eV Full-width At Half-maximum Research Articles

511-CAM mission: a pointed 511 keV gamma-ray telescope with a focal plane detector made of stacked transition edge sensor microcalorimeter arrays

The 511 keV γ-ray emission from the galactic center region may fully or partially originate from the annihilation of positrons from dark matter particles with electrons from the interstellar medium. Alternatively, the positrons could be created by astrophysical sources, involving exclusively standard model physics. We describe here a new concept for a 511 keV mission called 511-CAM (511 keV gamma-ray camera using microcalorimeters) that combines focusing γ-ray optics with a stack of transition edge sensor microcalorimeter arrays in the focal plane. The 511-CAM detector assembly has a projected 511 keV energy resolution of 390 eV full width half maximum or better, and improves by a factor of at least 11 on the performance of state-of-the-art Ge-based Compton telescopes. Combining this unprecedented energy resolution with sub-arcmin angular resolutions afforded by Laue lens or channeling optics could make substantial contributions toward identifying the origin of the 511 keV emission through discovering and characterizing point sources and measuring line-of-sight velocities of the emitting plasmas.

Simple, compact, high-resolution monochromatic x-ray source for characterization of x-ray calorimeter arrays.

X-ray calorimeters routinely achieve very high spectral resolution, typically a few eV full width at half maximum (FWHM). Measurements of calorimeter line shapes are usually dominated by the natural linewidth of most laboratory calibration sources. This compounds the data acquisition time necessary to statistically sample the instrumental line broadening and can add systematic uncertainty if the intrinsic line shape of the source is not well known. To address these issues, we have built a simple, compact monochromatic x-ray source using channel cut crystals. A commercial x-ray tube illuminates a pair of channel cut crystals that are aligned in a dispersive configuration to select the Kα1 line of the x-ray tube anode material. The entire device, including the x-ray tube, can be easily hand-carried by one person and may be positioned manually or using a mechanical translation stage. The output monochromatic beam provides a collimated image of the anode spot with magnification of unity in the dispersion direction (typically 100 μm-200 μm for the x-ray tubes used here) and is unfocused in the cross-dispersion direction so that the source image in the detector plane appears as a line. We measured output count rates as high as 10 count/s/pixel for the Hitomi soft x-ray spectrometer, which had 819 μm square pixels. We implemented different monochromator designs for energies of 5.4 keV (one design) and 8.0 keV (two designs), which have effective theoretical FWHM energy resolution of 0.125 eV, 0.197 eV, and 0.086 eV, respectively; these are well-suited for optimal calibration measurements of state-of-the art x-ray calorimeters. We measured an upper limit for the energy resolution of our Cr Kα1 monochromator of 0.7 eV FWHM at 5.4 keV, consistent with the theoretical prediction of 0.125 eV.

Optimized TES Microcalorimeters with 14 eV Energy Resolution at 30 keV for γ-Ray Measurements of the 229Th Isomer

We have developed a four-pixel array of superconducting transition-edge sensors with gold absorbers for the detection of a 29.2 keV $$\gamma$$ -ray doublet decay from $${}^{229}$$ Th. To identify the decay, an energy resolution better than 20 eV full width at half maximum (FWHM) is needed. We measured an energy resolution of 14 eV FWHM for 26 keV $$\gamma$$ -ray decay from an $${}^{241}$$ Am isotope in combined data of three pixels. We describe the design and the performance of the devices and discuss the baseline correction method to compensate the variation in the baseline, which was observed during the evaluation of the performance using the $${}^{241}$$ Am isotope.

Demonstration of Fine-Pitch High-Resolution X-ray Transition-Edge Sensor Microcalorimeters Optimized for Energies below 1 keV

In this paper, we report on X-ray transition-edge sensor (TES) microcalorimeters optimized to have the best possible energy resolution for a limited energy range for the incoming X-rays, such as an energy resolution of 0.3 eV full width half maximum (FWHM) for energies up to $$\approx 0.8\,{\mathrm{keV}}$$ as is desirable for one of the Lynx X-ray Microcalorimeter subarrays. The test array we have fabricated has $$60\times 60$$ sensors on a pitch of $$50\,\upmu {\mathrm{m}}$$, and has $$46\times 46\,\upmu {\mathrm{m}}^2$$ absorbers that are one micrometer thick. We have measured a spectral energy resolution of the same device using 3 eV photons delivered through an optical fiber. For the one-photon 3 eV line, we have obtained an energy resolution of 0.25 eV FWHM, which is consistent with the estimated performance based on the signal size and noise. Further measurements will determine how the energy resolution degrades with energy. Based upon measurements of the TES transition characteristics, it appears that this level of energy resolution should be achievable up to 0.5 keV, and the performance will then gradually degrade to the measured energy resolution of around 2.3 eV at 1.5 keV. In this paper, we describe the full design and characterization of this detector, and discuss the performance limits of pixels designs like this.

