A Line Pair Indicator Made of Gd Film for Evaluating Spatial Resolution

Abstract

A device for evaluating the spatial resolution of a neutron imaging system was developed. Using laser processes, line- pair patterns were fabricated on a 0.005-mm-thick Gd film evaporated on a glass plate. Large line pairs of widths ranging from 0.2 to 2 mm were machined using an Nd:YVO 4 laser (0.03 mm spot size) and displayed on a brightness field, while small line pairs of widths ranging from 0.01 to 0.1 mm were created using an eximer laser on a dark field. A scanning electron microscope (SEM) observation determined that, although the large line pairs machined using the Nd:YVO 4 laser were chipped on the corners of the Gd bars, the difference between the measured and designed line- pair widths was controlled absolutely within 0.02 mm. In the small line pairs of less than 0.1 mm width processed using the eximer laser, edges sharper than those of the large line pairs were formed. In neutron imaging tests using a LiF/ZnS(Ag) scintillator and a CCD camera system, good contrast images were obtained with the brightness field, even at 0.005 mm thickness. The small line pairs on the dark field were observed using a LiF single crystal detector having an ultra-high spatial resolution of approximately 0.005 mm. Splits in the small line pairs of as little as 0.01 mm wide were shown with good contrast on the images.