Test of time reversal invariance with TRINE

The new detector TRINE (time reversal invariance neutron experiment) was developed to test the time reversal invariance in the neutron decay. The precision of former experiments can be improved by one order of magnitude with an improved proton detection, a better background suppression and an angular resolving measurement using multiwire proportional chambers in coincidence with plastic scintillators, and the higher neutron flux and polarization available today. The concept of the detector and the status of the project is discussed.     

Optical absorption measurements with parametric down-converted photons

It has been known for some time that correlated detection of pairs of photons generated by parametric down-conversion can eliminate several sources of error that occur in single-beam measurements. In the correlated photon measurements, the down-converted photons are separated into two beams with one photon of a pair in each beam. The absolute detection efficiency of a detector in one beam can be determined from the count rate of a detector in the other beam and the coincidence rate for the two detectors. These ideas can be used to measure the optical absorbance of a sample placed in front of one of the detectors. Errors due to stray light and dark counts are substantially reduced and fluctuations in pump intensity largely eliminated.     

Determining activities of radionuclides from coincidence signatures

The spectral analysis of simultaneously observed photons in separate detectors may provide an invaluable tool for radioisotope identification applications. A general recursive method to determine the activity of an isotope from the observed coincidence signature rate is discussed. The method coherently accounts for effects of true coincidence summing within a single detector and detection efficiencies. A verification of the approach with computer simulations is also discussed.     

Two-dimensional infrared and mid-infrared imaging by single-photon frequency upconversion

Single-photon frequency upconversion is an effective method of infrared single-photon detection and imaging by converting the long-wavelength photons to shorter wavelengths to match the detector’s spectral response. We realized few-photon level 2D infrared imaging with a coincidence frequency upconversion system in a bulk periodically poled lithium niobate crystal. Moreover, the infrared photons carrying orbital angular momentum were converted to the visible regime with high efficiency, while the orbital angular momentum of the photons was well conserved during the frequency upconversion process. The single-photon frequency upconversion method was also used for mid-infrared imaging at 3.39 µm with high efficiency and low noise.     

A driftless gas proportional scintillation counter for muonic hydrogen X-ray spectroscopy under strong magnetic fields

An experiment involving muonic hydrogen requires an X-ray detector having large area and working under strong magnetic fields (5 T) with good energy and timing resolution. A compact, driftless gas proportional scintillation counter (GPSC) capable of operating under such magnetic fields is investigated. This GPSC uses a CsI photocathode deposited onto a microstrip plate as the UV scintillation readout photosensor. This photocathode has the advantage of operating in direct contact with the scintillation gas. The detector is filled with pure xenon and is designed to have a high detection efficiency for 2 keV X-rays. Energy resolutions of 23% and 22% were obtained for 1.74 and 2.3 keV X-rays, respectively. The low-energy detector limit due to the electronic noise is 300 eV. Its performance in the presence of strong magnetic fields was tested. At magnetic field of 5 T the detector pulse amplitudes are reduced by less than 25%, while the detector energy resolution and pulse rise time present a relative increase of less than 10%.     

Radiometric calibration of single photon detectors by a single photon source based on NV-centers in diamond

A widespread use of various relative calibration techniques is established in order to realize reliable and low uncertainty measurements of the detection efficiency, which is one key parameter characterizing single photon detectors. In the following paper we will present an approach to evaluate the relative detection efficiency of single photon avalanche photo diode (SPAD) detectors compared to a standard detector. This calibration technique is based upon the fiber-coupled relative efficiency calibration of analogue detectors, used in fiber-optic communication. For the first time, to our knowledge, an intrinsic single photon source based on the nitrogen-vacancy center in diamond was used for this purpose. Furthermore, the possible influence of different photon statistics, arising from different irradiation sources like thermal sources or lasers on the calibration results for the fiber exchange method has been theoretically studied.     

