Image Intensified CCD Camera Research Articles

Relationship between radar cross section and optical magnitude based on radar and optical simultaneous observations of faint meteors

Radar and optical simultaneous observations of meteors are important to understand the size distribution of the interplanetary dust. However, faint meteors detected by high power large aperture radar observations, which are typically as faint as 10 mag. In optical, have not been detected until recently in optical observations, mainly due to insufficient sensitivity of the optical observations. In this paper, two radar and optical simultaneous observations were organized. The first observation was carried out in 2009–2010 using Middle and Upper Atmosphere Radar (MU radar) and an image-intensified CCD camera. The second observation was carried out in 2018 using the MU radar and a mosaic CMOS camera, Tomo-e Gozen, mounted on the 1.05-m Kiso Schmidt Telescope. In total, 331 simultaneous meteors were detected. The relationship between radar cross sections and optical V-band magnitudes was well approximated by a linear function. A transformation function from the radar cross section to the V-band magnitude was derived for sporadic meteors. The transformation function was applied to about 150,000 meteors detected by the MU radar in 2009–2015, large part of which are sporadic, and a luminosity function was derived in the magnitude range of −1.5–9.5 mag. The luminosity function was well approximated by a single power-law function with the population index of r=3.52±0.12. The present observation indicates that the MU radar has capability to detect interplanetary dust of 10−5–100g in mass as meteors.

Two-Dimensional Tomographic Simultaneous Multi-Species Visualization—Part I: Experimental Methodology and Application to Laminar and Turbulent Flames

In recent years, the tomographic visualization of laminar and turbulent flames has received much attention due to the possibility of observing combustion processes on-line and with high temporal resolution. In most cases, either the spectrally non-resolved flame luminescence or the chemiluminescence of a single species is detected and used for the tomographic reconstruction. In this work, we present a novel 2D emission tomographic setup that allows for the simultaneous detection of multiple species (e.g., OH*, CH* and soot but not limited to these) using a single image intensified CCD camera. We demonstrate the simultaneous detection of OH* (310 nm), CH* (430 nm) and soot (750 nm) in laminar methane/air, as well as turbulent methane/air and ethylene/air diffusion flames. As expected, the reconstructed distributions of OH* and CH* in laminar and turbulent flames are highly correlated, which supports the feasibility of tomographic measurements on these kinds of flames and at timescales down to about 1 ms. In addition, the possibilities and limitations of the tomographic approach to distinguish between locally premixed, partially premixed and non-premixed conditions, based on evaluating the local intensity ratio of OH* and CH* is investigated. While the tomographic measurements allow a qualitative classification of the combustion conditions, a quantitative interpretation of instantaneous reconstructed intensities (single shot results) has a much greater uncertainty.

Machining behavior of additively manufactured and cast-wrought nickel-based superalloy (IN 625)

Additively manufactured (AM) and cast-wrought (CW) nickel-based superalloy (IN 625) with known processing history and quasi-static properties have been investigated for their relative machinability, in terms of tool temperature and wear, as well as machining force and chip morphology. Transparent cutting tools were used to cut tubular specimens of both materials. Visible and near infrared radiation emitted by the chip-tool interface was measured through the transparent tool using an image intensified CCD camera. A calibration procedure was used to convert this into apparent blackbody temperature from which the true temperature was inferred using literature values of emissivity of polished IN 625. Machining forces along the cutting and thrust force directions were measured using a dynamometer. Tool wear and chip morphology were characterized by measurement of tool volume loss and by scanning the chip upper side, using a 3D profilometer. It was found that during machining, AM IN 625 behaves differently from CW IN 625 of similar chemical composition. Significant differences in tool temperature, tool wear, and chip formation mechanisms were observed.

