Mon·Sep 13, 2021Monday·September 13, 2021

1. 01*

   ${}^{145}$Ba and ${}^{145,146}$La structure from lifetime measurements

   B. Olaizola🇨🇦 · A. Babu🇨🇦 · R. Umashankar🇨🇦 · A. B. Garnsworthy · G. C. Ball🇨🇦 · V. Bildstein🇨🇦 · M. Bowry · C. Burbadge🇨🇦 · R. Cabellero-Folch · I. Dillmann🇨🇦 · A. Diaz-Varela🇨🇦 · R. Dunlop🇨🇦 and 12 other authors

   The occurrence of octupole shapes in even-mass neutron-rich Ba isotopes has been well established. However, the situation with the odd-mass Ba and odd or odd-odd La nuclei around them is far from settled. In order to shed light on these less-studied isotopes, a fast-timing experiment was performed using GRIFFIN at TRIUMF-ISAC. A wealth of excited-state lifetimes in the 100~ps to few ns range have been measured in ${}^{144,145,146}$Ba and ${}^{145,146}$La populated in the ${\beta }^{-}$ and ${\beta }^{-}-n$ decay of ${}^{145,146}$Cs. The results do not allow to draw firm conclusions on the possible octupole deformation of these nuclei but suggest different spin and parity assignments than previous works. This work highlights the need for more detailed study of the odd and odd-odd isotopes in this region to properly understand their structure.

   nucl-exPRC(2021)·3 citations
2. 02*

   Exploring the halo character and dipole response in the dripline nucleus ${}^{31}$F

   G. Singh🇪🇸 · Jagjit Singh🇯🇵 · J. Casal🇪🇸 · L. Fortunato🇮🇹

   Lying at the lower edge of the `island of inversion', neutron-rich Fluorine isotopes (${}^{29-31}$F) provide a curious case to study the configuration mixing in this part of the nuclear landscape. Recent studies have suggested that a prospective two-neutron halo in the dripline nucleus ${}^{31}$F could be linked to the occupancy of the $pf$ intruder configurations. Focusing on configuration mixing, matter radii and neutron-neutron ($nn$) correlations in the ground-state of ${}^{31}$F, we explore various scenarios to analyze its possible halo nature as well as the low-lying electric dipole ($E$1) response within a three-body approach. We use an analytical, transformed harmonic oscillator basis under the aegis of a hyperspherical formalism to construct the ground state three-body wave function of ${}^{31}$F. The ${}^{31}$F ground-state configuration mixing and its matter radius are computed for different choices of the ${}^{30}$F structure coupled to the valence neutron. The admixture of {$p_{3/2}$, $d_{3/2}$, and $f_{7/2}$} components is found to play an important role, favouring the dominance of inverted configurations with dineutron spreads for two-neutron halo formation. The increase in matter radius with respect to the core radius, $\Delta r⩾$ 0.30 fm and the dipole distributions along with the integrated $B(E1)$ strengths of $⩾$ 2.6 $e^2$fm${}^2$ are large enough to be compatible with other two-neutron halo nuclei. Three-body results for ${}^{31}$F indicate a large spatial extension in its ground state due to the inversion of the energy levels of the normal shell model scheme. The increase is augmented by and is proportional to the extent of the $p_{3/2}$ component in the wave function. Additionally, the enhanced dipole distributions and large $B(E1)$ strengths all point to the two-neutron halo character of ${}^{31}$F.

   ↳ nucl-thnucl-exPRC(2022)·20 citations
3. 03*

   Left-right splitting of elliptic flow due to directed flow in heavy ion collisions

   Chao Zhang🇨🇳 · Zi-Wei Lin🇺🇸

   Recently the splitting of elliptic flow $v_2$ at finite rapidities has been proposed as a result of the global vorticity in non-central relativistic heavy ion collisions. In this study, we find that this left-right (i.e., on opposite sides of the impact parameter axis) splitting of the elliptic flow at finite rapidities is a result of the non-zero directed flow $v_1$, with the splitting magnitude $\approx 8v_1(1-3v_2)/(3\pi )$. We also use a multi-phase transport model, which automatically includes the vorticity field and flow fluctuations, to confirm the $v_2$ splitting. In addition, we find that the analytical expectations for the $v_2$ splitting work for the raw $v_2$ and $v_1$ (i.e., before event plane resolutions are applied) measured relative to either the first- or second-order event plane. Since the $v_2$ splitting is mostly driven by $v_1$, it vanishes at zero transverse momentum ($p_{\mathrm{T}}$), and its magnitude and sign may have non-trivial dependencies on $p_{\mathrm{T}}$, centrality, collision energy, and hadron species.

   ↳ nucl-thnucl-exPRC(2022)·8 citations
4. 04*

   Improvement of Geant4 Neutron-HP package: from methodology to evaluated nuclear data library

   Loic Thulliez🇫🇷 · Cédric Jouanne🇫🇷 · Eric Dumonteil🇫🇷

   An accurate description of interactions between thermal neutrons (below 4 eV) and materials is key to simulate the transport of neutrons in a wide range of applications such as criticality-safety, reactor physics, compact accelerator-driven neutron sources, radiological shielding or nuclear instrumentation, just to name a few. While the Monte Carlo transport code Geant4 was initially developed to simulate particle physics experiments, %-with a large emphasis given on modeled cross-sections for all known particles at all conceivable energies-, its use has spread to neutronics applications, requiring evaluated cross-sections for neutrons and gammas between $0$ and $20$ MeV (the so-called neutron High Precision -HP- package), as well as a proper offline or on-the-flight treatment of these cross-sections. In this paper we will point out limitations affecting Geant4 (version 10.07.p01) thermal neutron treatment and associated nuclear data libraries, by using comparisons with the reference Monte Carlo neutron transport code \tripoli, version 11, and we will present the results of various modifications of the Geant4 neutron-HP package, required to overcome these limitations. Also, in order to broaden the support of nuclear data libraries compatible with Geant4, a nuclear processing tool has been developed and validated allowing the use of the code together with ENDF-BVIII.0 and JEFF-3.3 libraries for example. These changes should be taken into account in an upcoming Geant4 release.

   ↳ physics.comp-phnucl-exNucl.Instrum.Meth.A(2022)·19 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.