Abstract
Gabor zone-plate (GZP) apertures have been developed for use in EG&G EM's mercuric iodide (HgI 2) gamma-ray camera. The purpose of such an aperture is to increase efficiency, while maintaining good resolution. The GZP is similar to the Fresnel zone plate (FZP) but it has continuous transitions between opaque and transparent regions. Because there are no sharp transitions in the transmission, the inherent interference noise in GZP imaging is lower than that in FZP imaging. GZP parameters were chosen by considering the effects of constraints such as detector pixel size, number of pixels, minimum field of view required, maximum angle of incidence tolerated, and the Nyquist criterion for the minimum sampling rate. As a result an aperture was designed and fabricated with eight zones and a diameter of 3 cm. Lead was chosen as the aperture medium due to its high attenuation coefficient. Experimental data were obtained from the camera with the above GZP aperture. The point spread function was determined and compared to the calculated response. Excellent agreement was obtained. The reconstruction process involves simulating, by computer, planar-wave illumination of a scaled transparency of the image and recording the intensity pattern at the focal plane.
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