Shigeru Kashiwazaki

Thin film alanine-polyethylene dosimeter

A thin-film dosimeter was prepared by homogeneously mixing ground DL-α-alanine crystalline powder and melted low-density polyethylene and by subsequent extrusion into a long tape with 8 mm width. The basic dosimetric characteristics of the 200-μm thick film dosimeter were studied for 60Co gamma-rays and 2.0-MeV electron beams. Dose responses were measured using a conventional electron spin resonance (ESR) spectrometer as well as a custom-made compact reader. The ESR measurement procedure was improved by the design of a dosimeter holder for high reproducibility, which avoided the orientation effect of samples during ESR readings. The random uncertainty of dose response among 20 irradiated replicate dosimeters is ±1% (1σ) for absorbed doses of 103–105 Gy, with correction being made for the weight differences of the dosimeters. The measurable dose range using the conventional ESR spectrometer is from 0.05 to 100 kGy. The compact reader can also be applied for dose evaluation above 1 kGy, with a precision within 1%, covering the measurable dose ranges of both FWT-60 radiochromic film and cellulose-triacetate film dosimeters. The estimated dose derived from two calibration curves for gamma-rays and electron beams was in good agreement. The thin-film polyethylene-alanine dosimeter can be useful as a reference dosimeter for medium energies of electron beams (∼2 MeV) as well as for comparison of radiation effects on various materials for photons and electron beams.

Orientation effects of ESR analysis of alanine-polymer dosimeters

Abstract Orientation effects during electron spin resonance (ESR) measurement are studied on alanine-polymer dosimeters prepared by different molding procedures (press-molding or extrusion), and also according to different shapes (rods with different lengths and thin-films). The variation in ESR signal amplitude was measured by rotating a dosimeter around the vertical mid-axis and at a right angle to the magnetic field in the ESR cavity, at a temperature of 22°C. Orientation effects for rod dosimeters with both molding procedures (press and extrusion), and with different lengths, were negligible. Thin-film dosimeters molded by extrusion show a pronounced orientation effect when the samples are cut into disks and positioned horizontally (parallel to the magnetic field) during readout in the ESR cavity. Orientation effects on the film dosimeters can be eliminated, however, when they are positioned vertically and parallel to the mid-axis of the ESR cavity.

Alanine-polystyrene dosimeters prepared by injection moulding

Abstract The alanine-polystyrene dosimeters analysed by electron spin resonance (ESR) spectrometry were manufactured for large-scale use as a routine dosimeter in industrial radiation processing facilities by using an injection moulding method. Injection moulding enables us to achieve mass production of uniform dosimeters at a reduced cost. Their primary characteristics for dosimetry were studied in terms of their gamma-ray dose-response at radiation processing dose levels, precision, and effect of temperature during irradiation at an absorbed dose of 1 kGy. The precision of dose-response in the range 0.1–100 kGy is within ± 2% at a 68% confidence level with and without correction for sample-to-sample mass scattering. The irradiation temperature coefficient for dosimeters irradiated to 1 kGy is estimated to be 0.25%/°C, by normalizing to those irradiated at 25°C in the temperature range from 5 to 45°C. The fading of the radiation-induced ESR signal at doses of 0.1–100 kGy at 25°C and r.h. 40% is

Alanine⧸ESR Dosimetry system for routine use in radiation processing

Abstract A new alanine-polystyrene (PS) dosimeter prepared with simplified molding procedure and an automatic desk-top dose-reader of alanine dosimeter were developed for the purpose of routine use. Combination of these two allows us to apply a reliable alanine/ESR dosimetry system to routine dosimetric process control in industrial gamma radiation processing.