Hard X-ray Detector Research Articles

Detection of Hard X-Rays from a Class I Protostar in the HH 24-26 Region in the Orion Molecular Cloud

We observed the HH 24-26 region in the L1630 Orion molecular cloud complex with the X-ray observatory ASCA in the 0.5-10 keV band. X-ray emission was detected from the T Tauri star SSV 61 and from the region in which the class I protostars SSV 63E and SSV 63W (hereafter SSV 63E+W) are located. The spectra of both SSV 63E+W and SSV 61 are well explained by an optically thin thermal plasma model. The spectrum of the T Tauri star SSV 61 has a low temperature of kT = 0.9 (0.7-1.2) keV and a moderate absorption of NH = 1.3 (0.9-1.7) × 1022 cm-2, while that of the protostar SSV 63E+W has a high temperature of kT = 5.0 (3.3-7.9) keV and a heavy absorption of NH = 1.5 (1.2-1.8) × 1023 cm-2. The X-ray light curve of SSV 63E+W showed a flare during the observation. The peak flux reached about 9 times the intensity of the quiescent flux. The temperature and the absorption column density do not change conspicuously during the flare. The 0.5-10 keV luminosity of SSV 63E+W was about 1 × 1032 ergs s-1 in the quiescent state. The present detection of hard X-rays from SSV 63E+W is remarkable, since this is the first X-ray detection of a protostar in Orion.

Activation of the ASTRO-E hard X-ray detector in low Earth orbit

ASTRO-E hard X-ray detector (HXD) is characterized by well-type phoswich counters in a compound-eye configuration which reduce the detector background to lower level than any other past hard X-ray mission. When operating in low Earth orbit, the expected background of the HXD is an order of 10/sup -5/ counts/s/keV/cm/sup 2/, mainly caused from the radioactivity induced within the detector materials by geomagnetically trapped protons. Results are presented from measurements of induced radioactivity in two phoswich scintillators, GSO (Gd/sub 2/SiO/sub 5/:Ce 0.5% mol) and BGO (Bi/sub 4/Ge/sub 3/O/sub 12/), irradiated by mono-energetic protons at an accelerator facility. Radiation transport computer codes are used to build the detector response functions for emissions from decays of spallation products. Based on the comparison between experimental and simulation results, the activation background level of HXD in the orbit is estimated.

The X-ray response of CdZnTe detectors to be used as future spectroscopic detectors for X-ray astronomy

The next generation of X-ray astrophysics missions may well extend the energy range beyond the current limit of about 10 keV studied by the existing X-ray Astrophysics space missions such as ASCA or future missions such as AXAF and XMM to be launched in the next few years. To address with a high degree of sensitivity the astrophysical problems associated with X-ray emission in the X-ray band from 0.2 to 100 keV a significant extension of the capabilities of focusing X-ray optics and imaging broad band hard X-ray detectors will be required. Future missions such as INTEGRAL, BASIS and EXIST will make use of CdZnTe or CdTe detectors for imaging spectroscopy down to about 5 keV with a spectral resolution between 3% and 7% at 100 keV. This is about a factor of 10 away from what is theoretically possible and mainly caused by the poor crystal quality. In this paper experimental results on the study of the X-ray response of CdZnTe detectors are presented. The detector response to photons with energies between 1 and 5 keV has been investigated using synchrotron radiation and a preliminary model to describe the detector response developed. The limitations on the energy resolution, due to incomplete charge collection and spatial non-uniformities, are presented based on the detailed mapping of the energy response of a detector exposed to highly monochromatised synchrotron radiation. At higher energies results have been obtained using a 241Am radioactive source and an electron cyclotron resonance source so as to establish the detector performance and overall response to medium- and higher-energy X-ray photons up to 60 keV. Based on these results the performance of the detectors are compared with Si(Li) and HPGe solid-state detectors.

Investigation of electron and ion beams in mega-ampere fiber pinch plasmas

The latter stages of fiber Z-pinch discharges at current levels up to 1.4 MA with a rise time of 150 ns have been investigated on the MAGPIE generator. Carbon fibers with a diameter of 33 /spl mu/m and deuterated polyethylene (CD/sub 2/) fibers with diameters between 50 and 200 /spl mu/m were used as loads. The detection of hard X-rays and neutrons provide evidence for MeV electrons and ions. The hard X-rays occur around 120-200 ns into the discharge and typically last for between 20 and 100 ns. Beam target neutrons have also been detected at this time with neutron energies of up to 5.2 MeV. Optical and X-ray diagnostics indicate that the dynamic hot spot phase of the pinch is over by this time and that no rapid pinching or expansion of dense plasma is occurring. The pinch is seen to be composed of high density regions along the axis interspersed by tenuous regions where the density is at least two orders of magnitude lower. A conceptual model which is consistent with the experimental data is proposed to explain the energy and duration of the X-ray and neutron pulses.

