Co-60 Γ-ray Research Articles

Fast neutron irradiation effect—II. Crosslinking of polyethylene, ethylene-propylene copolymer, and tetrafluoroethylene-propylene copolymer

Effect of fast neutron irradiation on polyethylene, ethylene-propylene copolymer, and tetrafluoroethylene-propylene copolymer was compared with those of Co-60 γ-ray by the measurements of gel fraction and of swelling ratio after irradiation under vacuum. Difference in the effect between fast neutron and Co-60 γ-ray for the three polymers was not detected by those methods in spite of a large difference of linear energy transfer (LET). The G values of crosslink and chain scission determined from gel fraction data were the same for both fast neutron and Co-60 γ-ray for each polymer within the experimental error. It is thought that energy absorbed in a local region of polymer by fast neutron irradiation generates radicals in a more spread region and the radicals move in the polymer matrix until their recombination to form crosslink.

Radiation Beam Mapping with Photographic Film

Mapping the intensity distribution across a radiation beam by means of photographic film is convenient and inexpensive, but the question of accuracy of this method requires investigation. An experiment was carried out at the National Bureau of Standards to examine, with film, the uniformity of some of the x- and γ-ray beams used in calibration work. By exercising certain precautions in film selection, positioning, processing, and photometric measurement, it was possible to determine the relative intensity of radiation across the beams with an accuracy of 1 per cent. A commercial x-ray film type was chosen, which, when exposed to Co60 γ-radiation and, for maximum contrast, processed for twice the prescribed time in a commercial x-ray developer, showed a fog density level of only 0.11 and a linear response up to a density level of 3.5, within the accuracy of the photometric readings. This film was available in 14 × 17-inch size, in individual envelopes with center position and orientation marked on the outside for easy and accurate positioning. During the exposure, the film was held rigidly between layers of plastic, thick enough for electronic equilibrium, in a plane perpendicular to the central ray of the beam. All other supporting materials were kept outside the beam, to avoid errors due to radiation scattering. Commercial x-ray developer was used for processing for ten minutes at 20° C. and, with vigorous, random, manual agitation, produced highly uniform densities on the large sheets of film. Certain photographic artefacts were avoided by using fresh developer, stop bath, and fixer, and by thorough washing and uniform drying. For the photometric measurement, a photoelectric densitometer was used, whose inherent accuracy over a density range from 0 to 5.00 was within 0.02 density units. Readings over a relatively narrow spread of densities were found to be reproducible within the reading accuracy that was limited by the resolution of the densitometer scale. With this procedure, relative intensity readings at any one point on several film sheets, exposed identically at a 1-meter distance in a Co60 γ-ray beam and processed in various orientations in the developer, showed agreement within 0.5 per cent. A plot of the intensity distribution for one direction across the beam is shown in Figure 1, A. The points represent average readings at the various positions on three different film sheets. More than 400 densitometric readings over a central area of 8 × 8 cm. of the exposed films showed a root mean square deviation of 0.7 per cent. This is within the 1 per cent accuracy limit of the photographic method. For this particular beam, only beyond a distance of 10 cm. from the center did the intensity decrease by a statistically significant value.

Universal apparatus with a Co60 ?-ray source with an activity of 60,000 g-eq of Ra for simulating radiation-chemical apparatus, and investigations (the ?K-60,000?)

The article describes a universal apparatus for radiation-chemical investigations with a Co60 γ-ray source possessing an activity of about 60,000 g-eq of Ra. The design of the apparatus makes it possible to simulate radiation-chemical apparatus with powerful isotopic γ-ray sources of various configurations and dimensions: a cylindrical radiating element, a radiating element in the form of two plates, a radiating element in the form of a “heat exchanger,” and a radiating element in the form of one or more rods. The dosage rate (without taking into account the attenuation in the protective vessels) varies from∼250 r/sec in a volume of 36 liters to∼ 3000 r/sec in a volume of 0.1 liter. The apparatus is designed for carrying out radiation-chemical investigations under practically any physicochemical parameters; it ensures the possibility of remote control and observations both of the experimental conditions and the processes taking place in the investigated systems during irradiation.

放射線(γ-線)の水産生物に及ぼす影響-I

Systematic experiments on the effects of Co60 (γ-ray) radiation upon the embryos of aquatic animals had not been carried out. We attempted preliminary studies on the eary development of gold-fish (Caracius auratus) projected with Co60 (γ-ray) radiation. In this experiment the embryos were projected with various quantities of γ-ray ranging from 730 r to 31, 500 r. The following observations were obtained during the early developmental stage of goldfish.(1) With increase of the intensity of radiation, the inhibition of hatch rate and retardation of hatcing time remarkably observed.(2) The embryoes were deformed to some exent under the effect of γ-radiation over 1, 000 r.