Hard X-ray Spectrometer Research Articles

Solar X-ray polarimetry and spectrometry instrument PING-M for the Interhelioprobe mission

The PING-M experiment is designed to investigate solar X-ray activity. The instrument includes a hard X-ray polarimeter (PING-P), a hard X-ray spectrometer (HXRS) and a soft X-ray spectrometer (SXRS). PING-P has the energy range of 20–150keV and an effective area of about 2.5cm2. It uses three organic scintillation detectors as active scatterers, which work in coincidence with six absorber detectors, based on CsI(Tl) scintillator. This technique allows us to considerably improve the polarimeter sensitivity. HXRS has the energy range of 20–600keV and an effective area of about 15cm2. It is based on a fast inorganic scintillator (LaBr3(Ce) or CeBr3) with a relatively high energy resolution of 3.5–4.5% at 662keV. The SXRS energy range is 1.5–25keV, and its aperture is ø0.1mm, which provides the registration of solar flares in the range from C1 to X20 class of GOES scale. It is based on a SDD semiconductor detector with an energy resolution better than 200eV at 5.9keV line. The experiment will be performed onboard the Russian interplanetary mission Interhelioprobe which is planned for launch after 2025.The instrument will allow us to investigate angular and energy distributions of accelerated electrons, plasma heating processes, etc. Stereoscopic polarimetry and spectrometric observations will be possible if a similar instrument is installed onboard a near Earth satellite, or the second probe of the Interhelioprobe mission.

Tunable hard X-ray spectrometer utilizing asymmetric planes of a quartz transmission crystal.

A Cauchois type hard x-ray spectrometer was developed that utilizes the (301) diffraction planes at an asymmetric angle of 23.51° to the normal to the surface of a cylindrically curved quartz transmission crystal. The energy coverage is tunable by rotating the crystal and the detector arm, and spectra were recorded in the 8 keV to 20 keV range with greater than 2000 resolving power. The high resolution results from low aberrations enabled by the nearly perpendicular angle of the diffracted rays with the back surface of the crystal. By using other asymmetric planes of the same crystal and rotating to selected angles, the spectrometer can operate with high resolution up to 50 keV.

Development of Hard X-ray and Gamma-ray Detector With Transition Edge Sensor for Nuclear Materials Analysis

We have designed and fabricated a hard X-ray and gamma-ray TES spectrometer for nuclear materials analysis. A superconducting tin (Sn) absorber is coupled to the TES film by using a gold (Au) bump post to improve the thermal contact between the absorber and the TES. To obtain a sufficient detection efficiency at the high energy photons near 100 keV, an 8-pixel array of TES microcalorimeters were developed. In this new device, the epoxy glue which is used to connect the absorber and the gold bump post was well controlled and hence the slow component of the decay time constant was improved from 7.82 ms to 4.46 ms compared to our old device. The energy resolution was 131 eV FWHM at 59.5 keV gamma rays, which is better than the limit of HPGe detectors (400 eV FWHM at 60 keV).

Photonuclear reaction based high-energy x-ray spectrometer to cover from 2 MeV to 20 MeV.

A photonuclear-reaction-based hard x-ray spectrometer is developed to measure the number and energy spectrum of fast electrons generated by interactions between plasma and intense laser light. In this spectrometer, x-rays are converted to neutrons through photonuclear reactions, and the neutrons are counted with a bubble detector that is insensitive to x-rays. The spectrometer consists of a bundle of hard x-ray detectors that respond to different photon-energy ranges. Proof-of-principle experiment was performed on a linear accelerator facility. A quasi-monoenergetic electron bunch (Ne = 1.0 × 10(-6) C, Ee = 16 ± 0.32 MeV) was injected into a 5-mm-thick lead plate. Bremsstrahlung x-rays, which emanate from the lead plate, were measured with the spectrometer. The measured spectral shape and intensity agree fairly well with those computed with a Monte Carlo simulation code. The result shows that high-energy x-rays can be measured absolutely with a photon-counting accuracy of 50%-70% in the energy range from 2 MeV to 20 MeV with a spectral resolution (Δhν/hν) of about 15%. Quantum efficiency of this spectrometer was designed to be 10(-7), 10(-4), 10(-5), respectively, for 2-10, 11-15, and 15-25 MeV of photon energy ranges.

