Improved setup for studying the low-frequency noise in semiconductor devices and structures

A setup is described for measuring the noise power density spectra of optical radiation detectors at frequencies from 1 to 10⁵ GHz in the detector and background temperature range from 80 to 500 K. Results obtained with lead sulfide photoresistors and silicon and indium antimonide photodiodes are presented. Translated from Izmertel'naya Tekhnika, No. 1, pp. 57–61, January, 1997.     

Discharge studies in micromegas detectors in a 150 GeV/c pion beam

A detailed study of several Micromegas detectors prototyped for the COMPASS and CLAS12 experiments is presented. Using a 150 GeV/c pion beam, the discharge probability was measured for several detector variants including bulk and non-bulk Micromegas. A detector equipped with an additional GEM foil as pre-amplification stage was also tested. A resistive coating of the readout strips was found to reduce the amplitude of the discharge by at least two orders of magnitude which was below the detection limit of the experimental setup. The effects of the micro-mesh type and material were investigated as well as the influence of the drift gap. Response in the presence of a 1.5 T transverse magnetic field was also studied. The measurements presented were performed during a RD51 beam test period.     

Detection of SNM by delayed gamma rays from induced fission

The Pulsed Neutron Interrogation Test Assembly (PUNITA) is an experimental device for research in NDA methods and field applicable instrumentation for nuclear safeguards and security applications. PUNITA incorporates a standard 14-MeV (D-T) pulsed neutron generator inside a large graphite mantle. The generator target is surrounded by a thick tungsten filter with the purpose to increase the neutron output and to tailor the neutron energy spectrum. In this configuration a sample may be exposed to a relatively high average thermal neutron flux of about (2.2±0.1)×10³ s⁻¹ cm⁻² at only 10% of the maximum target neutron emission. The sample cavity is large enough to allow variation of the experimental setup including the fissile sample, neutron and gamma detectors, and shielding materials.The response from SNM samples of different fissile material content was investigated with various field-applicable scintillation gamma detectors such as the 3×2 in. LaBr₃ detector. Shielding in the form of tungsten and cadmium was applied to the detector to improve the signal to background ratio. Gamma and neutron shields surrounding the samples were also tested for the purpose of simulating clandestine conduct. The energy spectra of delayed gamma rays were recorded in the range 100 keV-9 MeV. In addition time spectra of delayed gamma rays in the range 3.3-8 MeV were recorded in the time period of 10 ms-120 s after the 14-MeV neutron burst. The goal of the experiment was to optimize the sample/detector configuration including the energy range and time period for SNM detection. The results show, for example, that a 170 g sample of depleted uranium can be detected with the given setup in less than 3 min of investigation. Samples of higher enrichment or higher mass are detected in much shorter time.     

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.     

Improvement of semiconductor detector characteristics during supercurrent proton irradiation

Volt-ampère characteristics of Si p-type detectors are established to improve after pulse supercurrent irradiation with low energy protons. Appreciable improvement of energy resolution is observed for detectors irradiatied with the supercurrent proton beam within a dose interval from 10¹¹ to 5×10¹² proton cm⁻². Radiational resource of operation increases from 2.3 × 10¹⁰ to 3.7×10 ¹¹ proton cm⁻² for detectors which were pre-irradiated by the supercurrent proton beam.     

Development of an inconel self powered neutron detector for in-core reactor monitoring

