Electron-multiplying Charge-coupled Device Research Articles

Standoff alpha radiation detection for hot cell imaging and crime scene investigation

This paper presents the remote detection of alpha contamination in a nuclear facility. Alpha-active material in a shielded nuclear radiation containment chamber has been localized by optical means. Furthermore, sources of radiation danger have been identified in a staged crime scene setting. For this purpose, an electron-multiplying charge-coupled device camera was used to capture photons generated by alpha-induced air scintillation (radioluminescence). The detected radioluminescence was superimposed with a regular photograph to reveal the origin of the light and thereby the alpha radioactive material. The experimental results show that standoff detection of alpha contamination is a viable tool in radiation threat detection. Furthermore, the radioluminescence spectrum in the air is spectrally analyzed. Possibilities of camera-based alpha threat detection under various background lighting conditions are discussed.

Ageing and proton irradiation damage of a low voltage EMCCD in a CMOS process

Electron Multiplying Charge Coupled Devices (EMCCDs) have revolutionised low light level imaging, providing highly sensitive detection capabilities. Implementing Electron Multiplication (EM) in Charge Coupled Devices (CCDs) can increase the Signal to Noise Ratio (SNR) and lead to further developments in low light level applications such as improvements in image contrast and single photon imaging. Demand has grown for EMCCD devices with properties traditionally restricted to Complementary Metal-Oxide-Semiconductor (CMOS) image sensors, such as lower power consumption and higher radiation tolerance. However, EMCCDs are known to experience an ageing effect, such that the gain gradually decreases with time. This paper presents results detailing EM ageing in an Electron Multiplying Complementary Metal-Oxide-Semiconductor (EMCMOS) device and its effect on several device characteristics such as Charge Transfer Inefficiency (CTI) and thermal dark signal. When operated at room temperature an average decrease in gain of over 20% after an operational period of 175 hours was detected. With many image sensors deployed in harsh radiation environments, the radiation hardness of the device following proton irradiation was also tested. This paper presents the results of a proton irradiation completed at the Paul Scherrer Institut (PSI) at a 10 MeV equivalent fluence of 4.15× 1010 protons/cm2. The pre-irradiation characterisation, irradiation methodology and post-irradiation results are detailed, demonstrating an increase in dark current and a decrease in its activation energy. Finally, this paper presents a comparison of the damage caused by EM gain ageing and proton irradiation.

A $256\times256$ , 100-kfps, 61% Fill-Factor SPAD Image Sensor for Time-Resolved Microscopy Applications

A $256\times256$ single-photon avalanche diode image sensor operating at 100 kfps with fill factor of 61% and pixel pitch of $16~\mu \text{m}$ is reported. An all-nMOS 7T pixel allows gated operation down to 4 ns and ~600-ps fall time with on-chip delay generation. The sensor operates with 0.996 temporal aperture ratio in rolling shutter. Gating and cooling allow the suppression of dark noise, which, in combination with the high fill factor, enables competitive low-light performance with electron multiplying charge-coupled devices while offering time-resolved imaging modes.

Predicting Electron Population Characteristics in 2‐D Using Multispectral Ground‐Based Imaging

AbstractGround‐based imaging and in situ sounding rocket data are compared to electron transport modeling for an active inverted‐V type auroral event. The Ground‐to‐Rocket Electrodynamics‐Electrons Correlative Experiment (GREECE) mission successfully launched from Poker Flat, Alaska, on 3 March 2014 at 11:09:50 UT and reached an apogee of approximately 335 km over the aurora. Multiple ground‐based electron‐multiplying charge‐coupled device (EMCCD) imagers were positioned at Venetie, Alaska, and aimed toward magnetic zenith. The imagers observed the intensity of different auroral emission lines (427.8, 557.7, and 844.6 nm) at the magnetic foot point of the rocket payload. Emission line intensity data are correlated with electron characteristics measured by the GREECE onboard electron spectrometer. A modified version of the GLobal airglOW (GLOW) model is used to estimate precipitating electron characteristics based on optical emissions. GLOW predicted the electron population characteristics with 20% error given the observed spectral intensities within 10° of magnetic zenith. Predictions are within 30% of the actual values within 20° of magnetic zenith for inverted‐V‐type aurora. Therefore, it is argued that this technique can be used, at least in certain types of aurora, such as the inverted‐V type presented here, to derive 2‐D maps of electron characteristics. These can then be used to further derive 2‐D maps of ionospheric parameters as a function of time, based solely on multispectral optical imaging data.

