High Resolution Neutron Spectrometers

HIGH RESOLUTION NEUTRON SPECTROMETERS
See also Ultra-High Resolution Gamma-Ray Sprectrometers

SELECTED PUBLICATIONS

Microcalorimeter Design for Fast Neutron Spectroscopy

Neutron Absorption Spectroscopy for Identification of Light Elements in Actinides

PROJECT SUMMARY
The following content has been extracted from NNSA Office of Nonproliferation Research and Engineering (NA-22) Radiation Detection Technologies Program R&D Portfolio 2003.

High energy resolution neutron spectroscopy is acheived with superconducting sensors operated at temperatures close to absolute zero (-460ºF) where noise due to thermal motion is greatly reduced. The sensor consists of a neutron absorbing crystal attached to a sensitive molybdenum–copper thermometer held at the transition between the superconducting and normal state where its resistance changes rapidly with temperature.

A fast neutron captured in a boron- or lithium-containing absorber will heat the molybdenum–copper sensor in proportion to the neutron energy plus the energy released in the capture reaction. The precision of this measurement can be as high as 1 part in 1,000, one to two orders of magnitude better than with semiconductor or gas-based detectors, and with an instrument more compact than large, conventional time-of-flight spectrometers. High-resolution neutron spectroscopy can determine the composition of nuclear materials, particularly the presence of light elements, even through thick layers of shielding.

Simulations of neutron spectra from plutonium oxide show fine structure at energies corresponding to nuclear resonances in oxygen. The inset shows a high-resolution spectrum from a thermal neutron source using a superconducting spectrometer with a titanium diboride absorber.

HIGH RESOLUTION NEUTRON SPECTROMETERS
See also Ultra-High Resolution Gamma-Ray Sprectrometers

SELECTED PUBLICATIONS

Microcalorimeter Design for Fast Neutron Spectroscopy

Neutron Absorption Spectroscopy for Identification of Light Elements in Actinides

PROJECT SUMMARY
The following content has been extracted from NNSA Office of Nonproliferation Research and Engineering (NA-22) Radiation Detection Technologies Program R&D Portfolio 2003.

High energy resolution neutron spectroscopy is acheived with superconducting sensors operated at temperatures close to absolute zero (-460ºF) where noise due to thermal motion is greatly reduced. The sensor consists of a neutron absorbing crystal attached to a sensitive molybdenum–copper thermometer held at the transition between the superconducting and normal state where its resistance changes rapidly with temperature.

A fast neutron captured in a boron- or lithium-containing absorber will heat the molybdenum–copper sensor in proportion to the neutron energy plus the energy released in the capture reaction. The precision of this measurement can be as high as 1 part in 1,000, one to two orders of magnitude better than with semiconductor or gas-based detectors, and with an instrument more compact than large, conventional time-of-flight spectrometers. High-resolution neutron spectroscopy can determine the composition of nuclear materials, particularly the presence of light elements, even through thick layers of shielding.