self-consistent relativistic mean fields acting on baryons and antibaryons, we study dynamical response of the nucleus to an antiproton implanted in its interior. By solving numerically the time-dependent Vlasov equation, we show that the compressed state is formed on a rather short time scale of about 4–10 fm/c. This justifies the assumption, that the antiproton annihilation may happen in the compressed nuclear environment. The evolution of the nucleus after antiproton annihilation is described by the same kinetic equation including collision terms. We show, that nucleon kinetic energy spectra and the total invariant mass distributions of produced mesons are quite sensitive observables to the antiproton annihilation in the compressed nucleus.

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Fission cycling in a supernova $r$ process

J. Beun, G. C. McLaughlin, R. Surman, and W. R. Hix

Phys. Rev. C 77, 035804 (2008) - Published 13 March, 2008

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Recent halo star abundance observations exhibit an important feature of consequence to the $r$ process: the presence of a main $r$ process between the second and third peaks that is consistent among halo stars. We explore fission cycling and steady β flow as the driving mechanisms behind this feature. The presence of fission cycling during the $r$ process can account for nucleosynthesis yields between the second and third peaks, whereas the presence of steady β flow can account for consistent $r$ -process patterns, robust under small variations in astrophysical conditions. We employ the neutrino-driven wind of the core-collapse supernova to examine fission cycling and steady β flow in the $r$ process. As the traditional neutrino-driven wind model does not produce the required very neutron-rich conditions for these mechanisms, we examine changes to the neutrino physics necessary for fission cycling to occur in the neutrino-driven wind environment, and we explore under what conditions steady β flow is obtained.

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First direct proof of internal conversion between bound states

T. Carreyre, M. R. Harston, M. Aiche, F. Bourgine, J. F. Chemin, G. Claverie, J. P. Goudour, J. N. Scheurer, F. Attallah, G. Bogaert, J. Kiener, A. Lefebvre, J. Durell, J. P. Grandin, W. E. Meyerhof, and W. Phillips

Phys. Rev. C 62, 024311 (2000) - Published 19 July, 2000

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We present direct evidence for the process of internal conversion between bound atomic states (BIC) when the binding energy of the converted electron becomes larger than the nuclear transition energy. This process has been proposed as an explanation of the measured, unexpectedly short lifetime of the first excited state of $^{125} Te$ with charge state larger than $44^{+} .$ We have detected the $K_{α}$ x rays emitted in flight which follow the filling of the K-shell vacancy created by the bound internal conversion process, together with $γ$ rays from Te ions in charge states ranging between $44^{+}$ and $48^{+} .$ For ${Te}^{45 +}$ and ${Te}^{46 +},$ the comparison of the x-ray to $γ$ -ray ratios with the theoretical calculations of the internal conversion coefficients including decay to bound atomic states, assuming Te ions in their ground electronic state, show poor agreement. The agreement becomes good if account is taken of BIC decay of excited initial states with different occupancies of the ${2 p}_{1 / 2}$ and ${2 p}_{3 / 2}$ subshells. In this situation, the half-life becomes sensitive to the precise initial state and simple specification of the charge state alone is no longer appropriate.

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Evidence for short-range correlations from high $Q^{2}$ (e,e’) reactions

L. L. Frankfurt, M. I. Strikman, D. B. Day, and M. Sargsyan

Phys. Rev. C 48, 2451 (1993) - Published 1 November, 1993

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We argue that the ratio of cross sections of quasielastic electron scattering for heavy and light nuclei at x>1 and $Q^{2}$ >1 (GeV/c $)^{2}$ should exhibit simple scaling relations which are ultimately expressed through the ratio of the light-cone nucleon distributions in nuclei. We extract these cross section ratios from existing data in a practically model independent way. The results are found to be in reasonable agreement with our x-scaling relations for the region of 2>x≥1.4 where the contribution of two-nucleon short-range correlations are expected to dominate. The ratios exhibit scaling in the light-cone fraction, α, of the struck nucleon for the range 2>x≥0.9. The α scaling is in agreement with the expectations of the light-cone quantum mechanics of nuclei, providing further evidence for the dominance of short-range correlations in nuclei at k>0.3 GeV/c. An extension of this analysis to the interpretation of color transparency experiments is discussed.

