Tamaki Watanabe

A 4πβ (ppc)-γ(HPGe) coincidence apparatus using a live-timed bi-dimensional data acquisition system and its application to measurement of gamma ray emission probability

Data accumulated automatically in a recently described coincidence counting system were used to calculate the photopeak efficiency of an HPGe γ ray detector simultaneously with the source activity. The system serves for the direct measurement of γ ray emission probabilities and as a check on γ ray emitting impurities in the 4π source. The relatively short source-detector distance needed to attain acceptable counting statistics requires accurate corrections for effects due to cascade summing.

A source preparation for 4πβ -counting with a aluminum compound

Abstract A simple method is proposed for preparing the sources used in 4 πβ -counting. With this method using aluminum chloride, the source material is uniformly distributed by the action of the fine particles of the aluminun compound produced in a radioactive solution. The self-absorption of the 59 Fe, 60 Co, 95 Nb, 103 Ru and 198 Au sources prepared by the method were measured by means of 4 πβ - γ coincidence counting, and the uniformity of activity distributed was examined by autoradiography. Also, the self-absorptions of the 60 Co and 95 Nb sources were measured as a function of the amount of the carrier or non-volatile material added in preparing the source. As a result, the self-absorption was found to be reduced below 2% for the 60 Co source when 2 μ /cm 2 of a carrier was added.

Optimisation of efficiency extrapolation functions in radioactivity standardisation

Abstract When radioactivity is measured by 4πβ-γ efficiency extrapolation the data is commonly fitted to a linear function, but also to a polynomial function of second or third order if this proves necessary. In order to justify the empirical fitting procedure, we compared the experimental results with some functions which could be expected theoretical grounds. The most suitable function was a linear function at high 4π counting efficiencies joined on to a second-order function at low 4π counting efficiencies, while a third-order polynomial function without second-order term produced accurate results regardless of the fitting region.

Self-induced space charge effect on gas gain in proportional counters

Abstract In the measurement of radiation using a proportional counter, energy linearity is lost at high gas gain, which is called the self-induced space charge effect. The dependence of the effect on the diameter of anode wire and the pressure of counting gas was investigated using methane gas flow proportional counters for X-rays with energies of 0.64, 1.5 and 5.9 keV. A theoretical explanation of the effect is also given. The effect increases with both increasing X-ray energy and pressure of the counting gas and with descreasing anode wire diameter.

Photoelectric Emission of Metals by X-Rays in the KeV Region

Electron emission yield from the metal surface under the irradiation of nearly monochromatic X-rays covering the energy range from 1.5 KeV to 7.9 KeV was measured. The yield was about 10-1 for gold and about 10-2 for aluminium, depending on the incident X-ray photon energy. The ratio of the electrons having the energy more than 30 eV to the total electrons depends also on the incident X-ray photon energy and on the material. According to the emission yield obtained theoretically, Auger electron emission is dominant when incident X-ray photon energy is just above the absorption edge of the material.

Position Sensitive Proportional Counter for Measurement of Tritium Labelled Gas Movement

A position sensitive proportional counter of a charge division type with a single resistive anode wire was constructed for the measurement of the movement of 3H labelled gas which is flowing or diffusing in a pipe. The introduction of resistors between the anode wire and pre-amplifiers brought a uniform detection efficiency for 3H β-rays throughout the counter. The position resolution was 3.1mm FWHM. Detection efficiency was almost 100% uniformly over about 700 mm in the total anode length of 740 mm. The movement of 3H labelled gas. could be measured effectively.

Electron Stopping Power in Aluminum in the Energy Region from 2 to 10.9 keV

By transmission technique of electrons the stopping power in aluminum has been measured in the energy region from 2 to 10.9 keV. The discussions are given for the characteristics of specimen films; the effect of the thickness non-uniformity, and those of the contamination with adsorbents and the oxidation of a specimen film surface. Through these discussions fairly accurate values of electron stopping power were obtained; they showed the E -1 dependence and smaller than given from the theory by Bethe or the semi-empirical values by Sugiyama in higher energy region, and in the region lower than 5 keV showed comparatively good agreement with the theory within the limit of the experimental error.

4πβ-γ coincidence counting by using a live-timed bi-dimensional data-acquisition system

Abstract Efficiency functions were measured by using a bi-dimensional data-acquisition system and a magnetic tape sub system. In the measurement, the data of pulse height and time relation of β and γ signals were recorded on a magnetic tape. After measurement, all data stored on the tape were analysed and the efficiency functions were obtained by the “computer-discrimination method”. This method was applicable for the sources with disintegration rates lower than 15 kBq and the smooth efficiency functions were obtained for the nuclides of 59 Fe and 134 Cs in short time.

A hybrid spark chamber for measuring radionuclide distributions

Abstract This paper describes the operational characteristics of a hybrid spark chamber designed to improve the instability of self-triggering spark chambers for measuring radionuclide distributions. The chamber consists of a parallel plate spark chamber and a parallel plate proportional chamber in the same gas space. This construction of the chamber enables us to obtain good counting plateaus, that is, good stability, and high spatial resolution for the incidence of minimum ionizing β-rays.

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.