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Using microcalorimeters, a high statistics, high-resolution calorimetric spectrum of electron capture in 163 Ho can be used to determine the neutrino mass. The spectral shape can be calculated from first principles with various assumptions and approximations. To determine the validity of these choices, the theoretical calculations must be compared to data from multiple isotopes. New calorimetric data for a 193 Pt-in-Pt absorber measured with a transition edge sensor are presented and compared to theoretical calculations and values from the literature. [ABSTRACT FROM AUTHOR]

We are developing an imaging capability ("Hyperspectral X-ray Imaging") for mapping chemical information (molecular formula, phase, oxidation state, hydration) that is based on ultra-high-resolution X-ray emission spectroscopy with large transition-edge sensor microcalorimeter arrays in the scanning electron microscope. By combining microcalorimeter arrays with hundreds of pixels, high-bandwidth microwave frequency-division multiplexing, and fast digital electronics for near real-time data processing, our goal is to enable measurements using laboratory-scale instrumentation rather than synchrotron beamlines. Our application focus here is on mapping the chemical form of uranium compounds on the nanoscale. We will present our approach to developing the Hyperspectral X-ray Imaging capability, progress toward a 128-pixel microwave multiplexed X-ray fluorescence instrument at LANL, and the path to high-throughput nanoscale chemical mapping. [ABSTRACT FROM AUTHOR]

The neutrino mass can be extracted from a high statistics, high resolution calorimetric spectrum of electron capture in 163Ho. In order to better understand the shape of the calorimetric electron capture spectrum, a second isotope was measured with a close to ideal absorber-source configuration. 193Pt was created by irradiating a 192Pt-enriched platinum foil in a nuclear reactor. This Pt-in-Pt absorber was designed to have a nearly ideal absorber-source configuration. The measured 193Pt calorimetric electron capture spectrum provides an independent check on the corresponding theoretical calculations, which have thus far been compared only for 163Ho. The first experimental and theoretically calculated spectra from this 193Pt-in-Pt absorber are presented and overlaid for preliminary comparison of theory with experiment. [ABSTRACT FROM AUTHOR]

The total reaction energy (Q) of individual nuclear decays was measured using microcalorimeters with transition-edge-sensor (TES) thermometers. For alpha-decaying actinides (e.g., U-235, Pu-239, Np-237, Am-241), Q is in the 4–6 MeV range. Nearly all of this energy goes into the relatively light alpha particle, and approximately 100 keV is left over for the much heavier, recoiling daughter atom. Alpha-particle energy spectroscopy with TES-microcalorimeters has shown the ability to simultaneously resolve peaks that overlap in conventional alpha spectroscopy, with resolution now less than 1 keV full-width-at-half-maximum (FWHM) at 5.3 MeV. For total reaction energy spectroscopy, we use the same TES design as our alpha detectors, but embed a small radioactive sample (of about 1 Bq) directly inside an absorber designed to capture all the emitted particles (alpha, recoil nucleus, electrons, X-rays) with near 100% efficiency. We have measured Q-spectra of alpha-decaying isotopes with spectral resolution of 2–3 keV FWHM. For some actinide analytical problems, the Q-spectrum is simpler than the alpha-spectrum: fewer peaks, further apart, and easier to quantify. We will discuss sensor design, methods for embedding radionuclides, and spectral data. [ABSTRACT FROM PUBLISHER]

Alpha-particle spectrometry is a powerful analytical tool for nuclear forensics and environmental monitoring. Superconducting transition-edge sensor microcalorimeters have been shown to yield unsurpassed energy resolution for alpha spectrometry. With nearly an order of magnitude better energy resolution (1.06 keV FWHM at 5.3 MeV) than the current state-of-the-art silicon detectors (8–10 keV at 5.3 MeV), it is possible to measure samples containing multiple radioisotopes that would require expensive and time-consuming radiochemical separation prior to measurement with a silicon detector. This paper presents recent results from the Los Alamos four-channel microcalorimeter alpha spectrometer. We have prepared a source from weapons-grade plutonium and demonstrated the ability of microcalorimeter alpha spectrometry to simultaneously resolve alpha energies from ^239Pu, ^240Pu, ^238Pu, and ^241Am. The low-energy performance of the spectrometer system has been improved to allow measurement of energies as low as 5 keV, which gives a dynamic range of 1000. We have demonstrated this capability by simultaneously measuring the alpha particles and low-energy x-rays and internal conversion electrons emitted by an electroplated ^240Pu source. [ABSTRACT FROM AUTHOR]

