The Gamow-Teller strength distribution covering the entire beta-decay window, up to 10.312(4) MeV, of 80g+mGa was measured for the first time in photofission of UCx induced by a 50 MeV electron beam. The new data show significant enhancement in the high-energy region with a jump structure. Simultaneously, the gamma deexciting behavior of beta-populated states presents a competition between deexcitation to 2+1 [beta 2 = 0.155(9)] and to 2+2 [beta 2 = 0.0530.008 0.009)] in 80Ge. To understand these data, we performed a realistic shell-model calculation and systematic analysis of log ft ratios between precursors' beta decay to 2+2 and to 2+1 of Ga isotopes. We conclude that these phenomena evidence simultaneous impacts of nuclear shell structure and collectivity on B(GT) distribution and therefore the half-life of the precursor.

The pygmy dipole resonance (PDR) has been the subject of numer-ous studies, both experimental and theoretical. Indeed, the study of the PDR has been and still is of great interest since it allows to constrain the symmetry energy, an important ingredient of the equation of state of nuclear matter that describes the matter within neutron stars. Moreover, the PDR is predicted to play a key role in the r-pro cess via the increase of the neutron capture rate. However, despite numerous experiments dedicated to the study of the PDR, a consistent description is still missing. In this context, we have proposed to study the PDR using a new probe: the neutron inelastic scattering reaction (n,n'-y). An experiment to study the pygmy resonance in 140Ce using the (n,n'-y) reaction has been performed in Septem-ber 2022. This experiment has been made possible thanks to the high-intensity proton beam of the new accelerator SPIRAL2 at GANIL and the NFS (Neutron For Science) facility. The experimental setup was composed of the new generation multi-detectors PARIS, for the detection of-y-rays coming from the de-excitation of the PDR, and MONSTER, for the detection of scattered neutrons. In this article, the experiment motivation and description are presented.

A new β-decay station, COnversion electrons Chasing at Orsay (COeCO), has been developed at ALTO to perform conversion electron spectroscopy studies of neutron-rich nuclei produced by photo-fission of a uranium carbide target. It is based on the collection of a low-energy ISOL beam on a mylar tape, and the transportation of the electrons emitted by the produced radioactive source through a magnetic field induced by two copper coils, towards a cooled Si(Li) detector. In this article, a detailed description of the new decay station and its components is given. The magnetic field induced by the coils was measured and compared to simulations performed with the COMSOL® software. The efficiency of the detection setup was estimated using a 207Bi and a 152Eu source as an off-line commissioning. Finally, the results obtained with a 96Rb radioactive beam for the on-line commissioning are presented.

In the paper, experimental results of high-energy gamma GDR (Giant Dipole Resonance) decay from the Pt-192 compound nucleus associated with the 4n decay channel leading to the Pt-188 evaporation residue are presented. The measurement, which was performed with the use of coupled nuBall and PARIS arrays, aimed to investigate the link between deformation of a hot nucleus and different deformations of the residual states. The high-energy gamma rays from the GDR decay measured using the PARIS phoswiches provided information on compound nucleus properties, particularly on its effective shape. Discrete transitions in evaporation residues, measured by the nuBall array, were used to select the final products of specific deforma-tions. As a result, the GDR strength functions measured for the particular decay paths were obtained.

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.

M4 resonances in light nuclei result from the p3/2 -> d5/2 stretched exci-tations. Their configurations should be relatively simple, which makes them good benchmarks for the theoretical calculations taking into account the role of continuum couplings. The first experimental studies aiming at trac-ing the decay of the M4 stretched resonance in 13C, located at 21.47 MeV, were undertaken at the Cyclotron Centre Bronowice at the Institute of Nu-clear Physics Polish Academy of Sciences in Krakow, Poland (IFJ PAN). They provided information on the proton and neutron decay channels of this resonance to 12B and 12C daughter nuclei, respectively. These ex-perimental results were then compared with the theoretical calculations based on the Gamow Shell Model approach, in terms of energy, width, and in particular, the decay pattern. Furthermore, the studies of the next cases, namely, 14N and 16O, where several M4 resonances appear at around 20 MeV, have been recently performed at CCB. The new experimental findings will serve as a testing ground for future calculations describing the heavier nuclei in this important region of the nuclear chart.