Use of Transition Models to Design High Performance TESs for the LCLS-II Soft X-Ray Spectrometer.

We are designing an array of transition-edge sensor (TES) microcalorimeters for a soft X-ray spectrometer at the Linac Coherent Light Source at SLAC National Accelerator Laboratory to coincide with upgrades to the free electron laser facility. The complete spectrometer will have 1000 TES pixels with energy resolution of 0.5 eV full-width at half-maximum (FWHM) for incident energies below 1 keV while maintaining pulse decay-time constants shorter than 100 μs. Historically, TES pixels have often been designed for a particular scientific application via a combination of simple scaling relations and trial-and-error experimentation with device geometry. We have improved upon this process by using our understanding of transition physics to guide TES design. Using the two-fluid approximation of the phase-slip line model for TES resistance, we determine how the geometry and critical temperature of a TES will affect the shape of the transition. We have used these techniques to design sensors with a critical temperature of 55 mK. The best sensors achieve an energy resolution of 0.75 eV FWHM at 1.25 keV. Building upon this result, we show how the next generation of sensors can be designed to reach our goal of 0.5 eV resolution.

Temperature study of Al0.52In0.48P detector photon counting X-ray spectrometer

A prototype 200 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiode (2 μm i-layer) was characterised at temperatures from 100 °C to −20 °C for the development of a temperature tolerant photon counting X-ray spectrometer. At each temperature, X-ray spectra were accumulated with the AlInP detector reverse biased at 0 V, 5 V, 10 V, and 15 V and using different shaping times. The detector was illuminated by an 55Fe radioisotope X-ray source. The best energy resolution, as quantified by the full width at half maximum (FWHM) at 5.9 keV, was observed at 15 V for all the temperatures studied; at 100 °C, a FWHM of 1.57 keV was achieved, and this value improved to 770 eV FWHM at −20 °C. System noise analysis was also carried out, and the different noise contributions were computed as functions of temperature. The results are the first demonstration of AlInP's suitability for photon counting X-ray spectroscopy at temperatures other than ≈20 °C.

A Transition Edge Sensor Microcalorimeter System for the Energy Dispersive Spectroscopy Performed on a Scanning-Transmission Electron Microscope

We are conducting the development of a transition edge sensor (TES) microcalorimeter system for energy-dispersive X-ray spectroscopy (EDS), performed using a scanning-transmission electron microscope (STEM). The operating temperature of the TES microcalorimeter was maintained using a compact dry \(^{3}\)He-\(^{4}\)He dilution refrigerator. This was pre-cooled by a remote helium cooling loop system and a Gifford-McMahon cooler. These conditions allowed for high-resolution STEM imaging to be achieved. A single-pixel TES microcalorimeter with a polycapillary optic was selected to demonstrate the analytical operation of the EDS system in the STEM. For a Ti-It-Pt sample, an X-ray energy resolution of 8.6 eV full-width at half maximum (FWHM) was obtained at Ir M\(_{\alpha 1}\), Pt M\(_{\alpha 1}\), and Ir M\(_{\beta }\). Using an electron device sample, element distribution maps of Si, Ti, and W were obtained using a Si K\(_{\alpha 1}\) X-ray energy resolution of 9.7 eV FWHM.

Uniformity of Kilo-Pixel Arrays of Transition-Edge Sensors for X-ray Astronomy

We are developing kilo-pixel arrays of transition-edge sensor (TES) microcalorimeters for use in future laboratory and space based X-ray astrophysics experiments. These arrays are required to achieve an energy resolution of ΔE FWHM <; 3 eV full-width-half-maximum (FWHM) in the soft X-ray energy range. In this contribution we report on the development of 32 × 32 arrays of Mo/Au TESs with Bi/Au X-ray absorbers. We present measurements from 8 × 8 test arrays and 32 × 32 uniform arrays. Measurements of the bias point resistance and magnetic field dependence of the transition properties show that by carefully tuning the applied magnetic field the requirements on T C and magnetic field uniformity can be reduced whilst maintaining the target energy resolution. Results show ΔE FWHM ≈ 2.0 - 2.5 eV FWHM at a photon energy of 6 keV, measured across several pixels. Despite larger than typical T C variation across the detector, time division multiplexed readout of 30 common electrically biased pixels in the 32 × 32 array (in a 2 column × 16 row configuration) show an average ΔE FWHM = 3.0 ± 0.3 eV.

