Radiographic noise is mainly composed of X-ray photographic grain noise, fluorescent screen noise called structure mottle and quantum noise called quantum mottle. They consist of inhomogeneously distributed pattern of the grain. In order to analyze the statistical properties of radiographic noise, the random-dot model which is commonly used for photographic grain noise is extended. The extended random-dot model is composed of inhomogeneously distributed pattern of the model grain. Rigorous expressions of the mean transmittance and autocorrelation function of transmittance of the model pattern are obtained theoretically. For a simple inhomogeneous distribution of the grain number, useful approximate expressions of the mean transmittance and autocorrelation function of the model pattern are obtained. Showing numerical examples, theoretical results of the extended random-dot model are compared with experimental results in a practical fluorescent screenfilm system.
An effective method for measuring water velocity in an aerated zone has been developed by means of fast neutron transmission. Velocity υ, can be determined from the derived equation υ=a•(tan φ)/(No-N1), where a is the detection width of transmitted fast neutron, tan φ is decrement of the detected counting rate, and No and N1 are counting rates before and after infiltration in the soil layer, respectively. When 252Cf (273 μCi) is used for the fast neutron source and NE-213 liquid scintillator (2“φ×2”l) is used for the detector in the experiment, the result obtained indicates that this method gives an accuracy within 10% error for a column diameter of 3_??_40cm at an arbitrary depth. In addition the method is found to be more sensitive for a large diameter column than for a small one.