X-ray luminescence computed tomography using a focused x-ray beam.

Due to the low x-ray photon utilization efficiency and low measurement sensitivity of the electron multiplying charge coupled device camera setup, the collimator-based narrow beam x-ray luminescence computed tomography (XLCT) usually requires a long measurement time. We, for the first time, report a focused x-ray beam-based XLCT imaging system with measurements by a single optical fiber bundle and a photomultiplier tube (PMT). An x-ray tube with a polycapillary lens was used to generate a focused x-ray beam whose x-ray photon density is 1200 times larger than a collimated x-ray beam. An optical fiber bundle was employed to collect and deliver the emitted photons on the phantom surface to the PMT. The total measurement time was reduced to 12.5min. For numerical simulations of both single and six fiber bundle cases, we were able to reconstruct six targets successfully. For the phantom experiment, two targets with an edge-to-edge distance of 0.4mm and a center-to-center distance of 0.8mm were successfully reconstructed by the measurement setup with a single fiber bundle and a PMT.

In silico optimization of radioluminescence microscopy.

Radioluminescence microscopy (RLM) is a high-resolution method for imaging radionuclide uptake in live cells within a fluorescence microscopy environment. Although RLM currently provides sufficient spatial resolution and sensitivity for cell imaging, it has not been systematically optimized. This study seeks to optimize the parameters of the system by computational simulation using a combination of numerical models for the system's various components: Monte-Carlo simulation for radiation transport, 3D optical point-spread function for the microscope, and stochastic photosensor model for the electron multiplying charge coupled device (EMCCD) camera. The relationship between key parameters and performance metrics relevant to image quality is examined. Results show that Lu2 O3 :Eu yields the best performance among 5 different scintillator materials, and a thickness: 8 μm can best balance spatial resolution and sensitivity. For this configuration, a spatial resolution of ~20 μm and sensitivity of 40% can be achieved for all 3 magnifications investigated, provided that the user adjusts pixel binning and electron multiplying (EM) gain accordingly. Hence the primary consideration for selecting the magnification should be the desired field of view and magnification for concurrent optical microscopy studies. In conclusion, this study estimates the optimal imaging performance achievable with RLM and promotes further development for more robust imaging of cellular processes using radiotracers.

Development of a new pinhole camera for imaging in high dose-rate environments

After Fukushima’s nuclear disaster in Japan, the decontamination operation is successfully ongoing, and restrictions from some areas were lifted in April 2017. However, the radiation dose rate in the Fukushima Daiichi Plant is still so high (e.g., from a few mSv/h up to 530 Sv/h) that the decommissioning operation of the reactor remains a serious problem. Visualization of radioactive materials would help address this, but no gamma camera is available at this moment that can take images in such a high dose-rate environment. In this study, we developed a new gamma camera featuring a wide dynamic range from sub-mSv/h to more than 680 Sv/h, for a quick and accurate visualization of radioactive materials. The camera consists of a pinhole collimator, a Gd2O2S:Tb (GOS) scintillator sheet, and an electron multiplying charge-coupled device (EM-CCD). Gamma rays passing through the pinhole collimator hit the GOS scintillator sheet, which emits scintillation light. The luminescence of the GOS scintillator sheet is monitored in real-time with an EM-CCD with an internal multiplication gain of up to 20. By changing the exposure time, electron multiplication gain, and aperture of the EM-CCD, a wider dynamic range covering five orders of magnitude in the radiation dose can be monitored for the first time. We show that the positions of a 137Cs source (662 keV) and 60Co source (1173, 1333 keV) are identified correctly with a typical angular resolution of 10° full width at half maximum (FWHM). We also confirmed a linear relation between the absorbed dose and the luminescence of the GOS scintillator sheet. Finally, we propose a new concept of ”color imaging”, by using multi-layered scintillators consisting of a Ga3Al2Gd3O12 (GAGG) scintillator, fluorescent glass, and a plastic scintillator.

Single atom imaging with an sCMOS camera

Single atom imaging requires discrimination of weak photon count events above the background and has typically been performed using electron-multiplying charge-coupled device cameras, photomultiplier tubes, or single photon counting modules. A scientific complementary metal-oxide semiconductor (sCMOS) provides a cost effective and highly scalable alternative to other single atom imaging technologies, offering fast readout and larger sensor dimensions. We demonstrate single atom resolved imaging of two site-addressable optical traps separated by 10 μm using an sCMOS camera, offering a competitive signal-to-noise ratio at intermediate count rates to allow high fidelity readout discrimination (error <10−6) and sub-μm spatial resolution for applications in quantum technologies.

