X-ray imaging with “edge-on” microchannel plate detector: first experimental results

A novel scanning slit X-ray imaging system based on an “edge-on” microchannel plate detector was developed and tested. Images were acquired at 50 kV(p) X-ray tube voltage with a limiting spatial resolution of 7 lp/mm. The pixel noise was measured to be 0.3 count/pixel/s for a 50×70 μm² pixel size. This photon counting detector can be considered to be virtually noise free.     

A novel gamma-ray imaging concept using “edge-on” microchannel plate detector

The “edge-on” illuminated microchannel plate (MCP) position-sensitive detector (PSD) is used for gamma-ray imaging for the first time. The superior position resolution of the MCP is combined with high detection efficiency due to the “edge-on” illumination mode. The results of imaging a 15 μCi ¹³⁷Cs source (662 keV quantum energy) are presented.     

ΔE−E Telescope systems for detecting charged particles produced with a “white” neutron beam

Highly stable ΔE−E telescope systems consisting of plastic scintillation detectors are operated as flux monitors in a “white” neutron beam between 15 and 50 MeV. Multiple telescope systems consisting of large area silicon ΔE detectors and NaI E detectors are set up in a scattering chamber to investigate charged particle reactions induced by fast neutrons up to 50 MeV.     

Silicon beam telescope for CMS detector tests

A beam telescope providing precision track measurements as reference for other detectors has been upgraded in the CERN H2 test beam. The apparatus was completely rebuilt from the detector wafers and front-end electronics to the data acquisition system. The new detector setup consists of eight 5.6×5.6 cm² sized DC coupled silicon microstrip detectors. Typical position resolution values of about 7.5 μm were measured. Details of the setup are described and results from the recent beam tests are reported.     

CD: A double sided silicon strip detector for radioactive nuclear beam experiments

A very compact double sided silicon strip detector array is described, designed for use in reaction studies involving radioactive nuclear beams. It is small enough to fit inside a large solid angle γ-detector array and will enable Doppler-shift corrections at energies in the vicinity of the Coulomb barrier. The detector provides sufficient energy and time-of-flight resolution for the identification of light reaction products and can be set up to cover a substantial part of the scattering angular distribution with good resolution.

The device is available in thicknesses of up to 500 μm to stop all interesting reaction products. Moreover, a very thin (35–40 μm) variant of this detector is described that can be used as an energy loss detector in a ΔE−E telescope geometry followed by a detector that measures the residual energy. This provides additional particle identification capabilities, e.g. in light exotic nuclei induced reactions. First results from a commissioning run using a post-accelerated radioactive beam are presented.     

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 10 keV. 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 50 μm 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.     

Infrared light charge injector as a tool for the study of silicon detectors

In order to study the local response of silicon strip detectors, we have developed a local charge generator using near-infrared ligh emitting diode. The edge properties of the strip detectors were studied precisely with this tool. In the case of our tested detector, the lateral extension of the depletion area was measured to be about 120 μm at a bias voltage of 40 V.     

The “switch off” baseline restorer for the 120 channel silicon detector system for EXAFS at NSLS

A new circuit for high precision baseline restoration in multichannel nuclear pulse spectrometers is proposed. It has been designed for the 120 channel silicon detector system for EXAFS research at NSLS (National Synchrotron Light Source), Brookhaven National Laboratory, USA [L.R. Furenlid et al., Nucl. Instr. and Meth. A 319 (1992) 408], and is based on a current “switch off” mechanism self-triggered on the input signal pulses. No auxiliary gate signals are required, and, consequently, the network is particularly compact. As opposed to Robinson restorers, this restorer is not affected by undershoot, and it does not involve the significant complexity of gated solutions. The restorer has been tested with a 7 pole quasi-Gaussian filter permitting very high resolution X-ray spectroscopy (160 eV FWHM on pulser peak). The signal-to-noise degradation due to the restorer is about 7%. The BLR response to 18 μs large trapezoidal input pulses shows an undershoot which is about 0.3%. Baseline is correctly recovered for repetition rates of up to 5 × 10⁴ trapezoidal signals/s, which corresponds to a duty cycle of 60%. The BLR has been layed out in SMT on a 0.8 in. × 0.8 in. area, which is suitable for multichannel applications where the circuit has to be largely used as the last stage of each individual unipolar shaping filter.     

