Speaker
Description
Scintillation detectors based on CsI(Tl) crystals are widely used in nuclear physics, especially in the field of gamma-ray spectrometry and/or fast light charged particles. Large CsI(Tl) crystals like ours with a volume of ~370 cm3, are used in many collaborations [1-3].
GADAST (GAmma-ray Detector Around the Secondary Target) is a compact detector array, that is a part of the EXPERT setup [3]. It is intended to be used in experiments with radioactive beams and positioned in the middle focal plane of the Super-conducting FRagment Separator (Super-FRS) facility [4], within FAIR. The array consists of 128 CsI(Tl) and 32 LaBr3 scintillators coupled with photomultipliers. The principal task of the GADAST detector in the context of the EXPERT physics program is to disentangle measurements of (few-)proton radioactivity by tagging the gamma-ray de-excitation of the heavy fragment in the excited state(s). In addition, due to its thickness, it is suitable to be used as the detector of charged particles.
The proton radioactivity processes are of significant interest due to the limited understanding of their formation mechanisms. Furthermore, many isotopes exhibiting this phenomenon are either insufficiently studied or not discovered at all. For example, the properties and potential proton radioactivity of exotic isotopes such as 17N, 30Ar, etc. can be studied in radioactive beam experiments, which employ GADAST.
In this work, the gamma-ray source measurements of 32 CsI(Tl)-based modules, which are an in-kind contribution from the Czech Republic to FAIR, are presented. Main properties of CsI(Tl)-based detectors were investigated, specifically, energy resolution, non-uniformity of the light output and efficiency.
The ExpertRoot package [3], based on the FairRoot framework, was used to produce a robust simulation of the experiment. Various algorithms were developed to account for pile-ups, light output non-uniformity and activities of the gamma-ray sources. Signal overlaps were observed in the experiment due to the high intensity of the gamma-ray sources. The need to consider the non-uniformity of the light output stems from the large size of the CsI(Tl) crystals.
The simulation and experiment are found to be in good agreement; the pile-ups were fully reproduced.
In the future, we will use the pulse pile-up algorithm, when GADAST modules are located near the target, bombarded by a high-intensity heavy ion beam.
