Mon·Jan 18, 2021Monday·January 18, 2021

1. 01*

   New $\alpha$-Emitting Isotope ${}^{214}$U and Abnormal Enhancement of $\alpha$-Particle Clustering in Lightest Uranium Isotopes

   Z. Y. Zhang🇨🇳 · H. B. Yang🇨🇳 · M. H. Huang🇨🇳 · Z. G. Gan🇨🇳 · C. X. Yuan🇨🇳 · C. Qi🇸🇪 · A. N. Andreyev🇬🇧 · M. L. Liu🇨🇳 · L. Ma🇨🇳 · M. M. Zhang🇨🇳 · Y. L. Tian🇨🇳 · Y. S. Wang🇨🇳 and 30 other authors

   A new $\alpha$-emitting isotope ${}^{214}$U, produced by fusion-evaporation reaction ${}^{182}$W(${}^{36}$Ar, 4n)${}^{214}$U, was identified by employing the gas-filled recoil separator SHANS and recoil-$\alpha$ correlation technique. More precise $\alpha$-decay properties of even-even nuclei ${}^{216,218}$U were also measured in reactions of ${}^{40}$Ar, ${}^{40}$Ca with ${}^{180,182,184}$W targets. By combining the experimental data, improved $\alpha$-decay reduced widths ${\delta }^2$ for the even-even Po--Pu nuclei in the vicinity of magic neutron number $N=126$ were deduced. Their systematic trends are discussed in terms of $N_p{N}_n$ scheme in order to study the influence of proton-neutron interaction on $\alpha$ decay in this region of nuclei. It is strikingly found that the reduced widths of ${}^{214,216}$U are significantly enhanced by a factor of two as compared with the $N_p{N}_n$ systematics for the $84\le Z\le 90$ and $N<126$ even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the $\pi 1f_{7/2}$ and $\nu 1f_{5/2}$ spin-orbit partner orbits, which is supported by a large-scale shell model calculation.

   nucl-exPRL(2021)·87 citations
2. 02*

   Isospin diffusion measurement from the direct detection of a Quasi-Projectile remnant

   A. Camaiani🇮🇹 · G. Casini🇮🇹 · S. Piantelli🇮🇹 · A. Ono🇯🇵 · E. Bonnet🇫🇷 · R. Alba🇮🇹 · S. Barlini🇮🇹 · B. Borderie🇫🇷 · R. Bougault🇫🇷 · C. Ciampi🇮🇹 · A. Chbihi🇫🇷 · M. Cicerchia🇮🇹 and 31 other authors

   The neutron-proton equilibration process in 48 Ca+ 40 Ca at 35 MeV/nucleon bombarding energy has been experimentally estimated by means of the isospin transport ratio. Experimental data have been collected with a subset of the FAZIA telescope array, which permitted to determine Z and N of detected fragments. For the first time, the QP evaporative channel has been compared with the QP break-up one in a homogeneous and consistent way, pointing out to a comparable n-p equilibration which suggests close interaction time between projectile and target independently of the exit channel. Moreover, in the QP evaporative channel n-p equilibration has been compared with the prediction of the Antisymmetrized Molecular Dynamics (AMD) model coupled to the GEMINI statistical model as an afterburner, showing a larger probability of proton and neutron transfers in the simulation with respect to the experimental data.

   nucl-exPRC(2021)·27 citations
3. 03*

   Some remarks on the discovery of Md-244

   F.P.Hessberger · M.Block · Ch.E.Duellmann · A.Yakushev · M.Leino · J.Uusitalo

   In two recent papers by Pore et al. and Khuyagbaatar et al. discovery of the new isotope Md-244 was reported. The decay data, however, are conflicting. While Pore et al. report two isomeric states decaying by alpha emission with E(1)=8.66(2) MeV, T_1/2=0.4+0.4/-0.1s and E(2)=8.31(2) MeV, T_1/2 approx 6 s, Khuyagbaatar et al. report only a single transition with a broad energy distribution of E=(8.73-8.86) MeV and T_1/2=0.30/-0.09 s. The data published by Pore et al. very similar to those published for Md-245 (E=8.64(2), 8.68(2) MeV T_1/2=0.35+0.23/-0.16}$ s ). Therefore, we compare the data presented for Md-244 by Pore et al. with those reported for Md-245 by Ninov et al. and also by Khuyagbaatar et al.. We conclude that the data presented by Pore et al. shall be attributed to Md-245 with small contributions (one event each) from Fm-245 and probably Md-246.