Raman scattering and photoluminescence studies on O+ implanted silicon

The effects of 125 keV oxygen ion implantation with fluences from 10 14 to 10 16 ions/cm 2 on (1 0 0) cut crystalline silicon (c-Si) have been investigated by Raman scattering and photoluminescence techniques. A systematic decrease in the area and frequency of longitudinal optical (LO) phonon Raman mode and increase in its full-width at half-maximum (FWHM) have been observed with increase of fluence. The temperature at the incident laser spot on the implanted Si increases with fluence. The behavior of peak position and FWHM is due to implantation-induced lattice damage. The decrease in area of the mode is due to the decrease in the volume fraction of c-Si in the implanted layer. The disappearance of the Raman LO mode of c-Si and the appearance of the Raman mode for the amorphous Si (a-Si) have been observed for 10 16 O + /cm 2 fluence, suggesting the amorphization of the implanted layer. The increase in the temperature is due to the poor thermal conductivity of a-Si and increased photon absorption due to implantation induced lattice disorder. Photoluminescence (PL) in the range of 1.8–2.52 eV shows a peak at 2.35 eV with 0.4 eV FWHM for all fluences. Its area increases with fluence and saturates. These results are due to a-Si nanozones created by the O + impact and coalesce of such nanozones at high fluences. The average size of the a-Si nanozone estimated from PL peak position (2.05 nm) and that from the critical fluence for amorphization (1.9 nm) match very well.

Electron emission characteristics of ZrO/W electron sources with a wide range of tip radii

AbstractEmitters of ZrO/W with a wide range of tip radii (0.43–4.2 µm) were prepared and evaluated. A unique tip‐forming method using local Joule heating was developed to make the tip radii &gt;2 µm. The tip radius dependency of the energy spread agrees qualitatively with the energy spread calculated by Knauer's formula when evaluating the Boersch effect. Emitters with tip radii &gt;2 µm show their energy spread to be close to the theoretically predicted energy spread without the Boersch effect. Even at 400 µA sr−1 operation, the emitter with a 4.2 µm tip radius shows a 0.47 eV full width at half‐maximum (FWHM) energy spread and the emitter with a 0.43 µm tip radius shows a 0.98 eV FWHM energy spread. Emitters with tip radii &gt;2 µm, fabricated by local Joule heating, are expected to suppress chromatic aberration in low beam voltage application and thus would be helpful for industrial uses such as critical dimension and defect review SEM. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Cooling negative-ion beams

Studies have been conducted to determine the feasibility of using the collisional cooling technique as a means of reducing energy spreads and emittances of sputter-generated negative-ion beams. A gas-filled rf-quadrupole ion cooler, equipped with provisions for decelerating ion beams to sufficiently low energies prior to cooling and reaccelerating them to high energies following the cooling process, has been designed and used to cool O− and F− ion beams with initial energy spreads, ΔE&amp;gt;10 eV to final energy spreads, ΔE∼2 eV full width half-maximum. Overall transmission efficiencies of ∼14% for F− beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions.

High resolution x-ray spectroscopy using GaAs arrays

We have produced a number of small format gallium arsenide (GaAs) arrays to address the material, electronic, and technological problems that need to be solved in order to develop mega pixel, Fano-limited spectroscopic x-ray imagers. Results will be presented of a series of x-ray measurements carried out on a prototype 5×5 array, fabricated from 40 μm thick epitaxial GaAs. The device has pixel sizes of 200×200 μm2 and pitch 250 μm. As a preliminary investigation of performance, two pixels have been instrumented. Measurements from 5.9 to 98 keV were carried out both in our laboratory and at the Hamburger Synchrotronstrahlungslabor research facility in Hamburg, Germany. Both pixels were found to be remarkably uniform, both in their spectral and spatial response to x-rays. The average nonlinearity in the spectral response is &amp;lt;1% across the energy range 5.9–98 keV. Using a 12 keV, 20×20 μm2 pencil beam, the spatial uniformity was found to be better than 98% over the entire pixel surfaces, consistent with the statistical precision of the measurement. The energy resolution at −40 °C is 400 eV full width at half maximum (FWHM) at 5.9 keV rising to 700 eV FWHM at 98 keV. No difference in energy resolution was found between full area and pencil beam illumination. An analysis of the resolution function has shown that the detector is dominated by electronic noise at low energies and Fano noise at energies above 30 keV. By best-fitting the expected resolution function to the entire data set, we derive a Fano factor of 0.140±0.05, together with a charge transport factor as low as 1.4×10−3. Further improvement in the resolution function has been achieved by replacing the conventional resistive feedback preamplifiers with a new resistorless design, which provides a lower component of electronic noise. In this case, a resolution of 266 eV FWHM at 5.9 keV has been achieved at room temperature (23 °C) and 219 eV FWHM with only modest cooling (−31 °C). The expected Fano noise at this energy is ∼140 eV.

