Mon·Nov 5, 2018Monday·November 5, 2018

1. 01*

   Isospin symmetry in $B(E2)$ values: Coulomb excitation study of ${}^{21}$Mg

   P. Ruotsalainen🇫🇮 · J. Henderson🇨🇦 · G. Hackman🇨🇦 · G.H. Sargsyan🇨🇭 · K. D. Launey🇺🇸 · A. Saxena🇮🇳 · P. C. Srivastava🇮🇳 · S. R. Stroberg🇨🇦 · T. Grahn🇫🇮 · J. Pakarinen🇫🇮 · G. C. Ball🇨🇦 · R. Julin🇫🇮 and 28 other authors

   The $T_z$~=~$-\frac{3}{2}$ nucleus ${}^{21}$Mg has been studied by Coulomb excitation on ${}^{196}$Pt and ${}^{110}$Pd targets. A 205.6(1)-keV $\gamma$-ray transition resulting from the Coulomb excitation of the ${\frac{5}{2}}^{+}$ ground state to the first excited ${\frac{1}{2}}^{+}$ state in ${}^{21}$Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the ${\frac{1}{2}}^{+}$ state yield an adopted value of $B(E2;{\frac{5}{2}}^{+}\to {\frac{1}{2}}^{+})$~=~13.3(4)~W.u. A new excited state at 1672(1)~keV with tentative ${\frac{9}{2}}^{+}$ assignment was also identified in ${}^{21}$Mg. This work demonstrates large difference of the $B(E2;{\frac{5}{2}}^{+}\to {\frac{1}{2}}^{+})$ values between $T$~=~$\frac{3}{2}$, $A$~=~21 mirror nuclei. The difference is investigated in the shell-model framework employing both isospin conserving and breaking USD interactions and using modern \textsl{ab initio} nuclear structure calculations, which have recently become applicable in the $sd$ shell.

   nucl-exPRC(2019)·42 citations
2. 02*

   Evolution of higher moments of multiplicity distribution

   Radka Sochorova🇨🇿 · Boris Tomasik🇸🇰

   Evolution of a multiplicity distribution can be described with the help of master equation. We first look at 3rd and 4th factorial moments of multiplicity distributions and derive their equilibrium values. From them central moments and other ratios can be calculated. We study the master equation for a fixed temperature, because we want to know how fast different moments of the multiplicity distribution approach their equilibrium value. Then we investigate the situation in which the temperature of the system decreases. We find out that in the non-equilibrium state, higher factorial moments differ more from their equilibrium values than the lower moments and that the behaviour of a combination of the central moments depends on the combination we choose.

   ↳ nucl-thhep-phnucl-exPoS(2019)·0 citations
3. 03*

   Kurtosis of elliptic flow fluctuations

   Rajeev S. Bhalerao🇮🇳 · Giuliano Giacalone🇫🇷 · Jean-Yves Ollitrault🇫🇷

   Elliptic flow ($v_2$) in ultrarelativistic nucleus-nucleus collisions fluctuates event to event, both in magnitude and in orientation with respect to the reaction plane. Even though the reaction plane is not known event to event in experiment, we show that the statistical properties of $v_2$ fluctuations in the reaction plane can be precisely extracted from experimental data. Previous studies have shown how to measure the mean, variance and skewness using the first three cumulants $v_2\{2\}$, $v_2\{4\}$ and $v_2\{6\}$. We complement these studies by providing a formula for the kurtosis, which requires an accurate determination of the next cumulant $v_2\{8\}$. Using existing data, we show that the kurtosis is positive for most centralities, in contrast with the kurtosis of triangular flow fluctuations, which is negative. We argue that these features are robust predictions of fluid-dynamical models.

   ↳ nucl-thhep-phnucl-exPRC(2019)·24 citations
4. 04*

   Anti-bubble effect of temperature \& deformation: a systematic study for nuclei across all mass regions between A $=$ 20$-$300

   G. Saxena🇮🇳 · M. Kumawat🇮🇳 · Mamta Aggarwal🇮🇳

   Temperature dependent relativistic mean-field (RMF) plus BCS approach has been used for the first time to investigate the anti-bubble effect of the temperature and deformation in the light, medium-heavy and superheavy nuclei. Influence of temperature is studied on density distribution, charge form-factor, single particle (s.p.) energies, occupancy, deformation and the depletion fraction (DF). At T $=$ 0, the quenching effect of deformation is predominant. DF is found usually less in oblate deformation than in prolate. DF decreases with increasing prolate deformation even though the 2s-orbit is empty which shows the role of deformation in central depletion apart from the unoccupancy in s-orbit as is usually believed. As T increases, the occupancy of s-orbit increases, shell structure melts, the deformation vanishes and the weakening of central depletion is solely due to the temperature. The bubble effect is eliminated at T $\approx$ 3$-$5 MeV as indicated by DF and the charge form factor. The temperature effect is found less prominent in superheavy bubble nuclei where the role of shell effects is indicated.

   ↳ nucl-thnucl-exPLB(2019)·19 citations
5. 05*

   Development of a gaseous proton-recoil detector for neutron flux measurements between 0.2 and 2 MeV neutron energy

   Paola Marini🇫🇷 · Ludovic Mathieu🇫🇷 · Mourad Aïche🇫🇷 · Serge Czajkowski🇫🇷 · Beatriz Jurado🇫🇷 · Igor Tsekhanovich🇫🇷

   Absolute measurements of neutron fluence are an essential prerequisite of neutron-induced cross section measurements, neutron beam lines characterization and dosimetric investigations. The H(n,p) elastic scattering cross section is a very well known standard used to perform precise neutron flux measurements in high precision measurements. The use of this technique, with proton recoil detectors, is not straightforward below incident neutron energy of 1 MeV, due to a high background in the detected proton spectrum. Experiments have been carried out at the AIFIRA facility to investigate such background and to determine its origin and components. Based on these investigations, a gaseous proton-recoil detector has been designed with a reduced low energy background. A first test of this detector has been carried out at the AIFIRA facility, and first results will be presented.

   ↳ physics.ins-detnucl-exRadiat.Meas.(2019)·1 citation

* 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.