Satoru Kawasaki

Radioactivity measurement of drum package waste by a computed-tomography technique

Abstract A method of evaluating the radionuclide content of low-level drum package waste using emission computed tomography (ECT) and transmission computed tomography (TCT) has been investigated. This method requires accurate correction for the γ-ray attenuation in the drum. The TCT and ECT analyses are performed according to the constrained least-squares technique. Satisfactory results were obtained in preliminary experiments carried out using test equipment with 20 NaI(Tl) scintillation detectors and sample 200-L drums which contained sealed γ-ray point sources of 60 Co and 137 Cs, and pipes and concrete blocks. The radioactive content of one or two 60 Co sources (about 3.5 MBq) in a drum of about 200 kg was evaluated in 6 × 6 × 9 voxel with an uncertainty of about ±15% for an ECT measurement time of about 12.5 min.

Response of silicon detector for high energy X-ray computed tomography

The suitability of an Si-SSD as a detector for high energy X-ray CT has been investigated. Two types of Si-SSDs which can take the place of ordinary scintillation detectors were proposed. Their predicted responses were compared with that of a CWO scintillation detector of almost the same dimensions by using the EGS4 Monte Carlo simulation code. The sensitivities of the sole-silicon detector and the metal-sandwiched detector were about ten times higher than that of the CWO scintillation detector at X-ray energies above 1 MeV. The metal-sandwiched detector was judged more useful than the sole Si-SSD when the width of the X-ray beam was less than about 0.2 mm. The silicon detector for high energy X-ray CT was fabricated and actual measurements of the depletion layer width and the electronic noise contribution were made. >

Characteristics of a silicon detector for industrial X-ray computed tomography

Abstract We have evaluated a silicon solid state detector (Si-SSD) as a detector for Industrial X-ray Computed Tomography (IXCT) from the viewpoints of sensitivity and radiation damage. The detector which we used in this work, is a diffused junction type Si-SSD (43 × 3.8 × 0.5 mm) fabricated on high purity n-type silicon. We measured pulse height distributions for narrow pencil beam 60 Co gamma rays parallelly incident to the detector. The expected deposit energy was 0.146 ± 0.001 MeV (11.7% of the incident photon energy). The calculated pulse height distribution using the general purpose EGS4 code was confirmed to be in good agreement with the measured one. The radiation damage was evaluated using the 60 Co gamma ray source. Exposure of up to 88 kGy(Si) was achieved over a period of 20 hours, with an exposure rate of 4.4 kGy(Si)/h (36 mC/kg s). It was confirmed that the Si-SSDs could be used at least up to 88 kGy(Si) with X-rays equivalent to 60 Co gamma rays.

A Measurement Technique for Trace Radioactivity Distributions in the Human Body by Using Gamma-Ray Spectra

A new technique is described to increase spatial resolution in the distribution measurement on amount of trace radioactivity in the human body by the response function method. The distribution is obtained by analysing the difference in gamma-ray spectra measured around the body, which contains information for not only unscattered gamma-rays, but also scattered ones within the body. Basic experiments involving the measurement of two-dimensional radioactivity distribution in a homogeneous acrylate block (40cmW × 20cmH × 50cmL) containing two 137Cs point sources (0.8 and 1.0 ¿Ci) were made using gamma-ray counts measured by twenty 2¿ ¿ × 2¿ NaI (Tl) scintillators arranged on a circle, and the response function calculated by the Monte Carlo technique. The distribution on a 10 × 5 mesh division was successfully analysed with a relative error of less than ± 20% for a measuring time of 10 min. The mesh size was 4cm × 4cm, which was about one-half that possible when analysing only unscattered rays.