Multi-anode sawtooth SDD for X-ray spectroscopy fabricated on NTD wafers

We are developing a multi-anode sawtooth silicon drift detector (MSSDD) with an anode pitch of 250 /spl mu/m for one-dimensional position-sensitive detection of low-energy X-rays down to /spl sim/200 eV. The detector is intended to be used in X-ray diffraction analysis. In this paper, we present new results of X-ray spectroscopy measurements with detectors fabricated on neutron transmutation doped (NTD) wafers with a thickness of 290 /spl mu/m. Using an MSSDD with an anode pitch of 250 /spl mu/m and having p/sup +/ strips on both sides, we have measured an energy resolution of 191-eV full-width half-maximum (FWHM) per anode pixel for the 5.89 keV line of /sup 55/Fe at 213 K. At room temperature the energy resolution is 375 eV FWHM. Split events are almost completely eliminated due to the sawtooth-shaped p/sup +/ strips.

Transition edge sensors as single photon detectors

We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.

Low-energy, electron-spin-polarized He+4 ion source

A source of low-energy, electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge is described. Ion polarizations P+ of ∼0.13 are achieved at beam currents of ∼0.1 nA, decreasing to ∼0.09 at currents of ∼0.5 nA. Ion beam energies as low as 10 eV have been realized, with an energy spread of ≲3 eV full width half maximum. The ion polarization can be reversed (P+→−P+) simply by changing the sense of circular polarization of the optical pumping radiation. The source is suitable for use in a wide variety of applications including surface physics studies.

High‐resolution, energy‐dispersive microcalorimeter spectrometer for X‐ray microanalysis

We have developed a prototype X‐ray microcalorimeter spectrometer with high energy resolution for use in X‐ray microanalysis. The microcalorimeter spectrometer system consists of a superconducting transition‐edge sensor X‐ray microcalorimeter cooled to an operating temperature near 100 mK by a compact adiabatic demagnetization refrigerator, a superconducting quantum interference device current amplifier followed by pulse‐shaping amplifiers and pileup rejection circuitry, and a multichannel analyser with computer interface for the real‐time acquisition of X‐ray spectra. With the spectrometer mounted on a scanning electron microscope, we have achieved an instrument response energy resolution of better than 10 eV full width at half‐maximum (FWHM) over a broad energy range at real‐time output count rates up to 150 s−1. Careful analysis of digitized X‐ray pulses yields an instrument‐response energy resolution of 7.2 ± 0.4 eV FWHM at 5.89 keV for Mn Kα1,2 X‐rays from a radioactive 55Fe source, the best reported energy resolution for any energy‐dispersive detector.

Pixel X-ray detectors in epitaxial gallium arsenide with high-energy resolution capabilities (Fano factor experimental determination)

Gallium Arsenide pixel detectors with an area of 170/spl times/320 /spl mu/m/sup 2/ and thickness of 5 /spl mu/m, realized by molecular beam epitaxy, have been designed and tested with X- and /spl gamma/ rays. No significant charge trapping effects have been observed, and a charge collection efficiency of 100% has been measured. At room temperature an energy resolution of 671 eV full width at half maximum (FWHM) at 59.54 keV has been obtained, with an electronic noise of 532 eV FWHM. With the detector cooled to 243 K, the electronic noise is reduced to 373 eV FWHM, and the K/sub /spl alpha// and K/sub /spl beta// lines of the /sup 55/Fe spectrum can be resolved. The Fano factor for GaAs has been measured at room temperature with 59.5 keV photons yielding F=0.12/spl plusmn/0.01.

