Semiconductor X-ray Detectors Research Articles

Investigations of Electron Behavior in the Gamma 10 Tandem Mirror on the Basis of X-Ray Analyses Using a Novel Theory on Semiconductor Detector Response

(i) A scaling law and its physics mechanism of potential formation for tandem-mirror plasma confinement are investigated. The first result of a generalized scaling covering over two typical plasma operational modes in the GAMMA 10 tandem mirror is presented; that is, a previously obtained potential-formation scaling in a plasma operational mode with a few-kV confinement potentials is found to be extended and generalized to a potential scaling in a hot-ion operational mode with thermal-neutron yield, when we take account of the dependence of potential formation on the ratio of the plug to the central-cell densities as well as the relation of electron temperatures in the central cell to thermal-barrier potentials. The finding of the existence of the same physics basis underlying in these two typical modes may provide the future possibility of simultaneously obtained hot-ion plasmas with high potentials. (ii) For these scaling studies, we have constructed the physics fundamentals of x-ray diagnostics; that is, we proposed a novel theory on the energy response of a widely utilized semiconductor x-ray detector. The theory solves a serious problem of a recent finding of the invalidity of the conventional standard theory on the response of such an x-ray detector; the conventional theory has widely been believed and employed over the last quarter of the century in various research fields including plasma-electron researches in most of plasma-confinement devices. The novel theory on the semiconductor x-ray response is characterized by the inclusion of a three-dimensional diffusion of x-ray-produced minority carriers in the field-free substrate of a detector, while the conventional theory is based only on the charges from an x-ray-sensitive depletion layer (i.e., the region of a p-n junction). Various and serious effects of the novel theory on the determination of electron temperatures and their radial profiles (i.e., the electron-temperature gradient) are also represented.

Newly developed matrix-type semiconductor detector for temporally and spatially resolved x-ray analyses ranging down to a few tens eV using a single plasma shot

For the purpose of the measurements of temporally and spatially resolved electron temperatures (Te) during a single plasma shot alone, we propose and fabricate a new matrix-type semiconductor x-ray detector. This detector is fabricated using the precise formation of thin dead layers (SiO2) with six different thicknesses (from 10 to 5000 Å) aligned in line on its surface compactly. Each “row” has seven channels for the measurements of plasma x-ray radial profiles so as to make x-ray tomographic reconstructions; namely, the compact-sized matrix detector having six rows and seven columns with a 5×5 mm2 active area for each matrix unit. These various SiO2 layers are proposed to be utilized as ultrathin “x-ray absorption filters” with different thicknesses, which are never obtained as “self-supporting material absorbers” because of their ultrathin properties. This novel idea enables us to analyze x-ray tomography data including in the Te region down to a few tens eV. The simultaneous comparison of each tomographically reconstructed data from each detector row provides the temporal evolution of energy-resolved x-ray or Te profiles using “the absorption method.” The first application of this newly developed matrix detector is made to obtain Te profiles in the GAMMA 10 tandem mirror.

Characterization and interpretation of the quantum efficiencies of multilayer semiconductor detectors using a new theory.

On the basis of a new theory of semiconductor X-ray detector response, a new type of multilayer semiconductor detector was designed and developed for convenient energy analyses of intense incident X-ray flux in a cumulative-current mode. Another anticipated useful property of the developed detector is a drastic improvement in high-energy X-ray response ranging over several hundred eV. The formula for the quantum efficiency of multilayer semiconductor detectors and its physical interpretations are proposed and have been successfully verified by synchrotron radiation experiments at the Photon Factory. These detectors are useful for data analyses under strong radiation-field conditions, including fusion-plasma-emitting X-rays and energetic heavy-particle beams, without the use of high-bias applications.

A simple pulsed drain feedback preamplifier for high resolution high rate nuclear spectroscopy

A non-optical, pulsed reset technique for use in charge sensitive preamplifiers with Si(Li) X-ray semiconductor detectors of conventional polarity is described. The phenomenon of impact ionization in the field effect transistor is used for charge restoration. The process is controlled via the detector capacitance. The method needs no extra components in the input circuitry. No significant resolution degradation can be detected up to 600 kcps Mn K intensity if following the 5 μs resetting pulse the signal processor is inhibited for 50 μs.