Highly Sensitive Detection of Catalase Modified Magnetic Nanoparticle Using Signal-Off ECL Imaging of Multichamber Electrode

Introduction Electrochemiluminescence (ECL) is the chemical luminescence reaction catalyzed by electrochemically active species. In the case of luminol-based ECL, the oxidation of luminol at the electrode and the reactive oxygen species (ROS) as coreactant result in excited intermediate and the release of photon upon relaxation. ECL is used in immunoassay and nucleic acid studies for its advantages such as low background and requiring no external light source. Many of these studies use H2O2 as target or coreactant since many biologically relevant events involve H2O2 and the results are often analyzed by the increase in ECL intensity. Particularly, many enzyme-based ECL that targets H2O2 are reported to date. In this study, catalase enzyme was used to take advantage of its fast turnover rate. However, use of enzymes are sometimes troublesome due to spontaneous reaction upon mixture containing enzyme and its substrate. We addressed this issue by generating substrate for enzyme that utilizes oxygen derivatives at electrode surface by oxygen reduction reaction (ORR). Also, magnetic nanoparticles are used for collection of target species to electrode proximity to elicit concentration effect. Therefore, combination of ORR-ECL and magnetic nanoparticles provide powerful tool for highly sensitive detection system. In this study, we report signal-off ECL using enzyme modified magnetic beads and electro-generated substrate reaction on a small volume multi-chamber screen printed electrode. Materials and Method Catalase enzyme was coupled to NHS modified magnetic nanoparticle (φ200 nm, Tamagawa Seiki) and the absorption spectra and enzyme activity of catalase modified magnetic nanoparticle (CAT-MB) were evaluated using spectroscopic method. For ECL measurement, screen printed electrode with 73 chambers (diameter 200 μm x height 10 μm) was used to limit the reaction volume to about 300 pL. Chambers were filled with solution containing CAT-MB and luminol and magnetic nanoparticles were attracted to the electrode surface using external magnet. Cover glass was placed on top of the electrode chip to cover the chambers to prevent diffusion of enclosed species. The substrate for catalase was electro-generated at the electrode surface. Constant negative potential was applied during the pretreatment time thereby generating ROS. ECL of chambers were recorded with image intensifier and electron magnifying CCD camera mounted on upright microscope. The enclosed catalase enzymes catalyzed H2O2 thus diminish of ECL intensity was observed with increasing magnetic particle concentrations. Electro-generation of ROS species on electrode surface was evaluated with various conditions including electrode pretreatment potential and pretreatment time to control the amount of ROS formed. Results and Discussion Spectroscopic characterization revealed absorbance peak shift from 280 nm to 220 nm from free catalase in aqueous phase to CAT-MB, respectively. Enzyme activity of CAT-MB was found to be lowered by factor of 10 compared to calculated value and the detection limit of CAT-MB was 0.2 μg/mL. The reduced enzyme activity was attributed to the structural modification of catalase molecule during the modification process. ROS electro-generation conditions were investigated by changing the pretreatment potential and time. Starting potential of CV sweep was changed from -1000 to 0 mV with 100 mV interval and the observed ECL intensity showed exponential reduction as the starting potential moved to more positive. Pretreatment time of 20 to 60 seconds were tested at various pretreatment potential and the ECL imaging at -500 mV showed clear difference in brightness at different pretreatment time conditions. The effect of bare magnetic nanoparticles and the use of external magnet on ECL response was also tested. Quantitative ECL imaging analysis using different concentrations of CAT-MB showed that this system can detect 1 ng/mL of magnetic nanoparticle on a multi-chamber chip, and each chamber was estimated to contain average of 5 magnetic nanoparticles. Conclusion In summary, this study successfully developed highly sensitive enzyme modified magnetic particle detection system using the combination of small volume multi-chamber electrode and magnet nanoparticles. Detection was conducted by observing the reduction of ECL signal caused by decomposition of H2O2 electro-generated at the electrode surface by catalase modified on the magnetic nanoparticles enclosed in small chambers. Difference in ECL signal with few nanoparticles as low as average of 5 magnetic nanoparticles in a chamber was detected.

Simultaneous radar and video meteors—II: Photometry and ionisation

Simultaneous radar and video measurements of meteors were made using the Canadian Meteor Orbit Radar (CMOR) and several Gen-III image-intensified CCD cameras primarily to relate radar meteor electron line density, q, to video meteor photon radiant power, I. We find that log10q=log10I+(12.56±0.49) leading to M=(38.7±1.2)−2.5log10q, where M is the meteor magnitude in the Gen-III video bandpass (470–850nm) corresponding to q at the radar specular point. The ratio of the ionisation coefficient to luminous efficiency, β/τI, was estimated from our observations of q/I to functionally depend on speed and radiant power. For our average meteor photon radiant power of I=64W, we find log10β/τI=(3.00±0.62)log10v−(4.27±1.37). By adopting β computed according to Jones (1997), which we approximate as log10β=5.84−0.09v0.5−9.56/log10v (roughly proportional to v4 between 20 and 40km/s), a corresponding estimate of τI for our intensified spectral bandpass was made using our measurements of q/I. We find a peak bolometric value of τI=5.9% at 41km/s. The main uncertainties associated with our analysis are the unknown spectra of individual meteors which affect our estimate of absolute radiant power, and uncertain values of the initial trail radius which makes estimates of q problematic. Our results suggest that the video meteor mass scale is an order of magnitude smaller than previously thought at these higher speeds, and implies that the total meteoroid mass influx between 10−5 and 10−8kg is lower than previous studies would suggest.

