Development of thin-film alanine dosimeter is required for application of reliable alanine/ESR dosimetry technique to short-range radiation. Molding condition and dose-response characteristics of the dosimeters were studied in terms of fine-grain alanine crystal prepared by grinding and recrystallization, five different lowdensity polyethylenes (PE) as binders, and two different molding methods of press and extrusion. Physical characteristics of the dosimeter after molding depend on grain size and shape of alanine crystal, fluidity and solidity of binders, and molding methods. The thin film alanine dosimeters of 150-200μm in thickness, were manufactured by two methods: (1) press-molding of the mixture of recrystallized alanine powder and PE with high melt index (MI) value, and (2) extrusion of the mixture of ground alanine powder and PE with relatively low MI value. The former method (1) is useful to prepare thinner films, and the latter method (2) enables us to achieve higher precision of dose responses within ± 2 % (at 95% confidence level) for the dose range of1-100 kGy.
A simple identification method was developed for spore-forming bacteria which are highly resistant against γ-rays. Among 23 species of Bacillus studied, the spores of Bacillus megaterium, B. cereus, B. thuringiensis, B. pumilus and B. aneurinolyticus showed high resistance against γ-rays as compared with other spores of Bacillus species. Combination of the seven kinds of biochemical tests, namely, the citrate utilization test, nitrate reduction test, starch hydrolysis test, Voges-Proskauer reaction test, gelatin hydrolysis test, mannitol utilization test and xylose utilization test showed a characteristic pattern for each species of Bacillus. The combination pattern of each the above tests with a few supplementary test, if necessary, was useful to identify Bacillus species showing high radiation resistance against γ-rays. The method is specific for B. megaterium, B. thuringiensis and B. pumilus, and highly selective for B. aneurinolyticus and B. cereus.
To make clear the cause of the reverse redistribution phenomenon (RR) in thallium-201 myocardial imaging using dipyridamole infusion method combined with low level exercise (DE-method), we investigated 73 patients (219 segments) including 23 cases with coronary artery bypass graft (CABG) and 50 cases with non-revascularization. RR was detected at the 10 segments in 55 post-CABG segments (18.2%), whereas only 4 RR segments were detected in 150 non-revascularized segments (2.7%) . All of RR segments in the post-CABG group had a partial myocardial damage. In each case with RR, washout rate of the RR segment showed higher value than those of non-RR segments. Therefore, RR was thought to be seen in the area with a partial myocardial damage and with sufficient coronary flow by the revascularization.
The myocardial blood flow (MBF) was measured with PET and the15Osteady-state method using a continuous infusion ofH215Oin 8 normal volunteers. The intra-vascular radioactivities were corrected by blood volume measured with a single inhalation ofC15O.The MBF values were obtained both invasively and non-invasively. As the15Osteady-state method is susceptible to a partial volume effect due to a relatively thin myocardial wall thickness and wall motion, the MBF values were corrected for the partial volume effect by tissue fraction measured with transmission scan. The MBF values obtained non-invasively were 90.7±20.6, 65.1±21.6 and 104.4±44.5ml/min/ml in the septum, anterior wall and lateral wall, respectively. They were close to the previously reported MBF values of 100 ml/min/100 ml. Therefore, we were able to obtain reasonably accurate MBF values non-invasively.
We developed an automatic device to measure etch pit density on cellulose nitrate film, which consisted of microscope, monochrome video camera, image processing device, monochrome display and personal computer. For 1-3 MeV energy alpha particle, high reproducibility of automatic counting was confirmed. In case of 4 MeV energy alpha particle, results of automatic counting were unstable. Counting efficiency for 4 MeV energy alpha particle can be decreased with increasing threshold level which was used when image data was converted into binary data. Correction for loss of etch pit density due to overlapping etch pit image was not necessary up to about 8000 tracks cm-2in case of about 10μm diameter etch pits. Radon concentration can be estimated up to 120 Bq m-3without correction due to overlapping etch pit image, when the measurement was carried out for 2 months with an electrostatic integrated radon monitor.