Test Bench for Highly Segmented GRIT Double-Sided Silicon Strip Detectors: A Detector Quality Control Protocol

This work deals with the characteristics of highly segmented double-sided silicon detectors. These are fundamental parts in many new state-of-the-art particle detection systems, and therefore they must perform optimally. We propose a test bench that can handle 256 electronic channels with off-the-shelf equipment, as well as a detector quality control protocol to ensure that the detectors meet the requirements. Detectors with a large number of strips bring new technological challenges and issues that need to be carefully monitored and understood. One of the standard 500 μ m thick detectors of the GRIT array was investigated, undergoing studies that revealed its IV curve, charge collection efficiency, and energy resolution. From the data obtained, we calculated, among other things, the depletion voltage (110 V), the resistivity of the bulk material (9 kΩ·cm), and the electronic noise contribution (8 keV). We present, for the first time, a methodology called “the energy triangle’’ to visualize the effect of charge sharing between two adjacent strips and to study the hit distribution with the interstrip-to-strip hit ratio (ISR).This research was partially supported by the MICINN of Spain, Grant No. EQC2018-004395-P, and European Regional Development Fund (FEDER) 2014-2020 and “Consejería deTransformación Económica, Industria, Conocimiento y Universidades de Junta de Andalucía”, under Project No. IE17_5380_UHU

Recent studies of heavy ion transfer reactions using large solid angle spectrometers

We present selected results recently obtained in the study of heavy ion transfer reactions at energies close to the Coulomb barrier by employing the large solid angle magnetic spectrometer PRISMA. We discuss the production of neutron-rich heavy nuclei via multinucleon transfer processes and the related effects of secondary processes, in particular nucleon evaporation, studied in a high resolution kinematic coincidence experiment. We also present the recent results in the studies of neutron-neutron correlations for closed shell and superfluid systems

Evidence of proton-proton correlations in the 116Sn+60Ni transfer reactions

One and two proton transfer channels have been measured in 116Sn+60Ni with the magnetic spectrometer PRISMA by making an excitation function at several bombarding energies, from above to well below the Coulomb barrier. The total kinetic energy loss distributions show the predominance of quasi-elastic processes in the sub-barrier regime. The data have been compared with calculations performed with the GRAZING program, based on semiclassical formalism, and in the Distorted Wave Born Approximation (DWBA), which provided a good theoretical description of the extracted transfer probabilities for the one proton transfers. The much larger values of the experimental two proton transfers compared with those evaluated within an independent particle transfer mechanism, indicate the presence of strong proton-proton correlations. The results complement the ones of the previously analyzed one- and two-neutron transfers, providing significant new information on the subject compared to past works

Fusion Hindrance and Pauli Blocking in 58Ni + 64Ni

58Ni +64Ni is the first case where the influence of positive Q-value transfer channels on sub-barrier fusion was evidenced, in a very well known experiment by Beckerman et al., by comparing with the two systems 58Ni + 58Ni and 64Ni+64Ni. Subsequent measurements on 64Ni + 64Ni showed that fusion hindrance is clearly present in this case. On the other hand, no indication of hindrance can be observed for 58Ni + 64Ni down to the measured level of 0.1 mb. In the present experiment the excitation function has been extended by two orders of magnitude downward. The cross sections for 58Ni + 64Ni continue decreasing very smoothly below the barrier, down to '1 µb. The logarithmic slope of the excitation function increases slowly, showing a tendency to saturate at the lowest energies. No maximum of the astrophysical S -factor is observed. Coupled-channels (CC) calculations using a Woods-Saxon potential and includinginelastic excitations only, underestimate the sub-barrier cross sections by a large amount. Good agreement is found by adding two-neutron transfer couplings to a schematical level. This behaviour is quite different from what already observed for 64Ni+ 64Ni (no positive Q-value transfer channels available), where a clear low-energy maximum of the S -factorappears, and whose excitation function is overestimated by a standard Woods-Saxon CC calculation. No hindrance effect is observed in 58Ni+ 64Ni in the measured energy range. This trend at deep sub-barrier energies reinforces the recent suggestion that the availability of several states following transfer with Q>0, effectively counterbalances the Pauli repulsion that, in general, is predicted to reduce tunneling probability inside the Coulomb barrier

Design study of a HPGe detector array for β-decay investigation in laboratory ECR plasmas

