Proof-of-Principle Experiment for Testing Strong-Field Quantum Electrodynamics with Exotic Atoms: High Precision X-Ray Spectroscopy of Muonic Neon.

To test bound-state quantum electrodynamics (BSQED) in the strong-field regime, we have performed high precision x-ray spectroscopy of the 5g-4f and 5f- 4d transitions (BSQED contribution of 2.4 and 5.2 eV, respectively) of muonic neon atoms in the low-pressure gas phase without bound electrons. Muonic atoms have been recently proposed as an alternative to few-electron high-Z ions for BSQED tests by focusing on circular Rydberg states where nuclear contributions are negligibly small. We determined the 5g_{9/2}- 4f_{7/2} transition energy to be 6297.08±0.04(stat)±0.13(syst) eV using superconducting transition-edge sensor microcalorimeters (5.2-5.5 eV FWHM resolution), which agrees well with the most advanced BSQED theoretical prediction of 6297.26 eV.

Measurements of Strong-Interaction Effects in Kaonic-Helium Isotopes at Sub-eV Precision with X-Ray Microcalorimeters.

We have measured the 3d→2p transition x rays of kaonic ^{3}He and ^{4}He atoms using superconducting transition-edge-sensor microcalorimeters with an energy resolution better than 6 eV (FWHM). We determined the energies to be 6224.5±0.4(stat)±0.2(syst) eV and 6463.7±0.3(stat)±0.1(syst) eV, and widths to be 2.5±1.0(stat)±0.4(syst) eV and 1.0±0.6(stat)±0.3(stat) eV, for kaonic ^{3}He and ^{4}He, respectively. These values are nearly 10 times more precise than in previous measurements. Our results exclude the large strong-interaction shifts and widths that are suggested by a coupled-channel approach and agree with calculations based on optical-potential models.

Energy Calibration of Nonlinear Microcalorimeters with Uncertainty Estimates from Gaussian Process Regression.

The nonlinear energy response of cryogenic microcalorimeters is usually corrected through an empirical calibration. X-ray or gamma-ray emission lines of known shape and energy anchor a smooth function that generalizes the calibration data and converts detector measurements to energies. We argue that this function should be an approximating spline. The theory of Gaussian process regression makes a case for this functional form. It also provides an important benefit previously absent from our calibration method: a quantitative uncertainty estimate for the calibrated energies, with lower uncertainty near the best-constrained calibration points.

Absolute energies and emission line shapes of the L x-ray transitions of lanthanide metals.

We use an array of transition-edge sensors, cryogenic microcalorimeters with 4 eV energy resolution, to measure L x-ray emission-line profiles of four elements of the lanthanide series: praseodymium, neodymium, terbium, and holmium. The spectrometer also surveys numerous x-ray standards in order to establish an absolute-energy calibration traceable to the international system of units for the energy range 4 keV to 10 keV. The new results include emission line profiles for 97 lines, each expressed as a sum of one or more Voigt functions; improved absolute energy uncertainty on 71 of these lines relative to existing reference data; a median uncertainty on the peak energy of 0.24 eV, four to ten times better than the median of prior work; and six lines that lack any measured values in existing reference tables. The 97 lines comprise nearly all of the most intense L lines from these elements under broad-band x-ray excitation. The work improves on previous measurements made with a similar cryogenic spectrometer by the use of sensors with better linearity in the absorbed energy and a gold x-ray absorbing layer that has a Gaussian energy-response function. It also employs a novel sample holder that enables rapid switching between science targets and calibration targets with excellent gain balancing. Most of the results for peak energy values shown here should be considered as replacements for the currently tabulated standard reference values, while the line shapes given here represent a significant expansion of the scope of available reference data.

Deexcitation Dynamics of Muonic Atoms Revealed by High-Precision Spectroscopy of Electronic K X Rays.

