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. Abstract Published by the Jagiellonian University 2026 authors

The collapse of the canonical N=28 magic number in nuclei with Z<20 has drawn significant interest as it relates to the emergence of an island of inversion centered on ^42Si and ^44S. In particular, interactions between the πs_1/2 orbital – empty in ^42Si and full in ^44S – and the neutron orbitals just above and below the N=28 gap are expected to be critical in this region, but remain relatively unexplored. In this paper, we expand upon the results of our previous study of the direct transfer reaction ^47K(d,pγ)^48K [C. J. Paxman et al., Phys. Rev. Lett. 134, 162504 (2025)] with the results of the complementary ^47K(d,tγ)^46K reaction. Through this study, we present a comprehensive scan of the interaction between the critical πs_1/2 orbital and a broad range of neutron orbitals spanning nearly two full shells. We identify several discrepancies between the experimental results and state-of-the-art shell model calculations, which suggest a deficiency of the shell model to fully capture the complex proton configuration mixing in this region, highlighting a significant challenge for single-particle descriptions of the island of inversion.

Background: The fission character changes along the mercury isotopic chain, from asymmetric (180Hg) through slightly asymmetric (190Hg) to symmetric (198Hg). Mercury isotopes have been studied using various techniques including 9-delayed fission, Coulomb-induced fission, and fusion-fission, but the isotope 194Hg has not been investigated until now. Purpose: To experimentally study the fusion-fission reaction of 194Hg at moderate excitation energy and to determine previously unknown independent fission yields and properties of emitted neutrons and y rays. Method: The compound nucleus was formed in the reaction 12C + 182W. Prompt gamma rays emitted during the reaction were measured with the v-ball2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting gamma-gamma cascades in the fission fragments and performing a maximum-likelihood analysis. The number of emitted neutrons was determined from the fragment distribution, as well as from the study of fission partners. Average momentum carried by the y rays was determined by the Manchester method. Additionally, the long-term 9 activity of fragment residues was measured as a complementary method. Results: The measured fission-fragment mass distribution is consistent with that of neighboring mercury isotopes, confirming the gradual change along the isotopic chain and influence of the Z = 36 deformed proton shell in the light fragment. The independent fragment yield and distribution of fission partners is well described by the GEF model. However, there are discrepancies concerning the angular momentum of the fragments and the width of the mass distribution, confirmed by the independent residual activity measurements. Conclusions: Our results demonstrate that the method based on fusion-fission and y spectroscopy is a valuable alternative to direct mass or charge measurements. Independent fission yields, correlation of fission partners, and the study of angular momentum of fragments open the possibility of a comprehensive description of the process. This is important both from a theoretical and experimental point of view and is needed to achieve further refinement of our understanding of the fission process.

The electromagnetic decay of the ≈40 μs isomer of ^250No has been investigated using the Geant4 toolkit for the simulations of the interaction of particles through matter. It is concluded that the decay does not follow the pattern established in the lighter isotones, where the isomer decays directly to members of the ground state rotational band. An alternative scenario is proposed. The implications on the location of the isotopic border for neutron deficient Rf isotopes are discussed.

Advanced theoretical methods can accurately calculate various atomic observables and predict electronic structure. Still, systematic computations of the radiative and non-radiative transition probabilities and energies are missing for the actinides and all the transfermium elements. However, these compilations are needed for comprehensive Monte-Carlo simulations (such as Geant4) of the radioactive decay of transfermium nuclei. These simulations can form a basis for data analysis of experiments, especially with complex detection setups. Investigation of the transfermium nuclei is crucial for understanding the nature of the nuclear force. In this study, simulations based on data from the Jena Atomic Calculator (JAC) and the data from the Evaluated Atomic Data Library (EADL) present in Geant4 were found compatible for the three elements Ba(Z=56), U(Z=92), and Fm(Z=100), thus, validating the JAC calculations. For Z>100, we also found sound agreement between simulations that used data generated with JAC and experimental results involving No(Z=102) and Rf(Z=104) isotopes. These results demonstrate that JAC can produce reliable atomic data sets for transfermium elements, which will assist in analyzing nuclear-decay-spectroscopy experiments.

This work reports on the study of the decay properties along the 257Db decay chain using the GABRIELA setup. The first observation of a high-K isomer in 257Db is presented. In addition, an unreported alpha-decay branch in 249Md has been evidenced, allowing constraints the differences in energy of the alpha-decaying levels in 249Md, 253Lr and 257Db. Finally, the combination of the observed fine structure alpha-decay from the high-spin state in 257Db with the first observation the internal decay in 253Lr requires a revision of the level and decay scheme. In particular, a change of parity for the high-spin state from 9/2+ to 9/2-in 257Db is suggested, and the implications of such a change are also discussed.

