Duc Vo

Large-Area Microcalorimeter Detectors for Ultra-High-Resolution X-Ray and Gamma-Ray Spectroscopy

We discuss recent developments in using cryogenic microcalorimeter detectors for x- and gamma-ray spectroscopy. We are currently operating a detector array consisting of thirteen pixels with time-domain multiplexed readout. With a single pixel from this detector, we have measured 97.43-keV gamma rays from 153-Gd with 22-eV resolution (FWHM). We have also made the first multiplexed array measurements of plutonium x- and gamma-rays with 45-eV resolution. We are currently testing a 66-pixel next-generation detector chip. Preliminary measurements with the new detector indicate improved energy linearity and single-pixel energy resolution of 50-100 eV at 100 keV. We present preliminary calibration data from this chip, and a high-statistics multiplexed 21-pixel spectrum of the Pu x-ray region between 90 and 130 keV.

Determination of Plutonium Isotopic Content by Microcalorimeter Gamma-Ray Spectroscopy

Microcalorimeter detectors provide unprecedented energy resolution for gamma-ray spectroscopy. One application is measuring the isotopic composition of plutonium-bearing samples by non-destructive gamma-ray spectroscopy to support nuclear safeguards and nonproliferation efforts. When measured with conventional high-purity germanium (HPGe) detectors, data from these samples contain significant peak overlaps requiring spectral deconvolution for analysis. The improved energy resolution of the microcalorimeter detector reduces peak overlaps leading to improvement in the statistical error component of the total measurement uncertainty. In this paper, we describe analysis code that was developed for spectral peak fitting and isotopic content determination from microcalorimeter and HPGe data. We apply the code to data collected from several plutonium standards to quantify the improvement of the statistical error derived from the improved energy resolution.

Application of GEANT4 to the Simulation of High Energy-Resolution Microcalorimeter Detectors

GEANT4 is a versatile Monte Carlo code for simulating the interactions of radiation with matter. GEANT4 has proven to be an effective toolkit for the simulation of a wide variety of detectors. We are interested in the application of GEANT4 to a new type of sensor technology being developed for X-ray and gamma-ray measurements. Microcalorimeter detectors based on transition-edge sensors coupled to bulk absorbers are an emerging technology for hard X-ray and soft gamma-ray measurements with unprecedented energy resolution. In this work, we assess the ability of the GEANT4 electromagnetic physics package to reproduce measured microcalorimeter data. We also use the simulations to explore the design space of absorber materials and cryostat design.

Microcalorimeter Nuclear Spectrometers

We present results from the initial testing of arrays of cryogenic microcalorimeter gamma-ray detectors. The successful fabrication and multiplexed operation of these arrays allow us to make pixel-to-pixel performance comparisons. The relationship between operating conditions and array performance is investigated. Advanced refrigerators for these detectors work without liquid cryogens, achieve temperatures below 100 mK, and operate continuously for many days.

AFCI Safeguards Enhancement Study: Technology Development Roadmap

The Advanced Fuel Cycle Initiative (AFCI) Safeguards Campaign aims to develop safeguards technologies and processes that will significantly reduce the risk of proliferation in the U.S. nuclear fuel cycle of tomorrow. The Safeguards Enhancement Study was chartered with identifying promising research and development (R&D) directions over timescales both near-term and long-term, and under safeguards oversight both domestic and international. This technology development roadmap documents recognized gaps and needs in the safeguarding of nuclear fuel cycles, and outlines corresponding performance targets for each of those needs. Drawing on the collective expertise of technologists and user-representatives, a list of over 30 technologies that have the potential to meet those needs was developed, along with brief summaries of each candidate technology. Each summary describes the potential impact of that technology, key research questions to be addressed, and prospective development milestones that could lead to a definitive viability or performance assessment. Important programmatic linkages between U.S. agencies and offices are also described, reflecting the emergence of several safeguards R&D programs in the U.S. and the reinvigoration of nuclear fuel cycles across the globe.

