Verification of simulation techniques in the study of nuclear processes

Abstract

Monte Karlo simulacije predstavljaju jedan od fundamentalnih alata u današnjem svetu nuklearne fizike koji se primenjuje već dugi niz godina, kako u validaciji postojećih tako i u potkrepljenju ideja novih eksperimenata. Prema tome, od velikog je značaja detaljno razumevanje algoritma transporta čestica i njenih interakcija kao srca Monte Karlo simulacija u cilju njihovih pouzdanih implementacija. Akcenat ove disertacije je bio na demonstraciji značaja Monte Karlo simulacija u okviru različitih nuklearnih primena. S’tim, disertacija je podeljena na dva dela, teorijski i eksperimentalno-simulacioni deo. I Deo - Teorijski uvod: Iznete su osnove Monte Karlo metode neophodne u razumevanju njene implementacije kod transporta čestica. U ovu svrhu takođe su opisane interakcije fotona i elektrona (pozitrona) sa sredinom na kojima se temeljene algoritmi transporta koje svi Monte Karlo kodovi implementiraju. Kao jedna od glavnih tačaka eksperimentalnog rada iznete su osnove tehnike 훾-spektrometrije i rada poluprovodničkih detektora u cilju boljeg razumevanja validacije simulacionih modela. II Deo - Eksperiment & Simulacija: Opisan je Geant4 simulacioni paket korišćen u svim prezentovanim simulacijama. Detaljno je ilustrovana procedura optimizacije HPGe sistema implementacijom Geant4 paketa radi izgradnje adekvatnih simulacionih modela koji se pouzdano mogu koristiti u naknadnim istraživanjima. U ovom smislu, opisana je primena Geant4 paketa u raznim nuklearnim istraživanjima poput kvantifikacije uzoraka nepravilnih geometrija i nepoznatih matrica. Takođe, ilustrovan je i princip generisanja visoko-realističnih 훾-spektara esencijalnih u današnjem svetu 훾-spektrometrije. Za kraj, opisana je potencijalna Monte Karlo primena u okviru nuklearne forenzike simulacijom (retrospektivnih) apsorbovanih doza u okviru različitih materijala. Zaključak & Motivacija: Demonstrirati versatilnost i primenljivost Monte Karlo simulacija u raznovrsnim istraživanjima nuklearnih procesa, ukazati na njene nedostatke i predložiti potencijalna unapređenja u ovom kontekstu.Monte Carlo simulations present one of the fundamental tools in today’s world of nuclear physics that have been applied for years, whether to verify existing or corroborate ideas of new experiments. Therefore, a detailed understanding of particle transport algorithms and their interactions, which are a beating heart of every simulation, is fundamental if one wants to achieve their reliable implementation. The accent of this dissertation was on demonstrating the importance of Monte Carlo simulations in various nuclear applications. As such, dissertation in split in two major parts, theoretical and experimental. Part I - Theoretical introduction: Describes the mathematical foundations of Monte Carlo method that are neccessary in understanding its use in particle transport. Photon and electron interactions are described on which transport algorithms are based which all Monte Carlo codes implement. As one of the key points of the experimental work, the fundamentals of 훾-spectrometry and semiconducting detectors are also presented in order to more clearly outline validation of the simulation models. Part II - Experiment & Simulation: Describes Geant4 simulation toolkit which was used in writing all presented simulations. Detailed optimization procedure of HPGe systems with the Geant4 code in order to build adequate simulation models which can afterwards be employed reliably in subsequent studies is presented. In that context, implementation of this toolkit in various nuclear applications is described, such as the quantification of different samples with irregular geometries or unknown matrices. Also, a procedure of generating high-realistic 훾-spectra essential in today’s 훾-spectrometry is outlined. At the end, the potentional use of Monte Carlo simulations in the field of nuclear forensics through (retrospective) dose estimations in different materials is presented. Conclusion & Motivation: Demonstrate versatility and applicability ofMonte Carlo simulations in study of various nuclear processes, point out their short-comings in these applications and propose possible solutions in this context