Automated grid-based XFEL diffraction studies of single macromolecular crystals

A major challenge of structural investigations of metalloproteins at synchrotrons is the damaging effects of radiation exposure. Even small X-ray doses can reduce or initiate reactions at metal centers modifying the active site. For example, in-situ visible absorption spectroscopy measurements have demonstrated that the heme/copper active site in oxidized ba3 cytochrome oxidase (ba3) is compromised during a single X-ray diffraction exposure. The use of ultrashort X-ray pulses at LCLS provides a means to measure high resolution diffraction before these damage processes occur. To this end, experiments were conducted at LCLS using large multiple crystals (> 50 µm) of ba3, hydrogenase and myoglobin. Crystals were mounted in `grids' or loops and flash frozen. The grids hold up to 75 crystals in known locations and are compatible with the Stanford Automounter used to exchange them. Following a semi-automated grid alignment procedure, a fully automated routine was used to position each crystal and collect a series of diffraction images and the Blu-Ice/DCS control system that coordinated with the LCLS EPICS system and XPP DAQ software. Single femtosecond X-ray pulses produced a `damage free' still diffraction image from each crystal. To provide additional information about crystal orientation, a series of pseudo-oscillation images were collected +/- 5.5 degrees spanning the orientation of the still image. For each one degree oscillation image the crystal was exposed to 120 attenuated X-ray pulses. A hard X-ray spectrometer was used to measure the energy spectrum of each individual X-ray pulse. The details and results of these experiments will be presented.

Time-resolved measurements of the hot-electron population in ignition-scale experiments on the National Ignition Facility (invited).

In laser-driven inertial confinement fusion, hot electrons can preheat the fuel and prevent fusion-pellet compression to ignition conditions. Measuring the hot-electron population is key to designing an optimized ignition platform. The hot electrons in these high-intensity, laser-driven experiments, created via laser-plasma interactions, can be inferred from the bremsstrahlung generated by hot electrons interacting with the target. At the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)], the filter-fluorescer x-ray (FFLEX) diagnostic-a multichannel, hard x-ray spectrometer operating in the 20-500 keV range-has been upgraded to provide fully time-resolved, absolute measurements of the bremsstrahlung spectrum with ∼300 ps resolution. Initial time-resolved data exhibited significant background and low signal-to-noise ratio, leading to a redesign of the FFLEX housing and enhanced shielding around the detector. The FFLEX x-ray sensitivity was characterized with an absolutely calibrated, energy-dispersive high-purity germanium detector using the high-energy x-ray source at NSTec Livermore Operations over a range of K-shell fluorescence energies up to 111 keV (U Kβ). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.

Gamma-Ray Spectrometer based on a Transition Edge Sensor for Nuclear Materials Analysis

We designed and fabricated a hard X-ray and gamma-ray TES spectrometer for nuclear materials analysis. The superconducting tin absorber is coupled to an Ir/Au TES by using a gold post to improve the thermal contact between the absorber and the TES. The reported energy resolution is 156 eV FWHM at 59.5 keV and 166 eV FWHM at 122 keV gamma-rays. We performed measurement of a Pu sample and clearly separated the \(^{239}\)Pu (56.828 keV) and the \(^{241}\)Am (59.5 keV) peaks by this TES microcalorimeter which cannot be resolved by the HPGe detector.

Comparative analysis of digital pulse processing methods at high count rates

An extensive study of digital pulse processing methods is presented. Existing methods, both traditional and more recent, are compared with original advanced techniques within an appropriate modeling and benchmarking framework. This comprehensive approach ensures general applicability to the broad field of pulse processing, even though the focus lies on hard X-ray spectrometers operated at high count rates. In this regime, pile-up is the main issue and the individual pulse shape characteristics play a minor role, although they remain important for the algorithm parameter optimization.The digital implementation of double-differentiating analog filters and trapezoidal FIR filter methods results in excellent performance that is second only to that of optimum digital FIR filters. Several more complex methods involving increased computational effort are found not to meet the expectations.