We report on a new spectroscopic study of the decay of high-K isomers in 254 102No152, a touchstone nucleus for testing models to understand the structure of superheavy nuclei. The experiment, performed using the Argonne gas-filled analyzer (AGFA), was geared toward resolving long-standing ambiguities in spin-parity and configuration assignments for the two-and four-quasiparticle (qp) intrinsic excitations identified in this nucleus. The isomer decay schemes are firmly established with the help of the highest-statistics gamma-gamma coincidence data collected to date, providing anchor points for competing theories. A newly measured half-life in the nanosecond range establishes a second 2-qp isomer in 254No. The preferred decay pathways for the 2-and 4-qp isomers are discussed, providing new insights into the underlying hindrance mechanisms at play in these heavy nuclei. With firm configuration assignments, the intrinsic excitations in this deformed mass region provide stringent constraints and challenge the different theoretical approaches at play in understanding the structure of superheavy nuclei.

We present the first measurement of the ^{47}K(d,pγ)^{48}K transfer reaction, performed in inverse kinematics using a reaccelerated beam of ^{47}K. The level scheme of ^{48}K has been greatly extended, with nine new bound excited states identified and spectroscopic factors deduced. Uniquely, the ^{47}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^{-} states suggests that the mixing between the πs_{1/2}^{1}d_{3/2}^{4} and πs_{1/2}^{2}d_{3/2}^{3} proton configurations in ^{48}K is not correctly described using current interactions, challenging our description of light nuclei around the N=28 island of inversion.

Fission shape isomers (SI) are poorly understood metastable states characterized by a second super-deformed potential energy minimum coexisting with normally-deformed states in the low-spin regime. Although many such isomers have been observed in the actinide region, our understanding of the states of the second minimum remains very limited. For most SIs, the only available information is their half-life, determined via their exclusive decay mode, delayed fission. However, the interesting possibility of a competing branch of 7-back decay towards normally-deformed states opens up as the number of protons decreases and the fission barrier becomes harder to penetrate, uranium isotopes being the heaviest candidates. In this context, two experiments were performed to study 236fU using the nu-Ball2/PARIS spectrometer at the ALTO facility of IJCLab. The nu-Ball2 setup consists of 24 High Purity Germanium (HPGe) Clovers and 64 phoswiches (LaBr3/NaI) from the PARIS Collaboration are added to cover more than 90% of the total solid angle. Additionally, a Double-sided Silicon Stripped Detector (DSSD) was used to measure the energy of outgoing light-charged particles. The state-of-the-art fully digital FASTER electronics allowed triggerless data acquisition at high data rates. The selectivity of this setup enabled us to probe rare decays with sub-microbarn cross sections.

We present studies of multinucleon transfer reactions in collisions of Ca-48 +Pb-208, Ti-50 +Pb-208, and Ar-40 +Bi-209 which lead to the population of nuclei with proton numbers greater than the target proton number. The target- like reaction products were separated in flight using the velocity filter SHELS of the Flerov Laboratory for Nuclear Reactions (FLNR), Dubna. Our goal was to examine transfer reactions for producing new heavy and superheavy nuclei and to assess the applicability of velocity filters for their investigation. We observed and studied about 40 different nuclides, resulting from the transfer of up to eight protons from the projectile to the target and moving in forward direction relative to the beam axis. We present cross-section systematics for isotopes of elements Z = (83 - 91) measured in our experiment and compare them with available data from transfer reactions with actinide targets which lead to isotopes up to Z = 103.

The study of the heaviest nuclei is not only an experimental challenge (due to the very low production cross sections involved), but it is also a theoretical one. Indeed, the combination of large Coulomb fields and high densities of single-particle states makes theoretical calculations difficult and leads to extreme model dependencies, such as for example the localisation of the so-called “island of stability” [1]. Moreover, recent experimental and theoretical studies have shed light on deficiencies of energy density functionals (EDF), which are used to describe nuclear properties across the entire nuclear chart [2], [3]. This suggests that further improvements of the EDF methods are necessary and that new reliable data are required to benchmark and constrain the theoretical models. In this talk, recent results on the structure of transfermium nuclei will be presented and discussed.

This study investigates the prompt fission neutron (PFN) multiplicity distribution in the spontaneous fission (SF) of ^244 Fm. Experimental data were obtained using the complete fusion reaction ^206 Pb( ^40 Ar,2n) ^244 Fm, obtaining a mean of 3.6 ± 0.1 emitted neutrons per SF event. The symmetry of the PFN multiplicity distribution suggests no significant influence of additional fission modes, aligning with theoretical predictions that indicate the dominance of the standard fission mode. At the same time, comparison with neighboring isotopes points at a possible additional fission mode in ^246 Fm.

