The (n, γ ) campaigns at EXILL

Journal of Instrumentation

A : In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 10 8 n s −1 cm −2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr 3 :(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 10 5 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr 3 :(Ce) detectors to analyze half-lives of excited levels in the pico-to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133 Ba, 60 Co and 152 Eu as well as data from the reactions 27 Al(n,γ) 28 Al and 35 Cl(n, γ) 36 Cl in the energy range from 30 keV up to 10 MeV.

EPJ Web of Conferences, 2019

The decay lifetime of free neutrons (∼880 s) is an important parameter of the weak interaction and for Big Bang Nucleosynthesis. However, results of measurements currently show discrepancies depending on the method used. As most experiments nowadays employ ultra cold neutrons, we have developed a new cold-beam experiment which we perform at the Japan Proton Accelerator Research Complex. As a special feature, a polarized neutron beam is bunched by a spin flip chopper. A time projection chamber operated with He and CO2gas, including a well-controlled amount of3He, is used for detection of the beta-decays and simultaneous determination of the beam intensity. Using the data between 2014 and 2016, we evaluated our first, preliminary result of the neutron lifetime as 896 ± 10(stat.)−10+14(sys.) s. We plan several upgrades to achieve our precision goal of 1 s.

Nuclear Data Sheets, 2014

The abundances of the chemical elements heavier than iron can be attributed in about equal parts to the r and s processes, which are taking place in supernova explosions and during the He and C burning phases of stellar evolution, respectively. So far, quantitative studies of the r-process are out of reach, because it involves reactions on extremely short-lived neutron-rich nuclei. On the contrary, the situation for the s-process is far advanced, thanks to a comprehensive database of experimental (n, γ) cross sections for most isotopes along the reaction path from 12 C to the Pb/Bi region. For the stable isotopes last gaps in the data are presently closed, but further studies are clearly needed to reach the required accuracy and to resolve remaining discrepancies. The quest for cross sections of unstable isotopes remains a persisting challenge though. In particular, nuclei which act as branching points are of prime interest, because they provide key information on the deep stellar interior. While the activation method is limited to a few exceptional branch-point nuclei, successful measurements via the time-of-flight technique are depending on intense pulsed neutron sources and elaborate methods for sample production. Current developments in Europe are providing promising perspectives in both areas.

AIP Conference Proceedings, 2013

One of the main challenges for the better understanding of nucleosynthesis in the rapid neutron capture process (r-process) concerns the enormous amount of very exotic neutron-rich nuclei involved in this kind of cataclysmic scenario, and the scarce information available about their nuclear properties. In particular, theoretical calculations in the mass region around N=126 are difficult to validate on the basis only of the experimental information available close to stability so far. Such information becomes relevant for a reliable interpretation of the third peak in the r-process abundance distribution. Present and next generation radioactive-beam facilities (RIB) will be instrumental towards the systematic measurement of such nuclei, for improving theoretical nuclear models, and for enhancing the accuracy of the nuclear physics input in r-process model calculations. Here we present an experiment carried out recently at Fragment Separator (FRS) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt (Germany), which allowed us to measure for the first time relevant nuclear properties of several neutron-rich isotopes in the region around 211 Hg and 215 Tl. Preliminary results about the identified species and their implantation statistics are reported in this contribution. The experimental setup was comprised of an array of silicon implantation detectors (SIMBA) and the BEta deLayEd Neutron detector (BELEN). The main advantage compared to previous experiments was due to an innovative self-triggered acquisition system, which allowed us to enhance the neutron detection probability when compared to conventional analogue acquisition systems. This setup has been developed in the framework of the NuSTAR (Nuclear Structure, Astrophysics and Reactions) in the DESPEC (DEcay SPECtroscopy) collaboration which will perform experiments at the future Super Fragment Separator (SuperFRS) at FAIR (Facility for Antiproton and Ion Research).

Physical Review Letters, 1987

EPJ Web of Conferences, 2016

The study of the resonant structures in neutron-nucleus cross-sections, and therefore of the compound-nucleus reaction mechanism, requires spectroscopic measurements to determine with high accuracy the energy of the neutron interacting with the material under study. To this purpose, the neutron time-of-flight facility n_TOF has been operating since 2001 at CERN. Its characteristics, such as the high intensity instantaneous neutron flux, the wide energy range from thermal to few GeV, and the very good energy resolution, are perfectly suited to perform high-quality measurements of neutron-induced reaction cross sections. The precise and accurate knowledge of these cross sections plays a fundamental role in nuclear technologies, nuclear astrophysics and nuclear physics.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015

The neutron sensitivity of a cylindrical ⊘1.5 in. Â 1.5 in. LaBr 3 :Ce scintillation detector was measured using quasi-monoenergetic neutron beams in the energy range from 40 keV to 2.5 MeV. In this energy range the detector is sensitive to γ-rays generated in neutron inelastic and capture processes. The experimental energy response was compared with Monte Carlo simulations performed with the Geant4 simulation toolkit using the so-called High Precision Neutron Models. These models rely on relevant information stored in evaluated nuclear data libraries. The performance of the Geant4 Neutron Data Library as well as several standard nuclear data libraries was investigated. In the latter case this was made possible by the use of a conversion tool that allowed the direct use of the data from other libraries in Geant4. Overall it was found that there was good agreement with experiment for some of the neutron data bases like ENDF/B-VII.0 or JENDL-3.3 but not with the others such as ENDF/B-VI.8 or JEFF-3.1.

Physical Review C, 2013

A new measurement of the neutron β-decay asymmetry A0 has been carried out by the UCNA collaboration using polarized ultracold neutrons (UCN) from the solid deuterium UCN source at the Los Alamos Neutron Science Center (LANSCE). Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to A0 = −0.11954(55)stat.(98)syst., corresponding to the ratio of axial-vector to vector coupling λ ≡ gA/gV = −1.2756(30).

EPJ Web of Conferences, 2013

A cold neutron induced fission experiment recently took place at the Institute Laue-Langevin (ILL) in Grenoble. The neutron beam was provided by the nuclear reactor facility at ILL and the detector setup that was used for the -spectroscopy of the fission products consisted mainly of the detectors of the EXOGAM array [1], thereby the name of the campaign is EXILL. The main purpose of our measurement was to investigate the nuclei in the region with N = 50 close to 78 Ni as well as the nuclei close to the N = 82 shell closure. In this paper, the motivation of the experiment is described as well as the experimental setup and the status of the ongoing data analysis. a