High Time Resolution Astronomical Polarimetry with GASP

AbstractThe Galway Astronomical Stokes Polarimeter (GASP) is a high time resolution, full-Stokes imaging polarimeter which utilises a Fresnel rhomb prism as a beam-splitter and quarter wave retarder. The ability to perform optical photometry and polarimetry at high frame rates enables more detailed studies of a multitude of compact objects including; optical pulsars, magnetars and Active Galactic Nuclei (AGN). We present a brief discussion of the instruments’ current capabilities and hardware design. GASP is currently configured with two Electron Multiplying Charge-Coupled Devices (EMCCDs), which offer sub-millisecond frame readout speeds over a defined region of interest on the sensor. We will report results from an observational campaign at the William Herschel Telescope (WHT) in December, 2015. During this campaign GASP was used to study the Crab Pulsar, V404 Cygni and polarisation standards. As a subset of our analysis we have identified a significant contribution from the Interstellar Medium (ISM) and the interaction of a varying polarised source with the ISM, the subsequent conversion of linearly polarised light to circular, and its dependence on the angle of the source emission electric field orientation. Further to the presentation of results we will discuss future observational work, which is planned for September 2017 and subsequent improvements to increase the temporal resolution of the detectors.

Novel laser induced breakdown spectroscopy – Raman instrumentation using a single pulsed laser and an echelle spectrometer

ABSTRACTRaman spectroscopy is a fast technique providing molecular and structural characteristics of analytes, while laser-induced breakdown spectroscopy (LIBS) is powerful for elemental analysis. In this work, a novel hybrid LIBS–Raman instrument (LIBRAS) was developed, which is capable of providing both atomic emission spectra as well as vibrational spectra of polyatomic ions. LIBS and Raman signals were recorded simultaneously with respective 1064 and 532 nm pulse beams emitted from the single pulse laser. Meanwhile, one echelle spectrometer, equipped with an electron multiplying charge-coupled device detector, was applied to collect all LIBS and Raman signals. Mineral samples were measured by this novel hybrid setup, with their main elements and molecular vibrations being studied.

Diffuse optical tomography for breast cancer imaging guided by computed tomography: A feasibility study.

Diffuse optical tomography (DOT) has attracted attentions in the last two decades due to its intrinsic sensitivity in imaging chromophores of tissues such as hemoglobin, water, and lipid. However, DOT has not been clinically accepted yet due to its low spatial resolution caused by strong optical scattering in tissues. Structural guidance provided by an anatomical imaging modality enhances the DOT imaging substantially. Here, we propose a computed tomography (CT) guided multispectral DOT imaging system for breast cancer imaging. To validate its feasibility, we have built a prototype DOT imaging system which consists of a laser at the wavelength of 650 nm and an electron multiplying charge coupled device (EMCCD) camera. We have validated the CT guided DOT reconstruction algorithms with numerical simulations and phantom experiments, in which different imaging setup parameters, such as projection number of measurements and width of measurement patch, have been investigated. Our results indicate that an air-cooling EMCCD camera is good enough for the transmission mode DOT imaging. We have also found that measurements at six angular projections are sufficient for DOT to reconstruct the optical targets with 2 and 4 times absorption contrast when the CT guidance is applied. Finally, we have described our future research plan on integration of a multispectral DOT imaging system into a breast CT scanner.

Observation of spatial quantum correlations in the macroscopic regime

Spatial quantum correlations in the transverse degree of freedom promise to enhance optical resolution, image detection, and quantum communications through parallel quantum information encoding. In particular, the ability to observe these spatial quantum correlations in a single shot will enable such enhancements in applications that require real time imaging, such as particle tracking and in-situ imaging of atomic systems. Here, we report on measurements in the far-field that show spatial quantum correlations in single images of bright twin-beams with $10^8$ photons in a 1~$\mu$s pulse using an electron-multiplying charge-coupled device camera. A four-wave mixing process in hot rubidium atoms is used to generate narrowband-bright pulsed twin-beams of light. Owing to momentum conservation in this process, the twin-beams are momentum correlated, which leads to spatial quantum correlations in the far field. We show around 2~dB of spatial quantum noise reduction with respect to the shot noise limit. The spatial squeezing is present over a large range of total number of photons in the pulsed twin-beams.