Poissonian-type new radiation imager

A new radiation imager is proposed, which is based on the recent detector technique in high-energy physics experiments; the wavelength shifter coupled to the position-sensitive photomultiplier. The concept model using a CsI(Na) crystal was successfully tested, and a remarkable space resolution, 1.0 mm in FWHM, with detection efficiency of 70% has been confirmed for 122 keV gamma rays of ⁵⁷Co. Improvement in time resolution and possible application of the device to high-flux X-ray imaging are discussed.     

Correlation-matrix analysis of two-color coincidence events in single-molecule fluorescence experiments

We introduce a robust and relatively easy-to-use method to evaluate the quality of two-color (or more) fluorescence coincidence measurements based on close investigation of the coincidence correlation-matrix. This matrix contains temporal correlations between the number of detected bursts in individual channels and their coincidences. We show that the Euclidian norm of a vector Γ derived from elements of the correlation matrix takes a value between 0 and 2 depending on the relative coincidence frequency. We characterized the Γ-norm and its dependence on various experimental conditions by computer simulations and fluorescence microscopy experiments. Single-molecule experiments with two differently colored dye molecules diffusing freely in aqueous solution, a sample that generates purely random coincidence events, return a Γ-norm less than one, depending on the concentration of the fluorescent dyes. As perfect coincidence sample we monitored broad autofluorescence of 2.8 μm beads and determined the Γ-norm to be maximal and close to two. As in realistic diagnostic applications, we show that two-color coincidence detection of single-stranded DNA molecules, using differently labeled Molecular Beacons hybridizing to the same target, reveal a value between one and two representing a mixture of an optimal coincidence sample and a sample generating random coincidences. The Γ-norm introduced for data analysis provides a quantifiable measure for quickly judging the outcome of single-molecule coincidence experiments and estimating the quality of detected coincidences.     

Two-dimensional photoacoustic imaging by use of Fourier-transform image reconstruction and a detector with an anisotropic response

Theoretical and experimental aspects of two-dimensional (2D) biomedical photoacoustic imaging have been investigated. A 2D Fourier-transform-based reconstruction algorithm that is significantly faster and produces fewer artifacts than simple radial backprojection methods is described. The image-reconstruction time for a 208 x 482 pixel image is approximately 1 s. For the practical implementation of 2D photoacoustic imaging, a rectangular detector geometry was used to obtain an anisotropic detection sensitivity in order to reject out-of-plane signals, thereby permitting a tomographic image slice to be reconstructed. This approach was investigated by the numerical modeling of the broadband directional response of a rectangular detector and imaging of various spatially calibrated absorbing targets immersed in a turbid phantom. The experimental setup was based on a Q-switched Nd:YAG excitation laser source and a mechanically line-scanned Fabry-Perot polymer-film ultrasound sensor. For a 800 microm x 200 microm rectangular detector, the reconstructed image slice thickness was 0.8 mm up to a vertical distance of z = 3.5 mm from the detector, increasing thereafter to 2 mm at z = 10 mm. Horizontal and vertical spatial resolutions within the reconstructed slice were approximately 200 and 60 microm, respectively.     

Microprocessor-Based Flow Measurement Using a Positron Active Tracer

Methods for liquid-flow measurement based on the transit time of a positron active source are described, and the accuracy of each method is estimated. A microprocessor-based system and a TTL integrator for studying a positron active flow is constructed. The theoretical and experimental studies show that the velocity of a point source, 111 kBq (3?Ci) Na22-isotope (? 1 mm) inside a metal pipe (? 42 mm) can be measured using annihilation coincidence detection (detector pairs 1 m apart) and microprocessor electronics with inaccuracies of 0.2, 0.5, 0.7 percent for velocities 0.1, 0.5, and 1.0 m/s, respectively, at the 95 percent level of significance. Greater accuracy can be achieved by increasing the activity of the source.     

