Room-temperature Semiconductor Detectors Research Articles

Gamma scanning of large-volume CdZnTe detectors to map their efficiency

An automated, computer-controlled scanning device to map the sensitivity of large-volume CdZnTe gamma detectors is described. It is of modular design and fully based on moderately priced commercial components. The collimated radiation source is moved in X– Y direction over the radiation detector under test using stepping motors. Synchronously, gamma spectra are taken for each X– Y position. Different regions of interest in a spectrum can be evaluated or re-evaluated and the measured gamma countrate (peak area) is displayed and documented in contour maps as a function of the X– Y coordinate. The system is meant for evaluation of new, large-volume room temperature semiconductor detectors and for quality-control measurements on detectors which are used in the Department of Safeguards for the verification of nuclear material.

Spectrum catalogue of gamma spectra taken with CdTe and CdZnTe detectors

The project of compiling a catalogue of gamma spectra for room-temperature semiconductor detectors is described. The catalogue is intended to help with the planning of measurements in various gamma spectrometric applications where these detectors are used such as the verification of nuclear material, waste characterization and nuclear medicine. Gamma spectra are measured with CdZnTe and CdTe detectors under well-defined conditions. The spectra are archived and plotted to allow the assessment and comparison of the detector performance for various sources and detector types. The format of collecting and presenting the data is described and sample spectra are given.

Pulse shape discrimination system for room-temperature semiconductor detectors

Easily adjustable pulse shape discrimination (PSD) system effectively operating in the wide range of registered energies is offered. Shape distortions of the detector output signal due to charge losses are clearly visible if one carries out shape analysis of the spectrometric signal for pulses restored up to the rectangular shape. The essence of the method consists in the analysis of difference of a restored signal form from rectangular. For this purpose the area of a pulse is measured within the given interval at once after incoming pulse and within the same time interval delayed concerning first. In case of an inequality of these areas, the signal is considered deformed and is not exposed to further analysis. Schematic decision and operation mode of PSD system is analysed, pulses diagrams are presented. The developed PSD system was applied in gamma-spectrometer with planar geometry CdTe detector with dimentions 5×5×3 mm 3. Detector had m–s–m structure with gold electrode. Initial energy resolution of the detector was 17 keV at 662 keV and peak-to-Compton ratio equal to 1.8. The PSD application improves energy resolution up to 3.2 keV and peak-to-Compton ratio to about 5.0. At this essential reduction of count rate (up to 75%) in a maximum of a total absorption peak is observed. But the energy resolution of about 6 keV can be received at insignificant (not more than 20%) reduction of count rate. Spectra of 137Cs and 133Ba obtained with and without PSD system application are shown. Diagrams of energy resolution at 662 keV line as well as count rate in the total absorption peak maximum versus pulse shape discrimination level are presented.

Proposal for a new room temperature X-ray detector-thallium lead iodide

Numerous compounds have been considered for room temperature semiconductor detector applications. Most of them however are difficult to obtain as crystals and to handle. TlPbI/sub 3/ is a promising candidate, because it forms rhombohedral crystals which do not have a structural phase transition between room temperature and their melting point. Its low vapour pressure facilitates the crystal growth and it has a low melting point (619 K), high Z, high density (6.6 g/cm/sup 3/), and a bandgap of 2.3 eV. X-ray photoconductivity measurements indicate that this material can be used in room temperature solid state detectors.

CdTe detectors' response to irradiation with high-energy gamma-rays

In recent years the performance of room-temperature semiconductor detectors such as CdTe are improved and they are now suitable candidates for several applications. However, some key parameters that can severely affect such performances have not been measured in detail yet. We have extended previous studies on the radiation damage of a set of CdTe detectors irradiated in a /sup 60/Co gamma-cell in a wide range of doses. A full characterization of the performance of irradiated detectors has been obtained by means of spectroscopic, electrostatic, photo-induced current transient spectroscopy and photo-deep level transient spectroscopy measurements to quote the energy resolution, the leakage current, the activation energy and capture cross-section of deep level defects, respectively.

CdTe and CdZnTe detectors in nuclear medicine

Nuclear medicine diagnostic applications are growing in search for more disease specific or more physiologically relevant imaging. The data are obtained non-invasively from large field γ cameras or from miniaturised probes. As far as single photon emitters are concerned, often labelled with 99mTc (140 keV, γ), nuclear instrumentation deals with poor counting statistics due to the method of spatial localisation and low contrast to noise due to scatter in the body. Since the 1960s attempts have been made to replace the NaI scintillator by semiconductor detectors with better spectrometric characteristics to improve contrast and quantitative measurements. They allow direct conversion of energy and thus more compact sensors. Room-temperature semiconductor detectors such as cadmium tellure and cadmium zinc tellure have favourable physical characteristics for medical applications which have been investigated in the 1980s. During one decade, they have been used in miniaturised probes such as for inter-operative surgery guidance which is today in a fast growing phase. This material suffers from charge transport problems which has slowed down imaging applications. Owing to a considerable research work on material, contacts and dedicated electronics small field of view compact pixellated γ cameras have been prototyped and one already marketed. Although extended clinical evaluation has to be conducted and long-term reliability assesed, the available data already confirm the expected gain in image contrast. Medical interest for dedicated imaging systems is greater than it was in the 1980s when the first mobile γ cameras were marketed. The future of CdTe or CdZnTe-based imager for routine use now relies at first on industrial costs.

