X-ray CCD Camera Research Articles

XRISM: X-ray imaging and spectroscopy mission

The X-Ray Imaging and Spectroscopy Mission (XRISM) is a JAXA/NASA X-ray observatory with collaboration from ESA and several institutes and academic institutions worldwide. It is proposed to fulfill the promise of high-resolution X-ray spectroscopy with imaging once realized but unexpectedly terminated by a mishap of ASTRO-H/Hitomi. XRISM carries two sets of X-ray mirror assemblies and is equipped on the focal plane with a [Formula: see text] pixelized X-ray micro-calorimeter array and an aligned X-ray CCD camera. With the combination of high-resolution spectroscopy imaging and the broader field of view, XIRSM is expected to pioneer a new horizon of the Universe in X-ray astrophysics. Aiming to launch the satellite in the Japanese Fiscal Year 2022, we fabricate the instruments and test for the satellite integration starting at the beginning of 2022. This paper reports the development status, reviewing the science objectives and the operation plan.

Screening and selection of XRISM/Xtend flight model CCD

X-ray Imaging Spectroscopy Mission (XRISM) is the next Japanese X-ray astronomical satellite to be launched in 2021 Japanese fiscal year. We are developing one of the XRISM instruments “Xtend”, which is an X-ray CCD camera combined with an X-ray telescope, and achieves the wide field of view of 38′×38′ in 0.4–13keV. In 2019, twelve flight-model (FM) candidate CCD chips were fabricated by Hamamatsu Photonics K.K. We conducted screening experiments to examine whether the FM candidates met requirements for the Xtend CCDs, and selected the four FM chips from them. We constructed a screening system, with which we can examine various CCD performances by illuminating characteristic X-ray lines in a ∼0.5–14keV band or optical lights. With this system, all the twelve candidates were confirmed to satisfy the requirements. We then selected four chips with the best performance, in terms of e.g., their charge transfer inefficiencies, energy resolutions, soft X-ray sensitivities, and optical light leakages. In this paper, we report an overview of the screening system, and procedures and results of the screening process.

Self-contraction process and hot spot formation in the SHOTGUN III-U divergent gas-puff Z pinch

A divergent gas-puff Z pinch has been devised for the realization of an efficient soft x-ray point source. In this device, a divergent hollow annular gas puff is ejected outward from the surface of the inner electrode, and the plasma is compressed three-dimensionally to generate a soft x-ray point source. In the SHOTGUN III-U device at Nihon University, the power supply was enhanced, and experiments were conducted over a larger current range. The peak current at the charging voltage of −25 kV was −190 kA. Ar was used as the discharge gas. The self-contraction process of the plasma was investigated in detail using a gated camera. Near the peak current, local contraction occurred in front of the inner electrode. The contraction velocity of the plasma was 5.5 × 104 m/s. As the plasma contracted, the discharge current decreased. The energy input was analyzed by induction acceleration. The net input energy was found to be 750 J, which corresponded to 13.3% of the stored energy of the capacitor, 5630 J. The soft x-ray source was observed using a soft x-ray CCD camera. A point source was observed 7 mm in front of the inner electrode. The size of the source was 35 µm in the axial direction and 14 µm in the radial direction.

Soft X-ray radiation from C3H8 and N2 discharges in the divergent gas-puff z pinch

The soft X-ray point radiation source in the “water window” was studied using a divergent gas-puff z pinch. C3H8 and N2 were used as discharge gases. C VI (3.373 nm) and C V (4.027 nm) were observed in the C3H8 discharge. Hot spots were observed using a soft X-ray CCD camera. The FWHM size of the hot spot in the C3H8 discharge was 120 μm in diameter and 460 μm in length. An m = 1 mode instability occurred in the N2 discharge. The hot spot was inclined from the central axis, and the FWHM size was 190 μm in diameter and 770 μm in length.

Towards Poisson noise limited optical pump soft X-ray probe NEXAFS spectroscopy using a laser-produced plasma source.

