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.     

Edge sensitivity of “edgeless” silicon pad detectors measured in a high-energy beam

We report measurements in a high-energy beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors. The edgeless side of these rectangular diodes is formed by a cut and break through the contact implants. A large surface current on such an edge prevents the normal reverse biasing of this device above the full depletion voltage, but we have shown that the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at a low temperature. A pair of these edgeless silicon diode pad sensors was exposed to the X5 high-energy pion beam at CERN, to determine the edge sensitivity. The signal of the detector pair triggered a reference telescope made of silicon microstrip detector modules. The gap width between the edgeless sensors, determined using the tracks measured by the reference telescope, was then compared with the results of precision metrology. It was concluded that the depth of the dead layer at the diced edge is compatible with zero within the statistical precision of ±8 μm and systematic error of ±6 μm.     

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 “Six Sigma”© Black Belt Case Study: G.E.P. Box's Paper Helicopter Experiment Part A

This article presents an application of the “Six Sigma” DMAIC model to G.E.P. Box's famous “paper helicopter” experiment. The define, measure, and analyze phases are presented here, and the improve and control phases are presented in a follow-up article. The intent of this article is to present the reader with a case study for structuring a “Six Sigma” Black Belt project.     

A Microbolometer Asynchronous Dynamic Vision Sensor for LWIR

In this paper, a novel event-based dynamic IR vision sensor is presented. The device combines an uncooled microbolometer array with biology-inspired (“neuromorphic”) readout circuitry to implement an asynchronous, “spiking” vision sensor for the 8–15 $mu{rm m}$ thermal infrared spectral range. The sensor's autonomous pixels independently respond to changes in thermal IR radiation and communicate detected variations in the form of asynchronous “address-events.” The 64 $times$ 64 pixel ROIC chip has been fabricated in a 0.35 $mu{rm m}$ 2P4M standard CMOS process, covers about $4times 4 {rm mm}^{2}$ of silicon area and consumes 8 mW of power. An amorphous silicon (a-Si) microbolometer array has been processed on top of the ROIC and contacted to the pixel circuits. We discuss the bolometer detector properties, describe the pixel circuits and the implemented sensor architecture, and show measurement results of the readout circuits. Subsequently, a DFT-based approach to the characterization of asynchronous, spiking sensor arrays is discussed and applied. Test results and analysis of sensitivity, bandwidth, and noise of the fabricated IR sensor prototype are presented.      

Addition of “Living” Polymers onto C60.

Various “living” polymers were grafted onto C₆₀ The number of arms of the so obtained “star” molecules can be controlled by stoechiometry and/or by varying the reactivity of the carbanion on the “living” chain against a double bond on the C₆₀. Even the oxanion of “living” polyethylenoxide is able to add onto the reactive double bonds on C₆₀. In some conditions, the carbanions present on these alkaline salts of grafted fullerenes becomes able to initiate anionic polymerization of vinyl monomers. Using “living” poly(phenylvinylsulfoxide) as a precursor polymer for PA, polyacetylene chains could be attached to the fullerene.     

Guides “bimorphes” d''ondes ultrasoniques “bimorph” ultrasonic wave guides”

An analysis of the dispersion of elastic waves is presented for two types of long ultrasonics wave-guides that we qualify of “bimorph”: (i) a “three-layer” guide made of two different materials and (ii) a “clad core” guide built up of a rectangular core surrounded by a cladding, the materials of the rod and cladding having different properties. An analytical model is proposed to describe the extensional, flexural and torsional motions in “bimorph” wave guides having two geometrical and material symmetry axes. The asymptotic behaviour of the model allows one to select the material properties which lead to modes guided essentially either in the central layer or in the core of the bimorph guide. Moreover, the dispersive properties of a “bimorph” can be controlled through the choice of geometrical and material parameters.     

