Use Of Detectors Research Articles

Viscous Shock Capturing in a Time-Explicit Discontinuous Galerkin Method

We present a novel, cell-local shock detector for use with discontinuous Galerkin (DG) methods. The output of this detector is a reliably scaled, element-wise smoothness estimate which is suited as a control input to a shock capture mechanism. Using an artificial viscosity in the latter role, we obtain a DG scheme for the numerical solution of nonlinear systems of conservation laws. Building on work by Persson and Peraire, we thoroughly justify the detector's design and analyze its performance on a number of benchmark problems. We further explain the scaling and smoothing steps necessary to turn the output of the detector into a local, artificial viscosity. We close by providing an extensive array of numerical tests of the detector in use.

Novel fluorescent nuclear track detectors for use in neutron and heavy charged particle dosimetry

Novel fluorescent nuclear track detectors for use in neutron and heavy charged particle dosimetry

Infrared detectors for space applications

Two of the main requirements for space situational awareness are to locate and identify dim and/or distant objects. At the Air Force Research Laboratory’s Space Vehicles Directorate, we are investigating how nanostructured metal surfaces can produce plasmon-enhanced fields to address the first function. We are also investigating quantum interference effects in semiconductor quantum dots inside photonic crystal cavities to address the amplification of weak signals. To address the second function of identification of space objects, we are investigating a wavelength-tunable detector scheme that involves a coupled double quantum well structure with a thin middle barrier between the two wells. The photocurrent from this structure will be swept out with a lateral bias. In order to eliminate the diffraction loss of incident photons by a surface grating structure for the z-polarization required in normal quantum well infrared photodetector structures, we will grow an array of self-organized quantum dots buried in one of the quantum wells of a symmetric double quantum well structure. In this paper, we will first describe the requirements for detectors in space, then we will describe our work in the above topics, and finally we will briefly mention our forays into other areas of quantum-structured detectors for use in space.

3He and BF3 neutron detector pressure effect and model comparison

Radiation detection systems for homeland security applications must possess the capability of detecting both gamma rays and neutrons. The radiation portal monitor systems that are currently deployed use a plastic scintillator for detecting gamma rays and 3He gas-filled proportional counters for detecting neutrons. Proportional counters filled with 3He are the preferred neutron detectors for use in radiation portal monitor systems because 3He has a large neutron cross-section, is relatively insensitive to gamma-rays, is neither toxic nor corrosive, can withstand extreme environments, and can be operated at a lower voltage than some of the alternative proportional counters. The amount of 3He required for homeland security and science applications has depleted the world supply and there is no longer enough available to fill the demand. Thus, alternative neutron detectors are being explored. Two possible temporary solutions that could be utilized while a more permanent solution is being identified are reducing the 3He pressure in the proportional counters and using boron trifluoride gas-filled proportional counters. Reducing the amount of 3He required in each of the proportional counters would decrease the rate at which 3He is being used; not enough to solve the shortage, but perhaps enough to increase the amount of time available to find a working replacement. Boron trifluoride is not appropriate for all situations as these detectors are less sensitive than 3He, boron trifluoride gas is corrosive, and a much higher voltage is required than what is used with 3He detectors. Measurements of the neutron detection efficiency of 3He and boron trifluoride as a function of tube pressure were made. The experimental results were also used to validate models of the radiation portal monitor systems.

Quantum dots: a bright future for photonic nanosensors

PurposeThe paper aims to provide a technical review of the application of quantum dot (QD) technology to sensors.Design/methodology/approachFollowing a brief introduction to QD technology, this paper considers recent research on QD‐based physical, chemical and gas sensors.FindingsThis shows that QDs are being exploited in a range of experimental sensors for detecting physical variables, notably radiant/electromagnetic quantities and temperature; chemical compounds, such as metals and many species of clinical interest; and a variety of gases and vapours. Prospects also exist to develop improved sources and detectors for use in optical gas sensors.Research limitations/implicationsThe paper does not consider biomedical uses of QDs such as cellular imaging, bioassays and biosensors.Originality/valueThis provides a detailed insight into recent research on physical, chemical and gas sensors based on QD technology.

