Primary Detector Research Articles

A Novel Adaptive Detection Scheme based on Parallel Interference Cancellation for V-BLAST System

In this paper, in order to reduce the computational complexity of the detector of vertical Bell Laboratories layered space-time (V-BLAST) system over time-varying channels, an adaptive detection scheme is proposed based on parallel interference cancellation (PIC). The presented scheme has three units, which are primary adaptive detector, detection ordering determiner, and adaptive PIC detector. The proposed scheme can employ many of known adaptive algorithms for detection of V-BLAST system. In this paper, we present computational complexity of the proposed scheme using LMS, RLS, APA and AMSER adaptive algorithms and evaluate its performance with numerical simulations.

The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells.

Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existance of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use.

SU-FF-T-120: Comparison of Detectors for Electron Depth-Dose Measurements and Investigation of Parallel-Plate Chamber Perturbation Factors

Purpose: In all international protocols for electron beamdosimetry the primary detector of choice for measuring depth‐dose distributions is the plane‐parallel ionization chamber. Diode detectors are permitted but their performance must be checked against a ‘gold‐standard’ ion chamber before use. Recent publications have indicated that parallel‐plate ion chambers can have a significant non‐zero perturbation correction, which varies with depth. If this is not corrected for then the chamber is not a ‘gold standard’ and any comparison with a diode will be biased. This also has implications for benchmarking of Monte‐Carlo simulations. Method and Materials: A precision 1‐D scanning phantom was developed with an absolute positioning accuracy of 0.15 mm and a dose uncertainty of 0.1%. Measurements were made with two types of plane‐parallel ion chamber (NACP and Roos) and two electron diodes (Scanditronix EFD and PTW 60012) at a range of electron energies (4–22 MeV) for 4 different linac types. Results: There was very good agreement between the plane‐parallel ion chambers (R50 values generally within 0.1 mm for all beams). i) There was a significant and consistent difference between the electron diode detectors, with a 0.7 mm difference in R50 (independent of energy) and small differences in the build‐up and bremsstrahlung regions. ii) The ion chamber plots (converted from ionization to dose using TG‐51 and corrected for chamber perturbation using published data) showed very good agreement with the EFD diode, except for in the build‐up region where a difference of ∼1–2% persists. The corrected ion chamber and EFD diode showed good agreement with a Monte‐Carlo simulation but neither matched perfectly. Conclusion: For the highest accuracy depth‐dose measurements (e.g. TG‐51 beam calibration,MC commissioning) perturbation corrections are required for plane‐parallel ion chambers. Further work is required to determine which detector (diode or ion chamber) is a true ‘gold standard’.

Design and preliminary Monte Carlo calculations of an active Compton-suppressed LaBr 3(Ce) detector system for TRU assay in remote-handled wastes

Recent studies indicate LaBr 3(Ce) scintillating detectors have desirable attributes, such as room temperature operability and excellent energy resolution, which may make them viable alternatives as primary detectors (PD) in a Compton suppression spectrometer (CSS) used for remote-handled transuranic (RH-TRU) waste assay. A CSS with a LaBr 3(Ce) PD has been designed and its expected performance evaluated using Monte Carlo analysis. These results indicate that this detector will have a relatively high Compton-suppression capability, with greater suppression ability for large angle-scattered photons in the PD.

Hybrid gamma ray imaging—Model and results

We report on a hybrid gamma-ray radiation imaging system for industrial applications that combine the advantages of a multi-aperture mechanical collimator with electronic collimation. The combination offers both efficiency and good angular resolution, and is unique since a single gamma ray can contribute information to both modalities simultaneously. The mechanically collimated camera is most effective for imaging lower energy photons while electronic collimation uncouples spatial resolution from efficiency for higher energies. Our proposed Hybrid Gamma Ray Imager combines a high-resolution URA coded aperture with a Compton scatter camera to provide a broader range of energy response suitable for a wider range of industrial applications (50 keV–2 MeV). The primary detector is a large-area LaCl 3:Ce scintillator coupled directly to a Hammamatsu PSPMT, chosen to provide portability, efficiency and energy resolution. A pixellated CsI(Na)/PSPMT combination serves as the secondary absorption detector. Point and ring-shaped radiation sources (140, 364, 662 and 1275 keV) are simulated. The results show coverage over a broad energy range of radiation and better images than either a mechanical or an electronic imager at intermediate energies. The sensitivity loss of the electronic imager due to the introduction of the mechanical collimator is recognized.