APPROACHING CRYOGENIC GE PERFORMANCE WITH PELTIER COOLED CDTE

A new class of hand-held, portable spectrometers based on large area (1cm2) CdTe detectors of thickness up to 3mm has been demonstrated to produce energy resolution of between 0.3 and 0.5% FWHM at 662 keV. The system uses a charge loss correction circuit for improved efficiency, and detector temperature stabilization to ensure consistent operation of the detector during field measurements over a wide range of ambient temperature. The system can operate continuously for up to 8hrs on rechargeable batteries. The signal output from the charge loss corrector is compatible with most analog and digital spectroscopy amplifiers and multi channel analyzers. Using a detector measuring 11.2 by 9.1 by 2.13 mm3, we have recently been able to obtain the first wide-range plutonium gamma-ray isotopic analysis with other than a cryogenically cooled germanium spectrometer. The CdTe spectrometer is capable of measuring small plutonium reference samples in about one hour, covering the range from low to high burnup. The isotopic analysis software used to obtain these results was FRAM Version 4 from LANL. The new spectrometer is expected to be useful for low-grade assay, as well as for some in-situ plutonium gamma-ray isotopics in lieu of cryogenically cooled Ge.

A First Application of the FRAM Isotopic Analysis Code to High-Resolution Microcalorimetry Gamma-Ray Spectra

Gamma-ray spectrometry systems based on High-Purity Germanium (HPGe) have been the long-standing leader in terms of resolution since their introduction many years ago. The application of this technology to the spectroscopic assay of special nuclear material led to the development of several isotopic analysis tools, including the advanced software package FRAM, which was, and continues to be, developed at Los Alamos National Laboratory. Although FRAM can be applied over a wide range of energies, the significantly higher intensity of the x-ray region in the neighborhood of 100 keV makes analysis of this area of the spectrum advantageous, especially in the case of plutonium. However, even with HPGe, the multitude of gamma-ray and x-ray peaks that exist in the 100-keV region are sufficiently convoluted so as to preclude determination of plutonium isotopic composition without the introduction of some error. The novel technology of cryogenic microcalorimeter detectors, shown to have an order of magnitude better spectral resolution than HPGe, has recently opened new doors with respect to these difficulties. Now, for the first time, the powerful capabilities of FRAM have been paired with the unparalleled resolution of microcalorimetry in the analysis of plutonium spectra. Preliminary results of these analyses, as well as an outlook for future measurements, heretofore unobtainable with HPGe, will be presented.

Improved Isotopic Analysis With a Large Array of Gamma-Ray Microcalorimeters

We present results from the largest array of gamma-ray microcalorimeters operated to date. The microcalorimeters consist of Mo/Cu transition-edge sensors with attached Sn absorbers. The detector array contains 66 pixels each with an active area 2.25 mm2. Out of 66 pixels, 55 are active, and 31 were used to acquire a high statistics Pu gamma-ray spectrum. The energy resolution of the best 21 pixels was found to be 120 eV FWHM. The array is read out using time domain SQUID multiplexing. Here, we describe the multiplexing and present a high statistics Pu spectra. Because of the large collecting area of our array, the statistical error in the 240Pu line intensity is approximately 0.7%, which is comparable to the systematic error in a measurement with a 500 eV germanium sensor. Hence, we have reached an important threshold for demonstrating improved isotopic measurements with microcalorimeter sensors. With straightforward changes, we plan to achieve a resolution of about 50 eV FWHM with 256 multiplexed detectors. Finally, we present early estimates of on-chip heating within our sensor array.

Development of large arrays of microcalorimeters for precision gamma-ray spectroscopy

We present measurements from a gamma-ray microcalorimeter with a FWHM energy resolution of 42 eV at 103 keV on a gadolinium test source and 52 eV FWHM at 103 keV on a complex mixture of plutonium isotopes. Additionally, we provide an overview of microcalorimeter technology, its specialized readout electronics, and the associated cryogenics. NIST is presently developing arrays of microcalorimeters and microbolometers for applications at submillimeter and X-ray wavelengths. The largest of these arrays will have 10,240 pixels and a sensing area of 102.4 cm2. This technology development is directly applicable to gamma-ray microcalorimeter arrays and we see no obstacles to gamma-ray microcalorimeter arrays of 100 or more pixels

Nondestructive Assay Data Integration with the SKB-50 Assemblies - FY16 Update

A project to research the application of non-destructive assay (NDA) techniques for spent fuel assemblies is underway at the Central Interim Storage Facility for Spent Nuclear Fuel (for which the S ...