Tue·Dec 24, 2024Tuesday·December 24, 2024

1. 01*

   The southern shore of the island of inversion studied via quasi-free scattering

   J. Kahlbow🇩🇪

   Neutron-rich nuclei exhibit a variety of intriguing features associated with nuclear structure evolution, deformation, and other phenomena. Particularly interesting is the region in the chart of nuclides around Z = 12 and N = 20, commonly referred to as "Island of Inversion", which is profoundly influenced by these features. Recent cutting-edge experiments performed at SAMURAI/RIBF have investigated the structure of the most neutron-rich O and F isotopes, including 27,28O and 28-30F, utilizing quasi-free scattering and invariant-mass spectroscopy techniques. This experimental campaign manifests the breakdown of the N = 20 magicity for O and F isotopes, placing them within the "Island of Inversion", as is discussed in this review article. The results are further supported by theoretical analyses employing state-of-the-art shell-model and ab-initio calculations. These nuclei serve as corner stones for the study of weak binding and continuum coupling, deformation, and halo formation. Signatures for the establishment of a superfluid regime in 28O and 29F are found. Future experimental and theoretical studies are needed to examine details.

   nucl-exnucl-thPTEP(2025)·2 citations
2. 02*

   The Island of Inversion at $N=40$

   Martha Liliana Cortes🇯🇵

   Our understanding of the structure of atomic nuclei largely derives from the nuclear shell model, which has proven widely successful. Further test to our interpretation of the nuclear properties is provided by the study of shell evolution. Increasing experimental information has shown that the nuclear energy shells change when going towards the most exotic nuclei, in turn making some shell closures disappear while others arise. In particular, the $N=40$ sub-shell closure has been the subject of extensive research due to the emergence of a so-called Island of Inversion, where deformed intruder configurations dominate the wave function of the ground state. An overview of recent experimental results in the $N=40$ Island of Inversion, particularly those performed with the combination of the MINOS hydrogen target and the DALI2 $\gamma$-ray array at the RIBF are discussed.

   nucl-exnucl-thPTEP(2026)·4 citations
3. 03*

   Competition of the shell closure and deformations across the doubly magic ${}^{78}$Ni

   Ryo Taniuchi

   The properties of the neutron-rich isotope ${}^{78}$Ni, long postulated to be doubly magic, have been extensively explored through recent experimental and theoretical studies. Confirmations of robust shell closures at $Z=28$ and $N=50$ as well as hints of competing deformations in neighboring isotopes have been obtained. Innovations of a thick liquid hydrogen target system with vertex reconstructions and the in-beam $\gamma$-ray spectroscopy technique have facilitated detailed investigations into the nuclear structure of these extreme systems. Proton knockout reactions conducted at relativistic energies have provided the first experimental evidence of shape coexistence at the cornerstone nucleus ${}^{78}$Ni and its vicinity. As the nuclear structure around ${}^{78}$Ni influences the description of very neutron-rich systems and r-process nucleosynthesis, these findings underscore the importance of further investigations. This review encapsulates the recent results concerning the nuclear structure at the vicinity of ${}^{78}$Ni on both experimental and theoretical aspects. It outlines prospective research directions that could further illuminate this complex and intriguing area of the nuclear chart.

   nucl-exnucl-thPTEP(2026)·3 citations
4. 04*

   Deformation from zinc to zirconium

   Sidong Chen🇨🇳 · Frank Browne🇯🇵 · Tomás R. Rodríguez🇪🇸 · Volker Werner🇩🇪

   Extensive gamma-ray spectroscopy of very neutron-rich nuclei of isotopes between the Ni and Sn isotopic chains was facilitated by the high luminosity LH2 target system, MINOS. Results show a persistence of deformation when going beyond the N = 60 threshold of the transition between spherical to deformed ground states at N < 60 and N > 60, respectively. Close to 78Ni, a more detailed image of the N > 50 Zn isotopes shows an erosion of the N = 50 shell closure, with core-breaking effects needed from theoretical models to replicate observation. As well as the experimental results indicating collective effects, the projected generator coordinate method is discussed in detail within the context of the neutron-rich Ge isotopes.

