Positronium annihilation process in mesoporous sputter-deposited silicon oxide thin films was studied by means of positron annihilation γ-ray spectroscopy. Positron 3γ annihilation probability (I3γ) and positron annihilation Doppler broadening (S parameter) were measured at various positron energies with a variable-energy positron beam. Refractive index at a wavelength of 630 nm was used as a measure of porosity of the deposited films. I3γand S of as-deposited films were found to have a correlation with refractive index and porosity. Both parameters considerably increased after annealing at 600°C without any significant change of refractive index. The observed increase of I3γand S was attributed to increased positronium formation due to the disappearance of paramagnetic defects introduced into films by deposition.
Effect of plasticization on free-volume hole size observed by means of positronium lifetime measurement was studied. Glass transition temperature significantly decreased with an increase of dioxane content while free-volume hole size increased Temperature dependence of the excess free-volume hole size by addition of dioxane was examined Hole formation energy EPsHfor the excess free-volume was estimated on an assumption of a Boltzmann type distribution. As the result, estimated value of EPsHwell agreed with those for several polymer systems previously obtained by means of heat capacimetry.
Radioactive iodine isotopes are necessary to be handled carefully, because they scatter easily. As air concentration limits of the radioisotopes are very low levels, we should prepare the measurement technique using a large-volume aspirator and largescale equipments for environment measurement in radiation controlled areas. In the present study, we designed and manufactured a simple set of holder and charcoal filter connected to a foot pump, and we examined the validity of the system. The collecting efficiency of airborne iodine-125 by this system was 0.379±0.107. However, in the case that 10 L air were filtered by this system and counted for 10 min by a NaI (Tl) well-type scintillation counter, it was shown that iodine-125 at air concentration limit could be measured.
We have developed an air monitor which is possible to measure rapidly and sensitively the concentration of plutonium for the environmental monitoring at an accident of a nuclear reprocessing plant. The monitor is designed to collect airborne plutonium by drawing the ambient air through a filter and to detect the activity by alpha spectroscopy. The following two methods are equipped with the monitor: continuous measuremeat at atmospheric pressure and batch measurement at vacuum. The description of the air monitor and the results of performance test are reported.