The X-Ray Spectrometer for the Clark mission

An X-Ray Spectrometer using state-of-the-art detector technology will be launched this year on the Clark spacecraft, one of two missions to be flown as part of the Small Spacecraft Technology Initiative. The primary objective of this mission is to demonstrate new technologies for small spacecraft. In keeping with this philosophy, we use two new types of semiconductor X-ray detectors, both operating near room temperature: avalanche photodiodes and cadmiumzinc-telluride detectors. The main purpose of flying these detectors is to test them in a space environment so that they can be used with confidence on future space missions. Measurements of solar flare and gamma-ray burst X-ray emissions will also be made.

Plasma electron temperature diagnostics using semiconductor x-ray detector data analysed by a new theory on the x-ray responses

Plasma electron temperature diagnostics using semiconductor x-ray detector data analysed by a new theory on the x-ray responses

Measurements of time parameters of X-ray semiconductor detectors using synchrotron radiation of the VEPP-3 storage ring

Synchrotron radiation (SR) with a well deterministic time structure from the VEPP-3 storage ring was used to measure the time parameters of silicon semiconductor X-ray detectors. The time pulse response and the pulse sensitivity of the detectors were investigated. A stroboscopic oscilloscope with further data digitizing and processing was employed to register the detector pulse signal generated by repetitive SR X-radiation bursts. it is shown that taking the time dependence of the SR bursts and the distortions of the signal registration path into account allows one to obtain the pulse time characteristic function of X-ray detectors with a time resolution of not worse than 0.5 ns. The pulse and the static sensitivities of the studied X-ray detectors were compared, and a discrepancy of about 10% was revealed. The results of independent measurements with a powerful pulse X-ray tube are in a good agreement with the ones obtained with SR.

Measurements of the absolute spectral sensitivity of X-ray semiconductor detectors in the photon energy range of 1.5–15 keV using “white” SR beam of the VEPP-3 storage ring

Results of measurements of the absolute spectral sensitivity of silicon semiconductor detectors in the X-ray quanta energy range of 1.5–15 keV are presented. The detectors, being calibrated, were placed into the direct “white” synchrotron radiation (SR) beam from the VEPP-3 storage ring. The spectrum of X-radiation at the entrance window of the detectors was changed by using sets of calibrated filters, as well as by varying the energy of the electrons in the storage ring. The possibility of accurate calculation of the SR spectrum on the calibrated detector under its irradiation in different conditions allowed us to determine the detector spectral sensitivity from a set of integral equations connecting the spectral sensitivity to the registered detector currents. The analysis of possible experimental errors indicates that the absolute spectral sensitivity of the detectors was restored with an accuracy of not worse than 10% in the total photon energy range under the study.

A newly developed multilayer semiconductor x-ray detector for the observations of wide energy-range x rays

For the purpose of the developments of wide-energy-range-sensitive x-ray detectors, we have designed and fabricated a new-type multilayer semiconductor x-ray detector. This new-type detector has been characterized using synchrotron radiation from a 2.5-GeV positron storage ring at the Photon Factory of the National Laboratory for High Energy Physics (KEK). This new detector is essentially composed of four layers of commercially available photodiodes. Each photodiode is made from a 300-μm thick, and a 10×10-mm square-shaped wafer. For the common affiliation of these individual photodiodes, the quantum efficiency normalized by the photon energy η/E begins to decrease at 8 keV, and then η/E decreases down to 26% at 20 keV. On the other hand, for our newly designed detector a flat response even in the 10–20-keV energy regime (beam line 15C at the Photon Factory) is observed, and even at 100 keV η/E<30% is still anticipated. This new x-ray detector has various advantages: (i) A compact, and (ii) outgas-free detector for a high-vacuum use, along with (iii) a high degree of immunity to ambient magnetic fields. Furthermore, (iv) the combination of the x-ray signal outputs from each detector layer provides information on the x-ray emitting electron energies. These properties are quite suitable for the use of the fusion-oriented plasma x-ray diagnostics under intense-magnetic field and high-vacuum conditions so as to interpret wide-band x-ray emitting electron-velocity distribution functions from the x-ray data.