In the frame of the PANDORA project, a new experimental approach aims at measuring in-plasma β-decay rate as a function of thermodynamical conditions of the environment, namely a laboratory magnetized plasma able to mimic some stellar-like conditions. The decay rates (expected to change dramatically as a function of the ionization state) will be measured as a function of the charge state distribution of the in-plasma ions. The new experimental approach aims at correlating the plasma environment and the decay rate. This can be performed by simultaneously identifying and discriminating—through an innovative multi-diagnostic system working synergically with a γ-ray detection system —the photons emitted by the plasma and γ-rays emitted after the isotope β-decay. In this study, the numerical simulations supporting the design of the γ-ray detector array, including a statistical significance study to check the feasibility of measuring the in-plasma decay rates, are presented. Geant4 simulations focused on the design of the array of γ-ray detectors and the evaluation of total efficiency depending on the detector type and the optimal displacement of detectors around the trap (including collimation systems and shielding). The simulation results showed that, due to technical limitations in the number of apertures that can be created in the magnetic trap, the best compromise is to use 14 HPGe (70% of relative efficiency) detectors surrounding the magnetic trap. The HPGe detectors were chosen for their excellent energy resolution (0.2% @ 1 MeV), since the harsh environment (the background is represented by the intense plasma self-emission) strongly affects the signal-to-background ratio. Once determined the total photopeak efficiency (0.1–0.2%), the sensitivity of the PANDORA experiment was checked in a "virtual experimental run," by exploring the measurability of isotope decay rates for the first three physical cases of PANDORA: 176Lu, 134Cs and 94Nb. The preliminary results demonstrated the feasibility of the measurement in terms of the signal-to-background ratio and significance that it is possible to reach. The results indicated that experimental run durations could take from several days to 3 months, depending on the isotope under investigation, thus shedding new light on the role of weak interactions in stellar nucleosynthesis

Multinucleon transfer reactions and proton transfer channels

Transfer reactions have always been of great importance for nuclear structure and reaction mechanism studies. So far, in multinucleon transfer studies, proton pickup channels have been completely identified in atomic and mass numbers at energies close to the Coulomb barrier only in few cases. We measured the multinucleon transfer reactions in the 40Ar+208Pb system near the Coulomb barrier, by employing the PRISMA magnetic spectrometer. By using the most neutron-rich stable 40Ar beam we could populate, besidesneutron pickup and proton stripping channels, also neutron stripping and proton pickup channels. Comparison ofcross sections between different systems with the 208Pb target and with projectiles going from neutron-poor to neutron-rich nuclei, as well as between the data and GRAZING calculations, was carried out.Finally, recent results concerning the measurement of the excitation function from the Coulomb barrier to far below for the 92Mo+54Fe system, where both proton stripping and pickup channels were populated with similar strength, will be discussed

Light and heavy fragments mass correlation in the 197Au+130Te transfer reaction

We studied multinucleon transfer (MNT) processes in the 197Au+130Te at Elab=1.07 GeV system coupling the PRISMA magnetic spectrometer to NOSE, an ancillary particle detector. We constructed a mass correlation matrix associating to each light fragment identified in PRISMA the corresponding mass distribution of the heavy partner detected in NOSE and, through the comparison with Monte Carlo simulations, we could infer about the role of neutron evaporation in multinucleon transfer reactions for the population of neutron-rich heavy nuclei