An improved hand-held four-detector γ-probe for radioassisted oncological surgery

The performance of an improved intraoperative γ-probe for radioassisted oncological surgery is presented and discussed. The probe is based on a square array of four 5×5 mm 2 coplanar CdTe room temperature semiconductor detectors and each detector has an independent read out electronic chain, allowing an original handling of the signal. Therefore, the search for γ-emission hot points may be carried out in two different, independent ways: (1) Finding out the position of the probe corresponding to the maximum value of the total counting rate, on the basis of a trial and error procedure (typical for the conventional probe); (2) Finding out the position of the probe where both the differences between the counting rate performed by orthogonal, adjacent halves of the array vanish (differential method). This makes the new probe sensitive to the bidimensional gradient of the γ-ray flux, measured on the scanned plane. Furthermore, the algebraic sign of the difference indicates in which direction the probe should be moved to best locate the γ-source. Due to these characteristics, both the errors in the localization of a single, small size γ-source and the average measuring time are practically halved with respect to those obtained with a conventional single detector probe. In addition, a computer analysis is performed in order to evaluate the performances of different types of collimators in reducing the contribution of a second source close to the source under examination. This situation occurs, for example, when the probe is used in the framework of the sentinel-node surgical technique.

Integrated-optics semiconductor detector using a prism coupling device

A room-temperature integrated-optics semiconductor detector is proposed. The sensitive element of the detector is a thin film of antimony-activated tin dioxide deposited on a prism coupling element. The sensitivity of the structure to ammonia, alcohol vapor, and acetone impurities is investigated. The range of detectable ammonia concentrations is 10−4–10−6%.

Room-Temperature Semiconductor Detectors for in Vivo Monitoring of Internal Contamination

Room-Temperature Semiconductor Detectors for in Vivo Monitoring of Internal Contamination

Comparison of four types of gamma- and X-ray detectors for environmental applications in the 10–450 keV energy range

The performance of four types of γ- and X-ray radiation detectors for environmental applications was evaluated in the 10–450 keV energy range. Two cadmium zinc telluride (CdZnTe) room temperature semiconductor detectors were evaluated along with a cryogenically cooled semiconductor detector and two different types of scintillation detectors. The energy resolution, absolute peak detection efficiency and peak-to-background ratio of each of the detectors were calculated and intercompared. The advantages and disadvantages of environmental applications of each detector, along with their performance results, are summarized.

Study of the Radiation Damage Induced by High Energy Gamma-Ray in CdTe Detectors

AbstractIn recent years the performance of room-temperature semiconductor detectors such as CdTe are improved and they are now suitable candidates for several applications. However, some key parameters that can severely affect such perfomances have not been measured yet. Thus we have studied the damaging of a set of CdTe detectors irradiated in a 60Co gamma-cell in a wide range of doses and dose-rates. A full characterization of the performance of irradiated detectors has been obtained by means of spectroscopic, electrostatic, photo-induced current transient spectroscopy and photo-deep level transient spectroscopy measurements to quote the energy resolution, the leakage current, the activation energy and capture cross-section of deep level defects, respectively.

Room temperature semiconductor detectors for safeguards measurements

A summary is given of the principal areas of application where CdTe detectors are presently used by the IAEA in nuclear material safeguards. Hemispheric detectors with a sensitive volume of about 20 mm 3 have their principal application in the verification of irradiated nuclear material. Larger volume hemispheric detectors are used for the verification of unirradiated material. Their availability, however, is still limited. Problems with the commercial supply of detectors and with ruggedizing the design of the miniature detection probes need to be solved. New results which are relevant for future applications are described. It has been shown that hemispheric detectors made of CdZnTe provide a resolution of 3–4% and a peak/Compton ratio larger than two for 137Cs. Large volume planar CdZnTe have been used in conjunction with pulse shape discrimination electronics. The detector efficiency, however, still remains below the values expected from their geometric dimensions. A new technique to achieve single charge collection in large volume CdZnTe detectors has been developed. Planar detectors with PIN structure and Peltier cooling have further improved. However, the problem of long term stability has not been solved yet. Silicon detectors are increasingly used in unattended radiation monitoring systems. They have a proven long term stability and can cover a signal range of 5–6 decades if used with fast pulse counting electronics.

1-D position sensitive single carrier semiconductor detectors

A single polarity charge sensing method has been studied using coplanar electrodes on 5 mm cubes of CdZnTe γ-ray detectors. This method can ameliorate the hole trapping problem of room-temperature semiconductor detectors. Our experimental results confirm that the energy resolution is dramatically improved compared with that obtained using the conventional readout method, but is still about an order of magnitude worse than the theoretical limit. A method to obtain the γ-ray interaction depth between the cathode and the anode is presented here. This technique could be used to correct for the electron trapping as a function of distance from the coplanar electrodes. Experimental results showed that a position resolution of about 0.9 mm FWHM at 122 keV can be obtained. These results will be of interest in the design of higher performance room-temperature semiconductor γ-ray detectors.

