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Abstract: 82-1

82-1

Validation of a photon transport simulation on the Monte Carlo Phits code through the efficiency parameter of a Sodium Iodide Scintillation Detector

Authors:
Celso Gonçalves de Paulo (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear) ; Elydio Jose Dias Soares (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear) ; Ester Maria Rodrigues de Andrade (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear) ; Guilherme Cavalcante de Albuquerque Souza (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear) ; Hyris Sales (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear) ; Bruno Mendes de Melo (CDTN - Centro de Desenvolvimento da Tecnologia Nuclear)

Abstract:

This study aims to validate the simulation of the transport of a monoenergetic photon beam using a suitable experimental setup. The simulation was performed using the multipurpose Monte Carlo Particle and Heavy Ion Transport Code System, PHITS, which has been shown in previous studies to satisfactorily simulate the transport analysis of many types of particles over a wide range of energies [1]. The photon source used was a metal disk containing caesium-137, which emits photons with an energy of 661.7 keV and a specific emission probability [2]. The experimental setup included a lead shield with an 8 mm aperture to collimate the gamma rays and a 3 "x3" NaI(Tl) scintillation detector whose material specifications used in the simulation are described in the literature [3]. Among radiation detectors, NaI(Tl) scintillators are characterized by the fact that they can be operated at room temperature, are cost-effective, and have a high counting efficiency due to the high atomic number of iodine and the density of the crystal [4]. Detector efficiency is defined as the fraction of radiation emitted by a source that the detector can detect. This efficiency depends on various factors, including the absorption cross-section, the shape and volume of the detector material, the distance and relative position between the detector and the source, etc. Due to these factors, estimating the detection efficiency can be a complex task. In this context, simulation of particle transport is an ideal tool for estimating detection efficiency. The validation was performed by determining the detection efficiency parameter, which is one of the most important for a detector. Similar studies have already been carried out, such as [5], where the MCNP code was used to estimate the efficiency using different emission sources and different positions. In the PHITS code, a number of particles of the order of 10^7 was simulated, resulting in an output file with relative errors below 5%. The simulation results were compared with experimental results and showed agreement within an error range of 10% to 20%. Sources of error include the activity value of the source and the geometry of the source itself, which proved to be an unexpected uncertainty factor on the obtained results. The geometry of the source has been shown to be a particularly important parameter and some computational investigations were made showing how to show how the error due to its uncertainty can be mitigated.

Keywords:
 Phits, Monte Carlo, Validation, Detector efficiency