Crystal structure of Thorotrast This paper describes a high resolution electron microscopy study on diameter distribution of Thorotrast particles. Specimens were prepared from a surgically removed Thorotrast granuloma taken from a patient. The diameter was calculated by mu. tiplying the lattice distance 3.2 A of Th02 (1,1,1) face by a lattice number of this face. The lattice number ranged from 13 to 59; the diameter ranged from 42to 187 A, and the average was 1081-32 A. The distribution showed a good agreement with a normal distribution N (108,322).

View full abstract

The formulae for effective mass stopping power ratio i n high-energy photon dosimetry given by Almond et al. and Shiragai include some parameters. In spite of fundamental difference in derivation of the two equations, there is a relation among those parameters. The cavity-wall transmission rate of secondary electrons originated in medium (introduced by Shiragai), exactly, is not equal to the fraction of the cavity ionisation from electrons originated in medium (introduced by Almond et al. ).

View full abstract

The Japanese Association of Radiologycal Physicist (JARP) chamber is frequently used with Mix-DP phantoms to measure precisely the absorbed dose rates of X-ray and 60Co gamma-ray apparatus. Differing phantom and room temperatures sometimes cause changes in phantom temperatures with time. The temperature time constants for the JARP chamber were measured by Hiraoka et al., but few data have been obtained for the Mix-DP phantom's time constants. Our data indicated that when the initial difference between the phantom and room temperatures was 20°C, the rate of maximal temperature change of the Mix-DP phantom was 3°C h-1. Separating the 0.5 cm - 2.5 cm Mix-DP phantom slices and exposing them to air to decrease the temperature differences necessitated at least 5 hours to cause a temperature difference less than 1°C when the initial temperature difference was 15°C. The temperature of the Mix-DP phantom also changed by several degrees Centigrade in a room air conditioned only during working hours. Our dosimetry during conditions causing the temperature change rate from 3.2 to 2.0°C h-1 revealed differences in corresponding doses in air of 0.4% or less.

View full abstract