A detector for filtering γ-ray spectra from weak fusion–evaporation reactions out of strong background and for Doppler correction: The recoil filter detector, RFD

A detector has been designed and built to assist in-beam γ-ray spectroscopy with fusion–evaporation reactions. It measures with high efficiency the evaporation residues that recoil out of a thin target into the angular interval from 1.8° to 9.0° at an adjustable distance of 1000–1350 mm from a target, in coincidence with γ-rays detected in a Ge-detector array. This permits filtering of such γ-rays out of a much stronger background of other reaction products and scattered beam. Evaporation residues are identified by their time-of-flight and the pulse height using a pulsed beam. The velocity vector of the γ-emitting recoil is also measured in the event-by-event mode, facilitating to correct the registered γ-ray energy for the Doppler shift, with the resulting significant improvement of the energy resolution. The heavy-ion detection scheme uses emission of secondary electrons caused by the recoiling ions when hitting a thin foil. These electrons are then electrostatically accelerated and focused onto a small scintillator that measures the summed electron energy, which is proportional to the number of electrons. The detector is able to operate at high frequency of the order of 1 MHz and detect very heavy nuclei with as low kinetic energy as 5 MeV. The paper describes the properties of the detector and gives examples of measurements with the OSIRIS, GAREL+ and EUROBALL IV γ-ray spectrometers. The usefulness of the technique for spectroscopic investigations of nuclei with a continuous beam is also discussed.     

Beam test results of an ion-implanted capacitively coupled silicon strip detector processed on a 100 mm silicon wafer

A capacitively coupled silicon strip detector with 50 μm readout pitch has been tested in a pion beam at CERN. The spatial resolution of the detector equipped with LSI readout chips was 4.9 μm and the most probable signal-to-single-channel noise ratio was 31.     

Preparation and microstructural evolution of carbon/carbon composites

Carbon/carbon (C/C) composites with characteristic matrix-crack pattern are key intermediate materials for preparation of carbon/silicon carbide (C/C–SiC) composites. The C/C composites were prepared by pyrolyzing carbon fiber/phenolic resin preform. The change of density, open porosity, mass loss and specially the microstructural evolution of the composites during pyrolysis at 200–900 °C was analyzed, which provided important information for preparation of C/SiC composites by infiltration of silicon. An increasing number of regular spacing cracks were formed above 400 °C. After pyrolysis at 900 °C, the pore volume was 0.17 cm³/g, and the pores in the radius range of 2.44–122.19 μm occupied 81% of the pore volume.     

A coated pixel device TimePix with micron spatial resolution for UCN detection

A position sensitive detector for ultra-cold neutrons (UCNs) has been developed. Here we present the first experimental results and compare them with Monte-Carlo simulations. The silicon pixel device “TimePix” with a spatial resolution below 1 μm for strongly ionizing particles has been coated with a conversion layer of ⁶LiF for the detection of UCN. A spatial resolution of 5.3 μm has been measured for UCN. An optimized setup with 10B as conversion layer can achieve a spatial resolution below 3 μm.     

Photoluminescence properties of the Yb:Er co-doped Al2O3 thin film fabricated by microwave ECR plasma source enhanced RF magnetron sputtering

The Yb:Er co-doped Al₂O₃ thin film was deposited on oxidized silicon wafers by microwave ECR plasma source enhanced RF magnetron sputtering, and annealed from 800 °C to 1000 °C. The photoluminescence at 1.53 μm of thin film was obtained under room temperature. The mixture phase structure of γ and θ is observed by XRD, and the compositions of the thin film are investigated by EPMA. The maximum PL intensity was achieved with O₂:Ar at 1:1, annealing temperature at 900 °C, and experimental ratio of Yb:Er at 1:3.6. The energy transfer mechanism between Er and Yb ions is supported by theoretical analysis and experiment results.     

Comparison of sensing characteristics of ChemFEC devices based on spin-coated thin films of calix[n]arenes

ChemFECs (chemical field effect capacitors) or EIS (Electrolyte-Insulator-Semiconductor) devices were coated with calix[n]arene macrocycles for cation sensors development. Silicon nitride surface electrodes were spin-coated with p-tert-butylcalix[n]arene molecules for n = 8, 9 and 11. Electrochemical capacitance measurements were carried out to evaluate the sensitivity of the calix[n]arene layers towards specific cations as calcium and copper ions. Sensor responses were due to the “host-guest” specific interaction between the rigid cavity of calix[n]arene receptors (ligand) and chemical ion species. The developed chemical sensors have demonstrated good analytical characteristic in terms of: stability, selectivity and lifetime. In addition, experimental results were fitted using the site binding model in order to determine complex association constants, pK (1.9 ≤ pK ≤ 6.39) and surface density of ligands, N_L (9.10¹⁴ ≤ N_L ≤ 2.10¹⁶). All results obtained in this work were compared with those obtained using silicon dioxide EIS electrodes coated with the same calix[n]arene receptors using both spin-coating and thermal evaporation deposit processes.     

Sol–gel alumina environmental barrier coatings for SiC grit

SiO₂ surface film is insufficient to protect SiC from the oxidation at widely varying partial pressures of oxygen, in particular in the presence of water vapor (e.g. in gas turbines) and also in other environments, e.g. during brazing for hard “tipping” of turbine blades. This work demonstrates that sol–gel alumina, coated on 0.5 mm coarse SiC grit, may form an acceptable, up to 10 μm thick “environmental barrier coating” EBC for some of these applications. The sol–gel has advantages over other methods (such as CVD) is the simplicity and low cost. We have used NH₄OH pre-treatment to hydroxylate surface of SiC prior to applying alumina coating. Such modified SiC/SiO₂ surface helped to deposit the positively charged alumina sol, and thus allowed to build thick coatings on the SiC grit. There is some indication that these coatings partially convert to mullite through reaction at the interface with the native silica on SiC. Oxidation resistance tests at 1200 °C were performed to show effectiveness of such coated SiC grit.     

