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 the 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 J.UIl 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 J.UIl spatial resolution. Images of a test mask consisting of <200 J.UIl 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.

Time-of-Flight Three Dimensional Neutron Diffraction in Transmission Mode for Mapping Crystal Grain Structures

“…The detector employs a microchannel plate (MCP) with an active area of 28×28 mm 2 , corresponding to 512×512 pixels, each with 55 µm size. The detector, suited for count rates of > 10 MHz in ToF mode, and up to GHz in counting mode, provides approximately 100 µm intrinsic spatial resolution, paired with < 1µs time resolution, which makes it well suited for a wide range of neutron ToF imaging applications [37,39,40]. The transmission data were recorded using the Pixelman software package [43].…”

Energy resolved neutron radiography at LANSCE pulsed neutron facility

“…However, variation of attenuation with neutron energy is not monotonic for most materials, which can be utilized for quantitative studies of various sample characteristics if the measurement is energy dispersive. Therefore an extension of conventional neutron radiography into energy resolved radiography provides a number of very attractive novel opportunities [4][5][6][7][8]. In these experiments the sample transmission is measured as a function of neutron energy and thus in each pixel of the image not only the integrated intensity is measured, but also the sample transmission spectra.…”

“…The combination of neutron energy resolved imaging with other experimental techniques available at LANSCE, namely conventional neutron diffraction and proton radiography as well as the capability to handle special materials, enables unique characterization capabilities at this facility. Recent development of high resolution neutron counting detectors capable of sub-100 μm and sub-100 ns (epithermal) and sub-1 μs (thermal) neutron imaging proved to provide some unique opportunities for energy resolved imaging at a pulsed neutron beamline [6,7]. Some experiments conducted at Flight Path 5 at LANSCE described in this paper demonstrate some unique opportunities of energy resolved imaging at a short-pulsed neutron source for materials and energy research, engineering and many other fi elds.…”

Boron-Based Neutron Scintillator Screens for Neutron Imaging

“…These resonances can be exploited using pulsed neutrons and time-of-flight techniques to determine the isotopic composition of a material [ 56 ]. Neutron scintillator screens with an improved detection efficiency for epithermal neutrons could also be useful in resonance imaging techniques [ 57 , 58 , 59 ].…”