Test beam results of Current Injected Detectors (CID) irradiated up to 5×10 1 MeV neq/cm

Two full size strip detectors were investigated in this study: one with p⁺ strips (p⁺/n⁻/n⁺) and another with n⁺ strips (n⁺/p⁻/p⁺). Both detectors, are made of magnetic Czochralski silicon (MCz-Si) and irradiated to S-LHC fluencies, were tested with 225 GeV muon beam in the CERN H2 area. The Current Injected Detector (CID) sensors were operated in a cooling box capable of providing a −53 °C temperature. Results indicate a relative charge collection efficiency (CCE) at 5×10¹⁵ n_eq/cm² above 30% in irradiated p⁺/n⁻/n⁺ CID detector at 600 V bias voltage. The signal to noise ratio of this CID module was about eight and a forward current of 30 μA was needed for detector biasing. In standard reverse bias, the same detector could not provide a sufficiently large signal for particle tracking purposes. A p-type (n⁺/p⁻/p⁺) sensor was irradiated to a fluence of 2×10¹⁵ n_eq/cm² and measured under the same test beam conditions. According to the theory of CIDs developed by the CERN RD39 Collaboration, this detector module could be biased up to only 230 V due to the low irradiation fluence. The CCE at 230 V was 35% in CID operation and 20% when reverse biased.     

Performance of a 6 mm thick CdTe detector for 166 keV gamma rays

In order to extend the utility of CdTe detectors to higher gamma ray energies, yet avoid increasing the charge collection problems of thick detectors, a 6 mm thick detector configuration has been developed consisting of three crystals 2 mm thick and of 16 mm diameter. The active volume is over 1.0 cm³. The performance of this detector has been evaluated for gamma rays of 166 keV energy by measuring the pulse height spectra and determining the intrinsic peak and total efficiencies over a range of bias voltages and amplifier time constants. A maximum peak and total efficiency of 41% and 80% were obtained with 200 V bias and 2 μs amplifier time constant, although under these conditions the noise width was almost 40 keV FWHM. A Monte Carlo model was used to simulate the gamma ray and electron interaction in this 6 mm detector. Charge collection, including trapping effects, was incorporated into the model. The model pulse height spectra could be approximately matched to the measured data using hole and electron effective mobility values of 60 and 600 cm²/V s, and hole and electron mean trapping times of 25 and 15 μs. Our findings indicate that detectors such as this will not be useful for high resolution spectroscopic applications, but the high gamma ray stopping power will be of interest for applications where the noise width is acceptable. Results from the modelling imply that in this detector shallow trapping sites (reducing the effective mobility) are more important than deep trapping sites in contributing to incomplete charge collection.     

Comparative measurements of highly irradiated n-in-p and p-in-n 3D silicon strip detectors

Silicon detectors in 3D technology are a candidate for applications in environments requiring an extreme radiation hardness, as in the innermost layers of the detectors at the proposed High-Luminosity LHC. In 3D detectors, the electrodes are made of columns etched into the silicon perpendicular to the surface. This leads to higher electric fields, a smaller depletion voltage and a reduced trapping probability of the charge carriers compared to standard planar detectors. In this article, the signal and the noise of irradiated n-in-p and p-in-n 3D silicon strip detectors are compared. The devices under test have been irradiated up to a fluence of 2×10¹⁶ 1 MeV neutron equivalent particles per square centimetre (n_eq/cm²), which corresponds to the fluence expected for the inner pixel detector layers at the High-Luminosity LHC. A relative charge collection efficiency of approximately 70% was obtained even after the highest irradiation fluence with both detector types. The influence of different temperatures on the signal and the noise is investigated and results of annealing measurements are reported.     

Concept of Double Peak electric field distribution in the development of radiation hard silicon detectors

The concept of Double Peak (DP) electric field distribution is considered for the analysis of operational characteristics of irradiated silicon detectors. The key point of the model is trapping of equilibrium carriers to the midgap energy levels of radiation-induced defects, which leads to a non-uniform distribution of space charge concentration with positively and negatively charged regions adjacent to the p⁺ and n⁺ contacts, respectively. In our new development of the DP model we consider a non-depleted base region in between the space charge regions as a high resistivity bulk, which operates as a drift region with a non-negligible electric field. Electric field characteristics of detectors processed from n-type MCZ Si wafers using various technological procedures, and irradiated by 1 MeV neutrons and 24 GeV/c protons, have been compared. Electric field profiles have been reconstructed from DP pulse response of heavily irradiated detectors and calculated by the simulation of DP electric field distribution caused by carrier trapping. It is shown that detectors from n-type MCZ Si irradiated by 24 GeV/c protons do not show typical space charge sign inversion up to the irradiation fluence of about 2.2×10¹⁵ p/cm² and the region with a positive charge dominates over a negatively charged region.     

