Measurement of Thermal Neutron Beam DensitiesnI:Precision Measurement Using a Helium-3 Proportional Counter II:Corrections to the Gold Foil Activation Method for Determining Neutron Beam Density

摘要

A new method, based on the He (n, p)T reaction, has been developed for the accurate determination of thermal neutron beam densities. Several comparisons were made with the conventional Au-foil activation method, and agreement was obtained between the two methods within an experimental un¬certainty of + 0.4%.nFundamental advantages of the method include the 1/v dependence of the He3(n, p)T cross section up to 1 keV, and the assurance of homogeneity even for very small macroscopic cross sections, because of the gaseous de¬tector material. Although the method requires a relatively clean neutron beam, it can be used over a wide range of neutron densities and, in partic¬ular, is capable of measuring extremely weak beams. A detector has been constructed with a well-defined efficiency and which is able to accept beams of diameters up to 10 cm.