针对韦布尔分布的循环剔除TLM-CFAR检测器

针对韦布尔分布杂波背景中的目标检测问题,本文提出了一种CFAR检测器—循环剔除TLM-CFAR检测器。该检测器基于TL矩估计方法,首先获得韦布尔分布的两参数估计值,进而确定CFAR检测门限,然后利用循环剔除法剔除干扰目标和强散射点的影响。文中证明了TLM-CFAR检测器具有恒虚警性,利用Monte Carlo仿真方法研究了这种检测器的性能,并与MLH-CFAR检测器进行了比较。仿真结果和实验结果表明,这种检测器不仅可以达到MLH-CFAR检测器的性能,同时避免了最大似然估计需要迭代计算的繁琐性,提高了检测算法的效率和适用性。     

Energy and Timing Measurement with Time-Based Detector Readout for PET Applications: Principle and Validation with Discrete Circuit Components

A new signal processing method for PET application has been developed, with discrete circuit components to measure energy and timing of a gamma interaction based solely on digital timing processing without using an amplitude-to-digital convertor (ADC) or a constant fraction discriminator (CFD). A single channel discrete component time-based readout (TBR) circuit was implemented in a PC board. Initial circuit functionality and performance evaluations have been conducted. Accuracy and linearity of signal amplitude measurement were excellent, as measured with test pulses. The measured timing accuracy from test pulses reached to less than 300 ps, a value limited mainly by the timing jitter of the prototype electronics circuit. Both suitable energy and coincidence timing resolutions (~18% and ~1.0 ns) have been achieved with 3 × 3 × 20 mm(3) LYSO scintillator and photomultiplier tube-based detectors. With its relatively simple circuit and low cost, TBR is expected to be a suitable front-end signal readout electronics for compact PET or other radiation detectors requiring the reading of a large number of detector channels and demanding high performance for energy and timing measurement.     

Particle Concentration Measurements in Process Liquids Using Light-Scattering Techniques

A mathematical model is presented to compensate for the optical coincidence of particles in a liquid particle counter (LPC) detector, which detects particles by means of light scattering. It compensates for the optical coincidence of particles (1) belonging to the same size category, (2) belonging to different size categories, or (3) promoted from two particles to a single particle, which belongs to the larger particle size category. With this improved method, particle concentration decays are studied in a continuous stirred tank reactor where the liquid is recirculated and filtered. Furthermore, it is found that the latex sphere-calibrated LPC makes large errors in particle sizing, which is caused by the differences between the refractive index (n) of the particles under study: polystyrene latex spheres (0.112–0.204 µm), silica (0.16 and 0.33 µm), and Si₃ N₄ (< 0.4 µm). This implies that many particle-removal studies based on light-scattering detection methods become unreliable.     

Resonance ionization image detectors: basic characteristics and potential applications

A type of spectrally selective imaging optical detector that is based on resonance ionization in an atomic vapor is proposed. It has the potential for improved spatial, spectral, and temporal resolutions compared with those of available techniques. Figures of merit are calculated and compared with those of existing techniques. Several potential applications such as the imaging of moving objects, ultrasonic fields, high-energy particle detection, and optical communications are discussed.     

A Fast-Response Logarithmic Electrometer for Pulse-Reactor Experiments

The response time of a logarithmic electrometer was improved for pulse reactor experiments requiring long detector cables. A new phase-compensation technique was used in the circuit and it is based on the idea that a current variable resistance inserted between a detector cable and the input terminal of the logarithmic electrometer recovers the phase lag caused by the input capacitance. This stable and fast-response logarithmic electrometer was successfully applied to transient power measurements of the one-shot pulse-reactor "YAYOI."     

Selective detection of volatile aromatic compounds using a compact laser ionization detector with fast gas chromatography

We report results for a new gas chromatography detector that is comparatively sensitive and far more selective for aromatic compounds than the traditional photoionization detector. The detection means is multiphoton ionization at atmospheric pressure. The ionization source in these experiments is a diode-pumped passively Q-switched microchip laser operating at 266 nm. Experiments were conducted with the detector interfaced to a fast gas chromatograph. For <20 s elution time, limits of detection were <1 pg for toluene, ethylbenzene, xylenes, and isopropylbenzene; the limit of detection for benzene is approximately 10 pg. Detector response was linear over 5 orders of magnitude, including these low levels. Negligible signals were observed for nonaromatic ketones, aldehydes, ethers, and cycloalkanes at levels as high as 0.1 microg (10 mg/L concentration). Detector efficiency after fast GC separation was 0.002% when using a detector cell with a radius of 1.1 cm and a purge gas flow of 500 mL/min. The advantages of this detector are further illustrated by the fast GC analysis of fuel samples.     

