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Area x-ray detector based on a lens-coupled charge-coupled device
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Image of FIG. 1.
FIG. 1.

Detector schematic. The top portion of the figure shows a cutaway view of the detector. The x-ray image, converted to visible light in the phosphor screen, is projected onto the CCD via a camera lens. The extension tube adjusts the distance from the lens to the CCD, allowing the image magnification factor to be changed. The CCD is contained within a hermetically sealed camera housing and cooled via a thermoelectric module (not shown). The bottom portion of the figure shows the mechanical fixture that supports the phosphor mounting tube from the CCD camera baseplate. This fixture allows micrometer adjustment of the phosphor position relative to the camera in order to achieve best focus. The detector assembly is approximately 30 cm in length when using the Sigma lens.

Image of FIG. 2.
FIG. 2.

Selected image areas of point illumination of the detector through a array of holes. Six of the holes, on a 1 mm pitch, are seen in each section. Images in the left column are taken from the central portion of the full image whereas the images in the right column are from the upper right corner. (), () Central and upper right portions, respectively, of image using the Sigma lens at demagnification. The comet-tail spreading of the spots in () is indicative of coma in the lens system. (), () Images from the detector using the Nikon lens at demagnification. Considerably more coma is seen compared to the Sigma lens. (), () Images from the detector using the Canon lens at demagnification. While the spots in the central region are sharp, the coma in the corners has spread the signal almost uniformly between the 1 mm spaced spots. (), () Images from the detector using the Canon lens in conjunction with 2 Canon 500D closeup attachments at demagnification. The central portion shows narrow spot surrounded by a wide halo spreading at the level of several percent. Coma has improved considerably from that in (). (), () Images taken using the lens configuration of () but with a 1 mm shift in the position of the phosphor plane. Note the spread of the spots at low level in () has reduced from that in (), but the FWHM is greater.

Image of FIG. 3.
FIG. 3.

Long range image flare from an extended source of illumination. Half the detector was placed under uniform x-ray illumination with the other half obstructed with a knife edge. Shown is the intensity of the signal spreading under the knife edge as a function of distance from the edge, both for this lens-coupled detector and a fiber-optically based detector constructed within our laboratory (see Ref. 15). Intensities are normalized to the intensity per pixel in the illuminated area. Both detectors exhibit similar behavior within 0.2 mm of the knife edge where the spread is dominated by the short length-scale point spread function. At longer length scales, the lens system shows a slowly varying scattering level on the order of one percent caused by reflections in the system. The spreading in the fiber-optic system comes from light scattering in the phosphor layer as well as incomplete absorption of light escaping the central cores of the optical fibers.

Image of FIG. 4.
FIG. 4.

DQE vs. dose for spot illumination by 8 keV x rays in the center (inverted closed triangles) and near the corners (closed circles) of the detector. Data was obtained using the Sigma lens at reduction. The dashed lines are fits to the data using a simple three parameter fit to the recorded noise in the image. The dash-dotted lines are lines of constant accuracy (noise/dose) at the levels indicated. A fixed system read noise limits the curves at low dose. Falloff at high dose, along lines of constant accuracy, is indicative of a fixed-pattern systematic noise. Also included is a curve obtained with a fiber-optic system (open circles) using the same test procedure (see Ref. 15).

Image of FIG. 5.
FIG. 5.

Small angle powder diffraction from lamellar phase sample of silver stearate . This one dimensional phase yields equally spaced, concentric diffraction rings. The beam in the center of the pattern is blocked by a circular beam stop. The first order ring is just outside the stop. The faint arcs on the right of the image are due to hydrocarbon chain packing in the direction transverse to the lamellar stacking. This image is the sum of seven 200 s exposures with a sample to detector distance of 10.4 cm. The image is displayed on a nonlinear scale to allow more of the diffraction features to be seen.

Image of FIG. 6.
FIG. 6.

Radial intensity of the small angle powder diffraction image of Fig. 5. The intensity was azimuthally averaged as a function of distance from the center of the diffraction rings. Note the intensity of the eight lamellar diffraction peaks span 3 orders of magnitude per pixel, with the signal in the 8th diffraction order arriving at per pixel. Negative values in distance correspond to pixels in the left half plane of Fig. 5 (relative to the beam), with positive values to the right of the beam. Values near pixel zero in this figure are shadowed by the beam stop.


Generic image for table
Table I.

Detector characterization.

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Table II.

Sensitivity and uniformity of response.

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Table III.

Point spread function.a


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Area x-ray detector based on a lens-coupled charge-coupled device