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A novel concept for improving gamma ray spectroscopy in compact instruments is presented. The dual-range photon detector (DRPD) consists of a silicon drift detector (SDD) which is optically coupled with a La[Br.sup.3]([Ce.sup.3+]) crystal. In contrast to similar configurations investigated so far the SDD points to the radiation source. Pulse shape discrimination allows separating the distinct detection mechanisms which correspond to gamma absorption in the SDD or in the scintillator, respectively. This arrangement combines for the first time the excellent performance of an SDD as X-ray detector on its own with the striking energy resolution of a La[Br.sub.3] ([Ce.sup.3+]) scintillator read out by an SDD. The concept was successfully demonstrated with two experimental SDD-La[Br.sub.3]([Ce.sup.3+]) systems. An energy resolution (FWHM) of 2.7% and 2.9% at 662 keV was measured with the two distinct systems operated in scintillator mode whereas scintillator-photomultiplier combinations with the same crystals yielded only 3.3% and 3.1%, respectively. The SDD mode provided an energy resolution surpassing the scintillator resolution by about one order of magnitude in the limited energy range up to 100 keV. Measurements with various radioactive sources demonstrated that this mode uncovers line structures which could never be resolved with scintillators or CZT detectors. Homeland security programs could profit from the proposed detector concept. Index Terms--Energy resolution, gamma-ray spectroscopy, homeland security, pulse shape discrimination, radioisotope identification, scintillation detectors, silicon detectors.

The resolution of a miniature spectrometer with a multichannel detector is limited by its throughput. A subpixel deconvolution method is proposed to enhance resolution without physically reducing the throughput. The method introduces subpixel reconstruction to overcome undersampling during deconvolution processing. The experimental result has shown a 36.6% reduction in FWHM of spectral lines, indicating the effectiveness of the method. OCIS codes: 300.6190, 300.6170.

In optical quantum information technology, a photon number resolving detector (PNRD) is the basic device for developing photonic quantum computers. The demands for the PNRD are high quantum efficiency and wide dynamic range. We have developed a charge integration photon detector (CIPD) with a quantum efficiency of 80% at telecom wavelengths. The repetition rate of the CIPD is as low as 40 Hz at present, but it can be applied for measurement of short pulses. We report the capability of the CIPD for multiphoton counting over 10 photons, its responsivity to the short pulses, and its high linearity using a binary intensity modulated short pulse (2 ns) train and simultaneous irradiation of two kinds of pulses. OCIS codes: 040.3060, 040.3780, 040.5160, 040.5350, 040.557, 040.607.

The effects of penetration are included in the formulas for the prediction of the resolution of pinhole collimators through the use of effective diameters. Expressions of the resolution-effective diameter for pinholes with a double-knife-edge (DKE) profile are available in the literature. In this paper the expressions applicable to asymmetric-knife-edge (AKE) profiles, which include the important case of the single-knife-edge (SKE), are presented. Results indicate that the simplest methods that are still accurate in the calculation of DKE effective diameters do not produce in general formulas with similar accuracy for AKE profiles, due to increased susceptibility to penetration. Especially at high energy (365 keV), for the SKE case more advanced formulas are necessary and were, therefore, derived. Index Terms--Collimator, image resolution, photon penetration, pinhole, single photon emission computed tomography, small-animal imaging, SPECT.

A prototype scanning-slit X-ray imaging system with microchannel plate (MCP) detector has recently been developed and tested for potential applications in medical imaging. For this purpose, the quantum efficiency of the MCP needs to be calculated and verified experimentally for polychromatic X-ray beams. X-ray detection in the MCP is a cascade of several processes including the absorption of the photon in the MCP material, the escape of created fast (photo, Compton, or Auger) electrons from the MCP channel walls into the channels, triggering an avalanche of secondary electrons in the microchannels, and detecting the resulted charge pulse. Because electron transport in the material is involved in this process, Monte Carlo simulations were used to calculate the quantum efficiency of an MCP for photon beams used in mammography, computed tomography (CT), and chest radiography. The quantum efficiency of the MCP with 5-[micro]m channel diameter was calculated to be 68%, 89%, and 81% at X-ray tube voltages of 45, 90, and 120 kVp, which are used in scanning slit mammography, breast CT, and chest radiography, respectively. The detection efficiencies of an MCP with 2 [micro]m channel diameter was calculated to be 91%, 92%, and 86% at 45, 90, and 120 kVp tube voltages, respectively. The efficiency of a recently introduced silica MCP (pure Si[O.sub.2]) with 5[micro]m channel diameter was calculated to be 86% and 76% at 35 kVp and 45 kVp, respectively, and is rapidly decreased at higher energies. Results of the calculations show that the detection efficiencies of the MCPs are comparable to the currently available detectors in the medical X-ray imaging. Index Terms--Microchannel plate (MCP) detectors, Monte Carlo method, photon counting, quantum efficiency, X-ray imaging.