HPLC DETECTORS: A BRIEF REVIEW

In an HPLC system the detector is the component responsible for turning a physical or chemical attribute into a measureable signal corresponding to concentration or identity.[ 1 , 2 ] In the early days of HPLC, detection was often carried out by collecting fractions and analyzing them off-line. It wasn't until the 1940's and 1950's that the first online detectors for HPLC were introduced.[ 3 , 4 ] Certainly an improvement over off-line approaches, sensitivity was an issue. The search for more sensitive universal detectors for HPLC led researchers to adapt GC detectors for use in HPLC,[ 5-8 ] but the removal of the HPLC mobile phase originally limited applicability. However, in the 1960s the first ultraviolet detector for HPLC was introduced,[ 9 ] and subsequent improvements in design led to better sensitivity[ 10 ] and improvements such as variable wavelength and diode array detectors. While a truly universal HPLC detector with GC/FID levels of sensitivity is still elusive, many different types of detectors have been developed that have been very successful for a wide variety of general or specific HPLC applications. To assist in choosing the proper HPLC detector for a given application, this review describes the principles and attributes of many of the common HPLC detectors in use today, and compares and contrasts the advantages and disadvantages of the various detectors discussed where appropriate. For additional detail on the HPLC detectors addressed here, the reader is encouraged to consult the references in each section along with additional general reviews.[ 11 , 12 ]

Electrochemical determination of xanthine and hypoxanthine in rat striatum with an acetylene black-dihexadecyl hydrogen phosphate composite film modified electrode by HPLC coupled with in vivo microdialysis

The fabrication and application of a new electrochemical detector for use in HPLC is presented. The detector consists of an electrode modified with a composite film composed of acetylene black and dihexadecyl hydrogen phosphate. The electrochemistry of xanthine and hypoxanthine at this chemically modified electrode (CME) was investigated by cyclic voltammetry. It is found that the CME exhibits efficient electrocatalytic activity towards xanthine and hypoxanthine, with good sensitivity, stability, and lifetime. The linear ranges cover three orders of magnitude, and the detection limits are 6.0 × 10−8 mol L−1 for xanthine and 2.5 × 10−7 mol L−1 for hypoxanthine (at an S/N ratio of 3). The method was coupled to in-vivo microdialysis sampling and successfully applied to quantify xanthine and hypoxanthine in rat striatal microdialysates of freely moving rats.

Development of a photothermal absorbance detector for use with microfluidic devices.

The development of a photothermal absorbance detector for use with microfluidic devices is described. Unlike thermo-optical techniques that rely on measuring refractive index changes, the solution viscosity is probed by continuously monitoring solution conductivity. Platinum electrodes microfabricated on a quartz substrate and bonded to a substrate containing the microchannels enable contact conductivity measurements. The effects of excitation frequency and voltage, electrode spacing, laser power, and laser modulation (chopping) frequency were evaluated experimentally. In the current configuration, a limit of detection of 5 nM for DABSYL-tagged glucosamine was obtained using long injections (to give flat-topped peaks). This corresponds to an absorbance of 4.4 x 10(-7) AU. Separation and detection of DABSYL-tagged glycine, proline, and tryptophan are also shown to demonstrate the feasibility of the method. In addition, simulations were used to investigate the applicability of the technique to small volume platforms.

Synchrotron Tests of a 3D Medipix2 X-Ray Detector

Three-dimensional (3D) photodiode detectors offer advantages over standard planar photodiodes in a range of applications, including X-ray detection for synchrotrons and medical imaging. The principal advantage of these sensors for X-ray imaging is their low charge sharing between adjacent pixels, which could improve spatial and spectral resolution. A 'double-sided' 3D detector has been bonded to a Medipix2 single-photon-counting readout chip, and tested in a monochromatic X-ray beam at the Diamond synchrotron. Tests of the 3D detector's response spectrum and its Line Spread Function have shown that it has substantially lower charge sharing than a standard planar Medipix2 sensor. Additionally, the 3D detector was used to image diffraction rings produced by a powdered silicon sample, demonstrating the detector's use in a standard synchrotron experiment.