High accuracy verification of a correlated-photon- based method for determining photoncounting detection efficiency

We have characterized an independent primary standard method to calibrate detection efficiency of photon-counting detectors based on twophoton correlations. We have verified this method and its uncertainty by comparing it to a substitution method using a conventionally calibrated transfer detector tied to a national primary standard detector scale. We obtained a relative standard uncertainty for the correlated-photon method of 0.18 % (k=1) and for the substitution method of 0.17 % (k=1). From a series of measurements we found that the two independent calibration techniques differ by 0.14 (14) %, which is within the established uncertainty of comparison. We believe this is the highest accuracy characterization and independent verification of the correlated-photon method yet achieved.

Increased immunofluorescence sensitivity using 532 nm laser excitation

We evaluated the use of a high power, diode pulsed solid-state laser emitting 532 nm light for immunofluorescence applications. We compared the sensitivity and utility of this laser with the standard 488 nm excitation. A flow cytometer was equipped with both a 488 nm and a 532 nm laser; fluorescence emissions from each laser were collected using the same filters and the same detector system. Cells or compensation beads (e.g. latex beads coated with anti-kappa antibodies) were stained with monoclonal antibodies conjugated to phycoerythrin (PE) as well as the PE tandem dyes TRPE, Cy5PE, Cy5.5PE, and Cy7PE. The sensitivity of detection of these reagents as well as those in heavily compensated channels was quantified by measuring the spreading error for a primary detector into a secondary detector. Measurement of the fluorescence emission of PE and PE-tandem dyes was considerably more sensitive when using 532 nm excitation (150 mW) as compared with 488 nm excitation (20 mW). In addition, as the absolute number of photoelectrons collected was greater, there was less measurement-error-induced spread into the compensated channels. As an example, when comparing the spreading error of PE labeled cells into the TRPE detector, the green laser was found to be 15-fold more sensitive as compared with the blue laser. In addition, the blue laser produced more autofluoresent signal from cells as compared with the green laser. Together, these advantages of the 532 nm excitation line provides for a significantly improved detection of immunofluorescence staining.

Calibration and characterization of semiconductor X-ray detectors with synchrotron radiation

Quantitative measurements of X-rays require absolutely calibrated detectors. In the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II in Berlin, X-ray detectors can be calibrated with low uncertainties. Two complementary approaches are realized for energy-dispersive detectors. One approach uses the storage ring as primary source standard and the detector response to the calculable spectral photon flux is measured in the undispersed synchrotron radiation. This requires the operation of the storage ring with only a few stored electrons. The other approach is the comparison to a primary detector standard, mainly a cryogenic electrical substitution radiometer. Here, monochromatized radiation of very high spectral purity has to be used which is available at different beamlines in the laboratory in the photon energy range from the UV up to about 120 keV. This method can also be applied for the calibration of non-energy-dispersive detectors. With monochromatized radiation, the response function of energy-dispersive detectors is recorded and compared to Monte Carlo simulations. A photon-energy-dependent parameterization of the response function allows deconvoluting the experimental spectra. The responsivity of Si photodiodes and the detection efficiency of Si(Li), HPGe and CdTe detectors are determined with low uncertainties in a broad spectral range.

SU-CC-ValA-03: A Directional Algorithm for An Electronically-Collimated Gamma-Ray Detector for Intraoperative Localization of Radiation Sources