   nucl-exPRL(2021)·5 citations
4. 04*

   Persistence of the $Z=28$ shell gap in $A=75$ isobars: Identification of a possible $(1/2^{-})$ $\mu$s isomer in ${}^{75}$Co and $\beta$ decay to ${}^{75}$Ni

   S. Escrig🇪🇸 · A. I. Morales🇪🇸 · S. Nishimura🇯🇵 · M. Niikura🇯🇵 · A. Poves🇪🇸 · Z. Y. Xu🇧🇪 · G. Lorusso🇯🇵 · F. Browne🇯🇵 · P. Doornenbal🇯🇵 · G. Gey🇫🇷 · H.-S. Jung🇺🇸 · Z. Li🇨🇳 and 31 other authors

   Background: The evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the `southwest' region of ${}^{78}$Ni, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. Purpose: We intend to measure the isomeric and $\beta$ decay of ${}^{75}$Co, with one-proton and two-neutron holes relative to ${}^{78}$Ni, to access new nuclear structure information in ${}^{75}$Co and its $\beta$-decay daughters ${}^{75}$Ni and ${}^{74}$Ni. Methods: The nucleus ${}^{75}$Co is produced in relativistic in-flight fission reactions of ${}^{238}$U at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and $\beta$ decay are studied exploiting the BigRIPS and EURICA setups. Results: We obtain partial $\beta$-decay spectra for ${}^{75}$Ni and ${}^{74}$Ni, and report a new isomeric transition in ${}^{75}$Co. The energy [$E_{\gamma }=1914(2)$ keV] and half-life [$t_{1/2}=13(6)$ $\mu$s] of the delayed $\gamma$ ray lend support for the existence of a $J^{\pi }=(1/2^{-})$ isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in ${}^{75}$Ni, but the first calculated $1/2^{-}$ level in ${}^{75}$Co, a prolate $K=1/2$ state, is predicted about 1 MeV below the observed $(1/2^{-})$ level. Conclusions: The spherical-like structure of the lowest-lying excited states in ${}^{75}$Ni is proved. In the case of ${}^{75}$Co, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below ${}^{78}$Ni. Further experimental efforts to discern the nature of the $J^{\pi }=(1/2^{-})$ isomer are necessary.

   nucl-exPRC(2021)·4 citations
5. 05*

   Hyper-order baryon number fluctuations at finite temperature and density

   Wei-jie Fu🇨🇳 · Xiaofeng Luo🇨🇳 · Jan M. Pawlowski🇩🇪 · Fabian Rennecke🇺🇸 · Rui Wen🇨🇳 · Shi Yin🇨🇳

   Fluctuations of conserved charges are sensitive to the QCD phase transition and a possible critical endpoint in the phase diagram at finite density. In this work, we compute the baryon number fluctuations up to tenth order at finite temperature and density. This is done in a QCD-assisted effective theory that accurately captures the quantum- and in-medium effects of QCD at low energies. A direct computation at finite density allows us to assess the applicability of expansions around vanishing density. By using different freeze-out scenarios in heavy-ion collisions, we translate these results into baryon number fluctuations as a function of collision energy. We show that a non-monotonic energy dependence of baryon number fluctuations can arise in the non-critical crossover region of the phase diagram. Our results compare well with recent experimental measurements of the kurtosis and the sixth-order cumulant of the net-proton distribution from the STAR collaboration. They indicate that the experimentally observed non-monotonic energy dependence of fourth-order net-proton fluctuations is highly non-trivial. It could be an experimental signature of an increasingly sharp chiral crossover and may indicate a QCD critical point. The physics implications and necessary upgrades of our analysis are discussed in detail.

   ↳ hep-phnucl-exnucl-thPRD(2021)·130 citations
6. 06*

   Statistical and dynamical bimodality in multifragmentation reactions

   S. Mallik🇮🇳 · G. Chaudhuri🇮🇳 · F. Gulminelli🇫🇷 · S. Das Gupta🇨🇦

   The bimodal behavior of the order parameter is studied in the framework of Boltzmann-Uehling-Uhlenbeck (BUU) transport model. In order to do that, simplified yet accurate method of BUU model is used which allow calculation of fluctuations in systems much larger than what was considered feasible in a well-known and already existing model. It is observed that depending on the projectile energy and centrality of the reaction, both entrance channel and exit channel effects can be at the origin of the experimentally observed bimodal behavior. Both dynamical and statistical bimodality mechanisms are associated in the theoretical model to different time scales of the reaction, and to different energy regimes.