Microstructural and mechanical properties evolution of magnesium AZ61 alloy processed through a combination of extrusion and thermomechanical processes

In this work, the microstructures and tensile properties of a commercial magnesium alloy “AZ61” processed by a combination of hot extrusion and thermomechanical processing (TMP) were investigated. The TMP was consisting of two or three hot rolling steps with large reductions per pass, thus allowing significant grain refinement. The microstructural evolution has been studied by means of optical and scanning electron microscopes, as well as X-ray diffraction analysis. The as-cast material is extruded in the form of a cylinder with initial diameter of 250 mm to a final diameter of 110 mm (80% reduction in cross-sectional area). Then hot rolling regimes were performed at 300 °C with different percentage of strain per pass. Tensile and hardness tests were performed in the samples (as-cast, extruded, and rolled) at room temperature in order to evaluate the mechanical properties of the material. The results of experiments demonstrated that fine grain size might be achieved in magnesium alloy AZ61 by using a two-step processing route involving an initial extrusion step followed by thermomechanical processing with large reduction in thickness per pass. This two-step process, designed to achieve average grain sizes of 10–20 μm.     

Demonstration of feasibility of operating a silicon ZIP detector with 20 eV threshold

100-g silicon detectors (known as “ZIPs,” Z-resolving Ionization and Phonon detectors) developed by the Cryogenic Dark Matter Search Experiment have been tested at charge bias voltages of up to 200 V/cm, significantly above their usual operating range (3–6 V/cm). Thermal gain factors in excess of 50 were observed due to the primary ionization drifting in the large applied field, with only minimal increase in phonon noise. The observed thermal gain corresponds to an intrinsic threshold of 20 eV, resulting in detectors that have direct application for use in a neutrino magnetic moment measurement based on a 40-MCi tritium source.     

STJ X-ray detectors with titanium sublayer

Superconducting tunnel junctions (STJs) with the structure Ti/Nb/Al, AlO_x/Al/Nb/NbN and corresponding layer thickness 30/100/8/13/150/30 nm were investigated as X-ray detectors at T=1.35 K. STJs with one active electrode in which the response of the other one is suppressed due to trapping layer on the surface opposite to the tunnel barrier have a number of potential advantages. The best line width (FWHM) is 78 eV for 6400 μm² junction. Contribution of the electronic noise is about 50 eV. The intrinsic detector line width is less than 60 eV. The collected charge from inactive electrode is more than 8 times less than that from the active one. Titanium proved to be an appropriate material for a sublayer and a trap.     

Approaching the fundamental noise limit in Mo/Au TES bolometers with transverse normal metal bars

Recent efforts in the Transition Edge Sensor (TES) bolometer/calorimeter community have focused on developing detectors whose noise properties are near the fundamental limits. These include the in-band phonon noise, the out-of-band Johnson noise, and the 1/f noise. We have investigated the noise performance of Mo/Au-bilayer TES bolometers designed for infrared detectors. These detectors use normal metal regions for the suppression of excess noise, which are oriented either parallel to (“bars”) or transverse to (“stripes”) the direction of current flow. Two nearly identical detectors, one with stripes and one with bars, were fabricated at the NASA/GSFC detector development facility. Significantly lower noise is found with the normal metal regions oriented transversely. We compare the detailed noise measurement and quantitative analysis of the noise level in each device as a function of the detector resistance. Our preliminary result is that the best detector features only moderate excess noise in both the in-band region and in the out-of-band region. This noise performance is suitable for instruments with multiplexed TES arrays, such as GSFC's FIBRE and SAFIRE.     

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.     

Noise characteristics of stacked CMOS active pixel sensor for charged particles

The noise characteristics of a stacked CMOS active pixel sensor (SCAPS) for incident charged particles have been analyzed under 4.5 keV Si⁺ ion irradiation. The source of SCAPS dark current was found to change from thermal to electron leakage with decreasing device temperature. Leakage current at charge integration part in a pixel has been reduced to 0.1 electrons s⁻¹ at 77 K. The incident ion signals are computed by subtracting reset frame values from each frame using a non-destructive readout operation. With increase of irradiated ions, the dominant noise source changed from read noise, and shot noise from the incident ions, to signal frame fixed-pattern noise from variations in sensitivity between pixels. Pixel read noise is equivalent to ten incident ions. The charge of an incident ion is converted to 1.5 electrons in the pixel capacitor. Shot noise corresponds to the statistical fluctuation of incident ions. Signal frame fixed-pattern noise is 0.7% of the signal. By comparing full well conditions to noise floor, a dynamic range of 80 dB is achieved. SCPAS is useful as a two-dimensional detector for microanalyses such as stigmatic secondary ion mass spectrometry.     

