Color X-ray Camera | PNDetector

Description

The Color X-ray Camera (CXC) is PNDetector’s high resolution spectroscopic X-ray imaging system based on an energy dispersive pnCCD detector.

Simultaneous time-, energy- and spatial-resolution
Ultra-fast readout of up to 1,000 fps
Wide energy range (200 eV - 30 keV)
Superior energy resolution for all X-ray events (145 eV for 6 keV)
High count rate of up to 10⁶ stored counts/s
Outstanding quantum efficiency (80% for 500 eV, 90% for 10 keV, 30% for 20 keV)
Several external trigger and sync signals

Full-Field Micro X-ray Fluorescence (FF-µXRF)

The CXC system in combination with a poly-capillary optics provides a spatially resolved elemental image of the sample. This can for example be used to image biological samples. A water flea (daphnia magna) was imaged at the BAM line at the BESSY synchrotron. The internal organs and overall structure of the insect are clearly visible, because the CXC system allows wet, small, unpolished specimens to be analyzed with trace level sensitivity and high position resolution.

Water flea: optical (left) and X-ray image (right); in cooperation with L. Vince, University Gent

With an X-ray source at a high incident angle, the CXC system enables imaging of samples with large topographic features with minimal shadowing. Thus, in places like the eyes on the statue shown below, the traces left behind by ancient paint can be identified. The iron based pigments show up as traces in this area of the statue, along with a lead based pigment in the middle. A flexible imaging system based on the CXC is capable of measuring many different types of samples, from flat, polished specimens, to rough samples with little to no sample preparation.

Phoenician ivory: optical (left) and X-ray image (right); in cooperation with I. Reiche, National Museum Berlin

Summarizing, the FF-µXRF technique satisfies the requirement of artists and archeologists for imaging and analysis of cultural heritage objects. It allows analysts to quickly identify critical areas and hidden structures, with the advantage that the imaging technology is extremely similar to other cameras commonly used for optical, UV-VIS and NIR imaging. The final result is always an image that contains spatial and spectroscopic information.

Polychromatic SAXS

Most Small Angle X-ray Scattering (SAXS) systems require an X-ray source that is monochromatic. Since monochromation is inherently inefficient, these systems require expensive monochromators and high flux X-ray systems. In contrast, with the CXC, no monochromation is required. The resulting X-ray data can be energy filtered or processed to create diffraction patterns or reciprocal space images. As shown in the SAXS images from a sample of silver behenate (AgC₂₂H₄₃O₂), monochromatic SAXS will result in the typical ring pattern (right image). Although the rings are larger in the polychromatic case (left image), the CXC enables energy dependent analysis of the diffraction rings, resulting in a faster measurement with more data and high angular resolution.

Polychromatic SAXS (left) vs. monochromatic SAXS (right); in cooperation with B. Nickel, Ludwig-Maximilians-Universität München

X-ray Micro-Tomography (µCT)

The movie below shows the X-ray micro-tomography measurement of a lavender flower. The flower was rotated in front of the pnCCD and the X-ray transmission images were taken for different angles to create cross-sections of the flower, which were used to recreate a virtual model without destroying the original object.

µCT measurement of a lavender flower

Simultaneous X-ray Fluorescence and Diffraction

Because the pnCCD records both the position and energy of each incoming X-ray photon, high speed, high resolution X-ray diffraction experiments are possible in both transmission and traditional forward scattering modes. At every single point in the image, a full diffraction pattern and fluorescence spectrum can be derived. This is done simultaneously, without monochromation, stage scanning or beam focusing, and the measurements take less than one minute to acquire.

$Fluorescence spectrum and diffraction pattern of a mineral sample$

Fluorescence spectrum and diffraction pattern of a mineral sample

The pnCCD Properties (typical values)

Physical pixel size	48 µm × 48 µm × 450 µm
Number of physical pixels	264 × 264 (69,696) image area 264 × 528 (139,392) in full frame mode
Active area	12.7 mm × 12.7 mm (161 mm²) 12.7 mm × 25.3 mm (321 mm²) in full frame mode
Frame rate	up to 1,000 Hz (264 × 264 pixel)
Pixel readout rate	up to 70 MegaPixels/s
Binning mode	up to 8-fold binning
Windowing mode	24 × 264 pixels (smallest window)
Externally triggerable	yes
Readout noise (rms)	ENC < 3 e^-/pixel at 400 Hz ENC < 4 e^-/pixel at 1,000 Hz
Energy resolution	145 eV for Mn-K_α
Sub-pixel spatial resolution	Δx < 15 µm (rms) for 1 keV X-rays
Charge handling capacity	up to 400,000 signal electrons per pixel
Radiation hardness	up to 10¹⁴ photons/cm² at 10 keV

Other types of pnCCDs are available on request.

pnCCD Camera
1. - Active sensor area of 12.7 mm × 12.7 mm
  - Dimensions of camera head: 120 mm × 212 mm × 80 mm (W × H × D)
  - Model options: beryllium window or vacuum solution
Complete electronic system and data acquisition system
1. - Mountable in 19 inch rack
  - High speed parallel data acquisition
  - Selectable amplifier bandwidth and analog gain for high dynamic range
Full software package for
1. - Camera control
  - Offline data analysis
High precision X-ray optics (optional)
1. - Exchangeable poly-capillary optics
  - Focusing, defocusing and 1:1 with capillary diameters from 15 µm to 30 µm

The pnCCDs are back illuminated, three-phase CCDs on a fully depleted silicon substrate. Their operation is based on the principle of sideward depletion and on transfer registers formed by pn-junctions. The outstanding characteristics include a homogeneous and thin photon entrance window leading to high quantum efficiency values between 100 eV and 20 keV and an excellent radiation hardness as well as high charge handling capacity.

Schematic cross section through a pnCCD

The CXC system is equipped with a 264 × 264 pixel pnCDD with a physical pixel size of 48 µm × 48 µm and an imaging area of 161 mm². The on-chip electronics in combination with a fully column-parallel readout enables low noise operation below 3 e^-/pixel (ENC), and frame rates of up to 1,000 Hz. Due to the advanced detector design, the internal potential distribution of the pnCCD can be adjusted by the operation voltages depending on the requirements of the individual experiments. Thus, excellent energy resolution (145 eV for Mn-K_α) and high spatial resolution modes (Δx < 15 µm) are available, as well as high charge handling capacity (up to 400,000 e^- per pixel), and anti-blooming modes for handling extremely high amounts of signal charges.

Spectroscopic performance
Excellent elemental information between 200 eV and 30 keV with an energy resolution of 145 eV (FWHM) at 5.9 keV (Mn-K_α) and 83 eV at 277 eV (C-K).
Spectrum of a radioactive ⁵⁵Fe source

Spectroscopic measurement of the carbon K-line at an energy of 277 eV
Quantum efficiency
High quantum efficiency of > 80% in the range of 2 keV to 20 keV due to back-illumination and optimized X-ray entrance window.
Quantum efficiency of the pnCCD
Ultra-fast readout and excellent signal-to-noise ratio
Standard full frame rate of 1,000 fps, up to 8,000 fps using windowing and binning. Excellent signal-to-noise ratio even at high readout speeds with < 4e^- at 1,000 fps.
High dynamic range
Inimitable single photon sensitivity (left image) and high intensity imaging (right image) with 400,000 e^- per pixel (corresponding to 10³ photons with an energy of 1 keV) at the same time.
Single photon (left) and high intensity images (right)