Signal Pulse Height Research Articles

Dopant concentration dependence of the response of SiC Schottky diodes to light ions

The responses of Silicon Carbide (SiC) Schottky diodes of different dopant concentration to 12C ions at 14.2, 28.1 and 37.6 MeV incident energies are compared. The relation between the applied reverse bias and the thickness of the depleted epitaxial region is studied for different dopant concentrations. The experimental data show that SiC diodes with lower dopant concentration need lower reverse bias to be depleted. Moreover it has been observed that the energy resolution, measured as a function of the applied reverse bias and of the ions incident energies, does not depend on the dopant concentration. The radiation damage, produced by irradiating SiC diodes of different dopant concentration with 16O ions at 35.2 MeV, was evaluated by measuring the degradation of both the signal pulse-height and the energy resolution as a function of the 16O fluence. Diodes having a factor 20 lower dopant concentration exhibit a radiation hardness reduced by 60%. No inversion in the signal at the breakdown fluence was observed for 16O ions stopped inside the diode epitaxial region.

Detection system built from commercial integrated circuits for real-time measurement of radiation dose and quality using the variance method

A small, specialised amplifier using commercial integrated circuits (ICs) was developed to measure radiation dose and quality in real time using a microdosimetric ion chamber and the variance method. The charges from a microdosimetric ion chamber, operated in the current mode, were repeatedly collected for a fixed period of time for 20 cycles of 100 integrations, and processed by this specialised amplifier to produce signal pulse heights between 0 and 10 V. These signals were recorded by a multi-channel analyser coupled to a computer. FORTRAN programs were written to calculate the dose and dose variance. The dose variance produced in the ion chamber is a microdosimetric measure of radiation quality. Benchmark measurements of different brands of ICs were conducted. Results demonstrate that this specialised amplifier is capable of distinguishing differences of radiation quality in various high-dose-rate radiation fields including X rays, gamma rays and mixed neutron-gamma radiation from the research reactor at Texas A&M University Nuclear Science Center.

Characterization of an Al-STJ-based X-ray detector with monochromatized synchrotron radiation

The characterization of an Al-STJ-based detector with Pb absorber was performed with monochromatized synchrotron radiation. Detector response was measured in the energy range from 3 to 10keV. A small non-linearity of the signal pulse height was detected, probably due to the escape of recombination phonons from the detector. The non-linearity can be described by a second order polynomial function. Additionally, detector signals were recorded while an X-ray beam of 50μm diameter was directed to several locations on and near the absorber. For a well-aligned beam, detector artefacts are of at least two orders of magnitude lower intensity than the absorber events.

Diamond X-ray personal dosimetry. Numerical evaluation against silicon response

The performances achieved by diamond planar detectors are presented in comparison with high-sensitive personal silicon semiconductor dosimetric responses. Numerical simulation results are discussed in terms of diode signal pulse height analysis. The study already allows the proposition of thin layers of diamond for personal dosimetry of X-rays ranging between 20 and 660 keV .

Signal characteristics of individual crystals in high resolution BGO detector designs using PMT-quadrant sharing

The PMT-quadrant sharing (PQS) detector design allows very high resolution detectors to be built with 70% fewer PMTs and lower cost. A common concern for the design is that there is a big gap (photo-insensitive area) between four circular PMTs and the photoelectron signal (pulse height) may be much lower for the central crystals. The concern increases with the use of smaller PMTs for high-resolution designs because small PMTs have relatively thicker walls and relatively larger tolerance spaces between them. The authors measured the pulse heights and energy resolution for each crystal in three different types of PQS blocks for 19 mm PMT. For a square 7 /spl times/ 7 block detector (2.66 mm /spl times/ 2.66 mm /spl times/ 18 mm BGO needles), the maximum photopeak signals occurred at the corner crystal of the block. The signals for the worst central five crystals (sitting on space with no PMT connection) had pulse heights 0.87 as high as that of the corner crystals. The 12 crystals (outside the central five) with coupling only to the glass wall but not to the photocathode had a relative pulse height of 0.92. The eight crystals with partial exposure to photocathodes had a 0.94 relative pulse height. The energy resolution for individual crystals was 22% - 30% with an average of 26%. Asymmetric photopeaks, especially for the corner crystals, were observed, and these were found to be the result of the depth-of-interaction effect. In the latest PQS design, extended blocks with asymmetric light distributions were used on the four edges and four corners of a large detector module so that the previously unused (wasted) half-row of peripheral PMT could be covered by crystals. An asymmetric block, single-extended (7 /spl times/ 8 crystals) was also tested. The pulse-height ratio between the worst and best group of crystals in the single-extended block was 0.72 and that of the double-extended block was also 0.72. In a more demanding, higher spatial resolution 8 /spl times/ 8 array (2.3 mm /spl times/ 2.3 mm /spl times/ 10 mm BGO) for mouse PET with shallower crystals, the pulse-height ratio was 0.73 with an average energy resolution of 20%. This study demonstrated that pulse height uniformity for the PQS design using circular PMT was excellent, better than the typical 3/1 pulse-height ratio in conventional block detectors.

