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Description
A Photon Array for the Studies with Radioactive Ion and Stable beams (PARIS) is being developed for studying the high energy γ-rays from the decay of highly collective sates in atomic nuclei [1,2]. The array consists of ~ 200 phoswich element, each of which is made up of 2'' x 2'' x 2'' LaBr3(Ce) crystal coupled with 2'' x 2'' x 6'' NaI(Tl) crystal followed by single PMT readout [3]. The study of neutron response of this detector is very important for the rejection of neutron contamination in the high γ-ray measurement as well as to optimize the distance between detector and centre of the target chamber. We have studied the neutron response of the PARISphoswich detector and compared with the GEANT4 simulation [4]. The measurement has been carried out at TIFR, Mumbai by time-of-flight (TOF) technique using three different neutron sources 252Cf , 241Am-9Be and 239Pu-13C. The relative neutron detection efficiency of LaBr3 and NaI components of the phoswich detector has been measured in the energy range of En = 1 – 9 MeV and compared with the GEANT4 simulations. It was found that for En > 3 MeV, ~ 95% of neutrons have the primary interaction in the LaBr3 crystal, indicating that a clear n-γ separation can be achieved even at ~ 15 cm flight path (TOF ~ 6 ns). At low energies En < 3 MeV, the corresponding TOF is sufficiently large (TOF > 6 ns for L ~ 15 cm) to enable the n-γ discrimination even in case of primary interaction in NaI. Hence, an overall neutron rejection probability of ~ 95 % can be achieved with flight paths of ~ 15 cm in the phoswich detector.
References [1] paris.ifj.edu.pl [2] A Maj et al., The PARIS project, Acta Phys Pol B 40, 565 (2009). [3] C. Ghosh et al., JINST, 11, P05023 (2016). [4] S Agostinelli et al., NIMA 506 (2003) 250.
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