Accurate determination of thermal neutron flux via cryogenic calorimetry

Absolute determination of thermal neutron flux is an important capability for several applications including neutron dosimetry, analytical chemistry, oil recovery, nuclear waste clean-up, and the determination of the neutron lifetime. Few methods exist that are calibrated to better than similar to 0.5% accuracy. As a corollary to this statement, it is also true that few thermal neutron absorption cross sections are known to better than similar to 0.5% accuracy. Several groups, including one at the National Institute of Standards and Technology (NIST) have worked for many years to develop methods for pushing the accuracy below the 0.1% level. This paper describes a calorimetric technique which avoids many of the problems associated with absolute counting methods. A description of the calorimetric method and results of system tests will be presented.