Development of a scattering probability method for accurate vapor fractionmeasurements by neutron radiography

Recent test results indicated drawbacks associated with the simple exponent ial attenuation method (SEAM) as currently applied to neutron radiography m easurements to determine vapor fractions in a hydrogenous two-phase flow in a metallic conduit. The scattering component of the neutron beam intensity exiting the flow system is not adequately accounted for by SEAM, and this leads to inaccurate results. To properly account for the scattering effect. a neutron scattering probability method (SPM) is developed. The method app lies a neutron-hydrogen scattering kernel to scattered thermal neutrons tha t leave the incident beam in narrow conduits but eventually show up elsewhe re in the measurements. The SPM has been tested with known vapor (void) dis tributions within an acrylic disk and a water/vapor channel. The vapor (voi d) fractions deduced by SPM are in good agreement with the known exact valu es. Details of the scattering correction method and the test results are di scussed. 1999 Published by Elsevier Science B.V.