Purpose: An electronically‐collimated gamma‐radiation detector for intraoperative localization of sentinel lymph nodes and metastases is under development. Analogous to Compton telescopes and Compton cameras, localization is achieved using the coincidence detection of Compton‐scattered gamma rays. Electronic collimation allows the device to operate without physical collimation, providing high sensitivity while also allowing directional information to be determined. We report on implementation of algorithms to calculate the direction to the source.Methods and Materials: Two approaches to direction reconstruction were evaluated. The first technique backprojects each event onto the surface of a sphere centered on the device's primary detector. To use Fourier filtering methods for deblurring, the sphere's surface is mapped by stereographic projection onto a plane, filtered in Fourier space, and then projected back onto the sphere. The second technique also backprojects events onto the sphere, then determines the rectangle that circumscribes the backprojected cone; localization is obtained by intersection of all circumscribed rectangles. Results: Performance of the algorithm has been evaluated using randomly generated ideal Compton‐scatter events from point sources for our detector geometry. Direction angles are calculated within 5% accuracy for source positions up to 45° off‐axis for the filtering approach and ∼30° for the circumscription approach. Error in calculated direction angles depends on the arbitrary diameter of the sphere; optimally, the sphere should intersect the source. The circumscription technique converges to an estimate of direction angles in ∼50 events; the filtering approach requires ∼1000 events. Conclusion: The two methods complement each other in speed and field‐of‐view. Monte Carlo simulations and experimental testing of a prototype system are ongoing as a separate part of the overall project; data from these will further supplement evaluation of the algorithms. Acknowledgment: Supported by Homeland Security Advanced Research Projects Agency, and Space and Naval Warfare Systems Center San Diego; Contract No. N66001‐05‐C‐6024.

TH‐D‐330A‐02: An Electronically‐Collimated Gamma‐Ray Detector for Intraoperative Localization of Radiation Sources

Purpose: We are developing a radiation detector for locating radiation sources, e.g. for intraoperative localization of sentinel lymph nodes and metastases. The design emphasizes compact size and portability, wide field of view, and efficiency and accuracy in source localization. Room‐temperature cadmium‐zinc‐telluride (CZT) detectors and electronic collimation via Compton‐scatter detection are used to achieve the design goals. Method and Materials: The detector design was simulated in GEANT4 to assess feasibility and optimize the design. The simulation model was a 6‐sided box with one detector module on each end and two modules per side. One end is the primary scatter detector; the other modules detect the scattered photons, operating in coincidence with the primary module. The simulations allowed variations of detector dimensions, pixel size, energy resolution, and source energies. Experimental measurements with a 3‐module partial prototype were used to validate the simulations; each module is a 16×16‐pixel 38×38×5‐mm3 CZT detector. Results: The simulations indicated ∼15% of incident gamma rays produce valid direction measurements; 30–70% of these events are Compton‐photoelectric interaction pairs. The measured angular resolution varied from a few degrees for 100‐keV gamma‐rays up to about 10° FWHM at 1 MeV. Above ∼1.5 MeV, multiple Compton‐scatter events limit accurate measurement of Compton cone angles; below ∼50 keV, few Compton‐scatter events occur. Experimental validation with the prototype system is in progress.Conclusion: Efficiency and angular resolution vary with source energy but reasonable performance seems achievable for radioisotopes from Am‐241 through Co‐60. Ongoing work is investigating the effect on performance of design parameters such as pixel size and detector thickness. Coupled with concurrent development of real‐time methods to calculate the directional information, this system provides localization of radiation sources with high sensitivity. Acknowledgment: Supported by Homeland Security Advanced Research Projects Agency, and Space and Naval Warfare Systems Center San Diego; Contract N66001‐05‐ C‐6024.

Simulating primary detector function in multifactor measurements

Simulation is considered for the transformation function of the primary detector subject to a given step in the changes in the influencing factors for performing multifactor measurements by the model method.

The PTB high-accuracy spectral responsivity scale in the VUV and x-ray range

At the electron storage ring BESSY II, the Physikalisch-Technische Bundesanstalt operates ten experimental stations at six synchrotron radiation beamlines for photon metrology in the spectral range from ultraviolet radiation to x-rays. Five of these beamlines are used to realize and disseminate a scale of spectral responsivity for photodetectors. Detector calibration is based on the use of cryogenic radiometers as primary detector standards. The current status of instrumentation and measurement capabilities is described. Best measurement capabilities (k = 2) for the calibration of photodiodes vary between 0.4% and 2.3%.