A Thomson scattering diagnostic on the Pegasus Toroidal experiment

By exploiting advances in high-energy pulsed lasers, volume phase holographic diffraction gratings, and image intensified CCD cameras, a new Thomson scattering system has been designed to operate from 532 - 592 nm on the Pegasus Toroidal Experiment. The system uses a frequency-doubled, Q-switched Nd:YAG laser operating with an energy of 2 J at 532 nm and a pulse duration of 7 ns FWHM. The beam path is < 7m, the beam diameter remains ≤ 3 mm throughout the plasma, and the beam dump and optical baffling is located in vacuum but can be removed for maintenance by closing a gate valve. A custom lens system collects scattered photons from 15 cm < R(maj) < 85 cm at ~F∕6 with 14 mm radial resolution. Initial measurements will be made at 12 spatial locations with 12 simultaneous background measurements at corresponding locations. The estimated signal at the machine-side collection optics is ~3.5 × 10(4) photons for plasma densities of 10(19) m(-3). Typical plasmas measured will range from densities of mid-10(18) to mid-10(19) m(-3) with electron temperatures from 10 to 1000 eV.

Simultaneous radar and video meteors—I: Metric comparisons

Simultaneous radar and video measurements were made using the Canadian Meteor Orbit Radar (CMOR) and several Gen-III image-intensified CCD cameras to observationally validate metric instrument errors determined through Monte Carlo modelling. We find that our radar interferometry accuracy is ∼0.8° using multiple independent techniques validated with video data. Our average radar–video radiant difference is 3.4°, suggesting that radiant errors for CMOR are dominated by errors in time-of-flight lag time determinations. Our video speeds were found to be consistently lower for slower speed meteors, with our modelled video speed errors following the relation log10δv=−1.64+0.02v. Our modelled video radiant errors had error distributions of 0.73°±0.51°. Errors in the fiducial picks for video meteors were found to be anisotropic, with errors along the meteor trail being larger than those perpendicular to the trail, primarily affecting the fit speed. We also find that the majority of our radar detections occur near the end of the observed video height interval. Our average video speeds are higher than our radar speeds, consistent with decelerations and specular reflections occurring preferentially near the end of trails. Range comparisons show our radar determined specular ranges to be systematically +0.32km farther in range, although this is smaller than the statistical spread. We find 7%±3% of our video events are simultaneously detected by our radar system. This is above the expected 2%–5% range determined through modelling, suggesting our observations are biased towards larger, non-fragmenting meteoroids.

P4-01-03: Establishment and Characterization of an Endocrine Resistance Model In Vitro and In Vivo by Inducible PTEN Knockdown.