Characterisation of a MeV Bremsstrahlung x-ray source produced from a high intensity laser for high areal density object radiography

Results of an experiment to characterise a MeV Bremsstrahlung x-ray emission created by a short (<10 ps) pulse, high intensity (1.4 × 1019 W/cm2) laser are presented. X-ray emission is characterized using several diagnostics; nuclear activation measurements, a calibrated hard x-ray spectrometer, and dosimeters. Results from the reconstructed x-ray energy spectra are consistent with numerical simulations using the PIC and Monte Carlo codes between 0.3 and 30 MeV. The intense Bremsstrahlung x-ray source is used to radiograph an image quality indicator (IQI) heavily filtered with thick tungsten absorbers. Observations suggest that internal features of the IQI can be resolved up to an external areal density of 85 g/cm2. The x-ray source size, inferred by the radiography of a thick resolution grid, is estimated to be approximately 400 μm (full width half maximum of the x-ray source Point Spread Function).

A seven-crystal Johann-type hard x-ray spectrometer at the Stanford Synchrotron Radiation Lightsource.

We present a multicrystal Johann-type hard x-ray spectrometer (~5-18 keV) recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The instrument is set at the wiggler beamline 6-2 equipped with two liquid nitrogen cooled monochromators--Si(111) and Si(311)--as well as collimating and focusing optics. The spectrometer consists of seven spherically bent crystal analyzers placed on intersecting vertical Rowland circles of 1 m of diameter. The spectrometer is scanned vertically capturing an extended backscattering Bragg angular range (88°-74°) while maintaining all crystals on the Rowland circle trace. The instrument operates in atmospheric pressure by means of a helium bag and when all the seven crystals are used (100 mm of projected diameter each), has a solid angle of about 0.45% of 4π sr. The typical resolving power is in the order of E/ΔE ~ 10,000. The spectrometer's high detection efficiency combined with the beamline 6-2 characteristics permits routine studies of x-ray emission, high energy resolution fluorescence detected x-ray absorption and resonant inelastic x-ray scattering of very diluted samples as well as implementation of demanding in situ environments.

High-Energy Bremsstrahlung Diagnostics to Characterize Hot-Electron Production in Short-Pulse Laser-Plasma Experiments

Short-pulse (<; 10 ps) high-intensity (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> W·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) laser-target interactions produce high-density plasmas, in which a hot (nonthermal) collisionless electron population is generated via a number of energy absorption mechanisms. A key requirement in many applications of these interactions is to achieve maximum conversion efficiency of laser energy into hot electrons of a specific energy. Measurement of the hot-electron temperature and the associated hot-electron fraction supports the understanding of energy absorption mechanisms present in the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sup> W·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> intensity regime. One highly useful signature of hot-electron generation is the bremsstrahlung radiation emission due to the hot electrons interacting electromagnetically with cold target atoms. We present the design, characterization, and modeling of two target diagnostics to measure the high-energy (100 keV-2 MeV) bremsstrahlung emission from hot electrons in laser-plasma experiments; a thermoluminescent dosimeter (TLD) array and a hard X-ray spectrometer (HXRS). These diagnostics will exploit new techniques to determine the hot-electron distribution generated with the short-pulse beamlines of the upcoming high-power Orion laser system at AWE. Past bremsstrahlung dose measurements obtained with a TLD array (of similar design to the Orion one) are used to demonstrate how the bremsstrahlung production efficiency, an indicator of hot-electron generation, can change with laser parameters, target type, and experimental geometry. In addition, we use results from characterization of the HXRS, a diagnostic which collects channel charges in defined bremsstrahlung spectral ranges, to establish a new method enabling the diagnosis of hot-electron temperatures.

