Eiichi Hiraoka

Discharge Figures in Dielectrics by Electron Irradiation

The electrical breakage of glass shielding windows by intense gamma irradiation presents a severe problem for hot caves. To understand this phenomenon the authors studied the discharge conditions, their natures, and the decay of the accumulated electric charge by electron irradiation. The samples used were lead glass F62‐R, nonbrowning lead glass F36‐N, nonbrowning glass C‐N, common window glass, polymethylmethacrylate (PMMA) and polyvinylchloride (PVC). Their specific gravities were 6.2, 3.6, 2.7, 2.5, 1.2, and 1.4 respectively. The samples were discharged by a steel needle pricking the surface prior to, or after, irradiation. The 2‐MeV Van de Graaff generator and 15‐MeV Linac were used in these experiments. The relation between irradiation doses and the largeness of discharge pattern in the samples and the decay of the discharge pattern after irradiation are described. The times in which the initial stored charge became its half‐value were 30 min for PMMA, 70 h for PVC, 8 h for C‐N and 90 h for F36‐N.

Depth profiling of tritium in solids with the nuclear reaction induced by deuteron bombardment

A method for the measurement of depth profiles of tritium in solids has been developed in which the 3H(d,n)4He reaction is used. This method is nondestructive with relatively high depth resolution in the surface region of the solids. The validity of the present method has been supported by the examination of the depth profile measured for a tritium target as is used for a neutron source.

Statistical Properties of Real-Time Neutron Radiographic Image

Actually statistical quality of raw images produced by neutron radiography is very poor. We analysed the statistical properties of neutron images obtained from the cyclotron-based real-time neutron radiography system of Sumitomo Heavy Industries, Ltd., which uses a set of LiF/ZnS(Ag) screen and high sensitive TV camera.

Intercomparison of Neutron Radiography Indicators Using Kur

ASTM and EURATON standard indicators have been used in order to determine image quality in thermal neutron radiographic testing, however it is thought that they have been some limitations for current application of precise measurements.

Application of Cyclotron-Based Real-Time Neutron Radiography System for Some Industrial Components

Reliable facility of cyclotron-based real-time neutron radiography system has been developed and applied to some industrial components. The equipment for neutron fluoroscopy is based on a sub-compact cyclotron and a LiF/ZnS(Ag) fluorescent screen viewed by a silicon intensifier target TV camera. The real-time image is monitored on a CRT, recorded with a standard video recorder and processed by a digital image processor.

Neutron Radiography Application to Ancient Arts

Neutron radiography testing (NRT) has been applied to several ancient relics at Kyoto University Research Reactor and the cyclotron-based facility of Sumitomo Heavy Industries, Ltd. Some of the results are presented with comments on the usage and applicability of NRT. The objects studied are an excavated bronze mirror with four bells (late 5c.A.D. to early 6c.A.D.), an unearthed corroded bronze mirror with cloth (4c.A.D.), unearthed Buddhist sutras in a bronze case (10c.A.D.), a Tibetan unglazed Buddhist statue cushioned with cloth in a copper box with a window and an excavated iron sword conserved and restored (4–5c.A.D.). From comparisons with X-ray radiography testing, it has been found that NRT can well identify the stones located inside the bells and suggest the casting procedure. Moreover, NRT has been found to be remarkably effective for elucidating unobserved organic objects in bronze fine arts.

Neutron Radiography Using Ultra-Compact Cyclotron

Neutron radiography test was performed with ultracompact cyclotron named “BABY CYCLOTRON” which produces 16MeV proton. 9Be(p,n)9B reaction was applied for neutron soruce. The collimation system has two collimators arranged horizontally, each having cross section 14in. × 17in., L/D ratio : 52, and thermal neutron flux of 3 × 105n/cm2·s was applied at the object. Radiographic image qualities measured with ASTM indicator have shown very useful results and JSW carried out inspection of exprosive devices for NASDA.

Cyclotron-Based Neutron Radiography Facility

Neutron radiography is not widely used yet due to lack of high intense thermal neutron source convenient and economical for practical use, A new neutron radiography facility, installing a sub-compact cyclotron accelerating 18 MeV proton and equipped with both vertical and horizontal ports, is presented.

Cyclotron-based Real-Time Neutron Radiography System

A real-time neutron radiography system was installed by using a sub-compact cyclotron as a neutron generator. We utilized the neutron radiography facilities of Sumitomg Heavy Industries, Ltd. in which nominal neutron flux is 1.1 × 106 n/cm2 /sec at L/D = 30 with field size of 14″ × 17″.

The Gamma-Ray Dose-rate Effect in the Sprout Inhibitionof Potato Tubers

The gamma-ray dose and dose-rate effects and the loss of weight in the sprout inhibition of potato tubers were studied. The potato tubers used for this experiments were “Danshaku” variety which were yielded in October in Hokkaido.The irradiation was carried out in the dose-rate range from 5 × 102 R/h to 5 × 105 R/h changing the dose from 3 kR to 15 KR in December of 1975 and 1976. 60Co-source used for those irradiation were 7300 Ci and 13000 Ci of a rod type one (1.4 cm ∅ × 30 cm), respectively. The irradiated potato tubers were stored for 5 to 7 months in dark natural condition, and their sprouting and their weight variation were observed.The obtained results are summarized as follows:1) The time of sprouting of the irradiated potato tubers is delayed compared to that of non-irradiated ones (control). The more the dose and the higher the dose-rate, the delayed time becomes larger. The potatoe tubers irradiated to 6 kR under 5 × 104 R/h are late about 60 days in sprouting from non-irradiated ones (Fig. 1).2) The sprout inhibition is more effective not only by heavier irradiation dose, but also by irradiation under higher exposurerate (Fig. 2 and Fig. 3).3) The necessary and sufficient dose for the sprout inhibition is estimated to be about 10.5 kR for exposure-rate of 5 × 103 R/h, and it increases rapidly for the lower exposure-rate, while it decreases with the rate of about 2 kR per one order of magnitude of exposure-rate for the higher exposure-rate (Fig. 4).4) The rate of weight loss of irradiated potato tubers is small compared to that of non-irradiated ones, and ones more irradiatedshow less rate of weight loss (Fig. 5 and Fig. 6). The exposure-rate dependence in weight loss is not apparent (Fig. 7).