Inexpensive position sensitive detector block for dedicated PET cameras using 40-mm diameter PMT in quadrant sharing configuration

Recent approvals by CMS (HCFA) for reimbursement of positron emission tomography (PET) scans fuels the rapid grow of the PET market, thus creating the need for more affordable dedicated PET scanners. The objective of the work presented here was the development of a BGO position-sensitive block with similar detector area (40 mm /spl times/ 40 mm) and same number of crystals (8 /spl times/ 8) as the block of a commercial BGO PET, using the less expensive photomultiplier quadrant sharing (PQS) technique. This block is coupled to four single-anode 40-mm diameter photomultipliers (PMT) instead of the 19-mm PMT used in a popular commercial BGO PET, and each PMT is shared by four adjacent detector blocks. Potentially, this design needs only 25% of the number of PMT used in the commercial BGO PET. In order not to waste the unused half-row of PMT at the edges of a detector panel/module when the module is made up solely of square blocks, an extended rectangular block has to be developed for the edge-blocks in the module, which maximized the use of the PMT and minimized the gap between modules. Only the extended block needs to be developed to derive the design for all the blocks in the module because the symmetric square block uses the same light-distributing partitions as those along the short side of the extended rectangular block. White-paint masks applied with accurate templates and airbrush were fine-tuned for every pair of adjacent crystals. The experimental block developed in this study provided good crystal-decoding. The composite energy spectrum of all 64 crystals showed a prominent photopeak. The worst crystal sitting in the air space between 4 round PMTs still has 60% of the signal pulse height as the best crystal. The average energy resolution was 21.8% for 511 keV gamma (range 17% - 28.7%) that compared well with the 22% - 44% measured with GE and CTI blocks. The image resolution provided by the PQS blocks is expected to be comparable to that of commercial BGO PETs as similar size crystals were decoded.

Performance of the BELLE silicon vertex detector

The performance of the Silicon Vertex Detector (SVD) in the Belle experiment is reviewed based on 6.8 fb/sup -1/ of data taken between October 1999 and July 2000. The main purpose of the SVD is to make precise measurements of the B decay vertex position, which are essential for the observation of CP asymmetries. Excellent vertex resolution and a good detection efficiency are required for the SVD. Basic performance parameters such as signal pulse height, noise, strip yield and intrinsic resolution are reported. The SVD performance parameters which are directly related to physics analysis such as track matching efficiency, impact parameter resolution and vertex resolution are also shown.

Energy Spectrum Improvement for CdZnTe Semiconductor Detector Based on Euclidian Distance with Digital-Analog Hybrid Signal Processing System

The application of a ‘digital-analog hybrid signal processing system’ combined with a Euclidian distance method is presented. The proposed method is used to improve gamma-ray energy spectrum characteristics of a CdZnTe semiconductor detector. A digital and an analog system are simultaneously applied to the detector output after passing through a preamplifier, where the digital system digitizes the signal pulse shape for the Euclidian distance determination, while the analog system measures the signal pulse height with a conventional analog method. In this paper, the digital and the analog data are combined to improve the energy spectrum characteristics; giving the increase of the photopeak area, the peak-to-valley ratio, and the photopeak sharpness.

