For precision measurement of diffracted X-ray intensity by G-M counter, durable stability of X-ray source is required first of all. The direct method of obtaining this stability is to keep the tube voltage and current strictly constant. For regulating the voltage, a transmitting tube is used in series in the X-ray tube circuit with which the voltage stabilization is attained satisfactorily. As for the tube current, the regulation is achieved, with no detectable fluctuation, by the use of a variable load for controlling the filament. In making up the counting losses correctly, it is desirable that the form factor, K, of the X-ray source (√K=root -mean-square intensity of source/mean intensity of source) be considered practically unity, so a discussion is given on the necessary capacity of the smoothing condenser to reduce the ripple. From the results of intensity measurements that lasted for 6 hours, relative standard deviation with this arrangement of the X-ray source and the detector system was found less than 0.16 per cent with 95 per cent confidence.
As to the window glass for shielding the hot cave, its density, index and transmittance should not be affected by radiation. Tests are made with pieces of window glass: the density by a picnometer, the index by a spectrometer and the transmittance by a Beckman's automatic recording spectrophotometer. The total doses of γ radiation given to these test pieces are varied: 106r, 3×106r, 107r, 3×107r and 1.16×108r with the dose rate of 4.0×105r/hr at 17.5cm from a source of 10 kc Co60. The result shows that the density and the index are not appreciably affected. As for the transmittance, medium density glass-non-brawing glass-undergoes a very slight change at a room temperature of 18°C with equally slight coloration. But high density glass is different: the transmittance is reduced great deal by coloration. The color, although fades in time, conspicuously at first, when the glass is left free from radiation effect, remains even after thirty days bringing in a serious problem concerning the quality of glass for shielding radiation. The cause of coloration and subsequent fading is discussed.
A liquid scintillation counter for measuring low level C14 and H3 beta activities has been constructed and its performance characteristics studied. The instrument is of the coincidence type. Scintillation induced in the sample, usually 140 cc in volume, contained in Terex glass ampoules, are observed with two photomultipliers (EMI 6262). The output pulses are fed to two respective linear amplifiers (gain 10, 000) and the coincidence count is taken. For reducing background count, the output of the coincidence circuit is anticoincidenced with the pulses that passed through the upper discriminator. The resolving time of the coincidence was 0.2μpsec, and as for the stability of the circuit in measuring C14, the variation of the counting efficiency was 1% in 24 hours. The counting efficiency of the instrument was of the order of 10% for H3 and about 40% for C14. For measuring the distribution of C14 in nature, quenching of various organic materials is studied. Ethanol is one of the best samples, for the quenching is not large and its preparation is easy. Various side-effects are also studied, such as 1) the temperature dependency of the thermal noise of photomultiplier, 2) the increase of the dark noise of photomultiplier after being exposed to light of the room, 3) the phosphorescence of the glass ampoule and that of the reflector, 4) the effect of the ampoule material on the background counting rate.
The contact charging in vacuum between polyethylene irradiated in an atomic pile and metal has been investigated. By successively bringing them into contact and then separating, the charge on polyethylene increases, at first rapidly then gradually, to its saturation. This seems to be due to an equilibrium being established by the successive transition of charge through the interface in one way in coming into contact and back in the other in separation. The saturation charge with one unit of dose (50×106r) of radiation is negative, the amount of which increases at first with every additional dose, then decreases to the initial small amount at 9 units of dose and eventually becomes a small positive charge at 72 units of dose. The saturation value varies with the work function of the metal. Hence a conclusion may be drawn that the change in the contact charge with the irradiation corresponds to the change in effective work function of polyethylene caused by formation and transition of electron trapping states in the irradiated polyethlene.
A parallel circular plate type ionization chamber (PCP) and a gamma ray compensated ionizattion chamber (CIC) to be used for reactor control have been made as much as possible with those home materials that are small in neutron absorption cross-section and induced activity and are also radiation and high temperature-resistive checked by activation analysis. Boron power (enriched 96% B) imported from ORNL, U.S.A. is used. During the preparatory work, technique of fine machining of reactor grade graphite, arc welding of magnesium in argon, and boron coating are developed. Neutron sensitivity, γ ray sensitivity, linearity, and induced activity of six kinds of neutron detectors including the author's PCP and CIC and one that was imported are tested by using JRR-I reactor and γ ray sources of 10 kc Co60 in JRERI and 1 kc Co60 in Toshiba radiation laboratory. Results of the tests show that the author's detectors are not only just as good as the imported but superior to it as regards the residual activity.