Software Development for Material Analysis by PIGE (Proton Induced Gamma Emission)

Abstract

PIGE (Proton Induced Gamma Emission) is an analytical technique based on accelerated proton beams (with most common energies around 1.5 to 3.0 MeV), hindered by the lack of availability of software tools derived from first principles for sample analysis, which have only been on active research in the last twenty years. Previously, sample composition was determined using the assumption of homogeneity in terms of area and depth and comparing with a standard sample (bulk analysis). For in-depth heterogeneous samples, depth profiling analysis was accomplished by the use of a single isolated resonance for which the concentration profile was easily deduced. To perform PIGE analysis using first principles, it was required to obtain all relevant cross-sections of many nuclear reactions for a wide range of energies, building a database of them, which became a major endeavor of the research team including the author of this thesis. From this foundation, the main objective was the development of software capable of performing bulk and depth analysis. Based on first efforts of the research team, recently a decision was made to upgrade to two versions: ERYA-Bulk for homogeneous bulk samples, and ERYA-Profiling for in-depth heterogeneous samples (the ERYA acronym meaning Emitted Radiation Yield Analysis) designed with the following requirements: compatibility with the major operating systems, a user-friendly graphical user interface with re-sizable windows and automatic scaling for different screen sizes, with support of different input and output file formats for relevant contexts. It also should be intuitive and easy to use. While ERYA-Bulk performs the analysis by direct integration using interpolation of the excitation function, a generalization was made for ERYA-Profiling so that for a specific resonance, overriding the excitation function, a set of parameters that models a resonance by a Lorentzian can be defined either by a Breit-Wigner or a Resonance Strength by filling the necessary parameters. Since ERYA-Profiling depth profiling analysis requires to take account of the energy dispersion effects (straggling) of proton beams due to the stochastic nature of beam energy loss in the interaction between the beam and the sample, it would require a elaborate numerical analysis of the energy distributions to perform the heavy computational task to evaluate them.

PIGE (Emiss„o Gama Induzida por Protıes) È uma das tÈcnicas analÌticas baseada em feixes de protıes acelerados (em geral 1.5 a 3.0 MeV) que para a qual, contrariamente a outras, atÈ h· cerca de duas dÈcadas n„o houve desenvolvimento de software baseado em princÌpios fÌsicos para o c·lculo da composiÁ„o das amostras a analisar. No pressuposto que as amostras eram homogÈneas em ·rea e profundidade era usado um mÈtodo comparativo com padrıes para an·lise em bloco (bulk analysis); para an·lise em profundidade eram usadas resson‚ncias isoladas para as quais a obtenÁ„o do perfil era imediata. Para avanÁar com c·lculos era necess·rio obter as secÁıes eficazes das reacÁıes nucleares relevantes que se tornou um dos objetivos do grupo de investigaÁ„o em que esta tese se insere. O grande passo seguinte seria o desenvolvimento de software para an·lise em bloco e em profundidade. Recentemente os primeiros esforÁos de desenvolvimento foram objeto de uma transformaÁ„o no sentido de criar uma vers„o para cada caso (ERYA-Bulk e ERYA-Profiling, sendo ERYA o acrÛnimo de Emitted Radiation Yield Analysis) obedecendo a: compatibilidade com todos os sistemas operativos; interface amiga do utilizador com rescalonamento autom·tico para diferentes Ècrans; aceitaÁ„o de v·rios formatos de entrada para os dados fÌsicos pertinentes; produÁ„o de v·rios formatos de saÌda. Para a an·lise de amostras heterogÈneas em profundidade, foi feita a generalizaÁ„o de trabalhar uma dada resson‚ncia (para a qual a entrada pode ser dado independentemente em par‚metros de uma Lorentziana definida quer por uma Breit-Wigner ou por uma amplitude de resson‚ncia) em conjunto com a restante funÁ„o de excitaÁ„o. Foi necess·rio fazer um grande investimento para a compreens„o e computaÁ„o da dispers„o em energia (straggling) do feixe de protıes, devida ao aspeto estoc·stico da sua perda de energia, e das distribuiÁıes que a descrevem, as quais, nomeadamente para pequenas perdas de energia s„o matematicamente elaboradas e computacionalmente pesadas.