A multi-crystal wavelength dispersive x-ray spectrometer

A multi-crystal wavelength dispersive hard x-ray spectrometer with high-energy resolution and large solid angle collection is described. The instrument is specifically designed for time-resolved applications of x-ray emission spectroscopy (XES) and x-ray Raman scattering (XRS) at X-ray Free Electron Lasers (XFEL) and synchrotron radiation facilities. It also simplifies resonant inelastic x-ray scattering (RIXS) studies of the whole 2d RIXS plane. The spectrometer is based on the Von Hamos geometry. This dispersive setup enables an XES or XRS spectrum to be measured in a single-shot mode, overcoming the scanning needs of the Rowland circle spectrometers. In conjunction with the XFEL temporal profile and high-flux, it is a powerful tool for studying the dynamics of time-dependent systems. Photo-induced processes and fast catalytic reaction kinetics, ranging from femtoseconds to milliseconds, will be resolvable in a wide array of systems circumventing radiation damage.

Balloon-Borne Hard X-Ray Spectrometer Using CdTe Detectors

Spectroscopic observation of solar flares in the hard X-ray energy range, particularly the 20 ∼ 100 keV region, is an invaluable tool for investigating the flare mechanism. This paper describes the design and performance of a balloon-borne hard X-ray spectrometer using CdTe detectors developed for solar flare observation. The instrument is a small balloon payload (gondola weight 70 kg) with sixteen 10×10×0.5 mm CdTe detectors, designed for a 1-day flight at 41 km altitude. It observes in an energy range of 20−120 keV and has an energy resolution of 3 keV at 60 keV. The second flight on 24 May 2002 succeeded in observing a class M1.1 flare.

Enhanced x-ray resolving power achieved behind the focal circles of Cauchois spectrometers

Maintaining high resolving power is a primary challenge in hard x-ray spectroscopy of newly developed bright and transient x-ray sources such as laser-produced plasmas. To address this challenge, the line widths in x-ray spectra with energies in the 17 keV to 70 keV range were recorded by positioning the detectors on and behind the focal circles of Cauchois type transmission-crystal spectrometers. To analyze and understand the observed line widths, we developed a geometrical model that accounts for source broadening and various instrumental broadening mechanisms. The x-ray sources were laboratory Mo or W electron-bombarded anodes, and the spectra were recorded on photostimulable phosphor image plates. For these relatively small x-ray sources, it was found that when the detector was placed on or near the focal circle, the line widths were dominated by the effective spatial resolution of the detector. When the detector was positioned beyond the focal circle, the line widths were determined primarily by source-size broadening. Moreover, the separation between the spectral lines increased with distance behind the focal circle faster than the line widths, resulting in increased resolving power with distance. Contributions to line broadenings caused by the crystal thickness, crystal rocking curve width, geometrical aberrations, and natural widths of the x-ray transitions were in all cases smaller than detector and source broadening, but were significant for some spectrometer geometries. The various contributions to the line widths, calculated using simple analytical expressions, were in good agreement with the measured line widths for a variety of spectrometer and source conditions. These modeling and experimental results enable the design of hard x-ray spectrometers that are optimized for high resolving power and for the measurement of the x-ray source size from the line widths recorded behind the focal circle.

Hard X‐Ray Spectral Observation of a High‐Temperature Thermal Flare

We report on the analysis of a thermal flare observed by a newly developed balloon-borne hard X-ray spectrometer. This instrument uses CdTe detectors and can observe the 20-120 keV hard X-ray range, with 3.0 keV energy resolution at 60 keV. During the 2002 May 24 flight, it successfully observed a class M1.1 flare. This flare observation shows no detectable flux above 35 keV, and its spectrum is consistent with a superhot thermal source with the temperature varying from 44 to 20 MK. Partial observation of the flare by the RHESSI satellite is consistent with this result. The Nobeyama Radio Polarimeters (NORP) observation of this flare shows no detectable polarization. The NORP light curves show impulsive features at 3.75 GHz that can be explained as thermal gyrosynchrotron emission, and this flux is consistent with observed X-ray spectra if a magnetic field of 275 G is assumed. Slower varying features seen in the NORP data are consistent with the lower temperature (hot) thermal source of 10-15 MK seen in soft X-rays. We conclude that this flare shows no observable signature of nonthermal electrons, and all observed features are consistent with a purely thermal event. This serves as a strong indication that a nonthermal electron beam is not always the dominant energy source of plasma heating in solar flares.