Evaluation of the possible use of a CdTe detector for the characterization of diagnostic X-ray beams

Abstract This work describes the initial stages in the development of a system which will allow a quick and easy in-field spectrometric characterization of diagnostic X-ray beams. The spectrometric approach to the quality control procedure on diagnostic X-ray beams constitutes an advanced investigation method for monitoring and evaluating the fundamental parameters (as kVp, exposure, HVL, total filtration, etc.) when compared to the classical methods performed by several and specific dedicated instruments. Toward this aim particular care has been taken in the choice and study of the best suited detector unit. Owing to the very promising characteristics of cadmium telluride (CdTe) as a room temperature semiconductor detector, the possibility was investigated of using it in order to elude the main technical problems associated with the use of cooled semiconductor detectors in such a specific application. The investigation was made both in term of dimensions and geometric configuration of the detector, in order to optimize the match between energy response and efficiency. The obtained results are reported and discussed.

Spectrometric characteristic improvement of CdTe detectors

A new pulse shape correction method combined with a pulse shape selection method has been proposed for a CdTe detectors energy resolution improvement and increasing the total absorption peak efficiency. The capabilities of the new technique for the spectrometric characteristic improvement are based on using specific features of the CdTe detectors output pulses. The energy resolution of about 1% FWHM at 662 keV has been achieved with planar CdTe detector under room temperature without decrease of peak efficiency. Standard measurement techniques give 3.7% FWHM. A significant spectrometric characteristic improvement of other room temperature semiconductor detectors such as HgI/sub 2/ and CdZnTe detectors was also obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Unipolar charge sensing with coplanar electrodes-application to semiconductor detectors

A novel method to perform preferential sensing of single-polarity charge carriers in ionization detectors is presented. It achieves the same function as Frisch grids commonly employed in gas ion chambers but uses a coplanar electrode configuration suitable for semiconductor detectors. Through the use of this method, good energy resolution can be obtained from room-temperature compound semiconductor detectors despite their poor hole-collection characteristics. Experiments using a CdZnTe detector demonstrate the effectiveness of this technique. Schemes to correct for electron trapping and to obtain position information are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Semiconductor arrays with multiplexer readout for gamma-ray imaging: results for a 48 × 48 Ge array

We are developing a new kind of gamma-ray imaging device that has sub-millimeter spatial resolution and excellent energy resolution. The device is composed of a slab of semiconductor detector partitioned into an array of detector cells by photolithography and connected to a monolithic circuit chip called a multiplexer (MUX) for readout. Our application is for an ultra-high-resolution SPECT system for functional brain imaging using an injected radiotracer. We report here on results obtained with a Hughes 48 × 48 Ge PIN-photodiode array with MUX readout, originally developed as an infrared focal-plane-array imaging sensor. The device functions as an array of individual gamma-ray detectors with minimal interpixel crosstalk. Linearity of energy response is excellent up to at least 140 keV. The array exhibits excellent energy resolution, ∼ 2 keV at ≤ 140 keV or 1.5% FWHM at 140 keV. The energy resolution is dominated by MUX readout noise and so should improve with MUX optimization for gamma-ray detection. The spatial resolution of the 48 × 48 Ge array is essentially the same as the pixel spacing, 125 μm. The quantum efficiency is limited by the thin Ge detector (0.25 mm), but this approach is readily applicable to thicker Ge detectors and room-temperature semiconductor detectors such as CdTe, HgI 2 and CdZnTe.

Cadmium zinc telluride detectors for industrial radiation measurement

Cd 1−xZn xTe room temperature semiconductor detectors offer improved measurement capability, stability and lifetime over currently employed devices such as CdTe and HgI 2 detectors. These improved features along with the compactness, durability and other properties inherent in solid-state devices often make it the correct decision to use Cd 1−xZn xTe in place of detectors such as NaI(Tl) scintillators and proportional counters, and provide the basis for new approaches to instrumentation, including the use of imaging arrays and current-mode operation.

Use of Room Temperature Semiconductor Detectors for the Verification of Nuclear Material in International Safeguards Recent Advances

ABSTRACTIn the paper the development and usage of radiation detection systems based on room temperature semiconductors are described. The detection systems are intended for use by safeguards inspectors to verify nuclear material. Because of their high intrinsic efficiency, these detectors have advantages compared to classical germanium or Nal detectors. Several measurement tasks which cannot be handled in an optimum manner by using standard detectors have been solved. The main problem in the application of room temperature semiconductor detectors is the limitation in the availability of large detector volumes.

The use of a mercuric iodide detector for X-ray fluorescence analysis in archaeometry

For about two decades, energy dispersive X-ray fluorescence (EDXRF) has been employed in Rome for the analysis of works of art. A short history of the applications of EDXRF to paintings and alloys is presented. Finally, the usefulness of mercuric iodide room-temperature semiconductor detectors in this field is shown.