   ↳ nucl-thnucl-ex1 citation
7. 07*

   Production of super-heavy nuclei in cold fusion reactions

   V. Yu. Denisov🇺🇦 · I. Yu. Sedykh🇷🇺

   The model for the cold-fusion reactions related to the synthesis of super-heavy nuclei in collisions of heavy projectile-nuclei with ${}^{208}$Pb target nucleus is discussed. In the framework of this model the production of the compound nucleus by two paths through, the di-nuclear system and the fusion way, are taken into account simultaneously. The formation of the compound nucleus in the framework of the di-nuclear system is related to the transfer of nucleons from the light nucleus to the heavy one. The fusion way is linked to the sequential evolution of the nuclear shape from the system of contacting nuclei to the compound nucleus. It is shown that the compound nucleus is mainly formed by the fusion way in the cold-fusion reactions. The landscape of the potential energy related to the fusion path is discussed in detail. This landscape for very heavy nucleus-nucleus systems has the intermediate state, which is linked to the formation of both the compound nucleus and the quasi-fission fragments. The decay of the intermediate state is taken into account in the calculation of the compound nucleus production cross sections and the quasi-fission cross sections. The values of the cold-fusion cross sections obtained in the model are well agreed with the experimental data.

   ↳ nucl-thnucl-exCPC(2021)·11 citations
8. 08*

   New signatures of phase transition from Statistical Models of Nuclear multifragmentation

   G. Chaudhuri🇮🇳 · S. Mallik🇮🇳 · P. Das🇮🇳 · S. Das Gupta🇨🇦

   The study of liquid-gas phase transition in heavy ion collisions has generated a lot of interest amongst the nuclear physicists in the recent years. In heavy ion collisions, there is no direct way of measuring the state variables like entropy, pressure, energy and hence unambiguous characterization of phase transition becomes difficult. This work proposes new signatures of phase transition that can be extracted from the observables which are easily accessible in experiments. It is observed that the temperature dependence of the first order derivative of the order parameters in nuclear liquid gas phase transition exhibit similar behavior as that of the variation of specific heat at constant volume Cv which is an established signature of first order phase transition. This motivates us to propose these derivatives as confirmatory signals of liquid-gas phase transition. The measurement of these signals in easily feasible in most experiments as compared to the other signatures like specific heat, caloric curve or bimodality. Total multiplicity, size of largest cluster are some of the order parameters which have been studied. Statistical Models based on canonical ensemble and lattice gas model has been used for the study. This temperature where the peak appears is designated to be the transition temperature and the effect of certain parameters on this has also been examined. The multiplicity derivative signature proposed in this work has been further confirmed by other theoretical models as well as in experimental study.

   ↳ nucl-thnucl-ex0 citations
9. 09*

   Electron beam studies of light collection in a scintillating counter with embedded fibers

   M. Lauß🇩🇪 · P. Achenbach🇩🇪 · S. Aulenbacher🇩🇪 · M. Ball🇩🇪 · I. Beltschikow · M. Biroth🇩🇪 · P. Brand🇩🇪 · S. Caiazza🇩🇪 · M. Christmann🇩🇪 · O. Corell · A. Denig🇩🇪 · L. Doria🇩🇪 and 19 other authors

   The light collection of several fiber configurations embedded in a box-shaped plastic scintillating counter was studied by scanning with minimum ionizing electrons. The light was read out by silicon photomultipliers at both ends. The light yield produced by the 855-MeV beam of the Mainz Microtron showed a strong dependence on the transverse distance from the beam position to the fibers. The observations were modeled by attributing the collection of indirect light inside of the counter and of direct light reaching a fiber to the total light yield. The light collection with fibers was compared to that of a scintillating counter without fibers. These studies were carried out within the development of plastic scintillating detectors as an active veto system for the DarkMESA electron beam-dump experiment that will search for light dark matter particles in the MeV mass range.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·5 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.