[An]Illustrated Re-visitation of Energy Transfer and Energy Absorption in Photon Interactions with Matter

This thesis revisits the processes of energy transfer and energy absorption in photon interactions with matter with particular focus paid towards the calculation of the mass energy transfer coefficient and the mass energy absorption coefficient. The concepts behind these two coefficients have been well enunciated, however, available references do not lend themselves to serve as a visual aid to promote better understanding of the dosimetric quantities related to energy transfer and energy absorption, as well as their relationship to the photon energy and absorber atomic number. An illustrative approach is utilized in explaining the functional relationships between the relevant quantities inherent to these coefficients. In addition, a Photon Energy Transfer and Absorption Coefficients (PETAC) software has been developed to allow for a graphical, dynamic, and interactive format upon which the student of medical physics may observe and intuitively grasp the processes behind energy transfer and energy absorption in photon interactions with matter .Cette thèse révise les procédés de transfer et d'absorbtion d'énergie causés par l'interaction des photons avec la matière en accordant une attention toute particulière aux calculs du coefficient de transfert d'énergie massique et du coefficient d'absorbtion d'énergeie massique. Les concepts définissant ces coefficients son déjà bien établis, mais ils ne proposent pas une excellente comprehension des quantités dosimétriques reliées au transfert et à l'absorbtion d'énergie de même qu'à la relation existant entre l'énergie photonique et le numéro atomique absorbé. Une approche nouvelle et visuellement coherente est proposée afin de metre en lumière une relation fonctionnelle entre ces quantités et ces coefficients. De plus un application informatique, graphique, dynamique et interactive appelée PETAC (Photon Energy Transfer and Absorbtion Coefficients) à été devellopee pour aider les étudiants en physique médicale a visualiser et déduire intuitivement les lien entre les processus de transfert d'énergie, et d'absorbtion d'énergie dû à l'interaction des photons avec la matière

ISSCREM: International Space Station cosmic radiation exposure model

A semi-empirical model is derived from operational data collected aboard the International Space Station (ISS) with the U.S. tissue equivalent proportional counter (TEPC). The model provides daily and cumulative mission predictions of the operational dose equivalent that space-crew may receive from galactic cosmic radiation (GCR) and trapped radiation (TR) sources as a function of the ISS orbit. The parametric model for GCR exposure correlates the TEPC dose equivalent rate to the cutoff rigidity at ISS altitudes while the TR parametric model relates this quantity to the mean atmospheric density at the crossing of the South Atlantic Anomaly (SAA). The influences of solar activity, flux asymmetry inside the SAA, detector orientation, and position aboard the ISS on the dose equivalent have been examined. The model has been successfully benchmarked against measured data for GCR and TR exposures to within ±10% and ±20%, respectively, over periods of time ranging from a single day to a full mission. In addition, preliminary estimates of the protection quantity of effective dose equivalent have been simulated using the PHITS Monte Carlo transport code. These simulations indicate that the TEPC dose equivalent is a conservative estimate of the effective dose equivalent

Comparison of dose and risk estimates between ISS Partner Agencies for a 30-day lunar mission

The International Partner Agencies of the International Space Station (ISS) present a comparison of the ionizing radiation absorbed dose and risk quantities used to characterize example missions in lunar space. This effort builds on previous collaborative work that characterizes radiation environments in space to support radiation protection for human spaceflight on ISS in low-Earth orbit (LEO) and exploration missions beyond (BLEO). A “shielded” ubiquitous galactic cosmic radiation (GCR) environment combined with––and separate from––the transient challenge of a solar particle event (SPE) was modelled for a simulated 30-day mission period. Simple geometries of relatively thin and uniform shields were chosen to represent the space vehicle and other available shielding, and male or female phantoms were used to represent the body’s self-shielding. Absorbed dose in organs and tissues and the effective dose were calculated for males and females. Risk parameters for cancer and other outcomes are presented for selected organs. The results of this intracomparison between ISS Partner Agencies itself provide insights to the level of agreement with which space agencies can perform organ dosimetry and calculate effective dose. This work was performed in collaboration with the advisory and guidance efforts of the International Commission on Radiological Protection (ICRP) Task Group 115 and will be presented in an ICRP Repor