Semiconductor X-ray Detectors Research Articles

Intrinsic spatial resolution of semiconductor X-ray detectors: a simulation study

We have investigated the intrinsic limitation of the spatial resolution of a directly absorbing semiconductor detector. The primary interaction of an incident X-ray quantum is followed by a series of processes that generate Compton or fluorescence photons and subsequent electrons. Their ranges determine the spatial resolution of the detector, expressed in terms of the modulation transfer function. The effects of carrier transport have been neglected in this work.Monte Carlo simulations have been carried out in the 10–100keV energy range with the program, ROSI (Roentgen Simulation), which is based on the well-established EGS4 algorithm. On a fine grid, the lateral distribution of deposited energy has been calculated in typical materials such as Se, CdTe, HgI2 and PbI2. The results can be used to either determine the point spread function of an energy-integrating detector, or to study multiple registration in adjacent pixels of photon-counting detectors.The results show that the complex absorption process determines the spatial resolution of the detector considerably. If a very high spatial resolution is required, a well-adapted semiconductor should be applied. Dependent on the energy range used, lists of favorable materials are given. At energies above 50keV, Compton scattering reduces spatial resolution in the high frequency range.

Deterioration and recovery effects in energy responses of semiconductor X-ray detectors due to nuclear-fusion produced neutron irradiation

Effects of neutron irradiation on X-ray energy responses of silicon semiconductor detectors have been investigated. Neutron irradiation experiments were carried out for n-type photodiode arrays utilized in the Joint European Torus (JET) using deuterium (D) beam-injection into a tritium (T) target for a well-calibrated deuterium–tritium (D–T) fusion neutron production at the Fusion Neutronics Source (FNS) facility of Japan Atomic Energy Research Institute. X-ray energy responses of these detectors are characterized before and after irradiation by the use of synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory of High Energy Accelerator Research Organization (KEK). A recovery of the degraded X-ray energy response after the neutron irradiation has been found at fluences beyond around 10 13 neutrons/cm 2. A further novel finding is followed as a “re-degradation” by a neutron irradiation level over about 10 14 neutrons/cm 2. This “non-linear response” may be physically interpreted in terms of a type inversion from n- to p-type silicon in the detectors. Long-term observations of X-ray energy responses of the detectors after neutron irradiation have also been made in order to clarify the “annealing effect”.

Spatially resolved electron cyclotron heated plasmas using novel matrix-type X-ray semiconductor–detector arrays

Temporally and spatially resolved X-ray analyses are carried out by using novel matrix-type X-ray semiconductor detector arrays in the GAMMA 10 tandem mirror. The detector array has seven “matrix columns” for the measurements of plasma X-ray profiles so as to make X-ray tomographic reconstructions. Further, six “matrix rows” having various dead layer thicknesses are fabricated as “unbreakable ultra-thin X-ray absorption filters” for simultaneous analyses of six different X-ray energy ranges. The characteristics of the detector array make it possible to obtain spatially resolved plasma electron temperatures down to a few tens of eV and investigate various magnetohydrodynamic activities during a single-plasma discharge alone. Several applications including investigations of electron energy confinement during a period with central-cell electron cyclotron heatings are made with the novel position sensitive semiconductor arrays.

Large dynamic range 64-channel ASIC for CZT or CdTe detectors

We present a customized 64-channel ASIC, named ALIX, developed in a 0.8μm CMOS technology. This circuit is dedicated to measure charges from semi-conductor X-ray detectors like Cadmium Zinc Telluride (CZT) or Cadmium Telluride CdTe.The specificity of ALIX is to be able to measure charges over a very large dynamic range (from 10fC to 3nC), and to store eight measurements in a very short time (from every 250ns to a few ms).Up to eight images are stored inside the ASIC and each image can be read out in 64μs. A new acquisition sequence can then be started. Two analog readouts are available, one for the X-ray signal and one for the offset and afterglow measurement in case of pulsed X-rays. The outputs are converted into digital values by two off-chip 14 bits Analog-to-Digital Converters (ADC).A first version of ALIX has been tested with CZT and CdTe detectors under high-energy pulsed X-ray photons (20MeV, 60ns pulses every 250ns). We will present the different results of linearity and signal-to-noise ratio. A second version of ALIX has been designed with some corrections. Electrical tests performed on 85 ASICS showed that the corrections were successful. We are now able to integrate them behind a 64×32 pixels 1mm pitch CZT detector. Such an ASIC could also be used for strip detectors where a large dynamic range and a fast response are necessary.

