Dieter Ackermann

Background: The nuclear structure in the region southwest of the doubly magic $^{208}\mathrm{Pb}$ is important to benchmark theoretical models relevant for neutron-rich heavy element formation and for the origin of the $A\ensuremath{\approx}195$ peak in the mass abundance distribution. Although neutron-rich Pb, Tl, and Hg ($Z=80\text{--}82$) isotopes are relatively well studied, experimental data for neutron-rich Au isotopes ($Z=79$) remain largely limited due to experimental challenges.Purpose: The purpose of this work is to investigate the evolution of the high-spin structure in neutron-rich Au isotopes near the $N=126$ shell closure and to characterize the underlying shell-model configurations, with a particular focus on the roles of the high-$j$ unique-parity $\ensuremath{\pi}{h}_{11/2}$ and $\ensuremath{\nu}{i}_{13/2}$ orbitals.Methods: Neutron-rich $^{195\text{--}202}\mathrm{Au}$ isotopes were produced using multinucleon transfer reactions of $^{198}\mathrm{Pt}(^{136}\mathrm{Xe}, ^{x}\mathrm{I})^{y}\mathrm{Au}$ at a beam energy of 7 MeV/nucleon. Prompt and delayed $\ensuremath{\gamma}$-ray spectroscopy of isotopically identified reaction products was performed with a unique experimental setup combining the $\mathrm{VAMOS}++$ large acceptance magnetic spectrometer, the AGATA high-purity germanium $\ensuremath{\gamma}$-ray tracking array, and the CATLIFE detection system.Results: In even-$A ^{196,198,200,202}\mathrm{Au}$ isotopes, prompt $\ensuremath{\gamma}$-ray transitions built on the ${12}^{\ensuremath{-}}$ isomer have been observed for the first time. The odd-$J$ band built on the ${11}^{\ensuremath{-}}$ state vanishes for $A\ensuremath{\ge}196$. In odd-$A ^{195,197,199,201}\mathrm{Au}$ isotopes, new prompt and delayed $\ensuremath{\gamma}$-ray transitions above the $11/{2}^{\ensuremath{-}}$ isomer were identified, confirming and extending the known level schemes. New isomeric states assigned to ($25/{2}^{+}$) have been established in $^{199}\mathrm{Au}$ and $^{201}\mathrm{Au}$. The minima in the excitation energies of the bands as a function of $N$ built on the $11/{2}^{\ensuremath{-}}$ and ${12}^{\ensuremath{-}}$ isomers occur at $^{198}\mathrm{Au}$ ($N=119$), showing a dip against an otherwise smooth evolution.Conclusions: Large-scale shell-model calculations based on the Kuo-Herling hole effective interaction show an overall good agreement with experimental level schemes. However, the present calculations do not reproduce the minima in excitation energies at $N=119$ observed in both Au and Hg isotopes. A systematic analysis of $\ensuremath{\pi}{h}_{11/2}$ and $\ensuremath{\nu}{i}_{13/2}$ hole occupancies, together with spin contributions of protons and neutrons, sheds light on the role of these high-$j$ unique-parity orbitals in the generation of high-spin states. Part of the results of this work have been reported in another publication [Y. Cho et al., Phys. Lett. B 878, 140558 (2026)].

Recent decay studies of \(^{244,245}\)Md at the GSI Helmholtzzentrum für Schwerionenforschung, Germany, and at the Lawrence Berkeley National Laboratory (LBNL) reported conflicting mass assignments to similar \(\alpha \)‑decay energies. This prompted a new experiment at the Fragment Mass Analyzer (FMA) at Argonne National Laboratory. Using the reaction \(^{209}\mathrm {Bi}(^{40}\mathrm {Ar},xn)^{249-x}\mathrm {Md}\), we performed simultaneous \(A/q\) identification and \(\alpha \)-decay energy measurement for neutron-deficient Md isotopes. Correlated recoil-\(\alpha \)-decay chains belonging to \(^{247}\)Md and \(^{245}\)Md were identified. Probabilistic mass identification was performed from focal-plane position using a test reaction, yielding consistent \(A=247\) and \(A=245\) mass assignments within uncertainties. This study re-examines the production cross sections, decay energies, and isotopic assignments for the \(^{247}\)Md and \(^{245}\)Md nuclei. Published by the Jagiellonian University 2026 authors

The superheavy nuclei (SHN), residing at the edge of nuclear stability at the highest atomic charge \(Z\) and mass \(A\), are in the focus of scientific efforts worldwide due to the high discovery potential offered by their investigation. In this paper, we report on some of the major challenges and how we intend to approach them at GANIL, with advanced instrumentation and state-of-the-art experimental methods, as well as reaction theory approaches to the SHN production mechanism. Decay Spectroscopy After Separation (DSAS) is an efficient tool to study nuclear structure features of the heaviest nuclear species such as single particle trends towards the predicted next spherical shell closures beyond \(^{208}\)Pb, and deformation and exotic shapes, leading also to the formation of meta-stable states, like, e.g. , \(K\)-isomers. The understanding of the reaction mechanism governing heavy collisions employed for the synthesis of the heaviest nuclei, despite decades of experimental and theoretical efforts, is still a challenging task. Being a fundamental topic by itself, mastering reaction theory and producing reliable cross-section predictions are essential for a successful experimental program. Detailed nuclear structure studies of the heaviest nuclei, as well as the synthesis of superheavy elements (SHE) are presently still hampered by the limited efficiencies of the existing experimental facilities. To overcome this restriction, substantial efforts are being made to upgrade and develop existing and new facilities worldwide, online since recently or planned for the future, including the linear accelerator facility SPIRAL2 at GANIL, equipped with the versatile separator–spectrometer set-up S\(^3\). Published by the Jagiellonian University 2026 authors

We present the first measurement of the $^{47}\mathrm{K}(d,p\ensuremath{\gamma})^{48}\mathrm{K}$ transfer reaction, performed in inverse kinematics using a reaccelerated beam of $^{47}\mathrm{K}$. The level scheme of $^{48}\mathrm{K}$ has been greatly extended, with nine new bound excited states identified and spectroscopic factors deduced. Uniquely, the $^{47}\mathrm{K}(d,p)$ reaction gives access to nuclear states that are sensitive to the interaction of protons and neutrons in the widely spaced $1s$ and $fp$ orbitals, respectively. Detailed comparisons with SDPF-U and SDPF-MU shell-model calculations reveal a number of discrepancies between theory and experiment. Intriguingly, a systematic overestimation of spectroscopic factors and a poor reproduction of the energies for ${1}^{\ensuremath{-}}$ states suggests that the mixing between the $\ensuremath{\pi}{s}_{1/2}^{1}{d}_{3/2}^{4}$ and $\ensuremath{\pi}{s}_{1/2}^{2}{d}_{3/2}^{3}$ proton configurations in $^{48}\mathrm{K}$ is not correctly described using current interactions, challenging our description of light nuclei around the $N=28$ island of inversion.