We present a laboratory setup for near edge X-ray absorption spectroscopy (NEXAFS) in the soft X-ray regime between 284 eV to 1303 eV with a resolving power of up to 1370. Based on a laser-produced plasma source, a pair of identical reflection zone plates and an X-ray CCD camera, the setup is intended for optical pump X-ray probe NEXAFS measurements with a detectable change in absorption of the excited sample down to 10-4 and 500 ps time resolution. Because of the high stability of the source the statistical error only depends on the detector response and the number of photons detected and can reach the detector noise limit after a couple of thousands single shots. Thus, structure-function relationship investigations of bio-molecules are rendered feasible in the laboratory.

Radiation hardness of a p-channel notch CCD developed for the X-ray CCD camera onboard the XRISM satellite

We report the radiation hardness of a p-channel CCD developed for the X-ray CCD camera onboard the XRISM satellite. This CCD has basically the same characteristics as the one used in the previous Hitomi satellite, but newly employs a notch structure of potential for signal charges by increasing the implant concentration in the channel . The new device was exposed up to approximately 7.9 × 1010 protons cm−2 at 100 MeV . The charge transfer inefficiency was estimated as a function of proton fluence with an 55Fe source. A device without the notch structure was also examined for comparison. The result shows that the notch device has a significantly higher radiation hardness than those without the notch structure including the device adopted for Hitomi. This proves that the new CCD is radiation tolerant for space applications with a sufficient margin.

Development of X-ray CCD camera based X-ray micro-CT system.

Availability of microfocus X-ray sources and high resolution X-ray area detectors has made it possible for high resolution microtomography studies to be performed outside the purview of synchrotron. In this paper, we present the work towards the use of an external shutter on a high resolution microtomography system using X-ray CCD camera as a detector. During micro computed tomography experiments, the X-ray source is continuously ON and owing to the readout mechanism of the CCD detector electronics, the detector registers photons reaching it during the read-out period too. This introduces a shadow like pattern in the image known as smear whose direction is defined by the vertical shift register. To resolve this issue, the developed system has been incorporated with a synchronized shutter just in front of the X-ray source. This is positioned in the X-ray beam path during the image readout period and out of the beam path during the image acquisition period. This technique has resulted in improved data quality and hence the same is reflected in the reconstructed images.

Detailed calibration of the PI-LCX:1300 high performance single photon counting hard x-ray CCD camera**Project supported by the Science Foundation of China Academy of Engineering Physics (Grant Nos. 2013A0103003 and 2012B0102008) and the National High-Tech Inertial Confinement Fusion Committee of China.

X-ray charge-coupled-device (CCD) camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode (model: PI-LCX: 1300) are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 keV with good energy resolution (E/ΔE ≈ 100 at 60 keV). The difference in detection efficiency between two CCD cameras is small (5.6% at 5.89 keV), but the difference in fraction of the single pixel event between them is much larger (25% at 8.04 keV). The obtained small relative error of detection efficiency (2.4% at 5.89 keV) makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 keV–30 keV.

X線CCDカメラによる全視野型蛍光X線定量イメージングに関する基礎的検討

フォトンカウンティングを用いたラボレベルでの全視野型蛍光X線イメージング装置を試作し，その性能を確認した．エネルギー分解能は142 eV @ Fe Kα，空間分解能は有効ピクセルサイズが2 binのとき52 μm @ Fe Kαとなり，それぞれエネルギー分散型検出器，微小部蛍光X線分析装置と同程度の性能を示した．また，プリント基板試料に対して多元素同時イメージングが可能であることを示した．全視野型XRFイメージング法はいまだに定量法が確立されていないが，Ni標準試料を用いた補正式をXRF強度に適応することでNiの定量化を検討した．X線CCDカメラの各ピクセルの強度から検量線を作成してR2値を評価したところ，その精度は良好だった．統合的な一つの検量線を全ピクセルに適応させることができ，本手法により全視野型蛍光X線イメージング装置において定量イメージングが可能であることが確認できた．

High-resolution X-ray CCD camera based on the first generation image intensifier

High-resolution X-ray CCD camera based on the first generation image intensifier

Calibration of scintillation-light filters for neutron time-of-flight spectrometers at the National Ignition Facility.

Sixty-four neutral density filters constructed of metal plates with 88 apertures of varying diameter have been radiographed with a soft x-ray source and CCD camera at National Security Technologies, Livermore. An analysis of the radiographs fits the radial dependence of the apertures' image intensities to sigmoid functions, which can describe the rapidly decreasing intensity towards the apertures' edges. The fitted image intensities determine the relative attenuation value of each filter. Absolute attenuation values of several imaged filters, measured in situ during calibration experiments, normalize the relative quantities which are now used in analyses of neutron spectrometer data at the National Ignition Facility.

