<title>Optimization of air gap for two-dimensional imaging system using synchrotron radiation</title>

Abstract

Since synchrotron radiation (SR) has several excellent properties such as high brilliance, broad continuous energy spectrum and small divergence, we can obtain x-ray images with high contrast and high spatial resolution by using of SR. In two-dimensional (2D) imaging using SR, air gap method is very effective to reduce the scatter contamination. However, to use air gap method, the geometrical effect of finite source size of SR must be considered because spatial resolution of image is degraded by air gap. For 2D x-ray imaging with SR, x-ray mammography was chosen to examine the effect of air gap method.We theoretically discussed the optimization of air gap distance using effective scatter point source (ESPS) model proposed by Muntz, and executed experiment with a newly manufactured monochromator with asymmetrical reflection and an imaging plate.The experiment using SR x-ray source was carried out at the bending-magnet beam line of the Tristan accumulation ring. The size of observation field was 6.4 X 6.2 cm2 and x-ray energy was set 18 keV. Air gap effect obtained by the experiment showed good agreement with that estimated from ESPS model. In the air gap distance of 100 cm, image contrast was improved 32 % compared with that of 0 cm, and the geometrical effect of SR source size was not observed. Air gap method is thought to be very effective to improve image contrast in 2D x-ray imaging with SR.