A new class of ultrafast single-photon detectors is described and discussed.

Single-photon 1-D imaging detectors, based on superconducting tunnel junctions, are described and discussed.

A new type of superconducting transition-edge photon and particle detector is described.

Fabrication of NbN superconducting single-photon detectors, based on the hotspot effect, is discussed.

Use of hot-electron microsensors for submillimeter space applications is discussed.

Penetration depth is investigated in terms of the performance of transverse image resolution and signal level in human cortex under single-, two-, and three-photon fluorescence microscopy. Simulation results show that, in a double-layer human cortex structure consisting of gray and white matter media, the signal level is strongly affected by the existence of the white matter medium under three-photon excitation. Compared with three-photon excitation, two-photon excitation keeps a better signal level and sacrifices a slight degradation in image resolution. In a thick gray matter medium, a penetration depth of 1500 [micro]m with a near-diffraction-limited resolution is obtainable under three-photon excitation. It is also demonstrated that the numerical aperture has a slight influence on image resolution and signal level under two- and three-photon excitation because of the nonlinear nature in the excitation process. OCIS codes: 170.3660, 180.2520, 290.4020.

A method is proposed for measuring the excess noise performance of electron multiplying charge-coupled devices.

A single photon avalanche detector (SPAD) in planar technology is described and discussd.

Design and testing of a monolithic integrated dual-detector for photon correlation analysis is described. The main element is a single photon avalanche diode (SPAD) with low noise- and high time-resolution.

A new high-sensitivity, solid-state image-sensor concept is described. The concept incorporates a charge-multiplication function similar to one used in vacuum tube image intensifiers.

Research describing single photon sensors is presented. In particular the properties of superconducting quantum interference device array amplifiers coupled to detector pixels are investigated.

Research is presented concerning the development of an all-purpose detector and its application to single photon spectroscopy. The resulting superconducting tunnel junction detector is described and examined.

Byline: C. Straubmeier (1,2), G. Kanbach (3), F. Schrey (4) Keywords: high-speed photometer; photon counting; GPS timing; software; hardware Abstract: OPTIMA is a small, versatile high-speed photometer which is primarily intended for time resolved observations of young high energy pulsars at optical wavelengths.The detector system consists of eight fiber fed photon counters based on avalanche photodiodes, a GPS timing receiver, an integrating CCD camera to ensure the correct pointing of the telescope and a computerized control unit.Since January 1999 OPTIMA proves its scientific potential by measuring a very detailed lightcurve of the Crab Pulsar as well as by observing cataclysmic variablestars on very short timescales.In this article we describe the design of the detector system focussing on thephoton counting units and the software control which correlates the detectedphotons with the GPS timing signal. Author Affiliation: (1) Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany (2) I. Physikalisches Institut, University of Cologne, Germany (3) Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany (4) Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany Article History: Registration Date: 12/10/2004

A UV sensitive multiwire photon detector has been tested as a possible candidate for the HERA-B RICH detector. The main obstacle to using such a TMAE+Methane filled gas detector in a high rate experiment appears to be rapid aging in the form of prohibitive loss of chamber gas gain. A special circuit has been designed for heating the anode wires in-situ with elevated currents, thus evaporating the polymer deposits. Heating almost completely recovers the initial gain, but this rejuvenation is unfortunately of short duration. Nevertheless, the cells exposed to periodic heat treatments have an average gain considerably higher than the non-heated cells.

A study was conducted to examine the quantum efficiency and time-domain response of superconducting NbN hot-electron photodetectors (HEPs). Experimental results show that the NbN HEPs exhibit much higher responsivities compared to other semiconductor photodetectors, having a coupling factor of 4 x 10(super 4) V/W, responsivity of 220 A/W and quantum efficiency of 340. NbN HEPs can be used for detecting single quanta of far-infrared radiation.

Research was conducted to illustrate optical photon detection including time and energy information from both calibrated laboratory sources and known astronomical objects using transition edge sensors. Results illustrate the best energy resolution reported for single photon energy dispersive spectroscopy with Delta-E(sub FWHM) - 0.12 plus or minus 0.01 eV for a 1 eV calibrated source.