Applications of avalanche multiplication in amorphous selenium to flat panel detectors for medical applications

A new concept of an indirect conversion flat panel detector utilizing avalanche multiplication phenomena in amorphous selenium (a-Se) is described. It is shown that high avalanche multiplication gain of 1,000 can be achieved for 35 μm thick a-Se layer. Combined with high quantum efficiency of charge photogeneration for peak emission from the CsI scintillator (almost unity) this significantly improves low dose detector performance. The avalanche gain dependence on both, applied electric field and photoconductor layer thickness is analyzed giving the possibility to program the gain (from 1 to 1,000) by adjusting applied field prior to exposure. This provides wide dynamic range required for the variety of clinical and biomedical applications.     

Characterization of polarization phenomenon in Al-Schottky CdTe detectors using a spectroscopic analysis method

CdTe radiation detectors equipped with Schottky contacts are known to show spectral response degradation over time under biasing. Nevertheless, they can be used as high-resolution spectrometers for X-rays and gamma-rays with moderate cooling and high voltage. Spectroscopic long-term measurements have been performed with Al/CdTe/Pt pixel detectors of 0.5, 1 and 2 mm thicknesses and ²⁴¹Am source from −13 to +16 °C to evaluate how long they can be operated. Experimental results are confronted to simulations using the charge accumulation model for electric field. Activation energy for collection efficiency stability and peak shift was measured at 1.0-1.2 eV although deep acceptor levels responsible for hole detrapping during polarization were evaluated by other methods at E_V +0.6-0.8 eV. The difference is probably due to a thermal effect of pre-polarization before biasing the detector.     

Study of polarization phenomena in Schottky CdTe diodes using infrared light illumination

Schottky CdTe diode detectors suffer from a polarization phenomenon, which is characterized by degradation of the spectral properties over time following exposure to high bias voltage. This is considered attributable to charge accumulation at deep acceptor levels. A Schottky CdTe diode was illuminated with an infrared light for a certain period during a bias operation, and two opposite behaviors emerged. The detector showed a recovery when illuminated after the bias-induced polarization had completely progressed. Conversely, when the detector was illuminated before the emergence of bias-induced polarization, the degradation of the spectral properties was accelerated. Interpretation of these effects and discussion on the energy level of deep acceptors are presented.     

Highly sensitive PtSi/porous Si Schottky detectors

Presents the first experimental results on PtSi/porous Si Schottky detectors. Si pores have been filled by Pt through electrodeposition. Under proper temperature treatment, Pt reacts with Si creating a PtSi layer that uniformly covers the walls of the pores. The excess unreacted Pt inside the pores is etched away leaving empty spaces behind. The spectral response of such a detector is very wide, covering from 0.9 up to at least 7 /spl mu/m of IR radiation in back illumination mode. Excellent responsivities, such as 60 A/W at 1 /spl mu/m and 0.96 A/W at 4 /spl mu/m of IR radiation is exhibited. Reverse bias current-voltage characteristics exhibit a breakdown type behavior with a breakdown voltage at about 10 V. The general shape of the reverse bias I-V curve, the wide spectral range, and high responsivity are explained through tunneling and avalanche multiplication. It is proposed that large fringing fields developed at sharp edges of the porous surface cause tunneling and avalanche multiplication.     

First results of the LHC longitudinal density monitor

The Large Hadron Collider (LHC) at CERN is the world's largest particle accelerator. It is designed to accelerate and collide protons or heavy ions up to the center-of-mass energies of 14 TeV.Knowledge of the longitudinal distribution of particles is important for various aspects of accelerator operation, in particular to check the injection quality and to measure the proportion of charge outside the nominally filled bunches during the physics periods. In order to study this so-called ghost charge at levels very much smaller than the main bunches, a longitudinal profile measurement with a very high dynamic range is needed.A new detector, the LHC Longitudinal Density Monitor (LDM) is a single-photon counting system measuring synchrotron light by means of an avalanche photodiode detector. The unprecedented energies reached in the LHC allow synchrotron light diagnostics to be used with both protons and heavy ions.A prototype was installed during the 2010 LHC run and was able to longitudinally profile the whole ring with a resolution close to the target of 50 ps. On-line correction for the effects of the detector deadtime, pile-up and afterpulsing allow a dynamic range of 10⁵ to be achieved.First measurements with the LDM are presented here along with an analysis of its performance and an outlook for future upgrades.     

Continuous measurement of radiation damage of standard CMOS imagers

In this work we have irradiated a standard CMOS VGA imager with a 24 MeV proton beam at INFN Laboratori Nazionali del Sud, up to a nominal fluence of 10¹⁴ protons/cm². The device under test was fabricated with a 130 nm technology without radiation hardening. During the damaging the detector was fully operational to monitor the progressive damaging of the sensor and the associated on-pixel electronics in terms of detection efficiency, charge collection and noise. We found that the detector is still working at 10¹³ protons/cm², with a moderate increase of the noise (20%).     

