Design of the BELEN detector for wide energy range with flat and high detection efficiency

Abstract

The main objective of this work is to design the BEta-deLayEd Neutron detector (BELEN) detector for FAIR (Facility for Antiproton Ion Research). The purpose of this detector is the measurement of neutron emission probabilities after ß-decay. The detector consist on a set of 3He tubes embedded in a polyethylene matrix. The design of the detector has been developed using Monte Carlo simulations with MCNPX and GEANT4 codes. The aim of these simulations was to choose a positon of tubes to achieve the maximum neutron detection efficiency while keeping a flat efficiency along the expected energy range for the neutrons. Prior to FAIR detector design, we have developed BELEN-20B prototype with 20 tubes and a mean efficiency for the energy range up to 2 MeV of 43% and BELEN-30 prototype with 30 tubes and a mean efficiency for the energy range up to 2 MeV of 38%. For the characterization of the BELEN-30 it was used a 252Cf neutron source at GSI laboratory, where the BELEN detector join in an experiment using the FRS (Fragment Separator) facility. The data obtained was in concordance with the result of the simulation. Also it has been designed the DESPEC candidates, with 48 tubes, BELEN-48 (AIDA), BELEN-48M1 and BELEN-48M2 with mean efficiency for the energy range up to 5 MeV of 38%, 41%, 55% respectively. The BELEN-48M1 efficiency was measured at PTB with a 252Cf neutron source and with some nuclear reactions that took place on targets located at the center of the BELEN symmetry axis. The results obtained with the 252Cf neutron source was according to the simulations. For some nuclear reactions there were some discrepancies with the expected values. Finally, we proposed a configuration for the future experimental campaigns to measure ß-delayed multiple neutron emission properties at the RIKEN Nishina Center. This detector called BRIKEN (Beta-delayed neutron measurements at RIKEN) will consist of 174 3He tubes (from UPC+GSI+ORNL+RIKEN). The design of all these detectors, has served to define a methodology, described in this work, to facilitate the process and assist in obtaining the optimal design. El principal objectiu d'aquest treball és el disseny del BEta-deLayEd Neutron detector (BELEN) detector per FAIR (Facility for Antiproton Ion Research). El propòsit del detector és la mesura de les probabilitats d'emisió després de un beta-decay. El detector consiteix en un conjunt de 3He tubs envoltats per una matriu de polietilè. El diseny del detector ha estat desenvolupat mitjançant simulacions de Monte Carlo amb els programes MCNPX y GEANT4. Els objectius d'aquestes simulacions eren poden escollir les posicions dels tubs per obtenir una eficiencia máxima en la detecció de neutrons mantenint una eficiencia constant al llarg del rang d'energia esperat pels neutrons. Abans del disseny del detector per FAIR, hem desenvolupat el prototipus BELEN-20B amb 20 tubs i una eficiència mitjana pel rang d'energia fins a 2 MeV del 43% i el prototipus BELEN-30 amb 30 tubs i una eficiència mitjana pel rang d'energia fins a 2MeV del 38%. Per la caracterització del BELEN-30 s'ha fet servir una font de neutrons de 252Cf en el laboratori del GSI, on el detector BELEN va participar en un experiment fent servir la instal.lació FRS(Fragment Separator).