A new operating mode for superconducting transition edge sensors used in cryogenic particle detection which utilize electrothermal feedback was developed. The decay time of the pulses from the detector was reduced by more than a factor of five through the use of the new method. Experimental analysis and results that illustrate a pulse decay time reduction by a factor of five are presented.

Image contrast enhancement is investigated for two-photon excitation fluorescence images of a microscopic sample that is buried underneath a turbid medium. The image contrast, which deteriorates rapidly with sample depth because of scattering loss, is enhanced by an increase in the average excitation power of the focused Gaussian (the [TEM.sub.00] mode) beam according to a compensation relation that has been derived by use of a Monte Carlo analysis of the scattering problem. A correct increase in the excitation power results in a detected fluorescence signal that remains invariant with sample depth. The scheme is demonstrated on images of DAPI-stained nuclei cells viewed underneath a suspension of 0.105-[Mu]m-diameter polystyrene spheres.

This work investigates the use of annihilation photons from gamma-ray-induced electron-positron pair production to inspect objects when only one side is accessible. The [Z.sup.2]dependence of the pair-production cross section and the high penetration of 511-keV photons allow this method to differentiate high-Z materials in low-Z matrices. The experimental results for the dependence of the backstreaming photon yield on Z shows a factor of 20 increase for elements over the range 4

EPIC, the European Photon Imaging Cameras is an experiment based on cooled CCDs on board the ESA X-ray Multi Mirrors satellite due to be launched in 1999. Since CCD's are sensitive to radiation other than X-rays, namely Optical and UV light, filters are necessary to prevent this radiation from reaching the detector sensitive area. Three types of filters were developed, to be used alternatively depending on target source. Here we report on the medium and thin filters developed by MOXTEK Inc. in Orem, Utah, while the thick ones, developed at the Max-Planck-Institut fur Extraterrestrische Physik (MPE, Germany) have been described elsewhere. The two filters, described here, have a 1600 [Angstrom], Polyimide substrate coated with 400 [Angstrom], and 800 [Angstrom] aluminium for the thin and medium filter, respectively. After manufacturing. the filters have been submitted to an intensive qualification and calibration programme at MOXTEK. Further calibrations, transmission measurements and performance stability, have been carried out or are in progress at one of the EPIC Institutes (Osservatorio Astronomico di Palermo).

CsI(T1), CsI(Na), and YAP light yield nonproportionality has been characterized using the Compton Coincidence Technique. Measured electron responses were used to calculate photon responses of the scintillators studied. These calculated photon responses were then compared with measured photon responses. In addition results from electron response measurements and photon response calculations were compared with previously reported results. While the CsI(Na) electron response was observed to have the largest deviation from proportionality (about 40%), YAP was observed to have a nearly proportional response. The CsI(TI) calculated photon response was observed to agree to within 1% with measured photon response in this study for all measured photon energies. While the CsI(Na) calculated photon response agreed to within 1% of measured data for photon energies above 60 keV, deviations up to 4% were observed below 60 keV.

A study of asymmetric NbN-NB-Al superconducting tunnel junctions as photon counting detectors at X-ray and ultraviolet-visible wavelengths has found that the quasiparticle loss rates were reduced as a thin NbN passivation layer was included in the top electrode of the devices, in place of the natural niobium oxides. This improved the probability of multiple tunnel processes, resulting in the increase in detector responsivity. With such responsivity level, single photon counting performance was made possible at wavelengths and temperatures of up to 700 nm and 830 mK, respectively.

The characteristics of shallow junction single photon avalanche diodes are described using numerical simulation. A bidimensional model is employed to establish photogenerated charge density profiles in the diffusion-assisted reaction. The photonassisted spreading mechanism is assessed. Its role in geometrical terms is insignificant in comparison to the diffusion-assisted reaction. The photon-assisted avalanche spreading reaction is described.

This paper describes an aerogel threshold particle identification detector developed for use in BABAR, the experiment to be run at the asymmetric [e.sup.+][e.sup.-] B-factory PEP-II under construction at the Stanford Linear Accelerator Center (SLAC). Results of extensive tests,performed at the CERN PS indicate that this detector is capable of separating pious from below-threshold particles in a wide momentum range. The detector is read by a new version of a hybrid photon detector (HPD). The HPD has been chosen because of its excellent behavior in high magnetic fields, where it can be successfully exploited to preserve the required particle identification (PID) performance.

Ta/Al superconducting tunnel junctions were subjected to photon counting experiments. The junctions feature predicted high energy resolving power making them ideal for photon counting applications. Successful photon detection was achieved in the lambda=200-2000 nm wavelength range with a specific resolving power. The detector exhibited excellent linearity with photon energy.