Development of a Photothermal Absorbance Detector for Use with Microfluidic Devices

Development of a Photothermal Absorbance Detector for Use with Microfluidic Devices

Commentary: New developments in single photon detection in the short wavelength infrared regime

Many new and exciting fields of scientific research rely on the efficient detection of single photons in the infrared regime. To give just two examples, quantum key distribution has the potential to offer verifiably secure methods of generating cryptographic keys and active imaging techniques permit the creation of detailed 3D models of distant objects. Currently, many of these technologies use photons in the wavelength range 400 to 1000 nm due to the ready availability of relatively efficient single photon detectors for use at these wavelengths (recent surveys may be found in Refs. [1] and [2]). However, extending the wavelength range to 1.3 µm and 1.55 µm would result in many benefits, for example compatibility with lowloss optical fiber spectral regions and atmospheric transmission windows, as well as infrared gas absorption features, notably those of greenhouse gases. Let us briefly consider the current status of the potential single photon detection technologies available for this spectral region. Currently, there are three main types of detector technology in widespread use; photomultipliers, semiconductor avalanche photodiodes and superconducting detectors. Within these different technologies, there are different material systems and micro-structure designs leading to a wide spread in key performance characteristics for similar devices. One figure of merit for such detectors is the noise equivalent power (NEP), defined as the signal power required to attain a unity signal-to-noise ratio within a one second integration time. Photomultiplier tubes (PMTs) operate by the cascade generation of a stream of electrons from an initial photo-generated electron. A photon incident on a photocathode will, with a probability less than unity, trigger the emission of an electron. This electron is accelerated towards an anode and, on collision, triggers the release of a number of secondary electrons. This process is repeated through a series of anodes, multiplying the total number of electrons each time, until a detectable current pulse is generated. These devices have large photocathode areas (typically of the order of a few mm 2 ) and gain which depends on dynode geometry and bias. PMTs typically operate with photons at lower wavelengths than those considered in this commentary but devices with an InGaAs photocathode such as the those produced by Hamamatsu have demonstrated an NEP ~ 4 × 10

Characterization of a HPHT diamond detector for clinical applications

An investigation of a high-pressure high-temperature (HPHT) synthetic diamond detector was performed with the aim to evaluate the potentiality of the detector for use in IMRT beams. Dosimetric parameters such as dynamics, stability of the response, linearity with dose and dose-rate dependence were studied and the HPHT sample behaviour was compared with that of a PTW natural diamond used as a reference system. In addition, a test in IMRT field using the step-and-shoot technique was also carried out on HPHT device. The main result of this study was the fast response shown by the HPHT sample, comparable to that of the natural diamond. Nevertheless, strong dose-rate dependence and the presence of the overshoot still limit the use of this system.

Simultaneous reconstruction of scintillation light and ionization charge produced by 511 keV photons in liquid xenon: Potential application to PET

In order to assess the performance of liquid xenon detectors for use in positron emission tomography we studied the scintillation light and ionization charge produced by 511 keV photons in a small prototype detector. Scintillation light was detected with large area avalanche photodiodes while ionization electrons were collected on an anode instrumented with low noise electronics after drifting up to 3 cm. Operational conditions were studied as a function of the electric field. Energy resolutions of < 10 % (FWHM) were achieved by combining the scintillation light and ionization charge signals. The relationship between scintillation light and ionization signals was investigated. An analysis of the sources of fluctuations was performed in order to optimize future detector designs.

Charge Collection Efficiency Measurements of Heavily Irradiated Segmented n-in-p and p-in-n Silicon Detectors for Use at the Super-LHC

The planned luminosity upgrade of the Large Hadron Collider at CERN (Super-LHC) will provide a challenging environment for the tracking and vertexing detector systems. With a proposed nearly 10-fold luminosity increase to 1035 cm2 middot s-1, the innermost devices will have to be able to withstand a hadron dose on the order of 1times1016 1 MeV neutron equivalent per square centimeter over the anticipated five year lifetime of the experiments. Planar, segmented silicon detectors with n-strip readout are one of the radiation tolerant technologies under consideration for use for the Super-LHC tracking detectors in either pixel or strip geometries. This paper details measurements made with n-strip (n-in-p) and p-strip (p-in-n) planar devices that have been irradiated to doses as high as 1times1016 neq cm-2 with reactor neutrons and fast protons. The doses under study cover the expected range of final fluences for the different tracking systems of the ATLAS and CMS experiments at the Super-LHC. The charge collection measurements have been carried out using analogue, high-speed (40 MHz) electronics and a Strontium electron source. These measurements show that p-in-n sensors are not radiation tolerant enough for the requirements of the micro-strip detectors at the SLHC; whereas, the charge collection properties exhibited by the n-in-p strip devices may be sufficient for all tracker regions (pixels and strips) of the SLHC assuming that appropriate low noise and threshold readout electronics are designed and adequate bias voltage can be routed to the sensors.

