We have designed and developed a small field of view gamma camera, the eZ SCOPE, based on use of a CdZnTe semiconductor. This device utilises proprietary signal processing technology and an interface to a computer-based imaging system. The purpose of this study was to evaluate the performance of the eZ scope in comparison with currently employed gamma camera technology. The detector is a single wafer of 5-mm-thick CdZnTe that is divided into a 16x16 array (256 pixels). The sensitive area of the detector is a square of dimension 3.2 cm. Two parallel-hole collimators are provided with the system and have a matching (256 hole) pattern to the CdZnTe detector array: a low-energy, high-resolution parallel-hole (LEHR) collimator fabricated of lead and a low-energy, high-sensitivity parallel-hole (LEHS) collimator fabricated of tungsten. Performance measurements and the data analysis were done according to the procedures of the NEMA standard. We also studied the long-term stability of the system with continuous use and variations in ambient temperature. Results were as follows. INTRINSIC ENERGY RESOLUTION: 8.6% FWHM at 141 keV.LINEARITY: There was excellent linearity between the observed photopeaks and the known gamma ray energies for the given isotopes. INTRINSIC SYSTEM UNIFORMITY: For the central field of view, the integral uniformity and the differential uniformity were, respectively, 1.6% and 1.3% with the LEHR collimator and 1.9% and 1.2% with the LEHS collimator. SYSTEM SPATIAL RESOLUTION: The FWHM measurements made at the surface of the collimator were 2.2 mm (LEHR) and 2.9 mm (LEHS).CONTRAST TEST: The average S/N ratios (i.e. counts in the irradiated pixel divided by counts in the surrounding pixels) for the inner ring pixels (8)/outer ring pixels (16) using the LEHS collimator and LEHR collimator were 3.2%/0.2% and 3.7%/0.3%, respectively. COUNT RATE CHARACTERISTICS: We could not determine the maximum count rate and the 20% loss count rate from these data because the plateau was not reached while using the solutions measured. SYSTEM SENSITIVITY: The average acquisitions were 11,052 cpm/MBq (LEHR) and 28,590 cpm/MBq (LEHS). TEMPERATURE DEPENDENCE: The system displayed minimum corresponding shift in cps with temperature changes in the measured temperature range. We designed and developed a semiconductor-based gamma camera using CdZnTe. The basic performance of this camera compares favourably with the existing gamma camera technology that is deployed in the medical field today. The most significant differences include the spatial resolution, sensitivity, high count rate characteristics and energy resolution. We believe that this device will be of value for a number of clinical applications including sentinel node detection and radiopharmaceutical-guided surgery.

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In order to acquire 3D data of high contrast objects such as bone, lung and vessels enhanced by contrast media for use of 3D image processing, we have developed a 3D CT-scanner using cone beam X-ray. A 3D CT-scanner consisted of a gantry and a patient couch. The gantry consisted of an X-ray tube designed for cone beam CT and a large area two-dimensional detector mounted on a single frame and rotated around an object in 12 seconds. The large area detector consisted of a fluorescent plate and a charge coupled device video camera. The size of detection area was 600mm x 450mm capable of covering total chest. While an X-ray tube was rotated around an object, pulsed X-ray was exposed 30 times a second and 360 projected images were collected in a 12 second scan. 256 x 256 x 256 matrix image (1.25 mm x 1.25 mm x 1.25mm voxel) was reconstructed by a high-speed reconstruction engine. Reconstruction time was approximately 6 minutes. Cylindrical water phantoms, anesthetized rabbits with or without contrast media, a Japanese macaque were scanned with the 3D CT-scanner. The results seemed promising because they showed high spatial resolution in three directions, though there existed several points to be improved. Possible improvements were discussed.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows an evaluation of seismic isolator design established in this project where several methods are newly developed. The major four accomplishments are as follows. One: establishment of design earthquake specially considered for seismically isolated nuclear power facilities. The design earthquakes are made to fit multiple target spectra with different damping factors considering a building, equipment and seismic isolators for more precise response analyses. Two: design and development of a high-performance seismic isolator. Against the large design earthquakes, a seismic isolator is newly developed which has a large diameter lead plug for more damping; the isolators were actually manufactured and tested. Three: seismic response analyses for seismically isolated nuclear power plants. Light water reactors are designed where the structural characteristics of the seismic isolation system is reflected. Four: evaluation of thermal effects on seismic isolators by a long-duration earthquake. Considering a long-duration earthquake, the heat generation phenomenon in the lead plug is analytically evaluated to ensure the lead plug’s damping performance. By introducing these accomplishments, the realistic design of a seismically isolated nuclear power plant is achieved.

Shinji KOSUGI, Tetsuo IMAOKA, Kenji KANAZAWA, Takafumi HIRAKI, Seiji NAGATA, Takashi NAKAYAMA, Kunihiko SATO, Masakazu JIMBO and Yoshito UMEKI Application of a seismic base-isolation system using lead rubber bearings (LRBs) has been developed for the purpose of enhancing the seismic safety of nuclear power plants (NPPs). To grasp the mechanical properties of the seismic isolator over the design limit, the break tests for a 1600-mm diameter LRB have been conducted using full-scale specimens in order to avoid the difficulties considering size effect. As a result, linearity limit state and break limit state of the full-scale LRBs were found to be well-evaluated as expected; i.e., the breaking shear strain under axial compression shall exceed the commercial reference value of 400%. Further, statistical models of linearity limit and break limit of LRBs are evaluated on the basis of the real-sized break tests. By using these statistical models of limit state of the LRBs, a residual risk for seismic base-isolated NPPs against earthquake events beyond design basis can be investigated more accurately.