YOHKOH/WBS Recalibration and a Comprehensive Catalogue of Solar Flares Observed by YOHKOH SXT, HXT and WBS Instruments

The flare catalogue of the Yohkoh mission is compiled and linked to this article as an electronic supplement. For showing flare characteristics over wide energy range concisely, we provide the images of Hard X-ray Telescope (HXT) and the Soft X-ray Telescope (SXT), and the spectra of Hard X-ray Spectrometer (HXS) and Gamma-Ray Spectrometer (GRS) with the Wide Band Spectrometer (WBS) time profiles. The energy versus pulse height (PH) data channels in HXS and GRS are re-calibrated by using the data of the whole mission period. Secular gain changes are recognized in HXS, and the characteristics of power-law flare spectra simultaneously observed by HXT and HXS confirms the trend. The GRS gains are different for the flare observations during the previous maximum and for the current maximum. The total of 33 γ -ray events are observed, and for 12 of them γ-ray flare spectra are obtained.

Forecasting methods for occurrence and magnitude of proton storms with solar hard X rays

A hard X‐ray spectrometer (HXRS) was developed jointly by the National Oceanic and Atmospheric Administration (NOAA) Space Environment Center and the Astronomical Institute of the Czech Republic to determine if proton storms could be forecast with greater accuracies than presently available by the existing methods. The HXRS experiment was conceived as a means of proof testing previously discovered empirical relationships between anomalous hard X‐ray spectra of hard X‐ray flares and solar energetic proton events (SEPs) for space weather forecasting applications. SEPs are showers of highly energetic electrons and ions, mostly protons, that can reach Earth's vicinity within minutes to hours following a moderate to large flare and have the potential of affecting the performance of civilian, military and research satellites as well as certain surface assets. The primary SEP predictor criterion educed during the present study is the requirement that the spectral index, γ, must decline (harden) to at least ≤4 for at least 3 min. Flares meeting this criterion have a high association with SEPs. Flares that fail this criterion do not. Other SEP correlative phenomena such as depressed hard X‐ray flux and anomalous low temperatures were studied to determine their utility for forecasting purposes. During the study period, March 2000 through December 2002, 107 hard X‐ray flares were spectrally analyzed including 16 SEP‐associated flares. Fourteen SEP flares were correctly identified, two SEPs were missed, and three false alarms (untrue predictions) were incurred.

Studies of runaway electrons in the Globus-M tokamak

Results are presented from experimental studies of runaway electrons in the ohmic heating regime in the Globus-M tokamak. The periodical hard X-ray bursts observed with the help of two hard X-ray spectrometers with high time resolution are attributed to MHD oscillations in the plasma core and at the periphery.

Hard X-ray solar flare polarimetry with RHESSI

Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20–100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine germanium detectors. The Ge detectors are segmented, with both a front and rear active volume. Low energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Sensitivity estimates, based on simulations and in-flight background measurements, indicate that a 20–100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares. The initial results from an analysis of data from the solar flare of 23 July 2002 indicate some modulation of the Be-scattered flux, but whether the modulation arises from polarization effects or whether it represents some instrumental effect is as yet unclear.

Observation of solar flare hard X-ray spectra using CdTe detectors

We present the design and initial flight results of a balloon-borne hard X-ray spectrometer for observing solar flares. The instrument is designed for quantitative observation of nonthermal and thermal components of solar flare hard X-ray emission, and has an energy range of 15–120 keV and an energy resolution of 3 keV. The instrument is a small (gondola weight 70 kg) system equipped with sixteen 10 × 10 × 0.5 mm CdTe detectors, and designed for a 1-day flight at 41 km altitude. Detector temperature of −15 °C was achieved through radiative cooling alone. Pre-flight tests confirmed that all detectors exceeded the target 3 keV resolution. No flares were observed during the 2001 flight, but the second flight on May 24, 2002 succeeded in observing a class M1.1 flare. Preliminary analysis indicates the observed spectrum is consistent with a purely thermal plasma at an unusually high temperature of 47 mK.