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Report No.

Design and performance of newly manufactured pinhole collimator of high-resolution gamma camera for imaging radiocesium

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

We developed a gamma camera specifically for use in plant nutrition research. The collimator of the gamma camera was designed for imaging high-energy $$gamma$$ photons from $$^{137}$$Cs. However, the prototype pinhole collimator causes small artifacts in the acquired images; moreover, the imaging time is quite long with the use of this collimator. To improve the image quality and to increase the sensitivity of the gamma camera, we designed new collimators made of tungsten, which has one of the highest attenuation coefficients for imaging 662 keV $$gamma$$ photons. These collimators are manufactured using wire-cut electrical discharge machining. One collimator is similar to a collimator that undergoes edge treatment, and the other has a smaller acceptance angle (13$$^{circ}$$) than the collimator currently in use. We will use the latter collimator to make a clustered multi-pinhole collimator. Experiments for evaluating the collimators installed in the gamma camera were performed with point sources of $$^{137}$$Cs. The images obtained indicated an improvement in the FWHM to 7.5% with the new single-hole collimator; a slight cancelation of image artifacts was also observed. The latter pinhole collimator maintains the image quality and sensitivity despite the smaller acceptance angle.



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