Characterization of detectors for extreme UV radiation

Accurate measurements of the radiant power and other quantities are a prerequisite for the development and optimization of suitable radiation sources for extreme ultraviolet (EUV) lithography. Photodiodes are established as easy-to-operate detectors also in the EUV range. The calibrations at the Physikalisch-Technische Bundesanstalt are based on the comparison of the detector to be calibrated with the cryogenic electrical substitution radiometer as a primary detector standard using monochromatized synchrotron radiation at the soft x-ray radiometry beamline in the spectral range from 1 nm up to 25 nm. The spectral responsivity is measured with a relative uncertainty of 0.3% or better. For the dissemination of these high-accuracy calibrations, we investigated the stability and linearity of silicon n-on-p junction photodiodes under intense EUV irradiation in ultra-high vacuum. The maximum current in linear operation (1% relative saturation) depends on the size of the photon beam and ranges from about 3 mA for a 6 mm photon beam diameter to 0.2 mA for a 0.25 mm diameter spot. Diodes with diamond-like carbon or a TiSiN top layer proved to be stable up to a radiant exposure of about 100 kJ cm−2. Furthermore, examples of the calibration of spectrally and spatially resolving radiometric tools for EUV-source characterization are presented.

Optimization studies of a Compton suppression spectrometer using experimentally validated Monte Carlo simulations

Recent developments associated with room temperature semiconductor detectors and inorganic scintillators suggest that these detectors may be viable alternatives for the primary detector in a Compton suppression spectrometer (CSS). The room temperature operation of these detectors allows removal of a substantial amount of material from between primary and secondary detectors, if properly designed and should afford substantially better suppression factors than can be achieved by germanium-based spectrometers. We have chosen to study the optimum properties of a CSS with a LaX 3:Ce scintillator (where X is chloride or bromide) as the primary gamma-ray detector. A Monte Carlo photon transport model is used to determine the optimum geometric properties of this spectrometer. To validate the assumptions and basic design of the Monte Carlo simulations, the energy distribution of a 137Cs point source is measured and simulated for two experimental systems. Comparison of the suppression factors for the measured and simulated data validates the model accuracy. A range of CSS physical parameters are studied to determine optimal detector geometry and to maximize the Compton suppression factor. These physical parameters and their optimum values are discussed.

The Spectral Irradiance Monitor: Measurement Equations and Calibration

The Spectral Irradiance Monitor (SIM) is a satellite-borne spectrometer aboard the Solar Radiation and Climate Experiment (SORCE) that measures solar irradiance between 200 and 2700 nm. This instrument employs a Fery prism as a dispersing element, an electrical substitution radiometer (ESR) as the primary detector, and four additional photodiode detectors for spectral scanning. Assembling unit level calibrations of critical components and expressing the sensitivity in terms of interrelated measurement equations supplies the instrument's radiant response. The calibration and analysis of the spectrometer's dispersive and transmissive properties, light aperture metrology, and detector characteristics provide the basis for these measurement equations. The values of critical calibration parameters, such as prism and detector response degradation, are re-measured throughout the mission to correct the ground-based calibration.

The Spectral Irradiance Monitor: Scientific Requirements, Instrument Design, and Operation Modes

The Spectral Irradiance Monitor (SIM) is a dual Fery prism spectrometer that employs 5 detectors per spectrometer channel to cover the wavelength range from 200 to 2700 nm. This instrument is used to monitor solar spectral variability throughout this wavelength region. Two identical, mirror-image, channels are used for redundancy and in-flight measurement of prism degradation. The primary detector for this instrument is an electrical substitution radiometer (ESR) designed to measure power levels ∼1000 times smaller than other radiometers used to measure TSI. The four complementary focal plane photodiodes are used in a fast-scan mode to acquire the solar spectrum, and the ESR calibrates their radiant sensitivity. Wavelength control is achieved by using a closed loop servo system that employs a linear charge coupled device (CCD) in the focal plane. This achieves 0.67 arcsec control of the prism rotation angle; this is equivalent to a wavelength positioning error of δλ/λ = 150 parts per million (ppm). This paper will describe the scientific measurement requirements used for instrument design and implementation, instrument performance, and the in-flight instrument operation modes.

Linearity tests of silicon photodiodes for EUV radiation

Photodiodes are used as easy-to-operate detectors in the extreme ultraviolet (EUV) spectral range. The Physikalisch-Technische Bundesanstalt (PTB) calibrates photodiodes with a 0.3% or better relative uncertainty for the spectral responsivity. These calibrations are based on the comparison of the photodiodes to a cryogenic electrical substitution radiometer as primary detector standard using monochromatized synchrotron radiation. The linearity of the diode signal with incident radiant power was studied with EUV radiation. The linearity of the photodiodes was tested with quasi-dc illumination for different photon beam spot sizes. A systematic and significant variation of the maximum external photocurrent of the diodes with the photon beam spot size was found. The maximum current in linear operation without bias voltage (less than 1% relative saturation) decreased from about 3 mA for a 6 mm photon beam diameter to 0.2 mA for a 0.25 mm diameter. The corresponding irradiance increased from 30 mW/cm 2 for the 6 mm aperture to about 2 W/cm 2 for the 0.25 mm aperture. This behaviour is attributed to a change in the effective serial resistance with the photon beam size. The values derived from the saturation measurement vary between 65 Ω for a 6 mm and 540 Ω for a 0.25 mm diameter beam. For spot sizes much smaller than the diode's active area, the serial resistance scales logarithmically with the spot size.

