Simulations of light collection in long tapered CsI(Tl) scintillators using real crystal surface data and comparisons to measurement

A Knyazev,T Kröll,B Heiss,O Tengblad,A Heinz,E Galiana,P Teubig,J Cederkäll,A.-L Hartig,J Park,G Rondeau,L Ponnath,D Galaviz,P Cabanelas,P Golubev,R Gernhäuser,P Klenze,E Casarejos,J Benlliure,L Causeret,H B Rhee ,J L Rodríguez-Sánchez ,P Fernåndez ,H Álvarez‐Pol ,David González ,D Cortina‐Gil ,Miguel Ángel Álvarez Feijoo ,H Johansson ,Zhongzhou Ren ,Ivan G Scheblykin ,Á Perea ,Rainer Timm

doi:10.1016/j.nima.2021.165302

Abstract

Simulation results for light transport in long tapered CsI(Tl) crystals using look-up tables (LUTs) are presented. The LUTs were derived from the topography of a polished and a lapped surface of a CsI(Tl) crystal measured with atomic force microscopy. Simulations with different combinations of polished and lapped surfaces were performed, to extract the non-uniformity of light collection depending on the interaction point, and compared to experimental results. The simulations reproduce the general trend given by the measurements, and show that more homogeneous light collection is attained when all lateral sides of the crystal are lapped. For the lapped crystal the simulation model is most sensitive to the reflectivity of the enhanced specular reflector (ESR) foil surrounding the crystal, which is one of several properties influencing the light transport examined in this study. The sensitivity of the light-output non-uniformity to variations in the absorption length observed in a batch of CsI(Tl) crystals in a previous study is also discussed. Residual differences between the simulation and the measurements can potentially be attributed to the scattering of scintillation photons inside the materials used. Additional measurements to further advance the construction of the simulation model are suggested.

Highlights

A thorough understanding of light transport and collection in scintillation detectors for nuclear physics is of importance for the understanding of light-output uniformity, and for the energy resolution that can be achieved with such detectors
This applies as well to the irradiation point closest to the sensor, i.e. it moves to approximately the same centroid position as the other photo peaks, but having already an outlier position when it comes to resolution it cannot be brought closer to the main cluster formed by the other nine irradiation points on the resolution axis of Fig. 5
The introduction of the Davis model [1] in light collection simulations, using look-up tables to describe optical surfaces based on real surface data, allows to circumvent the arbitrariness that alternative parameter-based models might introduce

Summary

Introduction

The purpose of this study is to investigate light transport in largevolume inorganic scintillators of CsI(Tl), used for nuclear calorimetry and spectroscopy, by exploiting a new promising simulation approach based on real crystal surface data that has become available recently [1,2]. A thorough understanding of light transport and collection in scintillation detectors for nuclear physics is of importance for the understanding of light-output uniformity, and for the energy resolution that can be achieved with such detectors. With the advent of improved crystal surface mapping techniques and increased computing power it is of interest to take advantage of these two developments for a comparison between simulated and measured data with a focus on improving light-output uniformity

Objectives

Methods

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Discussion

Conclusion