Intruder states in sd-shell nuclei : from 1p-1h to np-nh in Si isotopes

Des calculs de type modèle en couches ont été réalisés dans un espace de valence 1¯hω complet pour les noyaux de la couche sd. Ces calculs ont permis pour la première fois de prédire la durée de vie des états de parité positive et négative des noyaux riches en neutrons de la couche sd. Les durées de vie prédites (1 - 100 ps) sont mesurables par la méthode de décalage Doppler différentiel.Le démonstrateur du détecteur γ européen de nouvelle génération, AGATA, en coïncidence avec le spectromètre magnétique PRISMA du LNL (Italie) et le plunger de l’Université de Cologne ont été utilisés pour mesurer les durées de vie des états excités dans 32,33Si et 35,36S. Les structures plus complexes, à n¯hω ont également été étudiées dans le 28Si. Ce dernier est un noyau important pour comprendre la compétition entre les structures de type champ moyen et les structures en agrégats. La réaction résonante de capture radiative d’ions lourds-légers 12C+16O a été réalisée à des énergies sous-coulombiennes. La décroissance γ complète depuis les résonances peuplées par laréaction jusqu’au niveau fondamental de 28Si a été mesurée pour la première fois à ces énergies et montre une forte alimentation d’états intermédiaires autour de 10 MeV. Les comparaisons avec des études de captures radiatives au-dessus de la barrière de Coulomb ont été effectuées et les résultats ont été interprétés en termes de l’alimentation favorisée d’états à isospin T = 1 dans le noyau autoconjugué 28Si.New large-scale shell-model calculations with full 1¯hω valence space for the sd-nuclei has been used for the first time to predict lifetimes of positive and negative parity states in neutron rich Si isotopes. The predicted lifetimes (1 - 100 ps) fall in the range of the differential Doppler shift method. Using the demonstrator of the European next generation γ-ray array, AGATA, in coincidence with the large acceptance PRISMA magnetic spectrometer from LNL (Legnaro) and the differential plunger of the University of Cologne, lifetimes of excited states in 32,33Si and 35,36S nuclei were measured. In a second step, the n¯hω structure in the stable 28Si nucleus was also studied. 28Si is an important nucleus to understand the competition between mean-field and cluster structures. It displays a wealth of structures in terms of deformation and clustering. Light heavy-ion resonant radiative capture 12C+16O has been performed at energies below the Coulomb barrier. The measured γ-spectra indicate for the first time at these energies that the strongest part of the resonance decay proceeds though intermediate states around 10 MeV. Comparisons with previous radiative capture studies above the Coulomb barrier have been performed and the results have been interpreted in terms of a favoured feeding of T = 1 states in the 28Si self-conjugate nucleus

Intruder states in sd-shell nuclei : from 1p-1h to np-nh in Si isotopes

Des calculs de type modèle en couches ont été réalisés dans un espace de valence 1¯hω complet pour les noyaux de la couche sd. Ces calculs ont permis pour la première fois de prédire la durée de vie des états de parité positive et négative des noyaux riches en neutrons de la couche sd. Les durées de vie prédites (1 - 100 ps) sont mesurables par la méthode de décalage Doppler différentiel.Le démonstrateur du détecteur γ européen de nouvelle génération, AGATA, en coïncidence avec le spectromètre magnétique PRISMA du LNL (Italie) et le plunger de l’Université de Cologne ont été utilisés pour mesurer les durées de vie des états excités dans 32,33Si et 35,36S. Les structures plus complexes, à n¯hω ont également été étudiées dans le 28Si. Ce dernier est un noyau important pour comprendre la compétition entre les structures de type champ moyen et les structures en agrégats. La réaction résonante de capture radiative d’ions lourds-légers 12C+16O a été réalisée à des énergies sous-coulombiennes. La décroissance γ complète depuis les résonances peuplées par laréaction jusqu’au niveau fondamental de 28Si a été mesurée pour la première fois à ces énergies et montre une forte alimentation d’états intermédiaires autour de 10 MeV. Les comparaisons avec des études de captures radiatives au-dessus de la barrière de Coulomb ont été effectuées et les résultats ont été interprétés en termes de l’alimentation favorisée d’états à isospin T = 1 dans le noyau autoconjugué 28Si.New large-scale shell-model calculations with full 1¯hω valence space for the sd-nuclei has been used for the first time to predict lifetimes of positive and negative parity states in neutron rich Si isotopes. The predicted lifetimes (1 - 100 ps) fall in the range of the differential Doppler shift method. Using the demonstrator of the European next generation γ-ray array, AGATA, in coincidence with the large acceptance PRISMA magnetic spectrometer from LNL (Legnaro) and the differential plunger of the University of Cologne, lifetimes of excited states in 32,33Si and 35,36S nuclei were measured. In a second step, the n¯hω structure in the stable 28Si nucleus was also studied. 28Si is an important nucleus to understand the competition between mean-field and cluster structures. It displays a wealth of structures in terms of deformation and clustering. Light heavy-ion resonant radiative capture 12C+16O has been performed at energies below the Coulomb barrier. The measured γ-spectra indicate for the first time at these energies that the strongest part of the resonance decay proceeds though intermediate states around 10 MeV. Comparisons with previous radiative capture studies above the Coulomb barrier have been performed and the results have been interpreted in terms of a favoured feeding of T = 1 states in the 28Si self-conjugate nucleus