Mon·Oct 31, 2022Monday·October 31, 2022

1. 01*

   Measurement of the transverse asymmetry of $\gamma$-rays in the ${}^{117}$Sn(n,$\gamma$)${}^{118}$Sn reaction

   S. Endo🇯🇵 · T. Okudaira🇯🇵 · R. Abe · H. Fujioka🇯🇵 · K. Hirota🇯🇵 · A. Kimura🇯🇵 · M. Kitaguchi🇯🇵 · T. Oku🇯🇵 · K. Sakai🇯🇵 · T. Shima🇯🇵 · H. M. Shimizu🇯🇵 · S. Takada🇯🇵 and 4 other authors

   Largely enhanced parity-violating effects observed in compound resonances induced by epithermal neutrons are currently attributed to the mixing of parity-unfavored partial amplitudes in the entrance channel of the compound states. Furthermore, it is proposed that the same mechanism that enhances the parity-violation also enhances the breaking of time-reversal-invariance in the compound nucleus. The entrance-channel mixing induces energy-dependent spin-angular correlations of individual $\gamma$-rays emitted from the compound nuclear state. For a detailed study of the mixing model, a $\gamma$-ray yield in the reaction of ${}^{117}$Sn(n,$\gamma$)${}^{118}$Sn was measured using the pulsed beam of polarized epithermal neutrons and Ge detectors. An angular dependence of asymmetric $\gamma$-ray yields for the orientation of the neutron polarization was observed.

   nucl-exPRC(2022)·8 citations
2. 02*

   ${\beta }^{+}$ Gamow-Teller strengths from unstable ${}^{14}$O via the $(d,{}^2\text{He})$ reaction in inverse kinematics

   S. Giraud🇫🇷 · J. C. Zamora🇧🇷 · R. Zegers🇺🇸 · D. Bazin🇺🇸 · Y. Ayyad🇪🇸 · S. Bacca🇩🇪 · S. Beceiro-Novo🇪🇸 · B. A. Brown🇺🇸 · A. Carls · J. Chen🇨🇳 · M. Cortesi🇺🇸 · M. DeNudt and 15 other authors

   For the first time, the $(d,{}^2\text{He})$ reaction was successfully used in inverse kinematics to extract the Gamow-Teller transition strength in the ${\beta }^{+}$ direction from an unstable nucleus. The nucleus studied was ${}^{14}$O, and the Gamow-Teller transition strength to ${}^{14}$N was extracted up to an excitation energy of 22 MeV. The measurement of the $(d,{}^2\text{He})$ reaction in inverse kinematics was made possible by the combination of an active target time projection chamber and a magnetic spectrometer. The data were used to test shell-model and state-of-the-art coupled cluster calculations. Shell-model calculations reproduce the measured Gamow-Teller strength distribution up to about 15 MeV reasonably well, after the application of a phenomenological quenching factor. Coupled-cluster calculation reproduces the full strength distribution well without such quenching, owing to the large model space, the inclusion of strong correlations, and the coupling of the weak interaction to two nucleons through two-body currents. This indicates that such calculations provide a very promising path for answering long-standing questions about the observed quenching of Gamow-Teller strengths in nuclei.

   nucl-exnucl-thPRL(2023)·15 citations
3. 03*

   Experimental study of the isospin transport with 40,48 Ca+ 40,48 Ca reactions at 35 MeV/nucleon

   Q. Fable (L2IT) · A. Chbihi (GANIL) · J.D. Frankland (GANIL) · P. Napolitani (IJCLab) · G. Verde (L2IT, INFN) · E. Bonnet (SUBATECH) · B. Borderie (IJCLab) · R. Bougault (LPCC) · E. Galichet (IJCLab, CNAM) · T. Génard (GANIL) · Diego D. Gruyer (LPCC) · M. Henri (GANIL) and 9 other authors

   We investigate the isospin transport with 40,48 Ca+ 40,48 Ca reactions at 35 MeV/nucleon, measured with the coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector. Using the quasi-projectile remnant measured with VAMOS and carefully selected light-charged-particles measured in coincidence with INDRA, a reconstruction method is applied to estimate the excited quasi-projectile (QP) on an event-by-event basis. The isospin diffusion is investigated using the isospin transport ratio with the asymmetry $\delta$ = (N -- Z)/A of the projectile as an isospin-sensitive observable and the total transverse energy of Z $\le$ 2 nuclei for experimental centrality sorting. The experimental isospin transport ratios present, for both the reconstructed QP and its remnant, a clear evolution towards isospin equilibration with increasing dissipation of the collision while the full equilibration is not reached. A smoother evolution with less discrepancies between the two mixed systems in the case of the reconstructed QP is also observed. The isospin migration is investigated using the neutron-to-proton ratio of the light-charged-clusters and the velocity of the QP remnant as a sorting parameter. More particularly, we focused on an angular region centered around the mid-rapidity of the reaction so as to characterize the low-density neck emissions. A systematic neutron-enrichment is observed and interpreted as a consequence of isospin migration, more particularly for the symmetric systems which present no isospin gradient between the projectile and the target. We also noticed that the ^{2}H and ^{4}He particles exhibit very close multiplicities independently of the sorting variable for the symmetric systems.

   nucl-exphysics.acc-phPRC(2023)·14 citations
4. 04*

   On the multipole mixing ratio of the $1066$ keV transition from the 0.52 $\mu s$ isomer of ${}^{180}$Hf

   A. Chalil (1)🇫🇷 · T. J. Mertzimekis (1)🇬🇷 · A. Zyriliou (1) · P. Vasileiou (1)🇬🇷 · N. Florea (2)🇷🇴 · C. Mihai (2)🇷🇴 · R. Mihai (2) · C. Nita (2) · C. Sotty (2)🇷🇴 · A. Mitu (2) · L. Stan (2)🇷🇴 · A. Turturica (2)🇷🇴 · R. Mărginean (2)🇷🇴 · N. Mărginean (2) ( (1) National and Kapodistrian University of Athens, Department of Physics, GR-15784, Athens, Greece, (2) National Institute of Physics and Nuclear Engineering, Magurele, Romania )🇷🇴

   The nucleus ${}^{180}$Hf is one of the most primary of examples of an axially symmetric prolate rotor. Combined with the presence of high-$K$ isomers, spectroscopic studies can provide important information on the nature of its single-particle levels. Precise measurements are essential for constraining nuclear models and interpreting the nature of such isomeric states. In this work, the nucleus ${}^{180}$Hf was populated using the proton pick-up reaction ${}^{181}$Ta(${}^{11}$B,${}^{12}$C)${}^{180}$Hf at beam energy of 47 MeV at Horia Hulubei National Institute of Nuclear Physics and Engineering (IFIN-HH). The spin of the 1374 keV state and the mixing ratio of the $1066$ keV transition have been measured, the latter with an increased precision compared to the previous value from literature. The presently measured spin of the 1374 keV state, currently assigned a tentative value of $(4_1^{-})$, favors one of the two different values reported in the literature. The particular state constitutes the band-head of a rotational band in ${}^{180}$Hf. The measured multipolarity mixing ratio of the inter-band transition $1374\to 309$ keV can provide important information for the testing and constraining of theoretical nuclear models used for the study of the intrinsic properties of ${}^{180}$Hf as well as its neighboring isotopes.

   nucl-exNPA(2023)·0 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.