We observed electronic K x rays emitted from muonic iron atoms using superconducting transition-edge sensor microcalorimeters. The energy resolution of 5.2 eV in FWHM allowed us to observe the asymmetric broad profile of the electronic characteristic Kα and Kß x rays together with the hypersatellite K^{h}α x rays around 6 keV. This signature reflects the time-dependent screening of the nuclear charge by the negative muon and the L-shell electrons, accompanied by electron side feeding. Assisted by a simulation, these data clearly reveal the electronic K- and L-shell hole production and their temporal evolution on the 10-20 fs scale during the muon cascade process.

Optimization of Time- and Code-Division-Multiplexed Readout for Athena X-IFU.

Readout of a large, spacecraft-based array of superconducting transition-edge sensors (TESs) requires careful management of the layout area and power dissipation of the cryogenic-circuit components. We present three optimizations of our time- (TDM) and code-division-multiplexing (CDM) systems for the X-ray Integral Field Unit (X-IFU), a several-thousand-pixel-TES array for the planned Athena-satellite mission. The first optimization is a new readout scheme that is a hybrid of CDM and TDM. This C/TDM architecture balances CDM's noise advantage with TDM's layout compactness. The second is a redesign of a component: the shunt resistor that provides a dc-voltage bias to the TESs. A new layout and a thicker Pd-Au resistive layer combine to reduce this resistor's area by more than a factor of 5. Third, we have studied the power dissipated by the first-stage SQUIDs (superconducting quantum-interference devices) and the readout noise versus the critical current of the first-stage SqUIDs. As a result, the X-IFU TDM and C/TDM SQUIDs will have a specified junction critical current of 5 µA. Based on these design optimizations and TDM experiments described by Durkin, et al. (these proceedings), TDM meets all requirements to be X-IFU's backup-readout option. Hybrid C/TDM is another viable option that could save spacecraft resources.

Demonstration of Athena X-IFU Compatible 40-Row Time-Division-Multiplexed Readout.

Time-division multiplexing (TDM) is the backup readout technology for the X-ray Integral Field Unit (X-IFU), a 3,168-pixel X-ray transition-edge sensor (TES) array that will provide imaging spectroscopy for ESA's Athena satellite mission. X-0IFU design studies are considering readout with a multiplexing factor of up to 40. We present data showing 40-row TDM readout (32 TES rows + 8 repeats of the last row) of TESs that are of the same type as those being planned for X-IFU, using measurement and analysis parameters within the ranges specified for X-IFU. Singlecolumn TDM measurements have best-fit energy resolution of (1.91 ± 0.01) eV for the Al Kα complex (1.5 keV), (2.10 ± 0.02) eV for Ti Kα (4.5 keV), (2.23 ± 0.02) eV for Mn Kα (5.9 keV), (2.40 ± 0.02) eV for Co Kα (6.9 keV), and (3.44 ± 0.04) eV for Br Kα (11.9 keV). Three-column measurements have best-fit resolution of (2.03 ± 0.01) eV for Ti Kα and (2.40 ± 0.01) eV for Co Kα. The degradation due to the multiplexed readout ranges from 0.1 eV at the lower end of the energy range to 0.5 eV at the higher end. The demonstrated performance meets X-IFU's energy-resolution and energy-range requirements. True 40-row TDM readout, without repeated rows, of kilopixel scale arrays of X-IFU-like TESs is now under development.

A Robust Principal Component Analysis for Outlier Identification in Messy Microcalorimeter Data.

A principal component analysis (PCA) of clean microcalorimeter pulse records can be a first step beyond statistically optimal linear filtering of pulses toward a fully nonlinear analysis. For PCA to be practical on spectrometers with hundreds of sensors, an automated identification of clean pulses is required. Robust forms of PCA are the subject of active research in machine learning. We examine a version known as coherence pursuit that is simple and fast and well matched to the automatic identification of outlier records, as needed for microcalorimeter pulse analysis.

A transition-edge sensor-based x-ray spectrometer for the study of highly charged ions at the National Institute of Standards and Technology electron beam ion trap.

