Agnieszka Korgul

NUCLEAR REACTIONS 3 He (32 S, α) 31 S, E= 128 MeV; measured reaction products, Eγ, Iγ; deduced γ-ray energies, levels, T 1/2, resonances. Comparison with the shell-model code NuShellX calculations. Modern Markov chain Monte Carlo-based Bayesian statistical techniques. The Doppler Shift Lifetimes (DSL2) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility.

The long-lived xenon isomers 129 m Xe and 131 m Xe are of interest for the GAMMA-MRI project, which aims at developing a novel imaging modality based on magnetic resonance of polarized unstable tracers. Here, we present the steps leading to and following the production of these two isomers via neutron irradiation of highly-enriched 128 Xe and 130 Xe gas samples at two high-flux reactors, the High-Flux Reactor (Réacteur à haut flux, RHF) at the Institut Laue-Langevin (ILL) and the MARIA reactor at the National Centre for Nuclear Research (NCBJ). We describe the experimental setups and procedures used to prepare the stable xenon samples, to open the irradiated samples, and to transfer xenon isomers into reusable transport vials. The activity of 129 m Xe and 131 m Xe was measured to be in the range of tens of MBq per sample of 0.8 (1) mg, and was proportional to thermal neutron flux density. A small …

The magnetic dipole moments (μ) of 209 Tl g (N= 128) and 207 Tl m (N= 126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾ 207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ (Tl g, I π= 1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with I π= 1/2+.

Models of the β-delayed neutron emission (β n) assume that neutrons are emitted statistically via an intermediate compound nucleus post β decay. Evidence to the contrary was found in an In 134 β-decay experiment carried out at ISOLDE CERN. Neutron emission probabilities from the unbound states in Sn 134 to known low-lying, single-particle states in Sn 133 were measured. The neutron energies were determined using the time-of-flight technique, and the subsequent decay of excited states in Sn 133 was studied using γ-ray detectors. Individual β n probabilities were determined by correlating the relative intensities and energies of neutrons and γ rays. The experimental data disagree with the predictions of representative statistical models which are based upon the compound nucleus postulate. Our results suggest that violation of the compound nucleus assumption may occur in β-delayed neutron emission …

The decays from both the ground state and a long-lived isomer of In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to , , and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant -decay channels for the first time, including a low-energy Gamow-Teller transition and several First-Forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their decays selectively populate only a few isolated neutron unbound states in Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark -decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the decay of neutron-rich nuclei southeast of Sn and will serve as a guide for future theoretical development aiming to describe accurately the key decays in the rapid-neutron capture (r-) process.

β-delayed γ-neutron spectroscopy has been performed on the decay of A= 84 to 87 gallium isotopes at the RI-beam Factory at the RIKEN Nishina Center using a high-efficiency array of He 3 neutron counters (BRIKEN). β− 2 n− γ events were measured in the decays of all of the four isotopes for the first time, which is direct evidence for populating the excited states of two-neutron daughter nuclei. Detailed decay schemes with the γ branching ratios were obtained for these isotopes, and the neutron emission probabilities (P x n) were updated from the previous study. Hauser-Feshbach statistical model calculations were performed to understand the experimental branching ratios. We found that the P 1 n and P 2 n values are sensitive to the nuclear level densities of 1 n daughter nuclei and showed that the statistical model reproduced the P 2 n/P 1 n ratio better when experimental levels plus shell-model level densities …

The β decays from both the ground state and a long-lived isomer of 133In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to β, γ, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant β-decay channels for the first time, including a low-energy Gamow-Teller transition and several First-Forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their β decays selectively populate only a few isolated neutron unbound states in 133Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark β-decay theories at an unprecedented level in this region of the nuclear chart. The results were compared with the newly developed large-scale shell model (LSSM) calculations, revealing a critical role from both proton and neutron core excitations across 132Sn in understanding the observed GT strength. The experimental findings establish an archetype for the β decay of neutron-rich nuclei southeast of 132Sn and will serve as a clear guideline for future theoretical development aiming to describe accurately the key β decays in the rapid-neutron capture (r-) process.Introduction—The rapid-neutron capture (r-) process is responsible for the creation of half of the heavy elements in the universe [1, 2]. Many stable nuclei present today are decay products of the very short-lived nuclei produced in extreme environments such as neutron star mergers or extreme supernovae [3, 4]. Most of these progenitor nuclei have large neutron-to-proton ratios, and state-of-the-art nuclear research facilities cannot produce samples in …

Abstract The decay properties of In were studied in detail at the ISOLDE Decay Station (IDS). The implementation of the Resonance Ionization Laser Ion Source (RILIS) allowed separate measurements of its ground state ( In) and isomer ( In). With the use of -delayed neutron and spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition was located at 5.92 MeV in the In decay with a logft= 4.7 (1). In addition, several neutron-unbound states were populated at lower excitation energies by the First-Forbidden decays of In. We assigned spins and parities to those neutron-unbound states based on the -decay selection rules, the logft values, and systematics.

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 γ 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 Te 134, strongly populated in actinide fission, from the three different fissioning systems: Th 232 (n, f), U 238 (n, f), at two different neutron energies, as well as Cf 252 …

The proposed experiment aims to investigate the β decay of neutron-rich potassium isotopes (Z= 19), including 49K (N= 30) and 51K (N= 32), for which reinversion of the ground-state spin driven by the evolution of the proton πsd orbitals was observed in laser spectroscopy. We will apply a novel technique that utilises anisotropic β decay of oriented nuclei to firmly assign spins and parities of states populated in daughter nuclei through allowed transitions. Our experiment, which combines the strengths of β-decay spectroscopy and collinear laser spectroscopy, will be performed at the VITO beamline. A new β-decay spectroscopy station that accommodates β-particle, γ-ray, and neutron detection following the decay of laser-polarised nuclei will be commissioned.

