Neutron Distribution Measurement by the Self-Activation of a CsI Plate with CCD Camera Using a Decaying Self-Activation Imaging Technique

Abstract

Neutron intensity distribution on a CsI scintillator plate has been observed by a CCD camera and analyzed by using a "decaying self-activation imaging technique". The decaying self-activation imaging, which has been proposed recently by our group, is based on the analysis of time variation of specific radio-activities generated and remained inside the CsI plate after the termination of neutron irradiation. The luminance distributions of a CsI plate are recorded every one minute as a series of images by a cooling type CCD camera with a telescope lens in a black box. Then the time variations of luminance (mean pixel values) of the images are fitted on a "pixel-by-pixel basis" with a multi-exponential function. By this, two components of 128 I (half life : 25 min) and 134m Cs (half life : 174 min) are extracted as the fitting curves. The initial luminance values of individual component of radioactivity, which correspond to the values at the termination of neutron irradiation, are plotted as separate images. A conversion factor between the generated activity in a CsI plate and the observed luminance value is evaluated as "light yield".