Measuring the number of independent emitters in single-molecule fluorescence images and trajectories using coincident photons

A simple new approach is described and demonstrated for measuring the number of independent emitters along with the fluorescence intensity, lifetime, and emission wavelength for trajectories and images of single molecules and multichromophoric systems using a single PC plug-in card for time-correlated single-photon counting. The number of independent emitters present in the detection volume can be determined using the interphoton times in a manner similar to classical antibunching experiments. In contrast to traditional coincidence analysis based on pulsed laser excitation and direct measurement of coincident photon pairs using a time-to-amplitude converter, the interphoton distances are retrieved afterward by recording the absolute arrival time of each photon with nanosecond time resolution on two spectrally separated detectors. Intensity changes that result from fluctuations of a photophysical parameter can be distinguished from fluctuations due to changes in the number of emitters (e.g., photobleaching) in single chromophore and multichromophore intensity trajectories. This is the first report to demonstrate imaging with contrast based on the number of independently emitting species within the detection volume.     

Micropreconcentrator for Enhanced Trace Detection of Explosives and Chemical Agents

The design, fabrication, and testing of a sorbent-coated microfabricated preconcentrator device in complementary metal–oxide–semiconductor is presented. As a sorbent-coated device, the preconcentrator is used to collect, concentrate, and deliver analyte sampled from air for analysis with a detector. The preconcentrator in this paper is based on a perforated flowthrough microhotplate structure that is coated with a sorbent layer to maximize vapor trapping efficiency. The coating sorbs the analytes of interest during the collection phase at ambient temperatures. A thermal desorption cycle is then used to rapidly heat the preconcentrator to 180$^circhboxC$in 40 ms to release a concentrated wave of analyte. A finite-volume method was used to simulate the temperature distribution on a microhotplate and to model the time to reach the steady-state temperature. The experimental electrical measurements of the device were found to be in good agreement with the predicted values obtained using the finite-volume method. The preconcentrator device was demonstrated by interfacing to the front end of a handheld chemical agent detector and a handheld trace explosives detector. The preliminary results showed signal enhancement for the detection of the nerve agent simulant dimethylmethylphosphonate and the explosive 2,4,6-trinitrotoluene.     

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

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

A new synthetic formalism for true coincidence summing calculations

Simultaneous detection in one sensing crystal of photons emitted in cascade from the same radioactive atom gives rise to true coincidence summing effects (excess and deficit counting). Presented in this paper is a general formula to correct for true coincidence summing. This analytical formula enables calculation of the correction factor and its associated uncertainty for any gamma-ray placed in a decay scheme of any radionuclide (all decay modes treated) in any measuring configuration. It takes account of any cascade of photons either through the nature of the involved photons (γ-rays, X-rays, and annihilation photons) or the unlimited number of photons emitted in cascade. The requirement for this calculation is twofold. From the radionuclide part, theoretical knowledge of the decay scheme is necessary along with its characteristics (gamma-ray intensities and internal conversion coefficients for instances). Some atomic quantities such as fluorescence yields have also to be known. From the detector part, calibrations for full-energy peak efficiency and total efficiency in the measuring configuration have to be available. The demonstration of the formula is done with restrictive conditions (point source, no angular correlation, and no metastable state between the initial and final energy states) but adaptation can be implemented to partially or totally lift these limitations or approximations. Implementation of the formula in a computer code named Coincal is mentioned. Its successful application to point sources of ¹⁵²Eu placed 10 cm and 15 mm away from an n-type coaxial HPGe detector with 60% relative efficiency is also described.