We report on the design, commissioning, and initial measurements of a Transition-Edge Sensor (TES) x-ray spectrometer for the Electron Beam Ion Trap (EBIT) at the National Institute of Standards and Technology (NIST). Over the past few decades, the NIST EBIT has produced numerous studies of highly charged ions in diverse fields such as atomic physics, plasma spectroscopy, and laboratory astrophysics. The newly commissioned NIST EBIT TES Spectrometer (NETS) improves the measurement capabilities of the EBIT through a combination of high x-ray collection efficiency and resolving power. NETS utilizes 192 individual TES x-ray microcalorimeters (166/192 yield) to improve upon the collection area by a factor of ∼30 over the 4-pixel neutron transmutation doped germanium-based microcalorimeter spectrometer previously used at the NIST EBIT. The NETS microcalorimeters are optimized for the x-ray energies from roughly 500 eV to 8000 eV and achieve an energy resolution of 3.7 eV-5.0 eV over this range, a more modest (<2×) improvement over the previous microcalorimeters. Beyond this energy range, NETS can operate with various trade-offs, the most significant of which are reduced efficiency at lower energies and being limited to a subset of the pixels at higher energies. As an initial demonstration of the capabilities of NETS, we measured transitions in He-like and H-like O, Ne, and Ar as well as Ni-like W. We detail the energy calibration and data analysis techniques used to transform detector counts into x-ray spectra, a process that will be the basis for analyzing future data.

A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science.

We describe a series of microcalorimeter X-ray spectrometers designed for a broad suite of measurement applications. The chief advantage of this type of spectrometer is that it can be orders of magnitude more efficient at collecting X-rays than more traditional high-resolution spectrometers that rely on wavelength-dispersive techniques. This advantage is most useful in applications that are traditionally photon-starved and/or involve radiation-sensitive samples. Each energy-dispersive spectrometer is built around an array of several hundred transition-edge sensors (TESs). TESs are superconducting thin films that are biased into their superconducting-to-normal-metal transitions. The spectrometers share a common readout architecture and many design elements, such as a compact, 65 mK detector package, 8-column time-division-multiplexed superconducting quantum-interference device readout, and a liquid-cryogen-free cryogenic system that is a two-stage adiabatic-demagnetization refrigerator backed by a pulse-tube cryocooler. We have adapted this flexible architecture to mate to a variety of sample chambers and measurement systems that encompass a range of observing geometries. There are two different types of TES pixels employed. The first, designed for X-ray energies below 10 keV, has a best demonstrated energy resolution of 2.1 eV (full-width-at-half-maximum or FWHM) at 5.9 keV. The second, designed for X-ray energies below 2 keV, has a best demonstrated resolution of 1.0 eV (FWHM) at 500 eV. Our team has now deployed seven of these X-ray spectrometers to a variety of light sources, accelerator facilities, and laboratory-scale experiments; these seven spectrometers have already performed measurements related to their applications. Another five of these spectrometers will come online in the near future. We have applied our TES spectrometers to the following measurement applications: synchrotron-based absorption and emission spectroscopy and energy-resolved scattering; accelerator-based spectroscopy of hadronic atoms and particle-induced-emission spectroscopy; laboratory-based time-resolved absorption and emission spectroscopy with a tabletop, broadband source; and laboratory-based metrology of X-ray-emission lines. Here, we discuss the design, construction, and operation of our TES spectrometers and show first-light measurements from the various systems. Finally, because X-ray-TES technology continues to mature, we discuss improvements to array size, energy resolution, and counting speed that we anticipate in our next generation of TES-X-ray spectrometers and beyond.

Developments in Time-Division Multiplexing of X-ray Transition-Edge Sensors.