The paper describes the development and testing of an Inconel600 (2 mm diameter×21 cm long) self-powered neutron detector for in-core neutron monitoring. The detector has 3.5 mm overall diameter and 22 cm length and is integrally coupled to a 12 m long mineral insulated cable. The performance of the detector was compared with cobalt and platinum detectors of similar dimensions. Gamma sensitivity measurements performed at the ⁶⁰Co irradiation facility in 14 MR/h gamma field showed values of −4.4×10⁻¹⁸ A/R/h/cm (−9.3×10⁻²⁴ A/γ/cm²-s/cm), −5.2×10⁻¹⁸ A/R/h/cm (−1.133×10⁻²³ A/γ/cm²-s/cm) and 34×10⁻¹⁸ A/R/h/cm (7.14×10⁻²³ A/γ/cm²-s/cm) for the Inconel, Co and Pt detectors, respectively. The detectors together with a miniature gamma ion chamber and fission chamber were tested in the in-core Apsara Swimming Pool type reactor. The ion chambers were used to estimate the neutron and gamma fields. With an effective neutron cross-section of 4b, the Inconel detector has a total sensitivity of 6×10⁻²³ A/nv/cm while the corresponding sensitivities for the platinum and cobalt detectors were 1.69×10⁻²² and 2.64×10⁻²² A/nv/cm. The linearity of the detector responses at power levels ranging from 100 to 200 kW was within ±5%. The response of the detectors to reactor scram showed that the prompt response of the Inconel detector was 0.95 while it was 0.7 and 0.95 for the platinum and cobalt self-powered detectors, respectively. The detector was also installed in the horizontal flux unit of 540 MW Pressurised Heavy Water Reactor (PHWR). The neutron flux at the detector location was calculated by Triveni code. The detector response was measured from 0.02% to 0.07% of full power and showed good correlation between power level and detector signals. Long-term tests and the dynamic response of the detector to shut down in PHWR are in progress.     

Small pixel CZT detector for hard X-ray spectroscopy

A new small pixel cadmium zinc telluride (CZT) detector has been developed for hard X-ray spectroscopy. The X-ray performance of four detectors is presented and the detectors are analysed in terms of the energy resolution of each pixel. The detectors were made from CZT crystals grown by the travelling heater method (THM) bonded to a 20×20 application specific integrated circuit (ASIC) and data acquisition (DAQ) system. The detectors had an array of 20×20 pixels on a 250 μm pitch, with each pixel gold-stud bonded to an energy resolving circuit in the ASIC. The DAQ system digitised the ASIC output with 14 bit resolution, performing offset corrections and data storage to disc in real time at up to 40,000 frames per second. The detector geometry and ASIC design was optimised for X-ray spectroscopy up to 150 keV and made use of the small pixel effect to preferentially measure the electron signal. A ²⁴¹Am source was used to measure the spectroscopic performance and uniformity of the detectors. The average energy resolution (FWHM at 59.54 keV) of each pixel ranged from 1.09±0.46 to 1.50±0.57 keV across the four detectors. The detectors showed good spectral performance and uniform response over almost all pixels in the 20×20 array. A large area 80×80 pixel detector will be built that will utilise the scalable design of the ASIC and the large areas of monolithic spectroscopic grade THM grown CZT that are now available. The large area detector will have the same performance as that demonstrated here.     

Target set-up for measurements with the use of a Si-ball detector

The thin n-p⁺ layer of Si n⁺-n-p⁺ wafers composing the light charged particles detectors can be easily damaged by scattered beam projectiles or heavy products of the nuclear reaction in target material. Such damages of the sensitive part of the wafer may in consequence shorten the detector life-time. This could be avoided by protecting the sensitive part of the detector with shielding that stops the heavy projectiles.Due to the compact configuration of the detectors in a small Si-ball counters placing the shielding in front of each wafer could be difficult and therefore a target-shielding assembly is proposed.     

A new recoil distance technique using low energy coulomb excitation in inverse kinematics

We report on the first experiment combining the Recoil Distance Doppler Shift technique and multistep Coulomb excitation in inverse kinematics at beam energies of 3-10 A MeV. The setup involves a standard plunger device equipped with a degrader foil instead of the normally used stopper foil. An array of particle detectors is positioned at forward angles to detect target-like recoil nuclei which are used as a trigger to discriminate against excitations in the degrader foil. The method has been successfully applied to measure lifetimes in ¹²⁸Xe and is suited to be a useful tool for experiments with radioactive ion beams.     

Traceable laser power measurements of diode laser radiation in the near infrared

We report a new calibration setup for laser radiometry at the Physikalisch-Technische Bundesanstalt, the German National Metrology Institute. Measurements of laser diode power of free beam diode lasers in the near infrared spectral range at a wavelength of 808 nm for powers up to 250 W and at wavelengths of 915 nm, 940 nm, and 980 nm for laser powers up to 25 W have been established. The calibration setup, the standard detector, the uncertainty budget and first calibration results will be presented and discussed. The standard uncertainty of the HLR302 standard detector is 0.2%. This uncertainty might be the main contribution to the overall uncertainty in customer calibrations, depending on the quality of the transfer detectors.     