The complete-fusion reaction 204Pb(48Ca,2n)250No was used to study two activities of 250No with distinct half-lives.A total of 1357 events were observed in the SFiNx neutron detection system.The average number of neut-rons emitted per spontaneous fission of 250No was determined to be(4.1±0.1).The unusually symmetrical shape of the prompt neutron multiplicity distribution was restored and presented for the first time.Statistical tests were per-formed to compare the prompt neutron multiplicity distributions associated with the ground state and K-isomer state decays.

This study of isomeric states in 255No was performed with the GABRIELA detector array at the focal plane of the SHELS recoil separator. The 208Pb(48Ca, xn)256-xNo fusion-evaporation reaction was used to produce nobelium isotopes with a beam energy optimized for the one-neutron and two-neutron evaporation channels. These nobelium isotopes were studied by decay spectroscopy leading to the identification of isomeric states in 255No by means of the calorimetric method. In order to isolate the radioactive decays of 255No from the more numerous decays of 254No, the characteristic signal of the internal decay of the daughter 251Fm was used as a tag. Under these conditions, the decay of four isomeric states was observed. They are interpreted as high-K structures decaying in cascade. The first isomeric state is assigned to a v[725] 11 - neutron one quasiparticle (qp) configuration, in good agreement with the trend of this state in the neighboring isotones. The second and the third ones were attributed to three-qp 21/2+ and 27/2+ states and are interpreted as resulting from the coupling of the same v[725] 11 - one-qp configuration with the 2{[624] 9 + circle times [521] 1 -}5- and with the 2{[624] 9 + circle times [514] 7 -}8- two-qp configurations, respectively. According to its excitation energy E* 2.5 MeV, the fourth isomeric state should have a five-qp structure, which requires more statistics to be detailed.

The excited states of unstable ^{20}O were investigated via γ-ray spectroscopy following the ^{19}O(d,p)^{20}O reaction at 8  AMeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 2_{2}^{+} and 3_{1}^{+} states were firmly established. From the γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2_{2}^{+} and 3_{1}^{+} states, the B(E2) and B(M1) were determined. Various chiral effective field theory Hamiltonians, describing the nuclear properties beyond ground states, along with a standard USDB interaction, were compared with the experimentally obtained data. Such a comparison for a large set of γ-ray transition probabilities with the valence space in medium similarity renormalization group ab initio calculations was performed for the first time in a nucleus far from stability. It was shown that the ab initio approaches using chiral effective field theory forces are challenged by detailed high-precision spectroscopic properties of nuclei. The reduced transition probabilities were found to be a very constraining test of the performance of the ab initio models.

The Advanced GAmma Tracking Array (AGATA) has been installed at Laboratori Nazionali di Legnaro (LNL), Italy. In this installation, AGATA will consist, at the beginning, of 13 AGATA triple clusters (ATCs) with an angular coverage of 1π, and progressively the number of ATCs will increase up to a 2π angular coverage. This setup will exploit both stable and radioactive ion beams delivered by the Tandem–PIAVE-ALPI accelerator complex and the SPES facility. The new implementation of AGATA at LNL will be used in two different configurations, firstly one coupled to the PRISMA large-acceptance magnetic spectrometer and lately a second one at Zero Degrees, along the beam line. These two configurations will allow us to cover a broad physics program, using different reaction mechanisms, such as Coulomb excitation, fusion-evaporation, transfer and fission at energies close to the Coulomb barrier. These setups have been designed to be coupled with a large variety of complementary detectors such as charged particle detectors, neutron detectors, heavy-ion detectors, high-energy γ-ray arrays, cryogenic and gasjet targets and the plunger device for lifetime measurements. We present in this paper the conceptual design, characteristics and performance figures of this implementation of AGATA at LNL.

Nuclear-structure studies using fusion reactions are reviewed in terms of prospects for advancement using the next generation of γ -ray tracking arrays such as AGATA. Properties discussed include those of light N=Z nuclei and rotational behaviour in heavy nuclei at high values of angular momentum and internal excitation energy.

Background: Asymmetric fission is known to occur in two regions, the actinides and sub-lead, and is dependent on the fissioning system excitation energy. Experimental evidence in the sub-lead region show that this mode is surprisingly persistent with increasing energy and its origin is not fully understood. Purpose: To experimentally study the fusion-fission reaction of $^{215}$Fr at moderate excitation energy and determine previously unknown independent fission yields and other properties. Method: The compound nucleus was formed in the reaction $^{18}$O + $^{197}$Au. The prompt gamma-rays emitted during the reaction were measured with the high efficiency and high granularity $\nu$-ball2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting triple-gamma cascades in the fission fragments. Results: The observed yields, although dominated by a symmetric peak, show maxima for heavy fragment of $Z \approx 54-56$, which is consistent with the known results in the actinide region but unexpected for the nuclide of interest, and at the studied excitation energy. Conclusions: The mode of asymmetric fission is present even at relatively high excitation energies in the system studied. This observation matches experimental findings in the sub-lead region, contrary to the actinides, and so far there is no well-developed explanation of this phenomenon.