Effects of the polarity of bias voltage on the electrical performance of the diamond film detectors

The effect of the polarity of the applied bias voltage on the electrical response and the charge collection efficiency of sandwich structural diamond film detectors under 5.5 MeV ²⁴¹Am alpha-particle irradiation is investigated. Results show that, under the alpha irradiation the detector applied with a negative bias voltage has a higher response current and a better signal-to-noise ratio than that applied with a positive bias voltage. A better energy resolution of about 25.0% is obtained for the detector applied with a negative bias voltage, and however 38.4% for that with a positive bias voltage. Raman scattering studies demonstrate that these changes with the polarity of the bias voltage may be attributed to the different structural imperfection distributions along the thickness direction of the diamond film.     

GaN-based PIN alpha particle detectors

GaN-based PIN alpha particle detectors are studied in this article. The electrical properties of detectors have been investigated, such as current-voltage (I-V) and capacitance-voltage (C-V). The reverse current of all detectors is in nA range applied at 30 V, which is suitable for detector operation. The charge collection efficiency (CCE) is measured to be approximately 80% but the energy resolution is calculated to be about 40% mostly because the intrinsic layer is not sufficiently thick enough.     

Use of pixelated detectors for the identification of defects and charge collection effects in mercuric iodide (HgI2) single crystal material

Physical structure of pixelated detectors provides a unique tool to evaluate the effects of different types of defects in the semiconductor material that is used to fabricate the detectors. The spectroscopic performance measured for individual pixels or groups of pixels can be used to correlate point defects or fields of inhomogeneities within the material with the charge collected from photoelectric events. A block of single crystal mercuric iodide of approximately 18×18 mm² area and between 6 and 10 mm thick is prepared. The homogeneity of this material is then investigated with light in the transparent region for HgI₂ using an optical microscope. Several types of defects can be identified in this way by the scattering of light, for example, single large inclusions or voids and areas of haziness consisting of fields of small inclusions. Standard procedures are used to fabricate from this block a pixelated detector with a 121-pixel anode structure. The performance of each pixel is measured, and differences in charge collection are correlated with the optical data. Measurement data are presented, and possible mechanisms of the interactions between the defects and the charge carriers are discussed.     

Development of cryogenic alpha spectrometers using metallic magnetic calorimeters

Cryogenic particle detectors have recently been adopted in radiation detection and measurement because of their high energy resolution. Many of these detectors have demonstrated energy resolutions better than the theoretical limit of semiconductor detectors. We report the development of a micro-fabricated magnetic calorimeter coupled to a large-area particle absorber. It is based on a planar, 1 mm² large paramagnetic temperature sensor made of sputtered Au:Er, which covers a superconducting meander-shaped pickup coil coupled to a low-noise dc-SQUID to monitor the magnetization of the sensor. A piece of gold foil of 2.5×2.5×0.07 mm³ was glued to the Au:Er film to serve as an absorber for incident alpha particles. The detector performance was investigated with an ²⁴¹Am source. The signal size comparison for alpha and gamma peaks with a large difference in energy demonstrated that the detector had good linear behavior. An energy resolution of 2.83±0.05 keV in FWHM was obtained for 5.5 MeV alpha particles.     

Microchannel avalanche photodiode with broad linearity range

Design and operation principles of a new microchannel avalanche photodiode with an avalanche multiplication coefficient of up to 10⁵ and a linearity range expanded by an order of magnitude compared to the existing analogs are described. A distinctive feature of the new device design is that the forward-biased p_n junctions (playing the role of individual quenching resistors) are situated under each pixel. This circumstance ensures an increase in the density of multiplication channels up to 40000 mm-2 at a 100% sensitive device area.     

Photovoltaic X-ray detectors based on epitaxial GaAs structures

A new type of the photovoltaic X-ray detector based on epitaxial p ⁺-n-n′-n ⁺ GaAs structures is proposed, which provides for a high efficiency of charge carrier collection in a nonbiased operation regime at room temperature. The GaAs structures were grown by vapor phase epitaxy on heavily doped n ⁺-GaAs substrates. The X-ray sensitivity range covers the effective energies from 8 to 120 keV. The maximum output signal in the short-circuit regime is 30 μA min/(Gy cm²). The detector response to γ-radiation from a ¹³⁷Cs[660 keV] radioactive isotope was measured.     

