High Resolution Neutron Resonance Absorption Imaging at a Pulsed Neutron Beamline

Abstract

The existence of resonance peaks in neutron absorption spectra in the epithermal range of energies enables unique non-destructive testing techniques. The deep penetration of epithermal neutrons provides an opportunity to perform a compositional analysis of a sample which is opaque to X-rays and thermal neutrons. The neutron resonances in the transmission spectra constitute a characteristic pattern for many isotopes, which can be used to identify the isotope and to map the distribution of the isotope in a sample. The neutron transmission spectra can be measured with the time of flight (TOF) technique using a pulsed neutron source. Combining this method with a high resolution neutron counting detector enables substantial improvements of spatial resolution of neutron resonance transmission imaging. Such a detector has been developed to register neutrons with 55 μm spatial and 10-1000 ns temporal resolution Our proof-of-principle experiments at the ISIS pulsed neutron spallation source demonstrate that compositional analysis of multi-element samples can now be performed with ~150 μm spatial resolution. Images of a test mask consisting of <; 200 μm thick foils of Au, Ag, In and Gd were collected in the 1-100 eV energy range. The experimental results demonstrate the potential for compositional analysis via resonance absorption transmission with high spatial resolution. In-bulk temperature measurement through Doppler broadening analysis will also benefit from this technique.