X-ray diagnostic systems in the GAMMA 10 tandem mirror and new x-ray semiconductor-detector responses in the DIII–D tokamak

The energy response of a new semiconductor-detector array in the DIII–D tokamak for plasma x-ray diagnostics is characterized using synchrotron radiation at the Photon Factory (KEK) in Japan. This international cooperation research clarifies its good x-ray response ranging up to about 10 keV. The variations in detector-channel responses are also studied. Furthermore, new aluminum-coated x-ray semiconductor detectors are designed, fabricated, and characterized for the 10-keV-order DIII–D electron studies including the purpose of rf current-drive investigations; a flat response (the quantum efficiency η∼1) up to around 10-keV x rays, and a high efficiency (η≥0.3) even for the 20-keV x rays, are achieved. A wide variety of x-ray detection systems for the x-ray-energy range from a few tens eV to several hundreds keV in the GAMMA 10 tandem mirror is shown; that is, microchannel-plate tomography systems for the 0.01–60-keV x rays, a new ultra-low- energy-sensitive pure-Ge detector (0.2–50 keV), a Si(Li) detector (0.7–150 keV), a conventional pure-Ge detector (1.8–250 keV), and an NaI(Tl) detector (20–750 keV), silicon-surface-barrier detectors, and new semiconductor x-ray detectors for the purpose of the investigations of the effects of potentials on electron behavior in various tandem-mirror regions are represented.

Multiplexed readout electronics for imaging spectroscopy of high-energy X-ray and gamma photons

Silicon CMOS readout circuits for use with pixellated semiconductor X-ray and gamma photon detectors are reviewed. the paper considers three specific circuit types and their applications, as well as a sampling of relevant performance figures.

New findings of X-ray energy responses of silicon surface barrier detectors and their generalized theoretical extension to X-ray responses of position sensitive detectors

X-ray energy responses of silicon surface barrier (SSB) semiconductor detectors are found to be explained neither by the commonly believed conventional model using the depletion layer thickness of an SSB detector nor by a recently proposed model using its wafer thickness as the X-ray sensitive layer. Our new theory using both the depletion layer sensitivity and the X-ray response due to a three-dimensional charge diffusion effect in the field-free substrate region of a SSB detector can well fit the response data. This theory is newly extended to analyse each channel response of a multichannel semiconductor X-ray detector fabricated on one silicon wafer; these detectors are widely utilized as position sensitive X-ray detectors for nuclear fusion oriented plasma research as well as for high energy elementary particle studies. A numerical simulation of multichannel detector outputs using our three dimensional diffusion theory is carried out; generalised theoretical formulae are also presented.

Thallium bromide semiconductor X-ray and γ-ray detectors

Abstract Over the last few years, thallium bromide (TlBr) has been investigated for use as a semiconductor radiation detection material. This article reviews the history of TlBr detector development and describes the fabrication of state-of-the-art TlBr γ-ray detectors. Studies of TlBr detectors of different chemical purity indicate that their performance is no longer limited by chemical purity, as was true previously. This is a result of our purification methods, which employ multipass zone-refining. We also report on the performance of vacuum-deposited (by sublimation, ≅ 100 μm thick) TlBr films as single photon detectors. They have surprisingly high μτ for sublimed films, and X-ray detectors made from these films may find use in some X-ray imaging applications, including xeroradiography.

Using GaAs and GaP films with abnormal photovoltages for recording x rays

The authors assess the photovoltaic effect and sensitivity gallium arsenide and gallium phosphide films under exposure to x radiation for their possible application in x-ray semiconductor detectors. Their properties are measured against those of cadmium telluride and antimony selenide. The latter films were found to be sensitive to x radiation only in air whereas the gallium compounds demonstrated sensitivity both in air and in vacuum. Processing requirements were also found to be less demanding for gallium arsenide and gallium phosphide.

Ｓｉ（Ｌｉ）Ｘ線検出器で観測される特性Ｘ線のテイルスペクトル

Characteristic X-ray spectra are inherently accompanied by the tail spectra in the low energy side when X-rays are detected with a semiconductor X-ray detector. The tail spectra of Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr and Mn KX-rays have been observed using two different Si(Li) X-ray detectors. An annular source of 55Fe has been used to excite the Mg (1.25 keV) to Ti (4.5 keV) KX-rays, and 54Mn and 55Fe sources have been used for the detection of Cr (5.4 keV) and Mn (5.9 keV) KX-rays, respectively. Observed intensity ratios of the tail area Nt to the Gaussian X-ray peak area NP have exhibited to change remarkably at the Si-K adsorption edge energy 1.84 ke V. When X-ray spectra detected with different Si(Li) detectors are compared at some specific characteristic X-ray, different values of Nt/Np intensity ratios as well as different line shapes of tail spectra have been observed. Using a simple model, the thickness of Si layer which generates the tail spectrum has been estimated, i.e., the thicknesses are about 0.05 micron for one detector and 0.09 micron for the other detector. The generation of the tail spectrum is known to be partially due to the escape effect of photoelectrons or Auger electrons from the intrinsic region.(ABSTRACT TRUNCATED AT 250 WORDS)

