Dose Calculation When Using CCD Cameras

(For Titan 4Kx4K CCD,  gif CCD & CM200CCD)

  1. After final alignments, prepare to take a CCD image
  1. make sure all scope settings are what will be used to shoot images. i.e. spot size, beam diameter etc. beam diameter needs to be large enough to cover the CCD camera and beam should be parallel
  2. use a mag. high enough that the hole covers the entire CCD camera                
  3. use Expose and Acquire modes with  settings of Full Camera, bin=1
  4. any integration time may be used, but if 1 sec is not used, remember to do the conversion to change        to a dose rate of e-/Å/sec
  5. Make sure Results window is open        
  1. Shoot a CCD image with no specimen (hole with no ice, broken square, etc.)                
  1. Check quality of image. Should be smooth, without features, medium grey levels.
  2. If over or underexposed, change integration time
  3. If stitched together quadrants of CCD camera are too obvious, acquire new Dark and Gain references or linearization                
  1. Find Mean Counts number (this is NOT e-)        
  1. Left click on image
  2. Click Analysis in top menu
  3. Click Statistics
  4. Click Mean and STD
  5. The Mean Counts will now be displayed in the Results window        
  1. Find Pixel size for this camera and magnification        
  1. Right click on image
  2. Small Image Display menu will pop up
  3. Click Image Display                 
  4. Under Image sub menu, Click Info
  5. A new screen will come up with Image information. Look for Pixel size displayed in Nanometers. i.e., 0.51nm x 0.51nm        
  1. Convert Mean Counts to Mean e-        
  1. Divide Mean Counts by Counts per electron ratio for the CCD camera (Posted)        
  1. Titan 4K camera = 9.86 counts per electron
  2. Titan 2k camera (GIF) = 6.3 counts per electron        
  1. This equals total mean electrons        
  1. Convert Mean e- to Dose Rate                
  1. Divide Mean e- by Pixel size in Å2
  2. Divide by Integration time for e-/Å2/sec= Dose Rate