   nucl-exnucl-thPTEP(2026)·2 citations
5. 05*

   Shell Migration at N = 32, 34 around Ca Region

   Hongna Liu🇨🇳 · Sidong Chen🇨🇳 · Frank Browne🇯🇵

   The neutron numbers N = 32 and 34 are new magic numbers suggested in neutron-rich $pf$-shell nuclei. In this article, we discuss the experimental observables and state-of-the-art theoretical calculations that characterize and explain the shell evolution leading to new magic numbers. Particular focus shall be afforded to the experimental progress of the shell migration study at and beyond N = 32, 34 in Ar, K, Ca, and Sc isotopes at the RIBF using direct reactions with liquid hydrogen targets over the past ten years. The results prove the double magicity of \ts{52,54}Ca, and support the persistence of the N = 34 subshell closure below Z = 20 with a sharp weakening beyond Z = 20. Future measurements of intruder bands of N = 32, 34 nuclei and shell evolution towards N = 40 are discussed within the context of an upgraded RIBF facility and the development of novel detection systems.

   nucl-exnucl-thPTEP(2026)·2 citations
6. 06*

   B(E2) strength in ${}^{36,38}$Ca and in mirror nuclei 36S, 38Ar

   Jacek Okolowicz🇵🇱 · Marek Ploszajczak🇫🇷

   Recently, $B(E2,0_1^{+}\to 2_1^{+})$ transition strength have been measured in ${}^{36}$Ca and ${}^{38}$Ca. Surprisingly, the measured value in ${}^{36}$Ca: $B(E2\uparrow )=131(20)$ e${}^2$fm${}^4$, is significantly larger than in ${}^{38}$Ca, where $B(E2\uparrow )=101(11)$ e${}^2$fm${}^4$, whereas an opposite tendency of $B(E2)$ values is seen in the mirror nuclei ${}^{36}$S and ${}^{38}$Ar. The resonance $2_1^{+}$ in ${}^{36}$Ca lies 465 keV above the proton emission threshold and its description requires inclusion of the coupling to the continuum. In this work, we are analyzing $B(E2\uparrow )$ values in ${}^{36}$Ca, ${}^{36}$S, ${}^{38}$Ca, and ${}^{38}$Ar using the real-energy continuum shell model, the so-called shell model embedded in the continuum, in the $(1s_{1/2}0d_{3/2}0f_{7/2}1p_{3/2})$ model space with the monopole adjusted effective interaction ZBM-IO.

   ↳ nucl-thnucl-exActa Phys.Polon.Supp.(2025)·1 citation
7. 07*

   Nuclear structure properties of ${}^{193-200}$Hg isotopes within large-scale shell model calculations

   Subhrajit Sahoo🇮🇳 · Praveen C. Srivastava🇮🇳 · Noritaka Shimizu🇯🇵 · Yutaka Utsuno🇯🇵

   Large-scale shell-model calculations have been performed to study the nuclear structure properties of Hg isotopes with mass varying from $A=193$ to $A=200$. The shell-model calculations are carried out in the 50 $\le Z\le$ 82 and 82 $\le N\le$ 126 model space using monopole-based truncation. We present detailed studies on low-energy excitation spectra, energy systematics, and collective properties of Hg isotopes, such as reduced transition probabilities, quadrupole, and magnetic moments along the isotopic chain. The evolution of wave function configurations with spin is analyzed in the case of even-$A$ Hg isotopes. The shell-model results are in reasonable agreement with the experimental data and predictions are made where experimental data are unavailable. The shapes of Hg isotopes are also investigated through the energy-surface plots.

   ↳ nucl-thnucl-exPRC(2024)·6 citations
8. 08*

   Reaction mechanism of quasi-free knockout processes in exotic RI beam era

   Kazuki Yoshida🇯🇵 · Junki Tanaka🇯🇵

   The quasi-free nucleon knockout reaction has been revealed the single-particle nature of nuclei. Thanks to the advances in experimental techniques and reaction theory, various new aspects of nuclei are being revealed by knockout reactions. In this article, we review the basic concept of the quasi-free knockout reaction, and recent achievements in the SEASTAR project using the MINOS system. We also present our new findings on the low-energy nucleon knockout reaction and the $\alpha$ knockout reaction. The combination of the (microscopic) structure theory, reaction theory and experiments will be the key to a complete understanding of the $\alpha$ formation and its universality in the coming decades. Noble clusters, e.g., $d$, $t$, ${}^3$He, etc. are in the scope of the ONOKORO project. The implementation of the two (and more) nucleon correlation in the reaction theory is essential to connect the properties of such clusters and the reaction observables. A new framework, CDCCIA, is introduced for this purpose, which will also be applicable to the two-nucleon knockout reactions, e.g., $(p,3p)$, $(p,2pn)$, and $(p,p2n)$.

