EFFECT OF BEAM SPECTRUM ON QUANTITATIVENE SS OF COLD NEUTRON COMPUTED-TOMOGRAPHY

In case of radiography by a cold neutron beam having a continuous beam spectrum, neutron attenuation coefficients of many materials decrease with increasing the transmitting path length. As a result, quantitati ve analyses, such as determining the composition and density of the ob ject quantitatively, with cold neutron computed tomography (CN-CT) has been difficult. In order to improve quantitativeness of CN-CT, we exa mined two procedures for reducing the effect of the thickness-dependen t attenuation coefficient, and confirmed their effectiveness experimen tally. One procedure is modifying projected images by using the neutro n transmission curve as a kind of calibration curve, which is called t he inverse function method. Another, the spectrum-narrowing method, is depressing change of the attenuation coefficient by making the width of the neutron beam spectrum narrower with a neutron filter. Each proc edure was demonstrated experimentally to enable quantitative CN-CT. Th e inverse function method is simple, but it emphasizes noises of the p rojected image in, especially, the low neutron transmittance region. T he spectrum-narrowing method has an advantage of obtaining the simple exponential attenuation property on neutron radiograph, though the lon ger exposure time was required because of beam intensity loss.