Sample characterization by proton induced x-ray emission analysis

The emission of characteristic X-rays following atomic excitation has long been used for elemental analysis. The most widely used source of exciting radiation has been X-rays. Protons and other heavy ions are very effective as an excitation source because of the high X-ray production cross sections for many elements and background which is much lower than that from X-ray, γ- ray or electron induced excitation. The development of semiconductor X-ray detectors with good resolution has enabled extensive research into proton induced X-ray emission (PIXE) techniques and applications. The basic physics of the excitation process is discussed, together with the detection of the characteristic X-rays emitted from the sample atoms. Since the early 1980s, PIXE has been applied in many fields as disparate in archaeology and medicine. Some of these will be reviewed to show the success of the technique and to point out the difficulties, remembering that since proton ranges in most samples will be less than 100 μm, only surface and near-surface layers will be excited. New techniques such as external beam work and the use of microprobes are also discussed. Statistical techniques for dealing with the large amounts of data generated by PIXE analysis are also mentioned.

A method for the correction of self-absorption of low energy photons for use in routine INAA

Practical application of oow energy gamma rays and X-rays in I.N.A.A. was restricted because of the complexity of the X-ray spectrum and sample self-absorption. This paper describes a method for the calculation of sample self-absorption on the basis of the actual sample spectra only, as measured with a high resolution semiconductor X-ray detector. In the 20–400 keV energy range, the attenuation coefficient can be represented by a three parameter function of photon energy. This was verified by measuring the transmission of photons of different energies through a range of materials. Experiments with neutron irradiated U.S.G.S. standard reference materials with known major oxide composition showed that self-absorption thus calculated from the observed spectra is in good agreement with the results of theoretical calculations based on known attenuation coefficients.

An evaluation of HgI2 detectors for x-ray computed tomography.

Mercuric iodide (HgI2) presents a set of attractive features as a semiconductor x-ray detector for computed tomography (CT). Its response is stable, it operates at room temperature, and thin detectors have a high detection efficiency. The properties of HgI2 permit the assembly of high spatial resolution detectors in a compact configuration. On the other hand, HgI2 exhibits a long memory, and some detectors also exhibit polarization effects, both of which are detrimental in CT. A pulse-shaping technique has been used to overcome these effects, thus demonstrating the suitability of HgI2 for use in CT.

Efficiency Response Modelling of Semiconductor X-Ray Detectors

Semiconductor x-ray detectors, usually Si(Li) and Ge(Li), are routinely used in pure and applied science whenever high-resolution, energy-dispersive analysis is required. In many applications, the absolute full-energy efficiency of the detector needs to be known in order to derive the true intensity from the measured intensity. Investigators have used a variety of methods to determine the energy-dependent efficiency response of these detectors. This paper reviews some of these methods, with emphasis placed on the model-based parametric efficiency response determination procedure of Gallagher and Cipolla1.

Trace elements analysis in biological samples by radioisotopic x-ray fluorescence.

The X-ray fluorescence technique, induced by radioisotopic sources, provides a very simple method for the simultaneous analysis of trace elements in biological samples. For blood, serum, platelets, etc., samples of about 0.1 ml were deposited on filter paper disks, dried, and analyzed. In such a way the "thin specimen" approximation is realized, resulting in the following advantages: The X-ray intensity of a given element is a liner function of mass per unit area over several orders of magnitude. Interelement effects became negligible. The ratio of fluorescent X-rays to scattered radiation is increased. The sensitivity of the technique for elements with atomic number ranging from about 20-92 varies from some units to some tens of parts per million by weight in 100 s measuring time, by using a gas proportional counter, and from about some tenths to some parts per million by using an X-ray semiconductor detector, in a measuring time of 10(3)-10(4)s. In such a way and with the described features, the Cl, K, Ca, Fe, Cu, Zn, Br content of several speciments of blood and serum was determined. Measurements were further carried out in order to labelling blood components with stable tracers and to detect their concentration by means of the X-ray fluorescence technique. The life span of platelets was, for example, measured after labelling platelets with stable Selenocystine. The sensitivity of the XRF technique can further be enhanced by about three orders of magnitude by using a pre-enrichment step with ion-exchange resins and liquid volumes not lower than 500 ml. Urine analyses have been carried in such a way, and copper in about 20 ml serum after selective extraction.