Time-division multiplexing (TDM) is a mature scheme for the readout of arrays of transition-edge sensors (TESs). TDM is based on superconducting-quantum-interference-device (SQUID) current amplifiers. Multiple spectrometers based on gamma-ray and X-ray microcalorimeters have been operated with TDM readout, each at the scale of 200 sensors per spectrometer, as have several astronomical cameras with thousands of sub-mm or microwave bolometers. Here we present the details of two different versions of our TDM system designed to read out X-ray TESs. The first has been field-deployed in two 160-sensor (8 columns × 20 rows) spectrometers and four 240-sensor (8 columns × 30 rows) spectrometers. It has a three-SQUID-stage architecture, switches rows every 320 ns, and has total readout noise of 0.41 µΦ0/√Hz. The second, which is presently under development, has a two-SQUID-stage architecture, switches rows every 160 ns, and has total readout noise of 0.19 µΦ0/√Hz. Both quoted noise values are non-multiplexed and referred to the first-stage SQUID. In a demonstration of this new architecture, a multiplexed 1-column × 32-row array of NIST TESs achieved average energy resolution of 2.55±0.01 eV at 6 keV.

High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential.

X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a soft X-ray synchrotron beamline to perform emission spectroscopy with good chemical sensitivity over a very wide range of energies.

Laser plasma x-ray source for ultrafast time-resolved x-ray absorption spectroscopy.

We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 µm FWHM x-ray spot size, containing ∼10(6) photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >10(7) laser pulses, we also present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments.

The Practice of Pulse Processing.

The analysis of data from x-ray microcalorimeters requires great care; their excellent intrinsic energy resolution cannot usually be achieved in practice without a statistically near-optimal pulse analysis and corrections for important systematic errors. We describe the essential parts of a pulse-analysis pipeline for data from x-ray microcalorimeters, including steps taken to reduce systematic gain variation and the unwelcome dependence of filtered pulse heights on the exact pulse-arrival time. We find these steps collectively to be essential tools for getting the best results from a microcalorimeter-based x-ray spectrometer.

A high resolution gamma-ray spectrometer based on superconducting microcalorimeters.

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 cm(2). 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.

The role of flumazenil in the treatment of benzodiazepine dependence: physiological and psychological profiles.

Two-related studies are presented here, detailing our early experience with benzodiazepine-dependent patients treated with a four-day flumazenil infusion using a novel delivery technique. Patients with long-term benzodiazepine dependence who attended the Australian Medical Procedures Research Foundation (AMPRF, Perth, Australia) for treatment were recruited for these studies. Self-reported psychological and physical symptoms, as well as objective vital signs data were collected at intervals before, during and 2 weeks postinfusion. Study A is a case series with cardiovascular measures; study B is an open trial that tracks the psychological profiles of 13 subjects. Withdrawal symptoms were tracked, however, the nature and severity of these symptoms differed between patients. No major complications or discomfort prompting study dropout was observed. Significant benzodiazepine abstinence occurred with this flumazenil infusion method despite high levels of initial dependence, comorbid substance use and comorbid psychiatric illness. Low-dose flumazenil infusion appears to be a safe and effective treatment resulting in withdrawal symptoms of lesser severity than any other cessation method currently available. Recommendations for future research are discussed.

Observation of nonmagnetic resonant scattering effects by tunneling in dilute Al-mn alloy superconductors.

We have observed the BCS-like density of states predicted for energy-gap suppression by nonmagnetic Anderson impurities in superconductors. We show that Mn impurities in Al exhibit no magnetic character and act exclusively as strong resonant scattering sites without producing time-reverse symmetry breaking of Cooper pairs (pair breaking).

Histological changes over time around the site of sustained release naltrexone-poly(DL-lactide) implants in humans.