Boron-coated straws as a replacement for He-based neutron detectors

US and international government efforts to equip major seaports with large area neutron detectors, aimed to intercept the smuggling of nuclear materials, have precipitated a critical shortage of ³He gas. It is estimated that the annual demand of ³He for US security applications alone is more than the worldwide supply. This is strongly limiting the prospects of neutron science, safeguards, and other applications that rely heavily on ³He-based detectors. Clearly, alternate neutron detection technologies that can support large sensitive areas, and have low gamma sensitivity and low cost must be developed.We propose a low-cost technology based on long copper tubes (straws), coated on the inside with a thin layer of ¹⁰B-enriched boron carbide (¹⁰B₄C). In addition to the high abundance of boron on Earth and low cost of ¹⁰B enrichment, the boron-coated straw (BCS) detector offers distinct advantages over conventional ³He-based detectors, and alternate technologies such as ¹⁰BF₃ tubes and ¹⁰B-coated rigid tubes. These include better distribution inside moderator assemblies, many-times faster electronic signals, no pressurization, improved gamma-ray rejection, no toxic or flammable gases, and ease of serviceability.We present the performance of BCS detectors dispersed in a solid plastic moderator to address the need for portal monitoring. The design adopts the outer dimensions of currently deployed ³He-based monitors, but takes advantage of the small BCS diameter to achieve a more uniform distribution of neutron converter throughout the moderating material. We show that approximately 63 BCS detectors, each 205 cm long, distributed inside the moderator, can match or exceed the detection efficiency of typical monitors fitted with a 5 cm diameter ³He tube, 187 cm long, pressurized to 3 atm.     

Vapor‐Phase‐Gating‐Induced Ultrasensitive Ion Detection in Graphene and Single‐Walled Carbon Nanotube Networks

Designing ultrasensitive detectors often requires complex architectures, high‐voltage operations, and sophisticated low‐noise measurements. In this work, it is shown that simple low‐bias two‐terminal DC‐conductance values of graphene and single‐walled carbon nanotubes are extremely sensitive to ionized gas molecules. Incident ions form an electrode‐free, dielectric‐ or electrolyte‐free, bias‐free vapor‐phase top‐gate that can efficiently modulate carrier densities up to ≈0.6 × 10¹³ cm^?2. Surprisingly, the resulting current changes are several orders of magnitude larger than that expected from conventional electrostatic gating, suggesting the possible role of a current‐gain inducing mechanism similar to those seen in photodetectors. These miniature detectors demonstrate charge–current amplification factor values exceeding 10⁸ A C^?1 in vacuum with undiminished responses in open air, and clearly distinguish between positive and negative ions sources. At extremely low rates of ion incidence, detector currents show stepwise changes with time, and calculations suggest that these stepwise changes can result from arrival of individual ions. These sensitive ion detectors are used to demonstrate a proof‐of‐concept low‐cost, amplifier‐free, light‐emitting‐diode‐based low‐power ion‐indicator.     

Development of current-based microscopic defect analysis methods and associated optical filling techniques for the investigation on highly irradiated high resistivity silicon detectors

Current based microscopic defect analysis methods such as current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC) have been further developed in accordance with the need for the defect analysis of highly irradiated (Φ_n > 10¹³ n/cm²) high resistivity silicon detectors. The new I-DLTS/TSC system has a temperature range of 8 K ≤ T ≤ 450 K and a high sensitivity that can detect a defect concentration of less than 10¹⁰/cm³ (background noise as low as 10 fA). A new filling method using different wavelength laser illumination has been applied, which is more efficient and suitable than the traditional voltage pulse filling. It has been found that the filling of a defect level depends on such factors as the total concentration of free carriers generated or injected, the penetration length of the laser (laser wavelength), the temperature at which the filling is taking place, as well as the decay time after the filling (but before the measurement). The mechanism of the defect filling can be explained by the competition between trapping and detrapping of defect levels, possible capture cross section temperature dependence, and interaction among various defect levels in terms of charge transferring. Optimum defect filling conditions have been suggested for highly irradiated high resistivity silicon detectors.     

The TRACER instrument: A balloon-borne cosmic-ray detector

We describe a large-area detector for measurements of the intensity of cosmic-ray nuclei in balloon-borne exposures. In order to observe individual nuclei at very high energies, the instrument employs transition radiation detectors (TRD) whose energy response extends well beyond 10⁴ GeV amu⁻¹. The TR measurement is performed with arrays of single-wire proportional tubes interleaved with plastic-fiber radiators. An additional energy determination comes from the specific ionization in gas and its relativistic rise which is also measured with proportional tubes. The tubes also determine the trajectory of each cosmic-ray nucleus with mm-resolution. In total, nearly 1600 tubes are used. The instrument is triggered by large-area plastic scintillators. The scintillators, together with acrylic Cherenkov counters, also determine the nuclear charge Z of each cosmic-ray particle, measure the energy in the GeV amu⁻¹ region, and discriminate against low-energy background. We describe the details of this detector system, and discuss its performance in three high-altitude balloon flights, including two long-duration flights in 2003 and 2006 at Antarctic and Arctic latitudes, respectively. Scientific results from these flights are summarized, and possible future developments are reviewed.