Detector for use in voice communications systems

One or more methods and systems of detecting or identifying one or more types of algorithms used in the encoding of a voice or speech waveform is presented. The system and method may be used as a testing tool to identify whether a voice data stream is encoded using a linear G.711, μ-law G.711, or A-law G.711 algorithm. The system and method are applied to a voice data stream to ensure that a codec with the appropriate algorithm is used to reproduce an audio waveform.

Laboratory evaluation of smoke detectors for use in underground mines

Laboratory experiments were conducted to determine the responses of a prototype smoke detector and a commercially available photoelectric smoke detector to smoke particles generated from various combustion sources. The prototype smoke detector combines optical scattering measurements with ionization chamber measurements in order to reduce/eliminate nuisance alarms due to the presence of airborne dusts or diesel exhaust particles. The commercially available smoke detector is designed for use in harsh environments where airborne dust represents a major problem due to both nuisance alarms and detector contamination. In the experiments, the responses of the two detectors were measured when exposed to smoke particles from the exhaust of a diesel engine and from a variety of fire sources, including wood, coal, styrene butadiene rubber, and No. 2 diesel fuel. For the solid fuels, data were obtained for both smoldering and flaming combustions. This report describes the experiments, their results, and the use of these results as they apply to early-warning fire sensors capable of the rapid and reliable detection of fires in atmospheres that may or may not be contaminated by either airborne dust or the products produced from diesel engines.

Performance of Ge/Si Receivers at 1310 nm

We are studying three types of these detectors for use at 1310 nm; normal incident illuminated p-i-n detectors (NI-PD), waveguide p-i-n detectors (WG-PD), and avalanche photodetectors (APDs). NI-PDs have achieved -14.5 dBm sensitivity at 10 Gb/s and 850 nm, which is comparable to similarly packaged GaAs devices. Unlike GaAs detectors, however, the Ge detectors can also operate at 1310nm, with a ~0.5dB sensitivity improvement expected. WG-PDs have achieved bandwidths of approximately 30 GHz at 1550 nm with internal quantum efficiencies of 90%, and similar, or better, performance is also expected at 1310 nm. Normal incident APDs operating at 1310 nm have achieved a gain-bandwidth product of 153 GHz which exceeds that of a commercial InP-based APDs, These devices also have a primary responsivity of 0.54 A/W with a 3-dB bandwidth of 9GHz at a gain of 17.

Investigation on piezoelectric lead zirconate titanate detector bombarded obliquely with hypervelocity iron particles

A cosmic dust detector for use onboard a satellite is currently being constructed from piezoelectric lead zirconate titanate (PZT). The characteristics of the PZT detector were studied by bombarding it with hypervelocity iron particles, which were supplied by a Van de Graaff accelerator. There was a linear relationship between the rise time of the signal observed from the detector and the particle's velocity, which was above 10 km/s on impact. It was also found that the rise time was almost independent of the collisional angle between the particles and the PZT surface within the limits of the particle's parameters used in this experiment.

Femtosecond first-order autocorrelation measurement based one-photon induced photocurrent in Si Schottky diodes

Si Schottky diodes promise to provide cheap, reliable, and linear detectors for use in femtosecond and picosecond pulse width measurement. At low pulse excitation density (<100 pJ/cm 2), the pulse width can be deduced from the first-order autocorrelation, and the measured results are in agreement with the theoretical ones. When pulse excitation density is larger than 1 nJ/cm 2, the pulse trailing edge is distorted due to bandgap reduction in semiconductor Si and the pulse width cannot be measured accurately by means of the first-order autocorrelation. The interference fringes presented in the first-order autocorrelation measurement can provide a way of calibrating the delay, and the pulse width can also be obtained by calculating the number of interference fringes.

Measurement of incident position of hypervelocity particles on piezoelectric lead zirconate titanate detector

A cosmic dust detector for use onboard a satellite is currently being developed by using piezoelectric lead zirconate titanate (PZT). The characteristics of the PZT detector have been studied by bombarding it with hypervelocity iron (Fe) particles supplied by a Van de Graaff accelerator. One central electrode and four peripheral electrodes were placed on the front surface of the PZT detector to measure the impact positions of the incident Fe particles. It was demonstrated that the point of impact on the PZT detector could be identified by using information on the time at which the first peak of the output signal obtained from each electrode appeared.