1 / 15

Area Detectors

Area Detectors. Like film can detect position Like scintillation detector can measure intensity With modern computers can assign hkl from unaligned crystal Must convert pixel intensity to intensity by some sort of integration. Image Plates.

graham-king
Download Presentation

Area Detectors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Area Detectors • Like film can detect position • Like scintillation detector can measure intensity • With modern computers can assign hkl from unaligned crystal • Must convert pixel intensity to intensity by some sort of integration

  2. Image Plates • Use a phosphor which emits light proportional to x-ray exposure • Very large dynamic range • Very low background • Large input area • Not a “real time” device

  3. Rigaku r-axis

  4. Image Plate Schematic

  5. How IP works

  6. Small Molecule IP

  7. Schematic

  8. CCD Detector • The ccd is a standard camera chip • Need a phosphor to convert x-rays to light • The ccd pixel is a well that converts photons to electrons and stores them. • The wells are read out by shifting to special readout wells and using an a-to-d converter

  9. Schematic of a ccd

  10. Noise • Dark Current—stored electrons from dark exposure • Can reduce dark current by cooling the ccd. • Peltier cooling is frequently used • Readout Noise—from moving pixels to counting registers • Slower the movement the lower the noise

  11. Size • More most 1K ccd chips the pixels are too small. • Use glass taper to expand the face. • Taper introduces a distortion • Pixels still to small. • Binning—fold 4 pixels into 1 • Use large ccd chip 4K

  12. Phosphors • Thickness is important • Too thin and x-rays penetrate • Too thick and emitted photons are re-absorbed • For Mo radiation phosphor is only about 80% efficient

  13. KappaCCD Roughly 1K chip 12 electrons/photon Dark current 0.02electrons/second Read out at 200kHz—noise about 12electrons Pixel size 22.5 x 22.5 micrometers Binned 110 x 110 Readout time about 3 seconds

  14. KappaCCD

  15. Kappaccd

More Related