University of New Mexico Researchers Develop Method to Analyze Post-detonation Debris in the Field without the Need for Chemical Separation

Problem: Improving the speed and precision with which nuclear forensic samples can be characterized is important to enable response in near real-time. Related to this capability is the means to characterize materials in the field without losing time to the need to send samples back to a central laboratory. DTRA has funded basic research on microcalorimeters to identify higher energy resolution devices and evaluate their performance.

Schematic of the magnetic geometry employed in the novel UNM microcalorimeter.

Results: Professor Stephen Boyd of the University of New Mexico has developed a novel concept for microcalorimeter design. Unlike conventional calorimeters that measure heat during a phase change, Boyd’s design records a change in magnetic field; that is, Boyd’s devices measure a change in signal transduction due to the conversion of deposited energy into a magnetic dipole reorientation. The demonstrated high resolution and high signal-to-noise mean that larger absorber sizes can be used in multiplexed arrays. The magnetic geometry developed by this project was used by another group to achieve world record energy resolution for magnetic microcalorimeters of 2 eV @ 6 keV.

Potential: For nuclear forensics, this improved energy resolution will increase the ability to determine the radioactive composition of forensic samples containing isotopes with closely-spaced spectral lines and/or unknown radioactive constituents through simple region-of-interest sampling of the detected spectrum. This research has the potential to allow for multiple tests with a single sample of post-detonation debris without the need for chemical separation. Because samples do not need to be sent back to a lab for chemical separation, characterization of nuclear forensic samples in the field may be achievable using these microcalorimeter devices.

Transition/Impact: This project transitioned to DOE NNSA NA-22 under a new applied research project for detector characterization via a BAA. Under the NNSA program, progress is being made on the design, development, and initial reflectivity-map testing of a new optical pulser intended for the precise determination of the energy calibration of microcalorimeter pixels and pixel arrays.