Effects of Fusion Produced Neutrons on Semiconductor Detectors

Detailed plasma-physics investigations by the use of x-ray-tomography data supported by the fundamental theoretical studies of x-ray-detector responses enhance the importance of x-ray diagnostics for fusion-plasma analyses. However, degradation in responses of semiconductor x-ray detectors after fusion-produced neutron exposure still remains one of the most serious problems in recent fusion experiments even at this time. For the purpose of investigating and characterizing neutron effects on semiconductor x-ray detectors, detection characteristics of n-type silicon semiconductor detectors which are similar to those utilized for x-ray-tomography detectors in the Joint European Torus (JET) tokamak, are studied by the use of synchrotron radiation from a 2.5-GeV positron storage ring at the Photon Factory. The fusion neutronics source (FNS) of Japan Atomic Energy Research Institute is employed as well-calibrated deuterium-tritium (D-T) neutron source with fluences from 1013 to 1015 neutrons/cm2 onto these semiconductor detectors. Degradation in x-ray responses with increasing neutron fluences has been reported; however, our recent detailed investigations of detector responses show nonlinear dependence as a function of the neutron fluence.

Time- and Space-Resolved Spectroscopic Diagnostics of Magnetically Confined Plasmas Measurements of Temporally and Spatially Resolved Electron Temperatures Using a Matrix-Type Semiconductor Detector

A new matrix-type semiconductor x-ray detector was developed for the purpose of the measurements of temporally and spatially resolved electron temperatures (Te) during a single plasma shot. This detector is fabricated using precise formation of thin dead layers (SiO2) of six different thicknesses aligned compactly on its surface. Each ”row” has seven channels for the measurements of plasma x-ray radial profiles so as to make x-ray tomographic reconstructions. These various SiO2 layers are proposed to be utilized as ultrathin ”x-ray absorption filters”. This novel idea enables us to analyze x-ray tomography data including the Te region down to a few tens eV. The comparison of tomographically reconstructed data from the respective detector rows provides the temporal evolution of energy-resolved x-ray or Te profiles using ” the absorption method ”. Observations of internal core plasma structural behavior during the magnetohydrodynamic (MHD) destabilization are carried out by the use of a matrix-type semiconductor detector. Furthermore, a method is proposed for obtaining radial profiles of plasma temperatures of both plasma ions and electrons simultaneously.

Analyses of Temporally and Spatially Resolved Plasma Behavior Using X-Ray Data in a Single Plasma Discharge on Gamma 10

The direct detailed observations of temporally and spatially resolved plasma behavior of a magnetohydrodynamic (MHD) anchor stabilization for central-cell plasmas are carried out by the use of our newly developed semiconductor x-ray detector arrays installed in both central-cell and anchor regions of the GAMMA 10 tandem mirror. In comparison to the previous reports, the present x-ray observations directly clarify an unsolved issue of the behavior of the internal core-plasma structure during the MHD destabilization experiments. The present x-ray analyses by the use of our proposed method with our developed matrix-type semiconductor detector are, therefore, characterized in terms of providing the direct detailed “visible” structural information on the interior core-plasma behavior during the period with the MHD instability, as well as showing the important role of the minimum-B inboard anchor in the MHD plasma stabilization in GAMMA 10.

Observations of temporal and spatial behaviour of plasmas in relation to the interchange stability boundary scaling in GAMMA 10

Observations of internal core plasma structural behaviour during the magnetohydrodynamic (MHD) destabilization of the central cell plasmas are carried out by the use of our developed semiconductor x-ray detector arrays installed in both central cell and anchor regions of the GAMMA 10 tandem mirror. In the present paper, it is found from the developed x-ray diagnostics that the bulk plasmas rotate without a change in its shape and structure with an E×B velocity during the destabilization. The onset of the off-axis rotation is identified to be closely related to a scaling of the MHD stability boundary (i.e. the anchor beta requirements for stabilizing central cell hot ion plasmas). These data confirm pressure driven interchange instability in tandem mirror plasmas, and reveal the rigid rotational bulk plasma structure as the first demonstrated interior plasma property during the destabilization.

Absolute calibration of X-ray semiconductor detectors in the 0.3−1.5 keV photon energy range on synchrotron radiation from VEPP-2M storage ring

The paper presents the results of absolute spectral responsivity measurements for SPPD11 and SPPD11-04 pulse-type silicon detectors, carried out in the X-ray energy range from 0.3 to 1.5 keV with a relative uncertainty of about 8% (1 σ). The measurements were performed using the detector exposure to a well-calculable synchrotron radiation through the selective filters with well-known transmittance. Synchrotron radiation from the VEPP-2M storage ring was utilized for these measurements. The spectral responsivity of the detectors was restored by solving the proper system of integral equations on the base of measurement data. For increasing the calibration accuracy, the X-ray transmittance near the L-absorption edges of the filters used and the angular spread in the positron beam of the storage ring were experimentally determined.