Performance evaluation of 18 F radioluminescence microscopy using computational simulation.

Radioluminescence microscopy can visualize the distribution of beta-emitting radiotracers in live single cells with high resolution. Here, we perform a computational simulation of 18 F positron imaging using this modality to better understand how radioluminescence signals are formed and to assist in optimizing the experimental setup and image processing. First, the transport of charged particles through the cell and scintillator and the resulting scintillation is modeled using the GEANT4 Monte-Carlo simulation. Then, the propagation of the scintillation light through the microscope is modeled by a convolution with a depth-dependent point-spread function, which models the microscope response. Finally, the physical measurement of the scintillation light using an electron-multiplying charge-coupled device (EMCCD) camera is modeled using a stochastic numerical photosensor model, which accounts for various sources of noise. The simulated output of the EMCCD camera is further processed using our ORBIT image reconstruction methodology to evaluate the endpoint images. The EMCCD camera model was validated against experimentally acquired images and the simulated noise, as measured by the standard deviation of a blank image, was found to be accurate within 2% of the actual detection. Furthermore, point source simulations found that a reconstructed spatial resolution of 18.5 μm can be achieved near the scintillator. As the source is moved away from the scintillator, spatial resolution degrades at a rate of 3.5 μm per μm distance. These results agree well with the experimentally measured spatial resolution of 30-40 μm (live cells). The simulation also shows that the system sensitivity is 26.5%, which is also consistent with our previous experiments. Finally, an image of a simulated sparse set of single cells is visually similar to the measured cell image. Our simulation methodology agrees with experimental measurements taken with radioluminescence microscopy. This in silico approach can be used to guide further instrumentation developments and to provide a framework for improving image reconstruction.

A multichannel visible spectroscopy system for the ITER-like W divertor on EAST.

To facilitate long-pulse high power operation, an ITER-like actively cooled tungsten (W) divertor was installed in Experimental Advanced Superconducting Tokamak (EAST) to replace the original upper graphite divertor in 2014. A dedicated multichannel visible spectroscopic diagnostic system has been accordingly developed for the characterization of the plasma and impurities in the W divertor. An array of 22 lines-of-sight (LOSs) provides a profile measurement of the light emitted from the plasma along upper outer divertor, and the other 17 vertical LOSs view the upper inner divertor, achieving a 13 mm poloidal resolution in both regions. The light emitted from the plasma is collected by a specially designed optical lens assembly and then transferred to a Czerny-Turner spectrometer via 40 m quartz fibers. At the end, the spectra dispersed by the spectrometer are recorded with an Electron-Multiplying Charge Coupled Device (EMCCD). The optical throughput and quantum efficiency of the system are optimized in the wavelength range 350-700 nm. The spectral resolution/coverage can be adjusted from 0.01 nm/3 nm to 0.41 nm/140 nm by switching the grating with suitable groove density. The frame rate depends on the setting of LOS number in EMCCD and can reach nearly 2 kHz for single LOS detection. The light collected by the front optical lens can also be divided and partly transferred to a photomultiplier tube array with specified bandpass filter, which can provide faster sampling rates by up to 200 kHz. The spectroscopic diagnostic is routinely operated in EAST discharges with absolute optical calibrations applied before and after each campaign, monitoring photon fluxes from impurities and H recycling in the upper divertor. This paper presents the technical details of the diagnostic and typical measurements during EAST discharges.

Supersensitive single-particle plasmonic scattering-based cancer antigen 125 nanoimmunosensor by enhanced dark-field microscopy with dual-detection mode

A supersensitive nanoimmunosensor of cancer antigen 125 (CA125), which is a stage marker of several types of cancers, was developed based on characterization of single-particle plasmonic scattering by wavelength-dependent enhanced dark-field microscopy with dual-detection mode (EDFM-DM). Considering the optical properties of gold and silver nanoparticles (AuNPs/AgNPs), 40-nm AgNP was selected as an optimal fluorescence-free probe. CA125 was analyzed using the wavelength-dependent plasmonic scattering intensity of 40-nm AgNP-labeled CA125 immunoreacted on gold nanodots under the dual-detection mode. A color digital camera and an electron multiplying charge-coupled device camera were used for qualitative and quantitative analysis, respectively, based on the dark-field scattering images. Under optimal conditions, the developed immunosensor exhibited a lower detection limit of 4μU/mL (S/N=3) with a wide dynamic detection range of 4μU/mL-80U/mL (R=0.9935), which was a 100–375,000-fold lower detection limit with a 100–100,000-fold wider dynamic range than previous methods. In addition, recovery was greater than 98% with the spiking of standard CA125 in human serum samples. This method may be an excellent nanoimmunoassay platform for supersensitive detection at a wide dynamic detection range, supporting the earliest-stage detection of various disease-related protein molecules at the single-molecule level.