Special considerations and techniques are desired for the preparation of small actinide counting sources. Counting sources have been prepared on metal disk substrates (planchets) with an active area of only 0.079 mm2. This represents a 93.75% reduction in deposition area from standard electrodeposition methods. The actinide distribution upon the smaller planchet must remain thin and uniform to allow alpha particle emissions to escape the counting source with a minimal amount of self-attenuation. This work describes the development of micro-electrodeposition methods and optimization of the technique with respect to deposition time and current density for various planchet sizes. [ABSTRACT FROM AUTHOR]

Microcalorimeter detectors provide superior energy resolution for the detection of X-rays and gamma-rays. The technology utilizes a cryogenic transition-edge sensor (TES) coupled to a tin bulk absorber. We are working on fabrication methods for the production of arrays with many sensors. In this paper, we present data collected with an array of microcalorimeters using as many as 26 sensor elements simultaneously. Advances in sensor design have extended the useful dynamic range to photon energies up to ∼200 keV, while providing resolution performance in the 80–90 eV FWHM range, significantly better than planar high-purity germanium. These sensor arrays have applications in the measurement of nuclear materials. We present data collected from 153Gd, a highly-enriched uranium sample, and a plutonium isotopic standard source. We also demonstrate clean separation of the 235U 185.715 keV peak from the ubiquitous 226Ra 186.211 keV background peak interference. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microcalorimeter sensors operated near 0.1 K can measure the energy of individual x- and gamma-ray photons with significantly more precision than conventional semiconductor technologies. Both microcalorimeter arrays and higher per pixel count rates are desirable to increase the total throughput of spectrometers based on these devices. The millisecond recovery time of gamma-ray microcalorimeters and the resulting pulse pileup are significant obstacles to high per pixel count rates. Here, we demonstrate operation of a microcalorimeter detector at elevated count rates by use of convolution filters designed to be orthogonal to the exponential tail of a preceding pulse. These filters allow operation at 50% higher count rates than conventional filters while largely preserving sensor energy resolution. [ABSTRACT FROM AUTHOR]

High-resolution superconducting gamma-ray sensors show potential for the more accurate analysis of nuclear material. These devices are part of a larger class of microcalorimeters and bolometers based on transition edge sensors (TESs) that have two distinct thermal bodies. We derive the time domain behavior of the current and temperature for compound TES devices in the small signal limit and demonstrate the utility of these equations for device design and characterization. In particular, we use the model to fit pulses from our gamma-ray microcalorimeters and demonstrate how critical damping and electrothermal stability can be predicted. [ABSTRACT FROM AUTHOR]

The authors present a prototype for a high-energy-resolution, high-count-rate, gamma-ray spectrometer intended for nuclear forensics and international nuclear safeguards. The prototype spectrometer is an array of 14 transition-edge-sensor microcalorimeters with an average energy resolution of 47 eV (full width at half maximum) at 103 keV. The resolution of the best pixel is 25 eV. A cryogenic, time-division multiplexer reads out the array. Several important topics related to microcalorimeter arrays are discussed, including cross-talk, the uniformity of detector bias conditions, fabrication of the arrays, and the multiplexed readout. The measurements and calculations demonstrate that a kilopixel array of high-resolution microcalorimeters is feasible. [ABSTRACT FROM AUTHOR]

Improvements in superconductor device fabrication, detector hybridization techniques, and superconducting quantum interference device readout have made square-centimeter-sized arrays of gamma-ray microcalorimeters, based on transition-edge sensors (TESs), possible. At these collecting areas, gamma microcalorimeters can utilize their unprecedented energy resolution to perform spectroscopy in a number of applications that are limited by closely-spaced spectral peaks, for example, the nondestructive analysis of nuclear materials. We have built a 256 pixel spectrometer with an average full-width-at-half-maximum energy resolution of 53 eV at 97 keV, a useable dynamic range above 400 keV, and a collecting area of 5 cm2. We have demonstrated multiplexed readout of the full 256 pixel array with 236 of the pixels (91%) giving spectroscopic data. This is the largest multiplexed array of TES microcalorimeters to date. This paper will review the spectrometer, highlighting the instrument design, detector fabrication, readout, operation of the instrument, and data processing. Further, we describe the characterization and performance of the newest 256 pixel array. [ABSTRACT FROM AUTHOR]