EXILL—a high-efficiency, high-resolution setup for γ-spectroscopy at an intense cold neutron beam facility

Abstract

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 108 n s−1cm−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 LaBr3:(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 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(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 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,γ)28Al and 35Cl(n,γ)36Cl in the energy range from 30 keV up to 10 MeV.

Low- Z boundary of the N=88 –90 shape phase transition: Ce148 near the critical point

“…Prompt γ-rays from the fission fragments were detected using a hybrid array of HPGe and Ce-doped LaBr 3 detectors, the EX-ILL&FATIMA spectrometer [17,18]. The EXILL array [19] was composed of 8 BGO-shielded EXOGAM Clover detectors [20], each one consisting of 4 HPGe crystals. The target-to-detector distance was 14.5 cm.…”

Development of a liquid scintillator based active fission target for FIPPS

“…It is optically connected to the PMT by a light guiding system, both are also shown. 6 Li-loaded cylinders (represented in yellow) mounted around the neutron beam all along the vacuum chamber are used to absorb scattered neutrons, thus minimizing the γ-ray background tinguish between weakly and strongly ionizing particles, i.e. electrons, alpha particles and fission fragments.…”

“…with the EUROGAM/EUROBALL [4] and GAMMASPHERE [3,5] arrays as well as with neutroninduced fission, e.g. in the EXILL campaign [6] and heavya e-mail: kandzia@ill.fr (corresponding author) b e-mail: michelagnolic@ill.fr (corresponding author) ion induced fission [7,8]. In this kind of investigations, the identification of a given fission fragment relies on multiple γ-ray coincidence techniques.…”

Investigating Core Excitations in the $^{131}$Sn One-valence-hole Nucleus

“…The experiment was performed at the PF1B facility of Institut Laue-Langevin, within the EXILL campaign [10], where the 131 Sn nucleus was populated by cold-neutron-induced fission of both 235 U and 241 Pu radioactive targets. The fission yields for the 131 Sn isotope were 0.88% and 1.10%, respectively.…”