A 300MeV electron linear accelerator has been constructed at Tohoku University. Last May, the first accelerated beam was obtained after four years of construction period, and the accelerator has been operated stably for 2000 hours during the past year. Obtained energy and energy spect-rum of beam is satisfactory and the beam current is reached to the 60% of designed value. Afterthe historical process of construction is described, the general description of the accelerator and some detailed statements of each parts of the accelerator are followed. The beam characteristics are shown in the last section, and the experimental result of nuclear research which was obtained by nsine the 300MeV linacis demonstrated.
In order to estimate the quantity of fluorescence X-rays from a specimen irradiated with high energy γ-rays, the conversion yield of fluorescence X-rays was measured for plane targets and a beam of γ-rays from Cs-137source. Several procedures were followed to determine the absolute yield experimentally. The angular distribution of the yield and the intensity ratio of fluorescence X-rays to scattering γ-ays emerging from a lead target were also measured, as well as the vari-.ation of the yield with target thickness. It was shown that the backward yield finally saturates at a thickness corresponding to a few mean free paths of backscattering γ-rays, not of fluorescence X-rays. From this result the enhancement of the yield is considered to be mainly due to excitation by the scattered γ-rays within the target. Calculations of the yield were made for excitation by incident r-rays and by singly scattered γ-rays in the target. The approximate calculation roughly coincided with the experiment, but complete agreement was not obtained even though the inclusion of the enhancement effect of secondary electrons. It seems to be necessary that excitation by multiple scattering γ-rays is taken account of in the yield calculation.
Silicon nitride films were prepared by reactive sputtering of silicon in a nitrogen supported glow discharge. Some physical and chemical properties of these films were examined in terms of discharge current density. The film properties depend on current density and gas pressure but a current density higher than 3.3 mA/cm2 is found to have a detrimental effect. The dielectric constant is about 8.3, the breakdown voltage is in the range of approximately 7.5×106V/cm to 2.5×107V/cm and temperature coefficient is 23_??_35 ppm/°C. The resultant capacitors which have low dielectric losses and are very stable under life test conditions. It has been shown that these films prepared by a sputtering method can be used effectively as the dielectric in thin films devices.
NMR absorption of polytetrafluoroethylene 60Co γ-rays-irradiated with a total dose of about 2.2×106R in the presence of oxygen or nitrogen gas, or in a high vacuum and then heat-treated .at 300°C in vacuum were measured. As to the effect of irradiation-atmosphere, a very remarkable increase in crystallinity and the step-like broadening of narrow line width above 27°C were observed in the specimens heat-treated after γ-irradiation in oxygen gas. In contrast there was no difference in molecular motion, between the specimen heat-treated after γ-irradiation in nitrogen gas and that in vacuum. This remarkable increase in crystallinity is ascribed to the scission of molecular chains -following the reaction of -CE2-CF2 radicals with oxygen. The step-like broadening of line width of narrow component is due to the superposition of narrow component and paracrystalline compo-nent which segregated from broad component in the vicinity of the room temperature transition. The most part of the increase in crystallinity was paracrystalline component produced as a result of the post-irradiation heat treatment. The segregation of paracrystalline component from broad component in the vicinity of the room temperature is due not only to chain alignment in order but also to the transition in molecular motion of the crystalline regions. The paracrystalline component is ascribed to the regions which consist of the shorter polymer chains orderly aligned and affected by the crystalline regions.
In a previous report it was shown that the conversion yield of fluorescence X-rays for high energy γ-rays are enhanced by scattering γ-rays within a target. In order to establish the enhan-cement factor of fluorescence X-rays due to scattering γ-rays, an experiment was performed with Cs-137 source for several sets of a target and a backing which acts as a scattering source. It was found that the enhancement factor increases with backing thicknesswith the same dependency as the reflection coefficient of incident γ-rays does with scatterer thickness. Calculations were made for the yield of Pb-Xk excited by the scattering γ-rays in a backing by a few approximatemethods. Calculated values were about 30% less than those observed. The difference may be mainly due to the excitation processes of multiple scattering γ-rays within the target and of secondary electrons.