In order to assess the histological tissue changes over time around the site of implant, tissue biopsies were taken at 1 to 38 months post-implant from 54 (34 male) consenting human subjects who had received the Australian subcutaneous naltrexone-poly(DL-lactide) implant for heroin dependence. The implant consists of multiple tablets containing compressed naltrexone-poly[trans-3,6-dimethyl-1,4-dioxane-2,5-dione] (DL-lactide) loaded microspheres. Assessment of tissue samples by pathologists showed an early phase (up to 12 months post-implant) of inflammation, foreign body reaction, and fibrosis. This subsided gradually over the next 12 months until tissue returned to normal by 25+ months. Sufficient evidence was not available to conclude that the poly(DL-lactide) implant matrix was totally biodegradable within the study period. While implant material was not identified in most of the latter biopsies, its presence was noted in one biopsy at 26 months post-implant. Nevertheless the study results did demonstrate the implant's biocompatibility by the lack of inflammation, foreign body reaction, and fibrosis detected by 25+ months. It seems highly probable that surgical technique rather than the implant itself was associated with the additional finding of fat necrosis. Moderate fat necrosis was observed as a common feature of biopsies carried out during the first 6 months following implant. It subsided to mild levels over the next 18 months, and was notably absent by 25+ months. The results of the study indicated that the Australian naltrexone-poly(DL-lactide) implant is well tolerated and may have a role for use in the management of medical conditions such as heroin dependence.

Achieving long-term continuous blood naltrexone and 6-beta-naltrexol coverage following sequential naltrexone implants.

The aim of this study was to assess blood free naltrexone and 6-beta-naltrexol levels with time following treatment with sequential sustained-release naltrexone preparations. Data were collected from blood samples analysed independently for naltrexone and 6-beta-naltrexol and from clinical record review at a community heroin treatment clinic in Perth, Western Australia. Five patients received sequential 3.4 g (3.49+/-0.01 g and 3.36+/-0.05 g, respectively) naltrexone implants. The second implant was received on average within 131.2+/-15.67 days of the first implant. The mean length of follow-up was 307.2+/-18.28 days of the first implant. Blood naltrexone levels have the potential to remain above 2 and 1 ng/ml for a total of 390 and 524 days, respectively, and blood 6-beta-naltrexol was maintained above 10 ng/ml for a total of 222 days following insertion of these implants. No patient relapsed to dependent heroin use during the implant coverage period while blood naltrexone concentrations were above 2 ng/ml. Results indicate that blood naltrexone and 6-beta-naltrexol levels can be maintained above therapeutic levels for prolonged periods following use of sequential 3.4 g naltrexone implants. These extended periods of coverage will offer significant benefits for managing the heroin-dependent patient.

Blood naltrexone and 6-beta-naltrexol levels following naltrexone implant: comparing two naltrexone implants.

The aim of this study was to profile and compare blood naltrexone and 6-beta-naltrexol levels with time following treatment with two sustained-release naltrexone preparations produced by GoMedical Industries, Australia at a community heroin treatment clinic in Perth, Western Australia. A sample of 10 patients who each received a 1.7 g naltrexone implant were compared to 24 patients who each received a 3.4 g naltrexone implant as treatment for heroin dependence. Blood naltrexone levels following treatment with the 1.7 g naltrexone implant remained above 2 and 1 ng/ml for approximately 90 and 136 days, respectively. Use of the 3.4 g naltrexone implant extended the period of coverage to approximately 297 (1 ng/ml) or 188 (2 ng/ml) days. Blood 6-beta-naltrexol levels remained above 10 ng/ml for approximately 18 and 83 days, respectively, following use of the 1.7 g and 3.4 g naltrexone implants. The current study data indicate that blood naltrexone and 6-beta-naltrexol levels following treatment with either the 1.7 g or 3.4 g naltrexone implant are greater than those reported in other published data on other sustained-release naltrexone preparations. Furthermore, duration of blood naltrexone and 6-beta-naltrexol levels achieved following use of the 3.4 g implant were superior to those achieved with the 1.7 g naltrexone implant, with naltrexone blood levels maintained above 2 ng/ml for a period of approximately 6.3 months compared to 3 months, respectively. The implications of this in managing the heroin-dependent patient, especially those who find it difficult to shift away from dependent use patterns, are discussed.