(A) portable nuclear imaging system with estimation capability of exposure dose rate

Abstract

The conventional nuclear imaging system, which has widely been used in non-destructive testing, examination of nuclear contamination, disposal of nuclear fuel, transportation, and storage of high-level radioactive waste, provides the directional information of radiation sources such as the location or the distribution as an image of the radioactivity superimposed on a vision image of the same field of view. It is also possible to provide the radiation energy information in real time and distinguish two sources having different energies. But there are some issues to be considered to improve the system performance; (1) A special pinhole collimator is necessary for its application in the high-energy gamma-ray field. The conventional knife-edge pinhole collimator is not suitable for high-energy radiation field because much radiation scatters in the vicinity of the pinhole aperture and blurs the image. (2) In order to estimate the interaction position of gamma rays within the radiation detector, Anger algorithm is usually used in the nuclear imaging system. This method can be easily implemented and works well a medical gamma camera based on multi-PMT (a 2-D array of photomultiplier tubes). But Anger algorithm is not suitable for a nuclear imaging system using a single PSPMT (position sensitive PMT) because its output signals are not linear and are not uniform. (3) In addition to nuclear image, if the value of real-time exposure dose rate is supplied in the nuclear imaging system, it will be much useful. But the conventional system cannot measure the real-time exposure dose rate when obtaining the gamma image. For the optimum aperture design, a new-channeled collimator was introduced to reduce the image degradation by the scattering radiation, and its characteristics were analyzed by Monte Carlo simulation. Resolutions defined as the full-width at half-maximum (FWHM) of point spread functions and efficiency are calculated for collimators with several pinhole diam...