Abstract Background Growth factor receptor and estrogen receptor (ER) are two major driving pathways for initiating and sustaining breast cancer (BC) development and progression. We have previously shown that an inverse correlation exists between the PI3K pathway and ER expression/activity in luminal type BCs. High PI3K activation signaling correlates to the luminal B subtype of BC with low ER expression/activity. However, the involvement of the PI3K pathway tumor suppressor PTEN in resistance to endocrine therapy is less clear. Here we attempt to develop an experimental system to better understand the role of PTEN in this resistance. Materials and Methods: Two luminal BC cell lines, MCF7L and ZR75-B, were stably infected with a lentivirus pINDUCER (Meerbrey et al., PNAS, 2011), containing Tet-on responsive shPTEN, turboRFP (tRFP) as an inducible tag, and enhanced GFP (eGFP) as a constitutive expressed tag for positive cells selection. Immunoblotting of PTEN, phosphorylated (p) Akt, pMAPK, pc-Jun, ER, and ER's downstream gene products (PR, IGF-1R) was performed on cells after 6 days of doxycycline (Dox) incubation. After pre-starvation for 5 days in estrogen deprivation (ED) conditions, the cells -/+ Dox were subjected to induction with estrogen (E2) or to endocrine treatment [continued ED, tamoxifen (Tam, 10–7M), or fulvestrant (Ful, 10–7M)] in 96-well plate format for 9 days. In situ cell cytometry (Celigo, Cyntellect Inc., San Diego, CA) was applied to count the cell number by scanning the same 96-well plate every other day. Ovariectomized nude mice bearing MCF7L-shPTEN xenografts, established in the presence of E2 supplementation, were randomized to minus and plus Dox groups, with each treatment group continuing E2 or endocrine therapies (ED, Tam, or Ful). The in vivo GFP/RFP imaging was performed with a home-built cooled and image intensified CCD camera system. Results: Immunoblot analysis showed a striking loss of PTEN, and significant upregulation of pAkt, as well as pMAPK and pc-Jun in cells with +Dox. In contrast, levels of ER, PR and IGF1R were reduced in cells with +Dox compared to -Dox. In all -Dox groups, cell growth was significantly reduced in endocrine treated groups compared to the E2 group, whereas +Dox rescued the endocrine treatment growth suppression, especially in ED and Tam groups. In vivo induction of PTEN shRNA expression was confirmed by RFP imaging after feeding the mice with +Dox water. MCF7L-shPTEN xenografts randomized to +Dox under ED conditions continued to grow over 4 weeks, in contrast to the marked regression of control tumors (−Dox) under this endocrine regimen (p&amp;lt;0.05). Comparison between plus and minus Dox groups under E2, Tam, or Ful treatment is ongoing. Discussion: These data further support the existence of crosstalk between PI3K and ER pathways in luminal type BC. Decreasing PTEN levels by shRNA renders the luminal type BC cells de novo resistant to endocrine therapy both in vitro and in vivo. The pINDUCER PTEN knockdown system combined with live animal imaging offers successful real-time, noninvasive tracking of endocrine sensitivity by controllably manipulating the level of target gene. Combination therapies to overcome endocrine resistance under PTEN knockdown conditions are currently underway. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-01-03.

Ultrahigh-speed X-ray imaging of hypervelocity projectiles

High-speed X-ray imaging is an extremely important modality for healthcare, industrial, military and research applications such as medical computed tomography, non-destructive testing, imaging in-flight projectiles, characterizing exploding ordnance, and analyzing ballistic impacts. We report on the development of a modular, ultrahigh-speed, high-resolution digital X-ray imaging system with large active imaging area and microsecond time resolution, capable of acquiring at a rate of up to 150,000 frames per second. The system is based on a high-resolution, high-efficiency, and fast-decay scintillator screen optically coupled to an ultra-fast image-intensified CCD camera designed for ballistic impact studies and hypervelocity projectile imaging. A specially designed multi-anode, high-fluence X-ray source with 50 ns pulse duration provides a sequence of blur-free images of hypervelocity projectiles traveling at speeds exceeding 8 km/s (18,000 miles/h). This paper will discuss the design, performance, and high frame rate imaging capability of the system.

Cavitation Light Emission and Cavitation Erosion

Cavitation bubbles emit a very weak light due to bubble collapse. It is expected that the light emission may be closely related to cavitation erosion. In order to confirm the relationship between the erosion damage rate and the light intensity, experiments were performed for a water orifice cavitation flow. A circular pipe was used and water-cavitation generated around a column. For the measurement of light intensity, photon-counting method was used. And for visualization, the xenon gas-mixing method was adopted this by use of an image intensifier and chilled CCD camera. The damage rate was estimated by counting the number of damage pits. The light emission occurred around the end of cavitation, but the emission pattern was very different from the shape of the cavitation. The profile of the damage area was very similar to the light emission pattern and the maximum damage rate had a strong relationship with the maximum emission intensity.

Energy-selective neutron transmission imaging at a pulsed source

Energy-selective neutron radiography experiments were carried out at the ISIS pulsed spallation source. This neutron transmission imaging technique combines the hardware used for conventional neutron radiography with the Bragg edge transmission features of time-of-flight methods. The main component of the energy-selective radiography set-up was a gated image-intensified CCD camera that viewed a neutron sensitive scintillation screen via a mirror. Energy resolution was obtained via synchronization of the light-intensifier with the pulse structure of the neutron source. It is demonstrated that contrast enhancement of materials can be straightforwardly achieved, and that microstructural features in metal samples can be directly visualized with high spatial resolution by taking advantage of the Bragg edges in the energy dependent neutron cross sections.

