The Perturbation Produced in the Neutron Spectrum of an Assembly by a Spectrometer

An equation is derived to estimate the perturbing effects on the neutron spectrum caused by a spectrometer inserted in an experimental assembly. This equation is applied to estimate the spectrum perturbation by a miniature NE-213 fast neutron spectrometer in a graphite assembly. The results show that the perturbation effect is smaller than the experimental errors and uncertainties, and that the effect caused by the neutron-sensitive volume is smaller than that caused by the surrounding materials.