Photon Rejection Research Articles

9 MV LINAC Photoneutron Interrogation of Uranium With Advanced Acoustically Tensioned Metastable Fluid Detectors

Abstract Active special nuclear material (SNM) photoneutron interrogation research with acoustically tensioned metastable fluid detector (ATMFD) sensor technology is discussed, which provides evidence for enabling real-time detection of SNM even when deployed under extreme 15,000 R h−1 (9 MeV endpoint) X-ray beams. Experiments to detect 3.2 kg depleted uranium (DU) are described with the use of two designs of the economical acoustically tensioned metastable fluid detector (E-ATMFD), viz., E-ATMFD.Ver.0 and E-ATMFD.Ver.1, respectively, at standoffs ranging from 0.1 m to 10 m—including with the E-ATMFD directly within the interrogating beam. Under similar conditions and with 100% photon rejection (i.e., 0 cpm with beam on, and without SNM), the E-ATMFD.Ver.1 design operating at ∼0.9 W of drive power was shown capable of ∼6× (600%) higher gain over E-ATMFD.Ver.0 operating at ∼7 W (with beam on and with SNM). The sensitivity gain rises to ∼27× (i.e., 2700%) with the E-ATMFD.Ver.1 operating at 0.99 W and a background count rate of ∼1 cpm. The E-ATMFD.Ver.1 demonstrated 100% photon blindness (0 cpm) while operating at ∼0.56 W drive power and placed directly within the beam under 15,000 R/h; including the SNM target led to a count rate of up to 50 cpm—revealing the E-ATMFD.Ver.1 is potential field capable of detecting U-based SNMs within seconds from photofission neutron signals, even when deployed directly within the intense (15,000 R/h) high energy (9 MeV endpoint X-Ray) interrogating photon beam.

Multifunctional semitransparent organic solar cells with excellent infrared photon rejection

Semitransparent organic solar cells (ST-OSCs) have the potentials to open promising applications that differ from those of conventional inorganic ones, such as see-through power windows with both energy generation and heat insulation functions. However, to achieve so, there remain significant challenges, especially for balancing critical parameters, such as power conversion efficiency (PCE), average visible transparency (AVT) and low energy infrared photon radiation rejection (IRR) to realize the full potentials of ST-OSCs. Herein, we demonstrate the new design of ST-OSCs through the rational integration of organic materials, transparent electrode and infrared photon reflector in one device. With the assistance of optical simulation, new ST-OSCs with precise layout exhibit state-of-art performance, with near 30% AVT and PCE of 7.3%, as well as an excellent IRR of over 93% (780–2500 nm), representing one of best multifunctional ST-OSCs with promising perspective for window application.

Characterization of highly multiplexed monolithic PET / gamma camera detector modules

PET detectors use signal multiplexing to reduce the total number of electronics channels needed to cover a given area. Using measured thin-beam calibration data, we tested a principal component based multiplexing scheme for scintillation detectors. The highly-multiplexed detector signal is no longer amenable to standard calibration methodologies. In this study we report results of a prototype multiplexing circuit, and present a new method for calibrating the detector module with multiplexed data.A mm3 LYSO scintillation crystal was affixed to a position-sensitive photomultiplier tube with position-outputs and one channel that is the sum of the other 64. The 65-channel signal was multiplexed in a resistive circuit, with 65:5 or 65:7 multiplexing. A 0.9 mm beam of 511 keV photons was scanned across the face of the crystal in a 1.52 mm grid pattern in order to characterize the detector response. New methods are developed to reject scattered events and perform depth-estimation to characterize the detector response of the calibration data. Photon interaction position estimation of the testing data was performed using a Gaussian Maximum Likelihood estimator and the resolution and scatter-rejection capabilities of the detector were analyzed.We found that using a 7-channel multiplexing scheme (65:7 compression ratio) with 1.67 mm depth bins had the best performance with a beam-contour of 1.2 mm FWHM (from the 0.9 mm beam) near the center of the crystal and 1.9 mm FWHM near the edge of the crystal. The positioned events followed the expected Beer–Lambert depth distribution. The proposed calibration and positioning method exhibited a scattered photon rejection rate that was a 55% improvement over the summed signal energy-windowing method.

