It is necessary to know the incident direction of gamma rays to search for the position of radioactive materials or contamination remotely. In order to meet this demand, a new gamma ray detector, which positively raises directional sensitivity against incoming gamma rays, has been developed. This detector is composed of three kinds of different scintillators and a photomultiplier tube. The types of scintillators are NaI (Tl), CsI (Tl), and BGO. The section shape of each scintillator is sectorial of 120 degrees. The one cylindrical scintillator is made by optically connecting three sectorial scintillators. Gamma rays penetrate along a straight path through each scintillator of the detector, and the length of each path is dependent on the incident direction. Therefore the probability of photoelectric effect in each scintillator is changed, according to an incident direction of gamma rays. As a result, the gamma ray counts of three peaks observed in a spectrum obtained by a multi-channel analyzer have dependency with the direction. The response curve of each scintillator with respect to a peak count and an incident direction was made by experiments using a gamma ray source of ¹³⁷Cs. It has been recognized that these response curves have sensitivity in the total range from 0 to 360 degrees. Therefore the proposed detector has the possibility that the direction can be identified.

A non-linear thickness measurement model, which is based on a gamma-ray transmission technique and applied for a gamma-ray thickness gauge, has been proposed. Its performance has been evaluated by experiments using a real ¹³⁷Cs thickness gauge installed at heavy plate mills in the steel industry and the calculated results with the proposed model have agreed well with the experimental values.

This paper describes an X-ray radioscopy system which has been developed for on-line welding inspection of large diameter steel tubes incorporating X-ray image integration technique as well as simultaneous control method for X-ray tube voltage and current. The simultaneous control of X-ray voltage and current features regulation of X-ray intensity which has permeated through steel tubes of varying wall thickness. This system censures stable statistical error range which leads to clear image. Also an X-ray image integrating technique which places emphasis on the contrast of defects against background has been developed. These technologies feature stable integration process under tubes' fluctuating traveling speed in a mill. By utilizing the proposed methods, those images involving defects are integrated 20 to 30 times to reduce statistical errors and processed into clear and high contrast images. Our on-line and off-line tests show penetrameter sensitivity within 1.0 to 1.4% at the welding thickness ranging from 10 to 40mm. This X-ray radioscopy has been in operation at a large diameter steel tube mill and has contributed to improved quality control of the tube products.

A distance measurement method to make use of Compton scattering of gamma-ray was proposed. This method treated two cases. Concretely, the case that density of a measured object was constant and the case that the density was changed were examined.<BR>A source and a detector are set up at the same side of the object. When density is not varied, the amount of scattered gamma-ray is not depending on a distance. However, the number of gamma-rays detected becomes a function of distance. The function is in proportion to the solid angle to the detector from the efficient center of a scattering region. On the other hand, in the case that density is changed, the number of scattered gamma-rays is altered by density. Hence the number becomes a function of distance and density. Dual detectors are located at different positions and we make two equations on relation of detected gamma-rays, distance and density. Here if the count of gamma-rays detected is given, both distance and density can be calculated.<BR>By using computer simulations and experiments, a performance of the method was evaluated. As a result, the precision of the distance measurement was ±3% within a range of 10-100 cm in constant density. In the case that the density is changed with a range 1.707-1.885 g/cm³, the accuracy of this method was ±1 mm within a range of 8-10 cm.