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.     

Evaluation of large deuterated scintillators for fast neutron detection (E=0.5-20 MeV) using the D(d,n)He, C(d,n) and Al(d,n) reactions

The response of large deuterated liquid scintillators (up to 10 cm diameter by 15 cm) to neutrons 0.5-20 MeV has been studied using the 2.5 MeV neutron generator at the University of Michigan, and the d(d,n), ¹³C(d,n), ²⁷Al(d,n) and other reactions at the University of Notre Dame FN tandem accelerator. The latter utilize 9 and 16 MeV deuteron beams including a pulsed beam, which permitted time-of-flight measurements. Combining pulse-shape discrimination and time-of-flight allows gating on specific neutron energy groups to determine the detector response to specific neutron energies. This will permit accurate simulation of the detector response functions for applications of these detectors in nuclear research and homeland security applications.     

Avalanche effect in Si heavily irradiated detectors: Physical model and perspectives for application

The model explaining an enhanced collected charge in detectors irradiated to 10¹⁵-10¹⁶ n_eq/cm² is developed. This effect was first revealed in heavily irradiated n-on-p detectors operated at high bias voltage ranging from 900 to 1700 V. The model is based on the fundamental effect of carrier avalanche multiplication in the space charge region and in our case is extended with a consideration of p-n junctions with a high concentration of the deep levels. It is shown that the efficient trapping of free carriers from the bulk generation current to the deep levels of radiation induced defects leads to the stabilization of the irradiated detector operation in avalanche multiplication mode due to the reduction of the electric field at the junction. The charge collection efficiency and the detector reverse current dependences on the applied bias have been numerically simulated in this study and they well correlate to the recent experimental results of CERN RD50 collaboration. The developed model of enhanced collected charge predicts a controllable operation of heavily irradiated detectors that is promising for the detector application in the upcoming experiments in a high luminosity collider.     

Portable triple silicon detector telescope spectrometer for skin dosimetry

The features of a newly developed portable beta telescope spectrometer are described. The detector probe uses three silicon detectors with the thickness: 50 μm/150 μm/7000 μm covered by a 2 μm thick titanium window. Rejection of photon contributions from mixed beta/photon exposures is achieved by coincidence requirements between the detector signals. The silicon detectors, together with cooling aggregate, bias supplies, preamplifiers and charge generation for calibration are contained in a handy detector probe. Through a 3- or 10-m cable the detector unit is connected to a compact, portable processing unit including a laptop computer executing control, monitor, histogram and display tasks. The use of digital signal processing at an early stage of the signal chain has facilitated the achievement of a compact, low-weight device. 256 channels are available for each of the three detectors. The LabVIEW^TM software distributed by National Instruments was used for all program developments for the spectrometer, comprising also the capability of evaluating the absorbed dose rates from the measured beta spectra. The report describes the capability of the telescope spectrometer to measure beta and photon spectra as well as beta dose rates in mixed beta/photon radiation fields. It also describes the main features of the digital signal-processing electronics.     

Parallel Superconducting Strip-Line Detectors for Time-of-flight Mass Spectrometry

We present our achievements in the development of superconducting strip-line detectors (SSLDs) with parallel configuration for application in time-of-flight mass spectrometry. We have fabricated 2×2?mm² SSLDs by electron beam nano-lithography. In spite of the large area, the detector has a fast time response. To our knowledge our device is the largest cryogenic detector for macromolecules with nanosecond temporal response. Based on the obtained results, our simulations show that the presented parallel SSLD design should be able to cover an area of 4×2?mm² while keeping the signal pulse risetime below 1?ns.     