New Technologies for Microanalysis and Element Imaging in THJ Scanning Electron Microscope

RÖNTEC’s UHV Dewar detectors have established new standards for high resolution, lowmaintenance, low operating cost, and reliability in Si(Li) X-ray detectors. Now, the recently introduced XFlash® series X-ray detectors are enabling new methodologies for microanalysis and element imaging in the SEM. These detectors are compact, liquid-nitrogen-free semiconductor Xray detectors that are based on Silicon Drift Diode (SDD) technology. XFlash detectors produce extraordinarily high count rates with excellent energy resolution and have introduced ultra-fast microanalysis and element mapping to the SEM world. The addition of color to SEM images enables easy visualization of element distributions and allows the microstructural features and compositional variations of different materials to be more readily identified. Persons unfamiliar with electron microscopy can more readily interpret color images than black and white or gray scale images. This new technology has great potential to revolutionize electron microscopy.RÖNTEC’s UHV Dewar Detector offers the highest long-term stability and best energy resolution ever specified for a commercial Si(Li) detector (less than 129 eV). The UHV design leads to small size and weight (for reduced column loading) along with extremely low nitrogen consumption and low susceptibility to microphonics. The UHV detector never ices up and thus never requires defrosting or warm-ups. It is available with a variety of entrance windows for light element analysis.

Resolution and noise properties of scintillator coated X-ray detectors

The imaging properties of X-ray pixel detectors depend on the quantum efficiency of X-rays, the generated signal of each X-ray photon and the distribution of the generated signal between pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. The Signal-to-Noise Ratio in the image is then a function of the number of photons captured in each of these processes and the yield, in terms of electron–hole pairs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-ray photons captured within the sensitive layer. The spatial resolution is affected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout electrode. In this paper we discuss the theory underlying the imaging properties of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the two-layer detector are compared with those from a pure semiconductor X-ray detector.

Future space applications of compound semiconductor X-ray detectors

Detectors based on compound semiconductors have now reached a level of maturity, where they can be considered for use in a variety of space-based applications involving X-ray imaging optics. The possible range of space applications is reviewed and the key future requirements of these detectors are discussed. These X-ray detectors will play a major role in future astrophysics and planetary missions. Recent results on the agency's X-ray detector research and development program into such materials as TlBr, epitaxial GaAs and CdZnTe are presented.

Investigation of x-ray-energy responses of semiconductor detectors under deuterium–tritium fusion-produced neutron irradiation

For the purpose of investigating fusion-produced neutron effects on semiconductor x-ray detectors, detection characteristics of x-ray tomography detectors used before and after deuterium–tritium (DT) and/or DD fusion-plasma experiments in the Joint European Torus (JET) tokamak are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory. Degradations in the responses after neutron exposure into the detectors are found to have functional dependence on x-ray energy. Changes in the depletion thicknesses of the detectors are investigated by means of impedance analyses. The Fusion Neutronics Source (FNS) facility of the Japan Atomic Energy Research Institute is also employed for well calibrated DT fusion-produced neutron irradiation onto these semiconductor x-ray detectors. Recovery of the response degradation is found due to a method for supplying the operational bias to the degraded detector. Our theory is applied to interpret these detector characteristics under the irradiation of DT fusion-produced neutrons in the JET tokamak and the FNS facility.

Simultaneous observations of temporally and spatially resolved electron temperatures of both circular central-cell and elliptical anchor-region plasmas in GAMMA 10

The first results of simultaneous observations of temporally and spatially resolved electron temperatures (Te) in both circularly shaped central-cell and elliptically shaped anchor regions are reported in the GAMMA 10 tandem mirror. A data set is provided using a novel matrix-type x-ray semiconductor detector. The detector has seven “matrix columns” for the measurement of plasma x-ray profiles along with six “matrix rows” for simultaneous analyses of six different x-ray-energy ranges by the fabrication of six different thicknesses of SiO2 semiconductor surface layers from 1 to 495 nm as ultrathin and unbreakable “x-ray absorption filters.” Such a matrix idea enables us to analyze x-ray tomography data in the Te region down to a few tens of eV. Simultaneous application of the x-ray detectors in the central-cell and the anchor region gives information on not only detailed electron behavior in each region but also the mutually communicating relation between the two regions: The role of the anchor-region plasmas in magnetohydrodynamic plasma stabilization in the central-cell plasmas is confirmed by the data from these detailed simultaneous electron observations.