Scintillation detection using a silicon drift chamber with on-chip electronics

The performances of a Silicon Drift Chamber (SDC), having a diameter of 3 mm, as scintillation light photodetector have been experimentally evaluated on a prototype of hard X-ray spectrometer employing a Csl(Tl) crystal of the same diameter and 5 mm thick. The SDC, with on-chip electronics, is characterized by an electronics noise considerably lower than that exhibited by a conventional photodiode of equal area and thickness. Consequently, the present hard X-ray detector may operate on a wide energy range, with a minimum energy threshold of about 10 keV at room temperature or lower than 5 keV below 10°C. The measured energy resolution at room temperature is 7.49% FWHM at 122 keV and 4.34% FWHM at 662 keV. The same SDC photodetector has been also used together with a Csl(Tl) crystal having a thickness of 10 mm and, consequently, a useful energy range extending up to soft γ-ray energies. While at room temperature the energy resolutions of the two detector configurations are substantially identical, below 10°C the configuration using the smaller crystal shows appreciably better performances.

Hard X-ray detection model for microchannel plate detectors

A generalized hard X-ray detection model for microchannel plate detectors has been developed. This model includes all geometrical and compositional parameters of an MCP and the energy of a detected X-ray. An analytical investigation and numerical calculation of the detection efficiency was carried out; obtained data were compared with experimental results. A square and hexagonal channel MCP were considered in addition to a traditional circular channel MCP. Moreover, it is shown that the first ones have advantages as X-ray detectors.

Generalized hard x-ray detection model for microchannel plate detectors

A generalized hard x-ray detection model for microchannel plate (MCP) detectors has been developed. This model includes all geometrical and compositional parameters of an MCP and the energy of a detected x-ray. An analytical investigation and numerical calculation of the detection efficiency were carried out; data obtained were compared with experimental results. A square and hexagonal channel MCP were considered in addition to a traditional circular channel MCP. Moreover, it is shown that the first ones have advantages as x-ray detectors.

Investigating “Precursor Flows” in Solar Flares

Despite some measure of theoretical and predictive success of the electron-heated model of solar flares, observations of low levels of soft X-ray emission prior to the detection of hard X-rays in most flares present a problem for the paradigm, since it suggests some sort of preheating of the chromospheric plasma before electron acceleration. Particularly troublesome are assertions that plasma have been observed prior to hard X-ray emission, because they imply significant and rapid energy input by some agent without leaving a (currently) detectable hard X-ray signature. Given this challenge to a prevailing paradigm, it is imperative to investigate more comprehensively the existence of flows manifested in the asymmetry of X-ray spectral lines. In this paper, we examine a sample of 50 disk-center flares observed by the Yohkoh Bragg Crystal Spectrometer (BCS) between 1991 and 1993, and determine with the velocity differential emission measure the extent to which flows occur. We explore specifically the possibility that these flows are only apparent, arising from the existence of more than one emission region on the solar disk. The spatial separation between regions could cause the emission to be registered by the detector in a wavelength bin that is shifted relative to the line's nominal location, giving rise to line asymmetries. In our sample, we find that only five flares manifest flows, three of which can be explained definitively by the presence of other active regions. It also appears plausible that the remaining two events can be explained in terms of such spatial effects, although the evidence is more circumstantial. We conclude, therefore, that one can reasonably question the existence of flows in our sample and that the observations to date cannot contribute decisively to the electron versus proton debate. These results are contrasted with those of Plunkett & Simnett, who identified 14 events in a sample of 35 flares and hence concluded, without further analysis, that protons, rather than electrons, must be the primary energy carriers in flares. Our paper's sample included eight of Plunkett & Simnett's 14 events, and yet our analysis, which employed substantially different methods, identified only one of these eight as a precursor event. The remaining seven were either troubled by BCS data dropout or failed to exceed the 10% threshold required to classify a flare as aprecursor event.

Compound Semiconductor Detectors for X-Ray Astronomy: Spectroscopic Measurements and Material Characteristics

AbstractThe use of some specific compound semiconductors in the fabrication of high energy X-ray detectors shows significant potential for X-ray astrophysics space missions. We are currently investigating three high purity crystals - CdZnTe, GaAs and TlBr - as the basis for future hard X-ray detectors (above 10 keV). In this paper we present the first results on CdZnTe and GaAs based detectors and evaluate the factors currently still constraining the performance.Energy resolutions (FWHM) of 0.9 keV and 1.1 keV at 14 keV and 60 keV, respectively, have been obtained with an epitaxial GaAs detector, while 0.7 keV and 1.5 keV FWHM were measured at the same energies with a CdZnTe detector. Based on these results it is clear, that the next generation of X-ray astrophysics missions now in the planning phase may well consider extending the photon energy range up to ∼100 keV by use of efficient detectors with reasonable spectroscopic capabilities.