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.     

Gas pixel detectors for X-ray polarimetry applications

We discuss a new class of micro pattern gas detectors, the gas pixel detector (GPD), in which a complete integration between the gas amplification structure and the read-out electronics has been reached. An application-specific integrated circuit (ASIC) built in deep sub-micron technology has been developed to realize a monolithic device that is, at the same time, the pixelized charge collecting electrode and the amplifying, shaping and charge measuring front-end electronics. The CMOS chip has the top metal layer patterned in a matrix of 80 μm pitch hexagonal pixels, each of them directly connected to the underneath electronics chain which has been realized in the remaining five layers of the 0.35 μm VLSI technology. Results from tests of a first prototype of such detector with 2 k pixels and a full scale version with 22 k pixels are presented. The application of this device for Astronomical X-ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation is shown. Results from a full MonteCarlo simulation for two astronomical sources, the Crab Nebula and the Hercules X1, are also reported.     

An accurate redetermination of the Sn binding energy

The energy of well-known strong γ line from ¹⁹⁸Au, the “gold standard”, has been modified in the light of new adjustments in the fundamental constants and the value of 411.80176(12) keV was determined, which is 0.29 eV lower than the latest 1999 value. An energy calibration procedure for determining the neutron binding energy, B_n, from complicated (n, γ) spectra has been developed. A mathematically simple minimization function consisting only of terms having as parameters the coefficients of the energy calibration curve (polynomial) is used. A priori information about the relationships among the energies of different peaks on the spectrum is taken into account by a Monte-Carlo simulation. The procedure was used in obtaining B_n for ¹¹⁸Sn. The γ-ray spectrum from thermal neutron radiative capture by ¹¹⁷Sn has been measured on the IBR-2 pulsed reactor. γ-rays were detected by a 72 cm³ HPGe detector. For a better determination of B_n it was important to determine B_n for ⁶⁴Cu. This value was obtained from two γ-spectra. One spectrum was measured on the IBR-2 by the same detector. The other spectrum was measured with a pair spectrometer at the Brookhaven High Flux Beam Reactor. From these two spectra, B_n for ⁶⁴Cu was determined to be equal to 7915.52(8) keV. This result essentially differs from the previous value of 7915.96(11) keV. The mean value of the two most precise results of the B_n for ¹¹⁸Sn, was determined to be 9326.35(9) keV. The B_n for ⁵⁷Fe was determined to be 7646.08(9) keV.     

Internal friction during martensitic transformation in high manganese Mn–Cu alloys

Low-frequency internal friction and elastic modulus were studied for manganese-rich Mn–Cu alloys in the temperature range of martensitic transformation (20–300 °C). It is shown that the some special features of the transformation peak and its temperature are caused by the degree of the spinodal decomposition. The phenomenological model connecting an-elastic effects with the stages of evolution of the structure during martensitic transformation in manganese-rich Mn–Cu alloys (tweed structure–“parquet” structure–classical twinning martensite) is 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.     

PdSi focal-plane array detectors for short-wave infrared Raman spectroscopy of biological tissue: a feasibility study

We have used a PdSi focal-plane array detector to measure short-wave infrared Raman spectra of pure compounds and human tissue. Raman bands of the pure compounds are clearly visible in the spectra, and a calcification feature at 960 cm(-1) is readily identifiable in the spectra of diseased human aorta. The performance characteristics of our detection device were good; dark noise contributed approximately 60 (electrons/s)/pixel, and the read noise was ~50 rms electrons/pixel. The primary noise in the spectra was due to fixed-pattern noise, which is the variation in measured signal across a detector when it is uniformly illuminated.     

Measurements on a GaAs microstrip detector with 50 GeV/c electrons

A microstrip gallium arsenide detector (thickness 508 μm, strip width 100 μm, strip pitch and readout pitch 200 μm) has been tested in a 50 GeV/c electron beam at CERN. Using the low noise Viking preamplifier chip (shaping time 1.5 μs) signal to noise ratios up to 25 were measured depending on bias voltage and angle of incidence. Applying the so-called η-algorithm (using the impact position-sensitive charge sharing between adjacent strips) a resolution down to σ 20 μm could be obtained.