Somatotopic mapping of chordotonal organ neurons in a primitive ensiferan, the New Zealand tree weta Hemideina femorata: II. complex tibial organ.

Most ensiferan insects possess sets of highly specialized chordotonal organs in the proximal tibiae to detect conspecific auditory/vibratory signals or approach of predators. To date, most auditory/vibratory afferents have been classified according to their physiological properties and axonal projection morphology, but not to somatotopic origins. Hence, the functional specialization of identified receptor cells in the tibial organs remains uncertain. To address this question from an anatomical aspect, we investigated the structure of the weta, Hemideina femorata, tibial organs (the most elaborated tibial chordotonal organs among ensiferans) and their central projections by staining small numbers of receptor afferents from identified tibial organs. These organs comprise the "complex tibial organ," including the subgenual organ (primary vibration detector) and its posterior complement, the accessory organ, and the crista acustica (primary auditory organ) and its proximal complement, the intermediate organ. Unlike reports of a membranous organ structure for homologs in other ensiferans, weta tibial organs contain receptor cells embedded in thick solid masses. Primary afferents project ipsilaterally to the medial ventral association center of thoracic ganglia, where axon terminals are arrayed topographically in different areas specific to each organ, except for almost complete overlap of afferents originating from the distal part of the crista acustica and from the intermediate organ. In contrast to somatotopic reflection of sensilla position on limbs, as known for mechanoreceptor hairs, the somatotopic projection map of the insect ear reveals topographic association with acoustic tracheae or tibial cuticular attachment sites, which in turn must reflect determinants of response sensitivity (e.g., frequency or threshold).

Experiments in speech recognition using a modular MLP architecture for acoustic modelling

We have been investigating for some time the use of a layered modular/ensemble neural network architecture for acoustic modelling. In the particular instantiation investigated so far, this architecture decomposes the task of acoustic modelling by phone. In a first layer at least one multilayer perceptron (or ‘primary detector’) is trained to discriminate each phone and, in a second layer, outputs from the first layer are combined into posterior probabilities by further MLPs. In this paper we show how our approach provides good acoustic modelling in a series of experiments on the TIMIT speech corpus. Firstly we show that decomposition itself provides a gain through greater precision in MLP training. Secondly we show that primary detectors trained on different front-ends can be profitably combined. Our analysis of the correlations between different detectors for the same phone shows that some independent information is provided by different front-ends. Thirdly we show how to employ information from a wide context within our architectural framework and that this provides performance equivalent to the best context-dependent acoustic modelling systems.

Determination of some heavy metals (Fe, Cu, Zn and Pb) in blood by total reflection X-ray fluorescence

The main purpose of this study is the interaction between nutrition (micronutrients heavy metals: Fe, Zn, Cu) and toxic heavy metals such as Pb in blood of children living in Gharb region of Morocco. This region receives all pollution carried by the Sebou river coming mainly from industrial activities. A rapid and simple analytical procedure was used for the determination of Fe, Cu and Zn trace amounts in blood by total-reflection X-ray fluorescence technique. This method is an energy dispersive XRF technique in a special geometry of primary beam, sample and detector. The sample is deposited on a plane polished surface of a suitable reflector material. It is presented as a few drops (25 μl) from a solution of blood digested in a mixture of HNO 3 and H 2 O 2 using a microwaves accelerated reaction system. The accuracy of measurements has been investigated by using certified materials. The concentration of Cu was found to be normal in all samples (≅ 1 ppm) which ruled out any interaction between this element and the others. On the other hand, amounts of Fe and Zn are very variables, suggesting an interaction between Fe and Zn. However, amounts of Pb in blood are inferior to 50 ppb, suggesting that no interaction exist with this metal and micronutrients.