Attenuation of a non-parallel beam of gamma radiation by thick shielding—application to the determination of the U enrichment with NaI detectors

The traditional method used to determine the Uranium enrichment by nondestructive analysis is based on the “enrichment meter principle” [1]. It involves measuring the intensity of the 186 keV net peak area of ²³⁵U in “quasi-infinite” samples. A prominent factor, which affects the peak intensity, is the presence of gamma absorbing material (e.g., container wall, detector cover) between the sample and the detector. Its effect is taken into consideration in a commonly called “wall thickness” correction factor. Often calculated on the basis of approximations, its performance is adequate for small attenuation factors applicable to the case of narrow beams. However these approximations do not lead to precise results when wide non-parallel beams are attenuated through thick container walls.

This paper is dedicated to the calculation by numerical integration of the geometrical correction factor (K_wtc) which describes the effective mean path length of the radiation through the absorbing layer. This factor was calculated as a function of various measurement parameters (types and dimensions of the detector, of the collimator and of the shielding) for the most commonly used collimator shapes and detectors. Both coherent scattering (Rayleigh) and incoherent scattering (Compton) are taken into account for the calculation of the radiation interaction within the detector.     

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. II. Detectors

We describe the detectors for identification of charged particles and fragments in CHICSi, a large solid angle multi-telescope system mounted inside an ultra-high vacuum (UHV), cluster-jet target chamber. CHICSi performs nuclear reaction experiments at storage rings. The telescopes consist of a first very thin, 10–14 μm Si detector, a second 300 μm (or possibly 500 μm) ion implanted Si detector supplemented by a 6 mm GSO(Ce) scintillator read out by a photodiode (PD) or by a third 300 μm Si detector. The telescopes provide full charge separation up to Z=17 and mass resolution up to A=9 in the energy range 0.7–60A MeV. The thin p-i-n diode detector, etched out from a 280 μm Si wafer, and the GSO/PD detector, both exclusively developed for CHICSi, provide an energy resolution 8%, while the standard 300 μm detectors have 2% energy resolution. Radiation stability of the Si detectors is confirmed up to an integrated flux of 10¹⁰ alpha particles. The GSO detector has 70% light collection efficiency with the optical coupling to the PD a simple open, 0.2 mm, gap. A new method, developed to perform absolute energy calibration for the GSO/PD detector is presented.     

Physical models for cleavage fracture at various temperatures—Bases for local approach to fracture of HSLA steel

The author proposes the critical events controlling cleavage at various temperatures: at a very low temperature (−196 °C), critical event is the nucleation of a crack in ferrite at the precrack tip. At a moderate low temperature (around −100 °C), the critical event is the propagation of a carbide crack into the ferrite grain. With increasing temperature (around DBTT −80 °C), the carbide crack eligible to propagate into the ferrite grain should be the one initiated by a critical strain higher than that to initiate a carbide crack at low temperatures. The higher critical strain increases the flow stress by work hardening for making up the effect of lowering yield stress. At a higher temperature (−30 °C) after the crack tip is blunted to more than 60 μm and a fibrous crack extends, the critical event for cleavage fracture is the propagation of a grain-sized crack.     

Development of radiation hard edgeless detectors with current terminating structure on p-type silicon

The development of edgeless Si detectors was stimulated by the tasks of the total pp cross-section study in the TOTEM experiment at the Large Hadron Collider at CERN. For this, the dead region at the detector diced side should be reduced below 50 μm. This requirement is successfully realized in edgeless Si detectors with current terminating structure (CTS), which are now operating at LHC. The development of the experiment and future LHC upgrade need the elaboration of radiation hard version of edgeless Si detectors. The current investigation represents an extension in understanding on edgeless detectors operation and development of a new issue - edgeless detectors with CTS on p-type Si.     

Young’s modulus and interlaminar fracture toughness of SU-8 film on silicon wafer

SU-8 cantilever beams deposited on the polished sides or unpolished sides of silicon wafers were fabricated by MEMS and bulk micro-machining techniques. Bending tests were conducted to measure the Young’s modulus and interface fracture toughness. The results indicate that the Young’s modulus is increasing as the width of specimens is increasing because the specimen quality becomes better. When the width of SU-8 cantilever beam is 400 μm, the Young’s modulus is about 3.5 GPa. On the other hand, since the interface between SU-8 and silicon wafer does not suffer the attack of etchant, the measured interface fracture toughness has no clear dependence on the specimen width. The averaged interface fracture toughness is about 25–30 J/m² for the polished interface and 15–20 J/m² for the unpolished interface.