Application of Soft X-Ray Imaging System to the STE-2 RFP

A soft X-ray (SXR) imaging system (consisting of a microchannel plate, a phosphor plate and an image intensifier CCD camera) has been installed in the STE-2 RFP (R/a = 0.4 m/0.1 m) to obtain high-resolution two-dimensional (2-D) SXR images to see if 3-D magnetic structures can be deduced from the 2-D SXR image. The SXR images obtained in standard RFP plasmas have been compared with those in RFP plasmas with different MHD properties. We have identified characteristic structures in the 2-D SXR images depending upon the MHD properties with the present system. Optimization of the image data processing such as noise filtering from the data or tone correction of brightness distribution is also discussed.

OrientExpress: A new system for Laue neutron diffraction

A new automatic Laue neutron diffractometer has been developed at the ILL. The system is composed of a goniometer with two tilt stages mounted on an ω-rotation and a scintillator/CCD neutron detector which is mounted on a 2 θ arm. All movements are computer controlled. The intensified neutron imaging system is unique and allows electronic capture of neutron Laue diffraction patterns in a much shorter time (few seconds) than conventional film-based methods. The detection system is based upon two high-performance image-intensified CCD cameras coupled to a large-area neutron scintillator. The system is also unique in permitting full back-reflection geometry. A gain of about 100 in efficiency is obtained compared to the conventional film method with comparable spatial resolution. Some examples for Laue patterns are presented and compared to those obtained by film. A quantitative analysis of the integrated intensity of the Laue spots is also made.

High intensity solid‐state UV source for time‐gated luminescence microscopy

The unique discriminative ability of immunofluorescent probes can be severely compromised when probe emission competes against naturally occurring, intrinsically fluorescent substances (autofluorophores). Luminescence microscopes that operate in the time-domain can selectively resolve probes with long fluorescence lifetimes (tau > 100 micros) against short-lived fluorescence to deliver greatly improved signal-to-noise ratio (SNR). A novel time-gated luminescence microscope design is reported that employs an ultraviolet (UV) light emitting diode (LED) to excite fluorescence from a europium chelate immunoconjugate with a long fluorescence lifetime. A commercial Zeiss epifluorescence microscope was adapted for TGL operation by fitting with a time-gated image-intensified CCD camera and a high-power (100 mW) UV LED. Capture of the luminescence was delayed for a precise interval following excitation so that autofluorescence was suppressed. Giardia cysts were labeled in situ with antibody conjugated to a europium chelate (BHHST) with a fluorescence lifetime >500 micros. BHHST-labeled Giardia cysts emit at 617 nm when excited in the UV and were difficult to locate within the matrix of fluorescent algae using conventional fluorescence microscopy, and the SNR of probe to autofluorescent background was 0.51:1. However in time-gated luminescence mode with a gate-delay of 5 mus, the SNR was improved to 12.8:1, a 25-fold improvement. In comparison to xenon flashlamps, UV LEDs are inexpensive, easily powered, and extinguish quickly. Furthermore, the spiked emission of the LED enabled removal of spectral filters from the microscope to significantly improve efficiency of fluorescence excitation and capture.

Creeping Discharge and Light Emission Characteristics on Plane Electrodes with Stripe Backside Electrode

Creeping discharge and light emission characteristics in Ne gas for the configuration with plane electrodes on the dielectric plate with a stripe backside electrode have been investigated. In the case of the configuration without backside electrode, discharge inception voltage increased monotonically with increasing gas pressure. For the configuration with a backside electrode discharge inception voltage decreased when the backside electrode became wide. Moreover, it tended to saturate over 30kPa for the configuration with a backside electrode. By observations of discharge using image-intensified CCD camera, discharge developed along the dielectric plane surface at 30kPa on 60kPa, on the other hand, discharge grew in the gaseous space away from dielectric surface. These facts suggest that the effect of backside electrode strongly depends on the their width and gas pressure.

