A conventional 30 MeV betatron which will be used for the study of photonuclear reaction has been installed. In order to secure the energy stability of the machine, the size of the magnet was chosen rather large and the maximum flux density in the yoke small. In the present report the design of the magnet and its energizing system are described. Measurements made on the characteristics of the magnet such as n-values and bumps in the field distribution are also described in some detail. The bumps are rather large and seem to come from the mechanical stress in the yoke. The methods of correcting these defects in the field distribution are given and some problems in the construction of a betatron magnet are discussed. Various auxiliary circuits, controlling system and performance of the betatron will be described in the second part of this report which will soon appear in this Journal.
Growth of anthracene single crystals from melt by Bridgman method is described. The crystals are grown to a shape of a cylinder, about 2.5cm in both diameter and height, to be used for a scintillator. For designing the furnace, growth velocity, temperature, and rate of cooling of the crystal after solidification are obtained by calculation. Temperature of the furnace around the tube in which the crystal is grown is controlled enabling it to be maintained within ±0.03°C of fluctuation for several days. The tube has four small windows at solid-liquid interface level, through which the growth of crystal is watched. Removing the crystal from the tube is effective in avoid-ing the cracking in cooling. Growing of crystals from prepared seeds has been successful; good crystals grown in (001) direction can be made from seed. Crystals that originate spontaneously are apt to grow along (010) direction; they are not suited for the purpose. For the examination of scintillation characteristics of the grown crystals, scintillation spectra for radiations from Co60, Sr90, Cs187 and S35 are measured with satisfactory results.
X-ray fluorescencø spectroscopic analysis with a radioactive β-ray source is applied for analyz-ing binary alloys and measuring thickness of thin coating. β-rays from constituent elements by irradiation of n-rays from 90Sr-90Y (10mc) are discriminated by a filter or a pulse height analyzer. The detectors used are a proportional counter and a thin Nal scintillation counter, the resolving power of each of which is experimentally determined. β-rays scattered by the specimens are deflected off by an electromagnet provided in front of the counters. The results obtained are as follows. (1) From analysis of copper-zinc alloys carried out with a nickel filter of 12-36 microns thick, a calibration curve of almost linear form was obtained which gives measuring accuracy of 2% in error. (2) Tin-copper alloys were analyzed by the use of a pulse height analyzer coupled with a pro-portional counter. The accuracy obtained was 0.5% in error for specimens containing over 80% of copper. (3) Coating thickness of less than 10 microns of chromium or cadmium on copper was deter-mined by the same method as used in (2) with fair accuracy. For chromium coating of less than 4 microns, Cu KX-ray measurement gave an accuracy of 0.1 micron.
Since a 6 MeV electron linear accelerator was installed in Nagoya Government Industrial Research Institute, measurement of energy spectra of electron beams generated by the accelerator became necessary, and an adequate spectrometer has been developed. The spectrometer has the following specification: 1. Electron beam is resolved in homogeneous magnetic field. 2. Deflection angle is 90° (the half of semicircular system) 3. Faraday cup and carefully designed pre-amplifier is used for detection. 4. For monitoring, the spectrum is indicated by a cathode-ray oscilloscope, and for recording, an X-Y recorder is used. The sweep time of the former is 4 sec. and that of the latter is 2min. 5. The window and the in-put slit are cooled by water to protect from being damaged by the transmission of high power incident beam. 6. Since the electron beam is radiated pulsatively, some filter circuits are provided in the amplifier of the detection system. 7. This spectrometer is available in the range of about 2_??_10 MeV with discriminable resolu- tion of about 1%.
Some characteristics of a 3 MeV Van de Graaff electron accelerator constructed for the use in radiation chemistry have been investigated. The accelerator is equipped with an electron beam bending coil, a focussing coil, a quick closing valve, and a beam scanner. The voltage is divided by corona needles attached to the hoops. The voltage of the electrode can be varied easily by changing corona gaps. The relation be-tween the voltage and the corona gaps was found to be nearly linear in the pressure range of 8.5 kg/cm2 to 15 kg/cm2 of the insulating gas which was a mixture of CO2 and N2 in ratio of 1 to 4. Dependencies of focussing characterictics of the electron beam on Wehnelt voltage and corona gaps have been investigated. The uniformity of scanning was found to be fairly good.
Coloration of shielding window glass of various kinds by γ-ray irradiation is studied. With Co60-1 KC as radiation source, 23°±3°C as irradiation temperature, 105 r/h as irradiation dose rate and 105-107r as total dose, the coloration increases gradually. Volume resistivity of glass and its change by gamma-ray irradiation are measured. D. C. 100V is applied to a sheet of glass sandwitched between two electrodes to measure the time change of its electric resistance. Quantity of induced space charge by radiation is calculated by time integra-tion of the current which is obtained from reciprocal of the resistance. Resistance of high density glass is found to become minimum - hence the current becomes maximum - at the dose of 106 r and increases as the dose increases, but resistance of medium density glass decreases gradually. Change of the resistance is exponential and the charge is always positive at any dose. This testifies that glass is electretized by radiation. On the other hand, linearity is established between the quantity of space charge and the dose in a range of 105-4×106 r. This suggests the possibility of the electretization to be utilized for dosimetry. The above not only demonstrates the physical properties of shielding window glass and the effect of radiation on it but seems to help finding the means of preventing glass from breakdown by radiation.