We consider a concise method based on recurrent relations that permit rigorous computing of the first and the second moments of the components of the vector locating a randomly walking photon in an infinite homogeneous light-scattering medium. On assumption that the components obey a three-dimensional Gaussian distribution a probability density for the photon locations at the Nth scattering event can readily be written down and the light-intensity distribution in the medium may be calculated. The results from theoretical analyses are compared with the solution of a light-diffusion equation and with results of Monte Carlo simulations and show a better fit with simulated data than the diffusion approximation. Key words: Light scattering, random walks, statistical moments, probability distribution, Monte Carlo method

Standard statistical theory is used to calculate how the accuracy of a conversion-gain measurement depends on the number of samples. During the development of a theoretical basis for this calculation, a model is developed that predicts how the noise levels from different elements of an ideal detector array are distributed. The model can also be used to determine what dependence the accuracy of measured noise has on the size of the sample. These features have been confirmed by experiment, thus enhancing the credibility of the method for calculating the uncertainty of a measured conversion gain. Key words: Conversion gain, photon noise limit, detector-array uniformity, charge coupled device, active pixel sensor.

The simple structure of CdTe semiconductor detectors facilitates their downsizing, and their possible application to radiographic sensors has been studied. The escape of K X-rays from these detectors increases with reduction of their dimensions and affects the measurements of X- and gamma-ray spectra. K X-rays also produce crosstalk in multi-channel detectors with adjacent channels. Therefore, K X-rays which escape from the detector elements degrade both the precision of energy spectra and spatial resolution. The ratios of escape peak integrated counts to total photon counts for various sizes of CdTe single detectors were calculated for gamma rays using the Monte Carlo method. Also, escape and crosstalk ratios were simulated for the CdTe multi-channel detectors. The theoretical results were tested experimentally for 59.54-keV gamma rays from a 241 Am radioactive source. Results showed that escape ratios for single detectors were strongly dependent on element size and thickness. The escape and crosstalk ratios increased with closer channel pitch. Our calculated results showed a good agreement with the experimental data. The calculations made it clear that K X-rays which escaped to neighboring channels induced crosstalk more frequently at smaller channel pitch in multi-channel detectors. A radiation shielding grid which blocked incident photons between the boundary channels was also tested by experiment and by calculation. It was effective in reducing the probability of escape and crosstalk.

High-energy photon detectors have been constructed by engineering and fabricating p-i-n diode structures consisting of bulk CdZnTe and epitaxial HgCdTe. The p-i-n structure was obtained by liquid-phase epitaxial growth of p and n doped HgCdTe layers on 'intrinsic' CdZnTe material about 1mm thick and approximately 25mm square. Curve tracing shows I-V curves with diode characteristics having resistivity above [10.sup.11] [Ohms]-cm and leakage current of

Using correlated photons from spontaneous parametric downconversion, we have measured both the absolute quantum efficiencies and the time responses of four single-photon detectors. Efficiencies as high as (76.4 + or - 2.3)% (at 702 nm) were seen, which to our knowledge are the highest reported single-photon detection efficiencies. An auxiliary retroreflection mirror was found to increase the net detection efficiency by as much as a factor of 1.19. The narrowest time profile for coincidences between two detectors displays a peak with 300 ps FWHM. We also investigated the presence of afterpulses and the effects of saturation and varying device parameters.

A CsI(Tl) yield monitor has been constructed for the detection of quasi-monochromatic photons generated by Compton backscattering of laser light at the Electrotechnical laboratory (ETL). The monitor has dimensions of 150*150*300 |mm.sup.3~, consisting of 9-CsI(Tl) crystals. The fundamental performances of the CsI(Tl) monitor were measured with Radio Isotope (RI) sources and a quasimonochromatic photon beam. The detection efficiency was measured, and 100% efficiency was achieved for 20 MeV quasi-monochromatic photons. This monitor was also used as a photon spectrometer. The overall energy resolution was 3% for 3.2 MeV and 7% for 20 MeV quasi-monochromatic photons. Precise measurements of the LCS photon yield were done with the CsI(Tl) monitor. We confirmed that the photon yield was correctly expressed by the theoretical calculation.

The X-ray performance of Nb-based superconducting tunnel junctions was evaluated. A 50mCl Fe55 source emitting two line complexes with an intensity ratio of 8.4 was used to illuminate the junctions. The X-ray photons were collimated onto the junction barrier area by means of a metallic collimating mask. Results reveal that the collimation of the X-ray photons enhances the energy resolutions of the superconducting tunnel junctions.