Development of low-noise high-speed analog ASIC for X-ray CCD cameras and wide-band X-ray imaging sensors

We report on the development and performance evaluation of the mixed-signal Application Specific Integrated Circuit (ASIC) developed for the signal processing of onboard X-ray CCD cameras and various types of X-ray imaging sensors in astrophysics. The quick and low-noise readout is essential for the pile-up free imaging spectroscopy with a future X-ray telescope. Our goal is the readout noise of 5e−r.m.s. at the pixel rate of 1Mpix/s that is about 10times faster than those of the currently working detectors. We successfully developed a low-noise ASIC as the front-end electronics of the Soft X-ray Imager onboard Hitomi that was launched on February 17, 2016. However, it has two analog-to-digital converters per chain due to the limited processing speed and hence we need to correct the difference of gain to obtain the X-ray spectra. Furthermore, its input equivalent noise performance is not satisfactory (>100μV) at the pixel rate higher than 500kpix/s. Then we upgrade the design of the ASIC with the fourth-order ΔΣ modulators to enhance its inherent noise-shaping performance. Its performance is measured using pseudo CCD signals with variable processing speed. Although its input equivalent noise is comparable with the conventional one, the integrated non-linearity (0.1%) improves to about the half of that of the conventional one. The radiation tolerance is also measured with regard to the total ionizing dose effect and the single event latch-up using protons and Xenon, respectively. The former experiment shows that all of the performances does not change after imposing the dose corresponding to 590years in a low earth orbit. We also put the upper limit on the frequency of the latch-up to be once per 48years.

Modeling the spectral response for the soft X-ray imager onboard the ASTRO-H satellite

The ASTRO-H satellite is the 6th Japanese X-ray astronomical observatory to be launched in early 2016. The satellite carries four kinds of detectors, and one of them is an X-ray CCD camera, the soft X-ray imager (SXI), installed on the focal plane of an X-ray telescope. The SXI contains four CCD chips, each with an imaging area of 31mm×31mm, arrayed in mosaic, covering the field-of-view of 38′×38′, the widest ever flown in orbit. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200μm. We operate the CCDs in a photon counting mode in which the position and energy of each photon are measured in the energy band of 0.4–12keV. To evaluate the X-ray spectra obtained with the SXI, an accurate calibration of its response function is essential. For this purpose, we performed calibration experiments at Kyoto and Photon Factory of KEK, each with different X-ray sources with various X-ray energies. We fit the obtained spectra with 5 components; primary peak, secondary peak, constant tail, Si escape and Si fluorescence, and then model their energy dependence using physics-based or empirical formulae. Since this is the first adoption of P-channel BI-type CCDs on an X-ray astronomical satellite, we need to take special care on the constant tail component which is originated in partial charge collection. It is found that we need to assume a trapping layer at the incident surface of the CCD and implement it in the response model. In addition, the Si fluorescence component of the SXI response is significantly weak, compared with those of front-illuminated type CCDs.

Ionization injection effects in x-ray spectra generated by betatron oscillations in a laser wakefield accelerator

Single photon counting techniques were used with an x-ray CCD camera to measure features of synchrotron-like x-ray spectra generated by betatron oscillations of electrons in a laser wakefield accelerator (LWFA) with different injection techniques. Measurements were made using the Hercules laser system at the University of Michigan. With a single stage gas cell, we demonstrate that pure helium gas in our wakefield accelerator will produce spectra with higher critical energies than when helium mixed with nitrogen is used. This result was not evident when a two stage gas cell was used.