Discovery of Hard X-Rays from a Cluster of Protostars

We report on the detection of hard X-rays from protostar candidates (Class I sources) in the R Coronae Australis (R CrA) molecular cloud. The hard X-rays are found even in the quiescent states with extremely high temperature of about 6 keV. One of the sources, probably the embedded far-infrared source R1, exhibited a powerful X-ray flare. These phenomena are similar to, but with a significantly higher temperature than, those seen in T Tauri stars. The flare spectrum is unusual, showing a broadened or double emission-line structure between 6.2 and 6.8 keV. Since X-rays are unexpected from current protostellar theory, these ASCA observations should have a significant impact on our understanding of star formation and the earliest phases of stellar evolution.

Alternative Methods for Sub-eV Resolution Inelastic X-ray Scattering (invited)

A synopsis of SRI workshop 9 held on October 20, 1995, is given. Details concerning the oral presentations of speakers not contributing to these proceedings are included. The workshop consisted of the following invited presentations: 1. M. Schwoerer-Boehning (APS), ‘‘Experimental Needs for Milli-eV Resolution Inelastic X-ray Scattering, ’’ 2. E. E. Alp (APS), ‘‘Inelastic Nuclear Resonant X-ray Scattering,’’ 3. A. Baron (ESRF), ‘‘ Inelastic X-ray Scattering via Nuclear Resonant Analyzer,’’ 4. D. E. Moncton (APS), ‘‘ An Exact Backscattering Beamline,’’ 5. A. Caticha (SUNY-Albany), ‘‘X-ray Fabry-Perot Cavities,’’ 6. E. D. Isaacs (AT&T Bell Labs), ‘‘Flux and Resolution Requirements for Studies of Electronic Excitations in Solids,’’ 7. C. K. Stahle (NASA), ‘‘Hard X-ray Detectors with Very High Energy Resolution,’’ 8. A. K. Freund (ESRF), ‘‘Mosaic Crystal Analyzers.’’ These proceedings contain separate papers by Caticha, Isaacs, and Stahle for the above listed presentations, and we will not discuss them further here. The other presentations are summarized below.

A new hard X-ray detector based on microchannel plates

A high efficiency detector of hard X-ray based on microchannel plates is described. Since the hard X-ray interaction probability in microchannel plate (MCP) material is small, most quanta incident upon the MCP detector do not interact with the MCP material. If several MCP detectors are placed consecutively and their anodes are electrically connected, the efficiencies of these detectors will be summed up and the efficiency of this assembly will be much higher than that of a separate MCP detector. Using this simple idea a compact multilayer MCP detector consisting of 10 double-Chevrons was developed. The detection efficiency for 122 and 662 keV quanta was 14% and 28% respectively. The probability of X-ray interaction with detector material and the efficiency increasing possibility was investigated.

A novel high energy X-ray detector concept using CCDs

Abstract The X-ray detection efficiency of charge coupled devices (CCDs) is dependent on the thickness of the active depletion layer in the silicon, typically less than 40 μm and limited by the purity of available epitaxial substrates. For X-ray imaging, therefore, the CCD detection efficiency drops sharply above 8 keV. In this Letter, we show that, using a novel illumination geometry, CCDs can detect high energy (up to 100 keV) X-rays with reasonable efficiency and good energy resolution. A novel 2-D imaging hard X-ray detector based on this geometry is discussed.

Development of the pulse-shape discrimination LSI for Astro-E Hard X-ray Detector

We have developed a pulse-shape discrimination LSI for the Astro-E Hard X-ray Detector (HXD). In the detector, the X-ray and non X-ray background will be reduced drastically by use of well-type phoswich counters in the compound-eye configuration. The well-type phoswich counter will use GSO(Ce) or YAP(Ce) scintillator for its detection part, and well-shaped BGO for the shielding part. The pulse-shape discriminator (PSD) described here will be used to select clean hits on the detection part, rejecting those depositing some energy in BGO. The PSD is designed as a bipolar semi-custom LSI to reduce its power consumption and size, and to enhance its reliability. The first delivery of the PSD-LSI has been tested to be acceptable for Astro-E HXD.

Hard x-ray detector based on microchannel plates

A high efficiency detector of hard x ray based on microchannel plates is described. The detected x-ray beam was directed perpendicularly to the lateral surface of microchannel plate convertors. The detection efficiency for beams with 2×2 mm cross section and energies of 662 and 122 keV was 24% and 35%, respectively. The probability of x-ray interaction with microchannel plate material was measured. The detector position resolution is 0.5 and 1.5 mm for 122 and 662 keV radiation.