Pulse shape analysis based on similarity with digital–analog fusion method

We present the application of a “fusion method” combined with a “similarity” method to improve γ-ray energy spectrum characteristics of a CdZnTe semiconductor detector. A digital and an analog system are simultaneously applied to the detector output after passing through a preamplifier, where the digital system digitizes the signal pulse shape for the similarity determination, while the analog measures the signal pulse heights with a conventional analog method. In this paper, the digital and the analog data are fused to improve the energy spectrum characteristics, giving an increase of the photopeak area, the peak-to-valley ratio, and the photopeak sharpness.

Measurement of the response characteristics around K absorption edges of dead-layer materials of a charge-coupled device

We measure various spectral response characteristics around the oxygen, silicon, and nitrogen K absorption edges of a front-illuminated Charge-Coupled Device (CCD) X-ray detector used in the X-ray Imaging Spectrometer (XIS) developed for the ASTRO-E mission. We have evaluated X-ray Adsorption Fine Structure (XAFS) around oxygen K edge in detail. A strong absorption peak of 45% is confirmed just above the oxygen K edge and an oscillatory structure follows whose amplitude decreases from 20% at the edge to less than 1% at 0.9 keV. We also show XAFS and discuss on a change of the response function around the silicon K edge. The discontinuity of the signal-pulse–height at the silicon K edge is less than 2.9 eV. We determine the thickness of silicon, silicon dioxide, and silicon nitride in the dead-layer using the depth of the absorption edge.

Improvement of energy spectrum characteristics of CdZnTe semiconductor detector with a digital–analog fusion method

We present a new application of a `Fusion Method’ to improve gamma-ray energy spectrum characteristics of a CdZnTe semiconductor detector. A digital and an analog system are simultaneously applied for the detector output; The digital system digitizes the signal pulse shapes for pattern recognition based on a neural network algorithm. The analog measures the signal pulse heights with a conventional analog system. The digital and the analog output data are fused and then used for improvement of the energy spectrum characteristics, i.e. the photopeak area, the peak-to-valley ratio, and the FWHM of photopeaks.

Soft X-ray response of a CCD with a grating spectrometer

We calibrate the X-ray imaging spectrometers, which are CCD cameras installed on the ASTRO-E satellite, by using dispersed continuous soft X-rays from a grating spectrometer. We obtained the signal-pulse height and energy-resolution as a function of X-ray energies continuously. However, the wings of the line spread function of the grating distorts the center of the signal-pulse height derived by a simple analysis. An estimation of this distortion is presented. We also describe two methods of extracting the pure signal-pulse-height distribution from the data using the spectrometer. A brief description of the low-energy tail is presented.

Event-Driven 2D Detector for Digital Electron Imaging

An event-driven 2D pixel array detector designed for protein crystallography is being tested to determine its suitability as a direct electron detector for digital imaging in electron microscopy. The detector prototype consists of an 8×8 pixel array with an 150 μm pitch. The device configuration is illustrated in Fig. 1. The detector module consists of a reverse-biased 300 μm thick monolithic silicon diode array which is bump-bonded to an Application Specific Integrated Circuit (ASIC) which instruments each diode in the array. Each pixel cell of the ASIC forms a pixel processor which consists of an amplifier, discriminator, prescalar and readout circuit.When an incident electron enters the detector, a group of electron-hole pairs is created in the silicon. The detector bias of the diode array is such that holes are collected at the input to the amplifier where the signal is then amplified and shaped. When the output signal pulse height is greater than the discriminator threshold, the event is then registered in the prescalar, causing one count to be accumulated.

Observation of light from resistive plate chambers

Electrically induced signals and light emissions from Restrictive Plate Chamber (RPC) are simultaneously measured using a glass RPC with transparent high-voltage planes, operating in the streamer mode. With one exception, good correspondence is seen in between the electrical and optical signals in every aspect: signal shapes, pulse heights, timing and afterpulses. The one exception is a possible limiting effect observed on the optical signal pulse height for a given pulse height of electrically induced signal. Shapes of the signal visually observed by eye are also described.