FLUORESCENT X-RAY IMAGING WITH PINHOLE CAMERA

Pinhole camera is one of X-ray optics devices. The pinhole camera is used for obtaining the image of synchrotron and laboratory sources, and also as a lens in a method of X-ray fluorescent microscopy. This method allows to obtain information on a spatial distribution of various chemical elements to the areas of several square centimeters with spatial resolution at the level of 50–100 μm. As a rule energy-dispersive two-dimensional CCD cameras are used for imaging. Such cameras are expensive devices and have low sensitivity for X-rays with energy of photons higher than 8 keV. Therefore it is perspective to use for X-ray fluorescent microscopy more effective CCD cameras with a scintillator layer. The purpose of this work consists in development of the device for imaging with secondary fluorescent X-rays by using pinhole as a lens and CCD camera for registration of the X-ray image. The device for obtaining the image of objects in secondary X-rays is developed. The device consists of an X-ray tube, pinhole and CCD camera. The object of research was irradiated with radiation from the X-ray tube and emits secondary X-rays. 100-microns pinhole was used for formation of the image of the object at an entrance window of the CCD camera. Images of a number of the iron springs differing in the sizes are received. It is established that the spatial resolution of the device is about 200 μm at an exposition of 60 s. It is possible to improve permission of the device by increasing in an exposition, optimization imaging conditions and reduction of the pinhole size.

Development of variable-magnification X-ray Bragg optics.

A novel X-ray Bragg optics is proposed for variable-magnification of an X-ray beam. This X-ray Bragg optics is composed of two magnifiers in a crossed arrangement, and the magnification factor, M, is controlled through the azimuth angle of each magnifier. The basic properties of the X-ray optics such as the magnification factor, image transformation matrix and intrinsic acceptance angle are described based on the dynamical theory of X-ray diffraction. The feasibility of the variable-magnification X-ray Bragg optics was verified at the vertical-wiggler beamline BL-14B of the Photon Factory. For X-ray Bragg magnifiers, Si(220) crystals with an asymmetric angle of 14° were used. The magnification factor was calculated to be tunable between 0.1 and 10.0 at a wavelength of 0.112 nm. At various magnification factors (M ≥ 1.0), X-ray images of a nylon mesh were observed with an air-cooled X-ray CCD camera. Image deformation caused by the optics could be corrected by using a 2 × 2 transformation matrix and bilinear interpolation method. Not only absorption-contrast but also edge-contrast due to Fresnel diffraction was observed in the magnified images.

Application of X-ray CCD camera in X-ray spot diagnosis of rod-pinch diode

Application of X-ray CCD camera in X-ray spot diagnosis of rod-pinch diode

Spatial characterization of the focus produced by an EUV Schwarzschild objective

Schwarzschild objectives are used in the EUV spectral range because of their large aperture, high mechanical stability and excellent achromaticity. The large aperture results in a small, theoretically diffraction limited focus diameter with ideal values of below 200 nm with the current configuration. We employed a zone plate with matched numerical aperture (0.19) to image the focus onto an X-ray CCD camera. Emission from high harmonic generation and a liquid-jet laser-plasma were used as light sources. Images at magnifications of about 150-fold were acquired and focus diameters of 300 nm (FWHM) were observed.

Application of variable-magnification X-ray Bragg magnifier to analyzer-based phase-contrast computed tomography

A novel X-ray Bragg magnifier of variable magnification is proposed. Using a Si(220) asymmetric crystal as the Bragg magnifier, we successfully controlled the magnification factor, M, between 0.18 and 5.6 at a wavelength of 0.112 nm. The observed spatial resolution with a fiber-coupled X-ray CCD camera, the pixel size of which was 23 × 23 µm2, was 15 µm at M = 5.6, 50 µm at M = 1, and 250 µm at M = 0.17. The X-ray magnifier was successfully applied to analyzer-based phase-contrast computed tomography for the non-destructive observation of a sample at several magnification factors.

Development and application of variable-magnification x-ray Bragg magnifiers

A novel x-ray Bragg magnifier of variable magnification is proposed. We describe the basic properties of the magnifier based on the dynamical theory of x-ray diffraction, and experimentally investigated its performance at the vertical wiggler beamline BL-14B of the Photon Factory. Using a Si(220) asymmetric crystal as the Bragg magnifier, we successfully controlled the magnification factor, M, between 0.1 and 10.0 at a wavelength of 0.112nm. The observed spatial resolution with an x-ray CCD camera, the pixel size of which was 23μm×23μm, was 10μm at M=10, 50μm at M=1 and 250μm at M=0.17. As a demonstration, we successfully used the x-ray magnifier for computed tomography for the non-destructive observation of a glass tube at several magnification factors.