Constraints on Lμ−Lτ gauge interactions from rare kaon decay

A model with ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge symmetry is the least constrained model as a resolution to the disagreement of the muon anomalous magnetic moment between the theoretical predictions and the experimental results. In this paper, we discuss how well the ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ model can be constrained by looking for decays of the charged kaon associated with a ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ gauge boson. More concretely, we consider searches for single muon tracks from the decays of stopped charged kaon as in the E949 experiment. In our conservative estimation, we find that the favored parameter region for the muon anomalous magnetic moment can be tested by using a 10 times larger number of the stopped charged kaons and about a 100 times better photon rejection rate than the E949 experiment.

TWO NEW SINGLE-EXPOSURE, MULTI-DETECTOR NEUTRON SPECTROMETERS FOR RADIATION PROTECTION APPLICATIONS IN WORKPLACE MONITORING.

This communication describes two new instruments, based on multiple active thermal neutron detectors arranged within a single moderator, that permit to unfold the neutron spectrum (from thermal to hundreds of MeV) and to determine the corresponding integral quantities with only one exposure. This makes them especially advantageous for neutron field characterisation and workplace monitoring in neutron-producing facilities. One of the devices has spherical geometry and nearly isotropic response, the other one has cylindrical symmetry and it is only sensitive to neutrons incident along the cylinder axis. In both cases, active detectors have been specifically developed looking for the criteria of miniaturisation, high sensitivity, linear response and good photon rejection. The calculated response matrix has been validated by experimental irradiations in neutron reference fields with a global uncertainty of 3%. The measurements performed in realistic neutron fields permitted to determine the neutron spectra and the integral quantities, in particular H*(10).

A new active thermal neutron detector

This communication presents the main results about the design and in-house fabrication of a new solid-state neutron detector, which produces a DC output signal proportional to the thermal neutron fluence rate. The detector has been developed within the framework of the 3-y project NESCOFI@BTF of INFN (CSN V). Due to its sensitivity, photon rejection, low cost and minimum size, this device is suited to be used in moderator-based spectrometers.

SU‐E‐T‐310: Investigation of Neutron Survey Meter Response in Pulsed Fields

Purpose: To determine the behavior of neutron survey meters under conditions that are not representative of calibration conditions; specifically, when performing measurements in pulsed fields consisting of both photons and neutrons as opposed to an AmBe or Cf‐252 source. It is well understood that not all types of photon survey meters are suitable for use in pulsed fields, and experience suggests that this may also be the case for measurements made using typical neutron meters. Methods: A series of measurements were performed to evaluate the response of five different neutron survey meters. The first measurements evaluated their response in monoenergetic neutron fields between 50 keV and 18 MeV produced using a Van de Graaff accelerator. Dose conversion factors were applied to the known neutron fluence and the results were in turn compared to the measured dose rates. These results were also compared to the energy response curves provided by the manufacturers. The second set of measurements focused on photon rejection. The manufacturerˈs photon rejection specifications were first verified through Cs‐137 exposures at dose rates of up to 10 Sv/h. These results were then compared to photon rejection measurements from exposures in both a 6 MV and 18MV medical accelerator field. Results: A complete analysis of the results has not been completed at the time of submission. Initial results show that some neutron survey meters commonly used in accelerator facilities may be unreliable and susceptible to spurious high readings when used in the presence of pulsed photon fields, due to the relatively high peak photon dose rates during pulses. Conclusions: The conclusions will indicate the extent of any variations in neutron survey meter response resulting from use under non‐standard conditions and discuss what impact this may have for radiation surveys performed at accelerator facilities.

Photon — jet correlations measurement with ALICE at LHC: a feasibility study in proton-proton collisions

The feasibility to measure the imbalance distribution between direct isolated photons and charged hadrons is discussed within the context of the ALICE experiment at LHC. The case of proton-proton collisions at \(\sqrt s \) TeV is studied with Monte-Carlo simulations. Performances for prompt photon identification and rejection of the π0 decay photons are presented. Such a measurement will offer the possibilty to probe the medium formed in AA collisions with jets of energies below 50 GeV, which cannot be reconstructed in the heavy-ion environment.