Development of integrated ΔE-E silicon detector telescope using silicon planar technology

An integrated ΔE-E silicon detector telescope using silicon planar technology has been developed. The technology developed is based on standard integrated circuit technology and involves double sided wafer processing. The ΔE and E detectors have been realized in a PIN configuration with a common buried N⁺ layer. Detectors with ΔE thicknesses of 10, 15 and 25 μm, and E detector with thickness of 300 μm have been fabricated and tested with alpha particles using ²³⁸Pu-²³⁹Pu dual alpha source. The performance of the detector with ΔE detector of thickness 10 μm and E detector of thickness 300 μm has been studied for identification of charged particles using 12 MeV ⁷Li⁺ ion beam on carbon target. The results of these tests demonstrate that the integrated detector telescope clearly separates the charged particles, such as alpha particles, protons and ⁷Li. Due to good energy resolution of the E detector, discrete alpha groups corresponding to well known states of ¹⁵N populated during the reaction could be clearly identified.     

Observations on dual-ended readout of 100 mm long LYSO crystals

We are investigating using dual-ended readout of axially oriented long thin scintillator crystals in detectors for a compact geometry, small ring diameter animal PET system. The axial position of interaction is determined from the light sharing between two photodetectors at opposite ends of the crystal. We examine the light output, energy resolution and axial spatial resolution of 1.5-5×2×100 mm³ polished LYSO crystals by irradiating with an electronically collimated beam of 511 keV photons oriented perpendicular to the long axis and read out at either end by position sensitive photomultiplier tubes (PSPMTs). Three reflector materials, namely Teflon, 3 M enhanced specular reflector (ESR) and black paint are examined for the 2×2×100 mm³ crystal size. The light output increases and energy resolution improves with the crystal cross-section. Generally, the spatial resolution worsens with increase in crystal cross-section. For the 2×2×100 mm³ crystal size, the mean energy resolutions of the photopeak over the nine irradiation positions were 14.4±0.4%, 16.0±1.2% and 28.3±2.1% with mean spatial resolutions of 7.0±1.0, 9.4±3.3 and 26.0±5.0 mm using ESR, Teflon and black paint, respectively. ESR reflector gave the best light output, energy and axial spatial resolutions. These characterization results of PSPMT-based dual-ended long LYSO crystals will be useful in the design of detector modules for a highly compact geometry preclinical PET system using this detector technology.     

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.     

Hexagonal boron nitride epitaxial layers as neutron detector materials

Micro-strip metal-semiconductor-metal detectors for thermal neutron sensing were fabricated from hexagonal boron nitride (hBN) epilayers synthesized by metal organic chemical vapor deposition. Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.00361 μm⁻¹ and 277 μm, respectively. A continuous irradiation with a thermal neutron beam generated an appreciable current response in hBN detectors, corresponding to an effective conversion efficiency approaching ∼80% for absorbed neutrons. Our results indicate that hBN semiconductors would enable the development of essentially ideal solid-state thermal neutron detectors in which both neutron capture and carrier collection are accomplished in the same hBN semiconductor. These solid-state detectors have the potential to replace ³He gas detectors, which faces the very serious issue of ³He gas shortage.     

Effects of dielectric thickness and contact area on current-voltage characteristics of thin film metal-insulator-metal diodes

Planar asymmetric Ni-NiO-Cr/Au thin film Metal-Insulator-Metal (MIM) tunnel diodes were fabricated for use in an ultra-sensitive infrared detector operating at room temperature. MIM diodes with contact areas of 100 μm² and 1 μm² were fabricated using standard Micro-Electro Mechanical Systems techniques. A linear relationship between the thickness of reactively sputtered Nickel Oxide (NiO) and the breakdown voltage was experimentally determined, and the diode performance was verified using a theoretical approach. Current-Voltage measurements of the MIM diode revealed an increase in the current from 1.5 nA to 0.8 mA, when the thickness of the dielectric and the contact area of the detector decreased. Also, the rectification ratios of the detectors were determined, exhibiting an asymmetry of 4.5 at 1 V and 6 at 0.2 V for detectors A and B, respectively. Further, the ratio was observed to be increasing with bias voltage suggesting a strong asymmetric behavior. The results are in agreement with the theoretical predictions confirming conduction via tunneling. The nonlinearity and asymmetry exhibited by these diodes suggests their viability in infrared applications.