The β decays from both the ground state and a long-lived isomer of In 133 were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to β, γ, and neutron spectroscopy, the comparative partial half-lives (log f t) have been measured for all their dominant β-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their β decays selectively populate only a few isolated neutron unbound states in Sn 133. Precise energy and branching-ratio measurements of those resonances allow us to benchmark β-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the β decay of neutron-rich nuclei …

About half of the stable isotopes heavier than iron are the result of the rapid neutron capture process (r-process). The main signature of the solar r-process abundance distribution are two large abundance peaks, located at A≈ 130 and A≈ 195, which originate from the increased stability at the neutron shell closures N= 82 and N= 126. A smaller abundance peak exists in between these two peaks at A≈ 160, which is known as the “rareearth peak”(REP) formed during the freeze-out stage of the r-process [1]. Recently, an experiment was carried out in order to measure half-lives (T1/2) and β-delayed neutron emission probabilities (Pn) of isotopes most likely playing a role in the formation of REP [2].

Background: Asymmetric fission is known to occur in two regions, the actinides and sublead, and is dependent on the fissioning system excitation energy. Experimental evidence in the sublead 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 Fr 215 at moderate excitation energy and determine previously unknown independent fission yields and other properties.Method: The compound nucleus was formed in the reaction O 18+ Au 197. The prompt γ rays emitted during the reaction were measured with the high efficiency and high granularity ν-ball-2 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 …

The decay properties of In 133 were studied in detail at the ISOLDE Decay Station. The implementation of the Resonance Ionization Laser Ion Source allowed separate measurements of its 9/2+ ground state (In 133 g) and 1/2− isomer (In 133 m). With the use of β-delayed neutron and γ spectroscopy, the decay strengths above the neutron separation energy were quantified in this neutron-rich nucleus for the first time. The allowed Gamow-Teller transition 9/2+→ 7/2+ was located at 5.93 MeV in the In 133 g decay with a log f t= 4.7 (1). In addition, several neutron-unbound states were populated at lower excitation energies by the first-forbidden decays of In 133 g, m. We assigned spins and parities to those neutron-unbound states based on the β-decay selection rules, the log f t values, and systematics.

Half-lifes (T1/2) of exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured at the RIKEN Nishina Center. The experimental setup consisted of the BigRIPS in-flight separator for ion selection identification, the Advance Implantation Detector Array (AIDA) for ions and β detection, and the BRIKEN detector for neutron counting. Using this setup, 4 new T1/2 have been measured for the first time, and 38 T1/2 have been remeasured with improved precision in several cases. These new experimental data should help to constrain theoretical models for calculations of T1/2. The status of the experimental analysis and preliminary results are provided in this contribution.

The aim of this Letter of Intent is to propose the use of the Lucrecia total absorption spectrometer for the direct determination of ground state to ground state superallowed β transitions. These superallowed branching ratios are employed for testing the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, and they can be used to constrain models for isospin symmetry breaking corrections. Such branching ratios are usually indirectly obtained from γ-ray spectroscopy measurements, potentially impaired by Pandemonium effect for the nuclei we are considering. Cases for future proposals will be discussed and we will focus on the measurement of the yields, isobaric contaminants and release times of the two most challenging ones: 70gsBr and 74Rb.

Medium spin states of light N = 50 isotones have been populated using fast neutron-induced fission of Th. Online prompt  spectroscopy has been performed using the hybrid  spectrometer Ball coupled to the LICORNE directional neutron source at the ALTO facility of IJCLab. Medium spin states of the neutron-rich nucleus Ge have been investigated using - and -- coincidence data to exploit the resolving power of 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 () spin-parity, which is interpreted as a new core breaking state. This provides further insight into the energy evolution of the shell gap toward Ni.

Direct lifetime measurements via γ− γ coincidences using a fast timing detector array consisting of LaBr 3 (Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N= 50) nucleus Ru 94. The experiment was carried out as the first in a series of “FAIR-0” experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru 94 were populated primarily via the β-delayed proton emission of Pd 95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe 124 beam impinging on a 4 g/cm 2 Be 9 target. While the deduced E 2 strength for the 2+→ 0+ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4+→ 2+ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell …

The β-delayed one-and two-neutron emission probabilities (P 1 n and P 2 n) of 20 neutron-rich nuclei with N≥ 82 have been measured at the RIBF facility of the RIKEN Nishina Center. P 1 n of Ag 130, 131, Cd 133, 134, In 135, 136, and Sn 138, 139 were determined for the first time, and stringent upper limits were placed on P 2 n for nearly all cases. β-delayed two-neutron emission (β 2 n) was unambiguously identified in Cd 133 and In 135, 136, and their P 2 n were measured. Weak β 2 n was also detected from Sn 137, 138. Our results highlight the effect of the N= 82 and Z= 50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star …

We investigate the effect of ellipticity ratio of the polarized radiation field on optoelectronic properties of a two-dimensional (2D) semi-Dirac (SD) system. The optical conductivity is calculated within the energy balance equation approach derived from the semiclassical Boltzmann equation. We find that there exists the anisotropic optical absorption induced via both the intra-and interband electronic transition channels in the perpendicular x x and y y directions. Furthermore, we examine the effects of the ellipticity ratio, the temperature, the carrier density, and the band-gap parameter on the optical conductivity of the 2D SD system placed in transverse and vertical directions, respectively. It is shown that the ellipticity ratio, temperature, carrier density, and band-gap parameter can play the important roles in tuning the strength, peak position, and shape of the optical conductivity spectrum. The results obtained from this …