Absolute calibration of X-ray semiconductor detectors against synchrotron radiation of the VEPP-3 storage ring

The results are presented of absolute spectral responsivity measurements for SPPD11 and SPPD11-04 pulse-type silicon semiconductor detectors (developed by the Research Institute of Pulse Technique, Moscow), carried out over the X-ray energy range from 1.5 keV to 20 keV with a relative uncertainty (k = 1) of typically 5 × 10−2. In our measurements, the detector is positioned in a calculable synchrotron radiation flux behind filters of well-known transmittance. The spectral responsivity of the detector is restored on the basis of measurement data using a set of integral equations. Two procedures have been developed to improve the calibration accuracy: one for the experimental determination of the X-ray transmittance near the K absorption edge of the filters used, with a relative uncertainty not exceeding 2 × 10−2; and another for the estimation of the angular spread of the electrons.

X-ray detection characteristics of thallium bromide nuclear radiation detectors

Semiconductor X-ray detectors have been fabricated from high purity TlBr crystals grown by the traveling molten zone method. X-ray detection characteristics of the TlBr detectors in the individual quantum pulse mode as well as in the current mode have been studied. An energy resolution of 2.5 keV FWHM has been recorded for 22 keV X-rays with a TlBr detector operated in the individual quantum pulse mode at room temperature. The TlBr detectors in the current mode have been tested as flux detectors for an X-ray CT scanner system of a first generation type. The performance of the system has been tested using a wooden phantom. The X-ray CT system has shown good imaging capabilities.

Experimental characterization of low-energy X-ray semiconductor detectors

Six semiconductor detectors (Si(Li) and HPGe) are calibrated in the 1–10 keV energy range by means of tunable monochromatized synchrotron radiation. Significant improvement in the quality of the response is observed in very recent detectors. A peak shape calibration is established using a modified Hypermet-type function to model the detector response for each energy step; a strong enhancement of the peak tail is shown above the binding energy for each detector material. Fano factors for both semiconductor materials are experimentally derived. This characterization will allow the improved processing of low-energy X-ray spectra by providing the intrinsic response of either kind of detector.

エネルギー分散型蛍光X線分析装置を用いた製鋼スラグの迅速分析

An X-ray fluorescence method using a semiconductor X-ray detector was investigated for rapid analysis of slag in steelmaking process.Metallic rectangular solid was dipt in molten slag layer, and slag thin piece grew on the solid. Because this slag piece was rapidly solidified and was flat, it could be directly analyzed by X-ray fluorescence method.Slag thin pieces obtained by large volume steel sampler were excellent as uniformity and representativity of slag component. These features gave excellent result for the determination of CaO, SiO2, Al2O3, Fe and MnO in steelmaking slag. In this method, the analysis time was shortened to 5 minutes. As the results, rapid and simple analysis of slag for steelmaking was established.

Protonium X-ray spectroscopy

The Lyman and Balmer transitions from antiprotonic hydrogen and deuterium were studied extensively at the Low-Energy-Antiproton Ring LEAR at CERN in order to determine the strong interaction effects. A first series of experiments was performed with semiconductor and gaseous X-ray detectors. In the last years of LEAR operation using a Bragg crystal spectrometer, strong interaction parameters in the 2p states of antiprotonic hydrogen and deuterium were measured directly. The results of the measurements support the meson-exchange models describing the medium and long range part of the nucleon-antinucleon interaction.

Effects of neutrons on semiconductor x-ray detectors including n-type Joint European Torus and p-type GAMMA 10 tomography detectors

Characterization experiments have been carried out so as to investigate the effects of fusion-produced neutrons on the x-ray-energy responses of semiconductor detectors for x-ray tomography in the Joint European Torus (JET) tokamak (n-type silicon) and the GAMMA 10 tandem mirror (p-type silicon). Neutron effects on the x-ray-energy responses of these detectors are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory. Changes in the material properties of the detectors have been investigated using an impedance analyzer to estimate neutron effects on x-ray-sensitive depletion thicknesses. A cyclotron accelerator is employed for well-calibrated neutron irradiation onto these plasma x-ray detectors; a fluence of 2–5×1013 neutrons/cm2 is utilized for simulating the effects of fusion-produced neutrons in JET. Modifications of the x-ray responses after neutron exposure due to fusion plasma shots in JET as well as cyclotron-produced neutron irradiations are found to have a functional dependence on x-ray energy. Also, recovery of the detector energy response is found when detector bias is applied. Our theory consistently interprets such properties in terms of the neutron effects on the diffusion length and the resistivity of detectors.