Advances in Silicon Carbide Single Photon Detectors

We present overview of achieved results on 4H-SiC avalanche photodiodes (APDs) and arrays. Cost-effective solar-blind optical filter allows achieving high solar photon rejection ratio of more than 106 in combination with more than 40% single photon detection efficiency at 266nm. Three iterations of devices were fabricated and evaluated to compare their optical and electrical properties. Dark count rates and single photon detection efficiencies are the main characteristics compared for these three iterations of device designs.

Performance of Silicon Carbide Avalanche Photodiode Arrays and Photomultipliers

We present recent results on 4H-SiC avalanche photodiode arrays and SiC-based solid-state photomultiplier arrays suitable for ultraviolet and solar-blind light detection. A novel SiC-based photomultiplier array was demonstrated. An additional solar-blind filter enabled a solar photon rejection ratio of more than 106 in combination with 40% quantum efficiency at 280 nm.

Back Cover (Phys. Status Solidi A 10/2009)

physica status solidi (a)Volume 206, Issue 10 Back Cover Back Cover (Phys. Status Solidi A 10/2009) First published: 01 October 2009 https://doi.org/10.1002/pssa.200990014AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract The Feature Article by Vert and coworkers (pp. 2468–2477) reports on the recent development of solar-blind Geiger-mode 4H-SiC avalanche photodiodes, avalanche photodiode arrays and photomultipliers demonstrating appreciable single photon detection efficiencies and low dark count rates. Typical 4H-SiC photo detectors show response in the ultraviolet wavelength range of 200 to 400 nm with a peak value between 270 and 300 nm. An additional optical filter facilitates efficient solarblind light detection with a very good solar photon rejection. The back cover picture shows the image of a fabricated array. The upper right graph shows the comparison of the response amplitudes of a single pixel and of a photomultiplier array with the dark count amplitude. The graph on the lower left shows the external quantum efficiency of filtered and unfiltered devices. Volume206, Issue10October 2009 RelatedInformation

Solar-Blind 4H-SiC Avalanche Photodiodes

In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.

SOLAR-BLIND SINGLE-PHOTON 4H-SiC AVALANCHE PHOTODIODES

A solar blind 4 H - SiC single photon avalanche diode (SPAD) is reported. The SPAD with separate absorption and multiplication layers was designed for operation with low dark counts. A thin film optical filter deposited on a sapphire window of the device package provided sensitivity in the wavelength range between 240 and 280 nm with a very high solar photon rejection ratio. An estimated dark current of 0.4 pA (0.75 nA/cm2) at a gain of 1000 was measured on a device with an effective mesa diameter of 260 µm. A single photon detection efficiency of 9% (linear mode) and 9.5% (gated Geiger mode) were achieved at a wavelength of 266 nm for the same device. Corresponding dark count rate and dark count probability were 600 Hz and 4×10-4.

γ–hadron correlation measurements to study jets fragmentation with ALICE at LHC

The possibility to study the fragmentation function of jets with energies below 50 GeV, which cannot be reconstructed in the heavy-ion environment, is explored. We propose to measure the imbalance distribution between prompt photon and charged hadrons with the ALICE experiment at LHC. In the present article, the case of proton–proton collisions at $\sqrt{s}=14$ TeV is examined with Monte-Carlo simulations. Performances for prompt photon identification and rejection of the π 0 decay photons are presented. We find that the measurement in proton–proton is meaningful with respect to statistical and systematic errors for photon energies larger than 20 GeV.

Solar-Blind 4H-SiC Single-Photon Avalanche Diode Operating in Geiger Mode

A solar blind 4H-SiC single photon avalanche diode (SPAD) with a sharp cutoff at a wavelength of 280 nm is reported. The SPAD with separate absorption and multiplication layers was designed for operation in Geiger mode. A thin film optical filter deposited on a sapphire window of the device package provided sensitivity in the wavelength range between 240 and 280 nm with a very high solar photon rejection ratio. An estimated dark current of 0.4 pA (0.75 nA/cm2) at a gain of 1000 was measured on a device with an effective mesa diameter of 260 mum. A single photon detection efficiency of 9.4% and a dark count probability of 4 times 10-4 were demonstrated at a wavelength of 266 nm for the same device.

