Question

The Spencer Attix addition to Bragg Gray theory used a restriction on the range of stopping power to a minimum of ?. What is this ? value taken as generally in dosimetry and why is this value taken? How will the Spencer Attic addition impact the dose to water calculated above if you ignore track end effects and beam perturbation? What are the applied perturbation factors using the IAEA TRS398 implementation of dose to water.

Answer 1

Stopping power(misnomer) is defined as the energy lost by a radiation particle/electron per unit path length when its imparted into the material. It depends on the material characteristics and dimensionally it is a force.

The Bragg-Gray cavity theory does not consider the production of auxiliary high-energy (delta) electrons produced because of the moderating down of the primary electrons by means of hard impacts in the delicate volume of the dosimeter(a device used to measure the absorbed dose of ionizing radiation). The Spencer-Attix cavity hypothesis is a more broad detailing that represents the creation of these electrons that themselves have adequate energy to deliver further ionization. A portion of these electrons discharged inside the cavity will have adequate energy to escape from it, conveying a few of their energy with them. This lessens the energy assimilated in the cavity, and requires modifications to the measurement of stopping power of the material present inside the cavity.

Due to the effect of more elastic collisions inside the cavity than that of outside. The range of stopping power to a minimum value of stopping power of medium without cavity. This value need to be calculated first for the correspondinng medium before dosimetrical measurement inside the cavity.

The dose to the medium is related to the dose to the cavity

where is the  ratio of the average unrestricted mass collisional stopping powers of the medium and cavity.

Albeit just the water calorimeter permits the immediate assurance of the ingested dosage to water in a water phantom, the required transformation factor and perturbation factors for the different methodology are presently notable at numerous labs.

General perturbation factor for an ionization chamber for in-apparition estimations at a beam quality Q. It is equivalent to the result of different elements rectifying for various impacts, each rectifying for little perturbations, they are pcav, pcel, pdis and pwall.

pwall -- Factor that revises the reaction of an ionization chamber for the non-medium comparability of the chamber divider and any waterproofing material.