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Unified shell-model description of nuclear deformation

P. Federman and S. Pittel

Phys. Rev. C 20, 820 (1979) - Published 1 August, 1979

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A unified shell-model description of nuclear deformation valid throughout the periodic table is presented. Microscopic calculations for the Zr and Mo isotopes are carried out in the frameworks of the shell model and the Hartree-Fock-Bogoliubov method, respectively, to study the shape transition in these nuclei. It is shown that deformation is produced by the isoscalar component of the neutron-proton ( $n - p$ ) interaction in this region, as in the lighter ( $2 s$ , $1 d$ )-shell region. Deformation sets in when the $T = 0$ $n - p$ interaction dominates over the sphericity-favoring pairing interaction between $T = 1$ pairs of nucleons. When shell effects are important, as for the light and medium-weight regions mentioned above, the simultaneous occupation of neutrons and protons of spin-orbit "partner" orbitals plays a crucial role in determining the onset of deformation. However, their effect is probably less important in the rare-earth and transuranic regions due to the rapid accumulation of single-particle orbitals.

NUCLEAR STRUCTURE Microscopic description of nuclear deformation; shell-model calculations of ${}^{96}{Zr}$ , ${}^{98}{Zr}$ , and ${}^{100}{Zr}$ ; HFB calculations of ${}^{98}{Mo}$ - ${}^{110}{Mo}$ ; discussion of light and heavy deformed nuclei; relation to interacting boson approximation.

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Central collisions of relativistic heavy ions

J. Gosset, H. H. Gutbrod, W. G. Meyer, A. M. Poskanzer, A. Sandoval, R. Stock, and G. D. Westfall

Phys. Rev. C 16, 629 (1977) - Published 1 August, 1977

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The energy spectra of protons and light nuclei produced by the interaction of ${}^{4}{He}$ and ${}^{20}{Ne}$ projectiles with Al and U targets have been investigated at incident energies ranging from 0.25 to 2.1 GeV per nucleon. Single fragment inclusive spectra have been obtained at angles between 25° and 150°, in the energy range from 30 to 150 MeV/nucleon. The multiplicity of intermediate and high energy charged particles was determined in coincidence with the measured fragments. In a separate study, fragment spectra were obtained in the evaporation energy range from ${}^{12}C$ and ${}^{20}{Ne}$ bombardment of uranium. We observe structureless, exponentially decaying spectra throughout the range of studied fragment masses. There is evidence for two major classes of fragments; one with emission at intermediate temperature from a system moving slowly in the lab frame, and the other with high temperature emission from a system propagating at a velocity intermediate between target and projectile. The high energy proton spectra are fairly well reproduced by a nuclear fireball model based on simple geometrical, kinematical, and statistical assumptions. Light cluster emission is also discussed in the framework of statistical models.

NUCLEAR REACTIONS $U ({}^{20}{Ne}, X)$ , $E = 250$ MeV/nucl.; $U ({}^{20}{Ne}, X)$ , $U (α, X)$ $E = 400$ MeV/nucl.; $U ({}^{20}{Ne}, X)$ , $Al ({}^{20}{Ne}, X)$ , $E = 2.1$ GeV/nucl.; measured $σ (E, θ)$ , $X = p, d, t, {}^{3}{He}, {}^{4}{He}$ . $U ({}^{20}{Ne}, X)$ , $U (α, X)$ , $E = 400$ MeV/nucl.; $U ({}^{20}{Ne}, X)$ , $E = 2.1$ GeV/nucl.; measured $σ (E, θ)$ , Li to O. $U ({}^{20}{Ne}, X)$ , $U ({}^{12}C, X)$ , $E = 2.1$ GeV/nucl.; measured $σ (E, 90 °)$ , ${}^{4}{He}$ to B. Nuclear fireballs, coalescence, thermodynamics of light nuclei production.

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Highlights

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Covalent isomeric state in ${}^{12}{Be}$ induced by two-neutron transfers

Dynamical simulation of bound antiproton-nuclear systems and observable signals of cold nuclear compression

Fission cycling in a supernova $r$ process

First direct proof of internal conversion between bound states

Evidence for short-range correlations from high $Q^{2}$ (e,e’) reactions

Unified shell-model description of nuclear deformation

Central collisions of relativistic heavy ions

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