Dispersion-based optical coherence tomography OCT measurement of mixture concentrations

We present a low-coherence technique for the measurement of concentrations in aqueous solutions. It is based on a second-order dispersion measurement using the phase of the Fourier transform of the interferogram term obtained with an unbalanced Michelson interferometer. We demonstrate this approach by concentration measurements of aqueous mixtures of NaCl and glucose solutions. Results show errors between a few percent for high concentrations, up to 31% for low concentrations. The application of such a technique in OCT might require ultrahigh depth resolution and/or other scattered photon rejection techniques.

Development of an LENA instrument for planetary missions by numerical simulations

Low-energy neutral atom (LENA) observations bring us important information on particle environments around celestial objects such as Mercury and the Moon. In this paper, we report on new development of an LENA instrument for planetary explorations. The instrument is light weight (2 kg), and capable of mass and energy discrimination with a large sensitivity. The performance of the instrument is investigated by numerical simulations. By using our new computer code, we calculated 3D particle trajectories including ionization, neutralization, surface scattering, and secondary electron creation. This enables us to obtain detailed performance characterization of LENA measurements. We also made trajectory tracing of photons entering the instrument to acquire photon rejection capability. This LENA instrument has been selected for both the Indian lunar exploration mission Chandrayaan-1 and European–Japanese Mercury exploration mission BepiColombo.

An high efficiency photon veto detector for a [formula omitted] experiment

The P326 project aims to measure 40 events/year of the very rare decay K + → π + ν ν ¯ at the CERN SPS. This poses unprecedented requirements in terms of the tracking and identification of charged particles, and also calls for excellent photon rejection to fight the abundant π + π 0 background. A full angular coverage up to 50 mrad for photon detection will be provided by the NA48 liquid-krypton calorimeter complemented by a set of 13 photon counter rings along the decay tunnel at large angles, and by small angle calorimeters.

Measurements of Beta Ray Spectra in CANDU Nuclear Generating Stations Using a Silicon Detector Coincidence Telescope

The measurement of beta ray spectra at various work locations inside nuclear generating stations operated by Ontario Hydro is described. The measurements were carried out using an advanced coincidence telescope spectrometer using silicon detectors only. The spectrometer is capable of measuring electron energies over the range 60 keV-2500 keV with close to 100% coincidence efficiency. Photon rejection is carried out by requiring a coincidence between either two or three silicon detectors. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermoluminescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm -2 ) results in a value of 2.73 ± 0.77 and for the extremity dosemeter (240 mg.cm -2 ) an average value of 4.42 ± 1.17 is obtained. These values are 57% and 120% greater, respectively, than the current values used by Ontario Hydro. In addition, beta correction factors for nine representative spectra were calculated for 40 mg.cm -2 and 20 mg.cm -2 chips and the results demonstrate the benefits of decreased dosemeter thickness. The average value of the beta correction factor, as well as the spread in the beta correction factor, decreases dramatically from 4.80 ± 2.1 (240mg.cm -2 ) to 1.29 ± 0.1 (20 mg.cm -2 ).

Measurements of Beta Ray Spectra Inside Nuclear Generating Stations Using a Silicon Detector Coincidence Telescope: Skin Dose Beta Correction Factors for TL Elements

The measurement of beta ray spectra at various work locations inside nuclear generating stations operated by Ontario Hydro is described. The measurements were carried out using an advanced coincidence telescope spectrometer using silicon detectors only. The spectrometer is capable of measuring electron energies over the range 70-2500 keV with close to 100% efficiency. Over 40 beta ray spectra were measured at various work locations in three nuclear generating stations. Photon rejection is carried out by requiring a coincidence between either two or three detectors. Monte Carlo calculations were then used to estimate beta correction factors for the LiF:Mg,Ti elements used in the Ontario Hydro thermoluminescence dosemeters. Averaging over all the measured beta correction factors for the 'skin' chip (100 mg.cm -2 ) results in a value of 2.73 ± 0.77 and for the extremity dosemeter (240 mg.cm -2 ) an average value of 4.42 ± 1.17 is obtained. These values are 57% and 120% greater, respectively, than the current values used by Ontario Hydro. In addition, beta correction factors for nine representative spectra were calculated for 40 mg.cm -2 and 20 mg cm -2 chips, and the results demonstrate the benefits of decreased dosemeter thickness. The average value of the beta correction factor, as well as the spread in the beta correction factor, decreases dramatically from 4.80 ± 2.1 (240 mg.cm -2 ) to 1.29 ± 0.1 (20 mg.cm -2 ).