A multi-channel X-ray imaging sensor using a CdTe compound semiconductor radiation detector in photon counting mode was developed and tested for digital X-ray imaging and X-ray energy separation capability. The X-ray imaging sensor was constructed of CdTe detector elements at a pitch of 0.25 mm. High band amplifiers, discriminators and counters attached to each element formed the pulse counting circuit. Charge pulses generated by absorbed X-ray photons were directly counted and separated into two energy regions. Digitized X-ray images containing energy information were thus obtained. Using this sensor two separate X-ray images of different energy can be obtained simultaneously. A 256 channel X-ray imaging sensor was prepared and used to provide spatial resolution measurement for an X-ray chart. Low and high energy images of a hand phantom were thus obtained and both a soft tissue image and a bone image were produced using an energy subtraction method.

We report on the scintillation properties of lead sulfate ([PbSO.sub.4]), a scintillator that shows promise as a high energy photon detector. its physical properties are well suited for gamma detection, as it has a density of 6.4 [gm/cm.sup.3], a 1/e attenuation length for 511 keV photons of 1.2 cm, is not affected by air or moisture, and is cut and polished easily. In 99.998% pure [PbSO.sup.4] crystals at room temperature excited by 511 keV annihilation photons, the fluorescence decay lifetime contains significant fast components having 1.8 ns (5%) and 19 ns (36%) decay times, but with longer components having 95 ns (36%) and 425 ns (23%) decay times. The peak emission wavelength is 335 nm, which is transmitted by borosilicate glass windowed photomultiplier tubes. The total scintillation light output increases with decreasing temperature from 3,200 photons/MeV at +45 [degrees] C to 4,900 photons/MeV at room temperature (+25 [degrees] C) and 68,500 photons/MeV at -145 [degrees] C. In an imperfect, 3 mm cube of a naturally occurring mineral form of [PbSO.sup.4] (anglesite) at room temperature, a 511 keV photopeak is seen with a total light output of 60% that of BGO. There are significant sample to sample variations of the light output among anglesite samples, so the light output of lead sulfate may improve when large synthetic crystals become available.

The depth of investigation of logging tools is an important factor which affects the precise value of its measurements. Monte Carlo calculations were used to determine the most appropriate method of characterizing the depth of investigation, the most common of which is detector response to a limited thickness of formation with a vacuum beyond. Variation of penetration was also characterized as a function of the formation density, source collimation angle and short spacing detector collimation angle.

The photomultiplier tube is the most common type of detector used for very low photon intensity. Photon source can be localized by determining the arrival time of individual photons at the surface of the detector. The optimal arrival time estimators were formulated by using the weighted non-linear least squares estimate of the detection time for a high gain photomultiplier. Mean and covariance function of the photomultiplier output for different arrival times were used to formulate the least squares estimator.

A tracking system composed of scintillating fibers measuring 830 micrometers in diameter and four meters long was employed for the Solenoidal Detector Collaboration at the Superconducting Super Collider. Light distribution was found to be wider relative to its mean considering the different amounts of light produced by particles passing different thicknesses in the circular fiber. These results indicate that the visible-light photon spectrum does not always have a Poisson form as expected.

When Dutch naturalist Anton van Leeuwenhoek constructed a simple microscope in 1683, he opened a window to the previously hidden universe of microorganisms. Although it took biologists 200 years to [...]

A novel approach to single-photon detection by means of an avalanche photodiode is described and preliminary results obtained by implementation of a prototype are reported. The electronic circuit (breakdown voltage follower) avoids the use of complex temperature controls typically used with these devices, thus reducing system complexity and cost. Data obtained without any thermoregulation show the same behavior with respect to systems thermoregulated to within a few hundredths of a degree celsius. Key words: Photodiode, avalanche, photon counting.

A niobium-based superconducting tunnel junction (STJ) is useful in detecting individual photons at rates up to 2.5 kHz in the wavelength range 200-500 nm. The STJ detects the photons with an intrinsic spectral resolution of 45 nm and at a quantum efficiency of nearly 50%. The device eliminates the limitations of charge-couple devices which provide linear response to photons. The device may be able to attain the limiting theoretical resolution of nearly 20 nm at 350 nm if the electronic noise is further reduced.

The use of H4139 and XP4702 multianode photomultipliers in fiber scintillators was evaluated by determining cross-talk between adjacent pads as a function of the external axial magnetic field. The gain variations in the magnetic fields were also measured and it was shown that H4139 exhibits a larger cross-talk at low fields compared to XP4702. Both tubes were also found to have similar timing properties.