Effect of Nifekalant, a Class III Anti-Arrhythmic Agent, on Ca2+ Waves in Rat Intact Trabeculae

Nifekalant, a class III anti-arrhythmic agent, has been used clinically at serum concentrations of 1-10 micromol/L in patients with ventricular arrhythmias. However, the effect of nifekalant on triggered arrhythmias has not yet been established. Trabeculae were dissected from the right ventricles of 16 rat hearts. The force was measured using a silicon strain gauge, the membrane potential using ultra-compliant microelectrodes, and the regional intracellular Ca2+ ([Ca2+]i) using electrophoretically microinjected fura-2 and an image intensified CCD camera at a sarcomere length of 2.1 microm. Rapid cooling contractures (RCCs) were measured to estimate the Ca2+ content in the sarcoplasmic reticulum. Ca2+ waves and aftercontractions were measured after the induction of reproducible Ca2+ waves. Nifekalant at 1, 10 and 250 micromol/L increased significantly the action potential duration, the peak [Ca2+]i, the developed force and the amplitude of RCCs in a concentration-dependent manner (stimulus interval = 2 s, [Ca2+]o = 0.7 mmol/L, 26.0+/-0.2 degrees C). Nifekalant at 10 and 250 micromol/L increased significantly the velocity of Ca2+ waves with an enhancement of the aftercontractions (stimulus interval = 0.5 s for 7.5 s, [Ca2+]o = 1.8+/-0.1 mmol/L, 22.3+/-0.5 degrees C). Nifekalant, even at a therapeutic concentration, can increase muscle contraction, but may worsen triggered arrhythmias because of the acceleration of Ca2+ waves under Ca2+-overloaded conditions.

High-resolution heavy ion track structure imaging

Radiation action in matter depends on the details of the spatial distribution of energy transfer events on the nanometer scale. In this contribution, we present an instrument for experimental investigation of spatial ionisation patterns of ions in matter. The experimental system is based on a time projection chamber with a parallel drift field, parallel-plate charge and light amplification layers and optical readout with an image-intensified CCD camera (OPtical Avalanche Chamber (OPAC)). The chamber is operated with low pressure gas (4–40 hPa) to achieve a resolution of down to 50 nm in tissue density. Preliminary results of measurements and simulations are presented.

HIGH SPATIAL AND TEMPORAL RESOLUTION OPTICAL SEARCH FOR EVIDENCE OF METEOROID FRAGMENTATION

A digital image intensified CCD camera with an electronically gated image intensifier was used to produce very short duration images of meteors. The observational system employed a 0.40 m F/4.5 Newtonian telescope to obtain high spatial resolution. A second intensified CCD camera was used to yield height information using parallax. At a typical meteor height one pixel (for the vertically oriented system) corresponded to about 1.1 m. A sampling of 59 mainly sporadic meteors was analyzed. There is clear variability from meteor to meteor, with many meteors (nearly 50%) showing only a small amount of wake, while some meteors (approximately 20%) have the off segments completely filled in.

High-resolution heavy ion track structure imaging

Radiation action in matter depends on the details of the spatial distribution of energy transfer events on the nanometer scale. In this contribution, we present an instrument for experimental investigation of spatial ionisation patterns of ions in matter. The experimental system is based on a time projection chamber with a parallel drift field, parallel-plate charge and light amplification layers and optical readout with an image-intensified CCD camera (OPtical Avalanche Chamber (OPAC)). The chamber is operated with low pressure gas (4–40 hPa) to achieve a resolution of down to 50 nm in tissue density. Preliminary results of measurements and simulations are presented.

Measurement of X-ray polarization using optical imaging detector with capillary plate

The performance of the optical imaging capillary gas proportional counter (CGPC) was investigated using polarized X-rays with an energy of 15 keV at SPring-8. The CGPC with a fill gas of Ar+8% CH 4+2% TMA at 1 atm was operated at a gas gain of 15 000. The CGPC was irradiated by a polarized X-ray beam in the center region using a slit of 300 μm×300 μm. Images of single photoelectron tracks were obtained by an image-intensified CCD camera combined with the CGPC through a lens system. The average distance between the starting point and the barycenter for single photoelectron tracks was 1.1 mm. The angular distribution is obtained from the directions of the lines connected between the starting point and the barycenter for each image of the photoelectron tracks. From a least-squares fitting, the modulation factor was 25.1±2.0% for the X-rays with a polarization degree of 99%.