Katsuo Yanagida

Gamma-ray emission probability measurement by a two-dimensional 4πβ-γ coincidence system

Abstract A two-dimensional data-acquisition system has been applied to a coincidence system composed of a new 4πβ proportional counter operated with CF 4 gas and an HPGe detector. This system was capable of measuring the disintegration rates of short half-life nuclides. Making the most merit of this system, the emission probabilities of the principal γ-rays for 128 I were measured; they are smaller than the evaluated values by about 25% and the uncertainties have been reduced by more than one order.

Precise measurements of the gamma-ray emission probabilities of 186Re and 188Re.

Gamma-ray emission probabilities of 186Re and 188Re are important in nuclear medicine, and have been precisely measured by 4pibeta-gamma coincidence using a live-timed two-dimensional data-acquisition system. The gamma-ray emission probabilities of the 137.2 keV for 186Re and 155.1 keV for 188Re were 0.09487+/-0.00029 and 0.15425+/-0.00072, respectively.

Radioactivity distribution measurement of various natural material surfaces with Imaging Plate

Distribution images of natural radioactivity in natural materials such as vegetables were obtained by using Imaging Plate. In such cases, it is necessary to reduce background radiation intensity by one order or more. Graded shielding is very important. Especially, the innermost surface of a shielding box should be covered with acrylic resin plate. We obtained natural radioactivity distribution images of vegetables, sea food, meat etc. Mostly β-rays emitted from40K print the radioactivity distribution image. Comparison between γ-ray intensity of KCl solution measured with HPGe detector and that of natural material specimen gave the radioactivity around 0.06∼0.4 Bq/g depending on the kind and the part of specimens.

Radioactivity measurement of 85Kr with position-sensitive proportional counter

Abstract Direct radioactivity measurement of 85 Kr is difficult with ionization chambers, since it emits high-energy β-rays ( E β max = 667 keV) which results in a severe wall effect. Also with proportional counters, the end-effect must be taken into account. The position-sensitive proportional counter (PSPC) method which can eliminate the end-effect was applied to direct measurement of 85 Kr radioactivity. In the measurement, logarithmic amplifiers were employed to clearly distinguish between β-ray signals and noise signals, and to eliminate digital error in the calculation of position information. The radioactivity of 85 Kr was determined with ±0.80% standard deviation.

Effect of background radiation shielding on natural radioactivity distribution measurement with imaging plate

Abstract Distribution images of natural radioactivity contained in various natural materials such as vegetable, animal meat and pottery work can be obtained with an imaging plate which has high sensitivity for nuclear radiations. For such very low levels of radioactivity, natural background radiations must be reduced using a shielding box. The lining, on the inside of the box, with low atomic number material such as acrylic resin is very effective in reducing electrons, β-rays and low energy X- and γ-rays emitted from the inner surface of the shielding material. Some images of natural radioactivity distribution were obtained and the radioactivity, mainly 40 K, contained in natural materials was measured by using an HPGe detector and also the imaging plate itself.

Precise measurement of the gamma-ray emission probabilities of 38Cl

Abstract Accurate gamma-ray emission probabilities for 38 Cl have been determined from measurements of the disintegration rate and gamma-ray intensities. Recommended gamma-ray emission probabilities within the literature have systematic uncertainties of 4.8%, whereas the current measurements gave uncertainties less than 1%. The absolute emission probabilities of the 1642.7 and 2167.7 keV gamma rays were 0.3338 ± 0.0032 and 0.4477 ± 0.0031, respectively, and the relative intensities of the 1642.7, 2167.7 and 3810.3 keV gamma rays were 74.77 ± 0.41, 100.00 ± 0.42 and 0.062 ± 0.004, respectively.

Application of a logarithmic amplifier to a charge-division-type position-sensitive proportional counter

Abstract Fulfillment of both observation of pulses ranging from about 10 mV to 10 V through ADC and carrying out an arithmetic calculation with small digital errors for such digitized pulses is usually difficult, although it is required in measurements using a charge-division-type position-sensitive proportional counter (PSPC). However, the use of a logarithmic pulse amplifier sometimes solves this problem. The advantage of using a logarithmic pulse amplifier is described through the application of the amplifier to absolute-radioactivity measurements of gaseous samples and to the simultaneous measurement of geometrical distributions of neutrons and gamma-rays with the PSPC.

CHARACTERISTICS OF PROMPT SCINTILLATION FROM IMAGING PLATE

Abstract Imaging plate emits “prompt luminescence” when a radiation enters. The ratio of photo-stimulated luminescence intensity from latent image to prompt luminescence intensity depends on the type and energy of incident radiations. The ratio is smaller for the radiation with larger stopping power such as α-particle.

Optimization of counting time in the radioactivity measurement of gaseous samples with inner counting method

Abstract For absolute radioactivity measurements of gaseous radioisotopes using the “diffusion in a long proportional counter” method devised by the present authors, the counting time is optimized by balancing the diminution of the statistical error caused by prolonging the counting time and the increase of the counting loss caused by diffusion of the sample gas into the counter ends of lower electric field intensity. The counting loss is estimated from the diffusion behavior of the gas through the counter. The optimized counting time is that which minimizes the total error consisting of a statistical part and a counting time loss part. Trial measurements made applying the optimized counting time proved to provide good agreement with corresponding data obtained with the “position-sensitive proportional counter” method also devised by the present authors.

Emission probability for the 443 keV γ-rays of 128I

Abstract The emission probability for the 443 keV γ-rays of 128I was accurately measured, and the result is 0.1267 ± 0.0009, which is smaller than the evaluated values by about 20% and the uncertainty has been reduced by a factor of more than 10.