An analog decoding BGO block detector using circular photomultipliers

This is a positron camera detector design study using quadrant sharing of circular phototubes and optically cross-coupled BGO scintillation crystals. The goal is to design a very high spatial resolution detector using the larger and less expensive circular phototubes, so that the high production cost of high spatial resolution, multi-slice positron cameras may be lowered. Theoretical calculations and experimental studies have been performed using 19 mm diameter phototubes. The study shows that (a) BGO detector-pitch in the range of 2.2/spl times/2.2 mm to 3.0/spl times/3.0 mm (transaxial x axial) can be decoded with these 19 mm diameter phototubes, and (b) it is possible to achieve very uniform signal pulse-height for all the BGO crystals in the block with this design, even though there are relatively large air-gaps between circular phototubes. This study shows that very high spatial resolution, approaching the theoretical resolution of PET imaging, can be achieved using the cheaper 19 mm circular phototubes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A positron camera detector design with cross-coupled scintillators and quadrant sharing photomultipliers

A new positron camera scintillation detector design is proposed. This design uses discrete scintillators which are tightly optically coupled (glued) together to form a block. The coupling interfaces between crystals have different degrees of polish depending on the interface location within the block. Each block has the same dimension as that of the photomultipliers (PMTs) used, but the blocks and the PMT array are offset in both X-Y directions. The advantages of the design are: (a) higher detection efficiency with almost 100% packing fraction; (b) very uniform signal pulse-heights even for very small crystals at the edge of the block; (c) decoding which is less dependent on the depth of interaction; (d) significant decrease in the number of PMTs by up to 75%; and (e) with the smallest PMT (1.0 cm) currently available, spatial resolution in the range of 1-2 mm is possible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ion-implanted silicon detectors processed on a 100 mm wafer

A planar process for manufacturing large silicon detectors on a 100 mm wafer has been developed. Several oxidation and annealing temperatures were studied in order to optimize detector performance. A strip detector with an active area of 32 × 58 mm 2 together with various single detector diodes were processed and tested. The 1280 strip detector with 25 μm strip and readout pitch was connected to multiplexing LSI electronics and tested with tracks from a 90Sr beta source. The most probable signal pulse height was found to be 14 times the σ noise of any individual channel.

A new monitoring system for the thermal neutron fluence rate and gamma dose rate in boron neutron capture therapy

A new monitoring system for the thermal neutron fluence rate and gamma dose rate is described for boron neutron capture therapy (BNCT). A small pn junction Si diode was used as a new detector which was mechanically stronger and had better stability than a surface barrier detector. The pulse height of signals due to thermal neutrons was sufficiently high and was separated from signals due to gamma rays. The radiation damage to the detectors which results in a reduction of the pulse height was found to be quite small. By using the detectors, the thermal neutron fluence rate and gamma dose rate, not only in the head but also in the body, were measured simultaneously during therapy, and the new system has been efficiently used for BNCT of brain tumours.

Deterioration and recovery of BF 3 counters due to operation in intense radiation fields

A number of BF 3 counters was irradiated under operating conditions in a neutron field 1.2×10 4 n v and gamma ray fields of various fluxes between 15 and 64000 R/h. The counters underwent a degradation common to all regardless of the kind and flux of the external radiation. The degradation speed was slower for the operation at a lower gas multiplication and at a higher temperature, 40°C. Many of the counters exhibited a recovery at a certain amount of irradiation (∼ 10 4 R and ∼ 10 10 n vt) and were stable for further irradiation. The degradation was characterized by the signal pulse height reduction. The cathode inner surface analysis was conducted after the irradiation. More fluorine was found on the cathode surface of a recovered counter than on that of a non-recovered one. The deterioration-recovery mechanism is discussed.

Automatically sweeping dual-channel boxcar integrator

An automatically sweeping dual-channel boxcar integrator has been developed to automate the search for a signal that repeatedly follows a trigger pulse by a constant or slowly varying time delay when that signal is completely hidden in random electrical noise and dc-offset drifts. The automatically sweeping dual-channel boxcar integrator improves the signal-to-noise ratio and eliminates dc-drift errors in the same way that a conventional dual-channel boxcar integrator does, but, in addition, automatically locates the hidden signal. When the signal is found, its time delay is displayed with 100-ns resolution, and its peak value is automatically measured and displayed. This relieves the operator of the tedious, time-consuming, and error-prone search for the signal whenever the time delay changes. The automatically sweeping boxcar integrator can also be used as a conventional dual-channel boxcar integrator. In either mode, it can repeatedly integrate a signal up to 990 times and thus make accurate measurements of the signal pulse height in the presence of random noise, dc offsets, and unsynchronized interfering signals.