Performance of MBE grown CdTe photoconductor arrays for hard X-ray detection

Photoconductor linear array detectors for hard X-ray photon detection were fabricated using Molecular Beam Epitaxially (MBE) grown (111)B CdTe on (100) Si substrates. The ohmic contact to the CdTe was excellent and provided a linear response to the X-ray photons. The response current was linearly increased in a 7–19 keV energy range. The stability of the detectors was very satisfactory and they were tested over an extended period of time without noticeable degradation. The excellent response uniformity of a 64 linear array was obtained. The performance of the photoconductor was greatly improved when the detector was cooled. At 230 K, the dynamic range of the detector response increased to nearly four decades.

Effects of large aspect ratios and fluctuations on hard x-ray detection in lower hybrid driven divertor tokamaks

It is shown that lower hybrid wave scattering from fluctuations plays a critical role in large aspect ratio divertor plasmas even though the edge density fluctuation levels are only at 1%. This is seen in the theoretically calculated electron power-density profiles which can be directly correlated to the standard experimental chordal hard x-ray profiles. It thus seems that fluctuation effects must be included in determining rf current-density profiles.

Diagnostics for real-time plasma control in PBX-M

An important issue for future tokamaks is real-time plasma control for the avoidance of magnetohydrodynamic instabilities and other applications that require detailed plasma profile and fluctuation data. Although measurements from diagnostics providing this information require significantly more processing than magnetic flux data, recent advancements could make them practical for adjusting operational settings for plasma heating and current drive systems as well as field coil currents. On the Princeton Beta Experiment-Modification (PBX-M), the lower hybrid current drive phasing can be varied during a plasma shot using digitally programmable ferrite phase shifters, and neural beam functions can be fully computer controlled. PBX-M diagnostics that may be used for control purposes include motional Stark-effect polarimetry for magnetic field pitch angle profiles, soft x-ray arrays for plasma position control and the separation of βp from li, hard x-ray detectors for energetic electron distributions, a multichannel electron cyclotron emission radiometer for ballooning mode identification, and passive plate eddy current monitors for kink stabilization. We will describe the present status of these systems on PBX-M, and discuss their suitability for feedback applications.

Peak hold monolithic integrated circuit with built-in shaping amplifier for hard X-ray detector

A peak hold monolithic integrated circuit, a pulse shape discriminator (PSD), was designed and fabricated for a hard X-ray telescope of a well-type phoswich counter: Welcom-2. It will be loaded in an X-ray astronomical satellite, the Deep Universe Exploring Telescope (DUET). In order to fit the small area of the satellite, this PSD is manufactured by using a semi-custom bipolar junction transistor LSI. The circuit consists of two shaping amplifiers (100 and 500 ns), with peak hold circuits: a low level threshold comparator with a latch; a high level comparator; an auto reset circuit; and an input signal suppress circuit. Requirements for satellite use such as low power consumption under 200 mW/channel were satisfied. The circuit design and circuit analysis of the PSD have been carried out using the SPICE package. A quantitative measurement of the sample chips was carried out. The integral nonlinearity was measured to be less than 0.2% range, and the drop rate of the peak hold circuit was measured to be 0.2%/ mu s. >

Hard X-ray emission from a narrow-line radio galaxy IC 5063 and obscured active nucleus

view Abstract Citations (22) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hard X-Ray Emission from a Narrow-Line Radio Galaxy IC 5063 and Obscured Active Nucleus Koyama, Katsuji ; Awaki, Hisamitu ; Iwasawa, Kazushi ; Ward, Martin J. Abstract We report the first detection of hard X-rays (above 2 keV), from the narrow-line radio galaxy (NLRG) IC 5063. The hard X-ray spectrum is described by a power-law photon index of 1.5 with a large absorption corresponding to the N_H_ value of 2 x 10^23^ H cm^-2^. The X-ray luminosity (2-20 keV band) after the correction of the absorption is 2.5 x 10^43^ ergs s^-1^. Since the X-ray luminosity and spectral index are in the range found for Seyfert 1's and broad-line radio galaxies (BLRG), we conclude that IC 5063 has an intrinsic BLRG type nucleus hidden behind a high gas column. There is a hint of X-ray flux variations with time scales between 10^3^ s and 10 hr which, if confirmed, would further support that the hard X-rays are the direct beam from a compact nucleus penetrating the high gas column. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/186624 Bibcode: 1992ApJ...399L.129K Keywords: Active Galactic Nuclei; Emission Spectra; Radio Galaxies; Seyfert Galaxies; X Ray Spectra; Absorption Spectra; Ginga Satellite; Light Curve; Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 5063; GALAXIES: NUCLEI; GALAXIES: SEYFERT; RADIO CONTINUUM: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (4) NED (1)