The X-Ray/Gamma-ray spectrometer on the near Earth Asteroid Rendezvous mission

The X-ray/Gamma-ray Spectrometer on the Near Earth Asteroid Rendezvous spacecraft is a remote sensing instrument designed to develop elemental composition maps of the surface of the asteroid 433 Eros. This mapping operation will occur during about 10 months of orbital operations commencing in early 1999. Solar excited x-ray fluorescence in the 1 to 10 keV range will be used to measure the surface abundances of Mg, Al, Si, Ca, Ti, and Fe with spatial resolutions down to 2 km. Characteristic gamma-ray emissions in the 0.1 to 10 Mev range will be used to measure cosmic-ray excited elements O, Si, Fe, H and naturally radioactive elements K, Th, U to a depth of order 10 cm. The asteroid pointing portion of the x-ray spectrometer consists of three gas-filled proportional counters with an energy resolution of 850 eV full-width at half-maximum (FWHM) @ 5.9 keV. Two sunward looking x-ray detectors monitor the incident solar flux, one of which is the first flight of a new, miniature Si-PIN solid-state detector which achieves 600 eV FWHM @ 5.9 keV. The gamma-ray spectrometer consists of a NaI(Tl) scintillator situated in an active Bismuth Germanate (BGO) cup shield which confines the field of view, eliminates the need for a costly boom, and enables recovery of lost events in the central detector. The NaI(Tl) and BGO detectors achieve energy resolutions of 8.7% and 14% FWHM @ 0.662 MeV, respectively. A data processing unit using an RTX2010 provides the spacecraft interface and produces 256-channel spectra for x-ray detectors and 1024-channel spectra for integral, coincident, and anticoincident gamma-ray modes. We present an overview of the instrument and discuss design parameters and trade-offs.

Neutron-scattering studies of the two magnetic correlation lengths in terbium.

Extensive neutron-scattering experiments have been performed in order to characterize the nature of the two correlation lengths observed in Tb, a phenomenon common to Ho as well as ${\mathrm{SrTiO}}_{3}$. In the vicinity of the transition temeprature, each of those crystals exhibits an anomalous two-component q profile in the critical scattering; the usual broad peak and an unexpected additional narrow peak. In order to clarify the spatial origin of the narrow component, the (0,0,\ensuremath{\delta}) magnetic statellite peak of Tb has been closely examined using a very narrow neutron beam realized by a high spatial resolution reflectometer at the National Institute of Standards and Technology, which can produce well-defined beam widths of 0.3 mm and less. The small scattering angle (\ensuremath{\theta}\ensuremath{\approxeq}1.35 \ifmmode^\circ\else\textdegree\fi{}) and the narrow beam width result in an extraordinarily fine q and E resolution. As recently reported, we have confirmed that the intensity of the narrow component is enhanced near the edge of the crystal; it demonstrates that the major part is located within the near surface volume or ``skin'' of the crystal. A skin thickness of \ensuremath{\sim} 0.2 mm full width at half maximum (FWHM) is obtained by fitting the results to a model scatterer distribution which convolutes the beam profile. In contrast to the case of the central peak observed in ${\mathrm{SrTiO}}_{3}$, this unusual spatial distribution establishes the narrow component as a distinct entity in the critical fluctuations. We have shown that the narrow component possesses a different temperature dependence of \ensuremath{\delta} from that of the broad one. Moreover, high E resolution scans show that the narrow component has a distinct energy width which is smaller than our resolution limit (\ensuremath{\sim}2 \ensuremath{\mu}eV FWHM), and that it is essentially temperature independent. We believe that this quasistatic character of the narrow component is the important key to understanding its physical origin.

Transmission (e,2e) coincidence measurements of thin evaporated carbon, graphite, and aluminum-aluminum oxide foils.

Symmetric transmission (e,2e) coincidence data are presented from the valence region of evaporated amorphous carbon, graphite, and aluminum--aluminum oxide thin (between 100 and 200 \AA{}) foils. The count rate of this technique, within the plane-wave-impulse approximation, is directly proportional to the spectral momentum density. The data were accumulated at a probe energy of 7.5 keV with typical energy and momentum resolutions of 4.5 eV and 0.9 \AA{} $^{\mathrm{\ensuremath{-}}1}$ full width at half maximum (FWHM), respectively. The aluminum oxide foil was investigated close to 0 \AA{} $^{\mathrm{\ensuremath{-}}1}$ binding momentum with an improved energy resolution of 1.5 eV FWHM. The resolved electron states are related to the S and P nature of the valence electrons in these materials with a small atomic number. The similarity between amorphous carbon and graphite suggests that the amorphous sample was largely graphitically bonded. The results are discussed with special attention paid to the short, electron mean free paths within the solid samples.