Nuclei in the vicinity of 78Ni are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope 78Cu was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the beta decay of 78Ni produced by in-flight fission and

Excited states in Cu-78 were observed for the first time following the ss decay of Ni-78 created by in-flight fission of U-238. Based on the coincidence relationships between the observed gamma-ray transitions, it was possible to construct a level scheme comprising eight excited states with tentative spin assignments for 5 of them. In addition to the gamma-decaying states, an isomeric state with a lifetime of 3.8(4) ms was found to decay by internal conversion.

Abstract We predict the existence of medium spin PDR and find experimental evidence in 80Ge using β-decay of 80Ga. This nucleus was produced in the photo-fission of 238U. A hybrid γ-ray spectrometer was developed using a plastic detector for β-tagging, HPGe detectors for low-energy γ rays detection and phoswich detectors of PARIS for high-energy γ rays. The low-high energy coincidence spectrum shows two peaks at 7181(53) and 7337(53) keV in the β-decay of the 80mGa isomeric state only, in coincidence with the 21+ → 0+ transition of 80Ge. Combined with decay information, electric dipole character (E1) were assigned to these γ rays which de-excite 7.84 MeV and 7.996 MeV states. Based on this fact and the comparison with theoretical calculations, we conclude that these enhanced E1 transitions are driven by neutron-skin oscillation of 80Ge. The oscillation is triggered by a conversion of a deeply-bound neutron from the Z=N=28 proton-neutron saturated core into a proton in the Fermi surface. These results provide an evidence for a PDR state with spin different from 1− and built on a low-energy excited state. Consequently, it extends the PDR’s boundary along spin dimension for the first time and provides experimental data for testing the validity of the Brink-Axel hypothesis in the PDR region.

The β-delayed neutron emission in the 85,86As β-decays has been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyväskylä (JYFL-ACCLAB). The complete β-decays have been studied with a complex setup that consists of a plastic scintillator, the MOdular Neutron time-of-flight SpectromeTER (MONSTER), and two types of γ-ray detectors—an HPGe clover and four LaBr3 crystals. The β-delayed neutron energy distributions have been determined by unfolding the TOF spectra with an innovative methodology based on the iterative Bayesian unfolding method and accurate Monte Carlo simulations.

Excited states in the N = 50 nucleus Ge-82 have been investigated via beta decay of Ga-82 at the ALTO facility. More than 50 new gamma transitions were identified. The preliminary results are presented in this work.

Medium spin states of light N = 50 isotones have been populated using fast neutron-induced fission of ^232 Th. Online prompt γ spectroscopy has been performed using the hybrid γ spectrometer ν- Ball coupled to the LICORNE directional neutron source at the ALTO facility of IJCLab. Medium spin states of the neutron-rich nucleus ^82 Ge have been investigated using γ - γ and γ - γ - γ coincidence data to exploit the resolving power of ν- Ball. Two new transitions were assigned to this nucleus and a new level was placed in the level scheme. We tentatively assigned to this new state a ( 7^+ ) spin-parity, which is interpreted as a new N=50 core breaking state. This provides further insight into the energy evolution of the N=50 shell gap toward ^78 Ni.

The population of isomeric states in the prompt decay of fission fragments-so-called isomeric yield ratios (IYRs)-is known to be sensitive to the angular momentum J that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete gamma rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of 134Te, strongly populated in actinide fission, from the three different fissioning systems: 232Th(n, f), 238U(n, f), at two different neutron energies, as well as 252Cf(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum J of the binary partner, and the number of neutrons emitted on the IYR of 134Te are determined. The decay code TALYS is used in combination with the fission simulation code FREYA to calculate the primary fragment angular momentum from the IYR. We find that the IYR of 134Te has a slope of 0.004 +/- 0.002 with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with 134Te, it is revealed that the IYR of 134Te is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the FREYA+TALYS simulations reveal that the average angular momentum in 134Te following 238U(n, f) is 6.0 h over bar . This is not consistent with the value deduced from recent CGMF calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the gamma -ray heating problem of reactors.

The β-delayed neutron emission in the 85 As β-decay has been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyväskylä (JYFL). The complete β-decay has been studied with a setup which consists of a plastic scintillator, the MO dular N eutron time-of-flight S pectrome TER (MONSTER), and two types of γ-rays detectors (HPGe and LaBr 3 ). The, β-delayed neutron energy distribution has been determined by unfolding the TOF spectrum with the iterative Bayesian unfolding method.