   ↳ nucl-thnucl-exPTEP(2026)·2 citations
9. 09*

   Geant4-based technical simulation study of plastic scintillators for Positron Annihilation Lifetime Spectroscopy (PALS)

   Dominik Boras

   The influence of detector setup configuration and scintillator material choice on spectrum quality in Positron Annihilation Lifetime Spectroscopy (PALS) is fundamentally acknowledged primarily by empirical observation. However, this study quantifies the effects of ultra-fast plastic scintillators (BC422Q) within a conventional collinear (180-degree) detector setup used in the laboratory using the Geant4 simulation toolkit. We examine the impact of the scintillator's dimension and geometry (truncated cone vs. cylinder) on the detection efficiency for specific gamma-ray energies (1274 keV and 511 keV) and their proportion of corrupt events such as backscattering or multiple detections. Results indicate that the selection of scintillator dimension and shape significantly enhances detection efficiency albeit with an increase in corrupt events. Furthermore, we investigate the influence on the instrument response function (IRF) of the scintillators, showing how truncated cones offer superior precision and, thus, a narrower IRF compared to cylindrical shapes.

   ↳ physics.ins-detnucl-exJINST(2025)·1 citation
10. 10*

    Finite Temperature Quarkonia Spectral Functions in the Pseudoscalar Channel

    Dibyendu Bala🇩🇪 · Sajid Ali🇩🇪 · Olaf Kaczmarek🇩🇪 · Pavan🇩🇪

    Quarkonia, the bound states of heavy quark-antiquark pairs, are important tools for studying the quark-gluon plasma (QGP). In this study, we examine the behavior of in-medium quarkonium bound states in the QGP by analyzing their spectral functions at two temperatures, $T=220\text{MeV}$ and $T=293\text{MeV}$. We use physics-motivated information to reconstruct the spectral function from the Euclidean lattice correlator. Near the threshold, the spectral function is estimated through a complex potential, determined non-perturbatively from Wilson line correlators. Our results show that the real part of the potential undergoes color screening above $T_{pc}$, while the imaginary part grows rapidly with increasing distance and temperature. For the ultraviolet (UV) part of the spectral function, we use the perturbative vacuum spectral function, as the temperature effects are suppressed in this region. In the absence of a transport peak in the pseudoscalar channel, we find that this combination effectively describes the pseudoscalar correlator on the lattice, calculated using relativistic quark fields. Our results show that pseudoscalar charmonium (${\eta }_c$) experiences significant thermal effects, as indicated by the broadening of the ${\eta }_c(1S)$ state. In contrast, the ${\eta }_b(1S)$ state remains intact, with a sharp bound state peak.

    ↳ hep-lathep-phnucl-exJ.Subatomic Part.Cosmol.(2025)·3 citations
11. 11*

    Detectors for next-generation quasi-free scattering experiments at the RIBF

    Junki Tanaka🇯🇵 · Martha Liliana Cortés🇯🇵 · Hongna Liu🇨🇳 · Ryo Taniuchi

    The advent of high-intensity radioactive ion beams has opened new avenues for nuclear structure research. By studying exotic ions, phenomena such as shell evolution, halos, and the limits of stability have been studied. In particular, Quasi-Free Scattering (QFS) experiments on hydrogen targets have proven to be a valuable tool to investigate the structure of exotic ions. Recently, a series of QFS experiments were performed at the Radioactive Isotope Beam Factory (RIBF) of the RIKEN Nishina Center employing the MINOS liquid hydrogen system. A fundamental part of the success of these experiments was the use of dedicated devices to measure the gamma-rays, charged particles, and neutrons emitted in the reactions. The experience gained during the past campaigns, as well as the upcoming upgrade of the RIBF facility call for improvements on the existing devices, as well as for the development of new detection systems. Here we review the main detection devices used at the RIBF for QFS experiments, and give an overview of the ongoing and upcoming developments.

    ↳ physics.ins-detnucl-exPTEP(2026)·3 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.