Spectroscopic determination of the composition of a 50 kV hydrogen diagnostic neutral beam.

A grating spectrometer with an electron multiplying charge-coupled device camera is used to diagnose a 50 kV, 5 A, 20 ms hydrogen diagnostic neutral beam. The ion source density is determined from Stark broadened Hβ emission and the spectrum of Doppler-shifted Hα emission is used to quantify the fraction of ions at full, half, and one-third beam energy under a variety of operating conditions including fueling gas pressure and arc discharge current. Beam current is optimized at low-density conditions in the ion source while the energy fractions are found to be steady over most operating conditions.

Electrogenerated Chemiluminescence Bioassay of Two Protein Kinases Incorporating Peptide Phosphorylation and Versatile Probe.

A sensitive electrogenerated chemiluminescence (ECL) bioassay was developed for the detection of two protein kinases incorporating the peptide phosphorylation and a versatile ECL probe. Cyclic adenosine monophosphate-dependent protein kinase (PKA) and casein kinase II (CK2) were used as proof-of-concept targets while a PKA-specific peptide (CLRRASLG) and a CK2-specific peptide (CRRRADDSDDDDD) were used as the recognition substrates. Taking advantage of the ability of protein A binding with the Fc region of a variety of antibodies with high affinity, a ruthenium derivative-labeled protein A was utilized as a versatile ECL probe for bioassay of multiple protein kinases. A specific peptide substrate toward target protein kinase was first self-assembled on the surface of gold electrode and then serine in the specific peptide on the electrode was phosphorylated by target protein kinase in the presence of adenosine-5'-triphosphate. After recognition of the phosphorylated peptide by monoclonal antiphosphoserine antibody, the versatile ECL probe was specifically bound to the antiphosphoserine antibody on the electrode surface. The ECL bioassay was developed successfully in the individual detection of PKA and CK2 with detection limit of 0.005 U/mL and 0.004 U/mL, respectively. In addition, the ECL bioassay was applied to quantitative analysis of the kinase inhibitors and monitoring drug-triggered kinase activation in cell lysates. Moreover, an ECL imaging bioassay using electron-multiplying charged coupled device as detector on the gold electrode array was developed for the simultaneous detection of PKA and CK2 activity from 0.01 U/mL to 0.4 U/mL, respectively, at one time. This work demonstrates that the ingenious design and use of a versatile ECL probe are promising to simultaneous detection of multiple protein kinases and screening of kinase inhibitor.

Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials

Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness.

TH‐EF‐207A‐03: Photon Counting Implementation Challenges Using An Electron Multiplying Charged‐Coupled Device Based Micro‐CT System

Purpose:To successfully implement and operate a photon counting scheme on an electron multiplying charged‐coupled device (EMCCD) based micro‐CT system.Methods:We built an EMCCD based micro‐CT system and implemented a photon counting scheme. EMCCD detectors use avalanche transfer registries to multiply the input signal far above the readout noise floor. Due to intrinsic differences in the pixel array, using a global threshold for photon counting is not optimal. To address this shortcoming, we generated a threshold array based on sixty dark fields (no x‐ray exposure). We calculated an average matrix and a variance matrix of the dark field sequence. The average matrix was used for the offset correction while the variance matrix was used to set individual pixel thresholds for the photon counting scheme. Three hundred photon counting frames were added for each projection and 360 projections were acquired for each object. The system was used to scan various objects followed by reconstruction using an FDK algorithm.Results:Examination of the projection images and reconstructed slices of the objects indicated clear interior detail free of beam hardening artifacts. This suggests successful implementation of the photon counting scheme on our EMCCD based micro‐CT system.Conclusion:This work indicates that it is possible to implement and operate a photon counting scheme on an EMCCD based micro‐CT system, suggesting that these devices might be able to operate at very low x‐ray exposures in a photon counting mode. Such devices could have future implications in clinical CT protocols.NIH Grant R01EB002873; Toshiba Medical Systems Corp.

Luminescence evolution from alumina ceramic surface before flashover under direct and alternating current voltage in vacuum

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under a higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.