The decay of the 21.47-MeV stretched resonance in 13C, arising from p3/2→d5/2 nucleon excitation coupled to maximum spin, was investigated in a (p,p′) experiment at 135 MeV proton bombarding energy, performed at the Cyclotron Centre Bronowice (CCB) at IFJ PAN in Krakow. First experimental information on the proton and neutron decay branches from this state was obtained by using coincidence measurement of protons inelastically scattered on a 13C target and γ rays from daughter nuclei, namely, 12B (proton decay) and 12C (neutron decay). The main branches lead to the Jπ=2+, first-excited state at 0.953 MeV in 12B, and to the Jπ=1+, T=1 level at 15.110 MeV in 12C. The results were compared with predictions from the Gamow Shell Model (GSM), which was used to describe the stretched resonance in terms of its energy, width, electromagnetic transition strengths and decay pattern. A very good agreement was obtained between the measured and calculated properties of the 21.47-MeV stretched resonance in 13C, demonstrating the high-quality and precision of the GSM wave function calculations, which include coupling to the resonant and non-resonant particle continuum.

The structure of the unbound F-15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O-14 beam impinging on a CH2 target. The analysis of H-1(O-14, p) O-14 and H-1(O-14, 2p) N-13 reactions allowed the confirmation of the previously observed narrow 1/2(-) resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2(-) and 3/2(-) resonances. The newly observed levels decay by 1p emission to the ground of O-14, and by sequential 2p emission to the ground state of N-13 via the 1(-) resonance of O-14. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2(-) and 3/2(-) resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function H-1(O-14, p) O-14 and resonance spectrum in F-15 are well reproduced in the unified framework of the GSM.

In an experiment performed at the SPIRAL1 facility of GANIL, the $$\beta $$ decay of $$^{32}$$ Ar has been studied by means of the “Silicon Cube” device associated with germanium clover detectors from the EXOGAM array. Beta-delayed protons and $$\gamma $$ rays have been observed and allowed the determination of all relevant decay branches. The Gamow–Teller strength distribution is compared to shell-model calculations and excellent agreement is found. The Fermi strength is inline with expectations. A quasi-complete decay scheme of $$^{32}$$ Ar is established.

We report on spectroscopic information and lifetime measurements of even-even neutron-rich Te isotopes. Excited states were populated in fast-neutron induced fission of U-238 at the ALTO facility of IJCLab with the LICORNE neutron source and detected using the hybrid.-ball spectrometer. We provide first results on lifetimes of the 6(1)(+) state in Te-136 and the (6(1)(+)), (4(1)(+)), and (2(1)(+)) states in Te-138 and discuss the results in the context of large-scale shell-model calculations. The level schemes of Te-136 and Te-138 are revised in terms of lifetimes of their 2(1)(+), 4(1)(+) states and updated information on the (4(2)(+)) state in Te-136 is presented. In addition, previously reported data on spectroscopy and lifetimes in Te-134 are reexamined. This work provides new insights into the evolution of collectivity for Te isotopes with N = 82, 84, 86.

A novel Monte Carlo technique has been developed to determine lifetimes of excited states in the tens-to-hundreds femtoseconds range in products of low-energy heavy-ion binary reactions, with complex velocity distributions. The method is based on a detailed study of Doppler-broadened $$\gamma $$ -ray lineshapes. Its relevance is demonstrated in connection with the $$^{18}\text {O}(7.0\, \text {MeV/u})+\,^{181}\text {Ta}$$ experiment, performed at GANIL with the AGATA+VAMOS+PARIS setup, to study neutron-rich O, C, N, ... nuclei. Excited states in $$^{17}\text {O}$$ and $$^{19}\text {O}$$ , with known lifetimes, are used to validate the method over the $$\sim 20{-}400\,\text {fs}$$ lifetime-sensitivity range. Emphasis is given to the unprecedented position resolution provided by $$\gamma $$ -tracking arrays, which turns out to be essential for reaching the required accuracy in Doppler-shift correction. The technique is anticipated to be an important tool for lifetime investigations in exotic neutron-rich nuclei, produced with intense ISOL-type beams.