why the base intensity of some samples start at different level on XRD graph. i mean for some sample base line start at 50 and for some base line starts at 1500 intensity level. Also for some sample the base line start at 1000 and end at 1500 , why it is so ?
It will depend upon the sample type and instrumental settings. There could be many reasons: If there is a lot of scattering rather than coherent diffraction then the background will be elevated. Poorly crystalline material will scatter rather than diffract well and will give higher background. Also if your material contains elements that may fluoresce under the incident beam (e.g. Fe will fluoresce in a Cu Ka beam) then this will also cause the backgrounds to be higher; this can also cause backgrounds to rise rather than fall. We have a knife edge installed as we use a position sensitive detector; the height of the knife edge can cause the low angle background to vary in intensity. If your beam is too broad then it might be hitting the sample holder and you will get scattering from that and cause the low angle background to rise. As has been mentioned by Weiran Zheng slit size and count time will indeed have an effect on the base level.
Tell us more about your system, post some diffractograms.
I got the similar problems before I figured out that the baseline intensity is determined by the intensity of your X-ray. Sometimes, people just forget to change the scattering slit at the end of the X-ray as shown in the picture, or some people forget to check the output intensity. Also, if you didn't use the same scan rate, it would change the intensity of your baseline. But I am not sure about the case that the intensity changes from 1000 to 1500.
It will depend upon the sample type and instrumental settings. There could be many reasons: If there is a lot of scattering rather than coherent diffraction then the background will be elevated. Poorly crystalline material will scatter rather than diffract well and will give higher background. Also if your material contains elements that may fluoresce under the incident beam (e.g. Fe will fluoresce in a Cu Ka beam) then this will also cause the backgrounds to be higher; this can also cause backgrounds to rise rather than fall. We have a knife edge installed as we use a position sensitive detector; the height of the knife edge can cause the low angle background to vary in intensity. If your beam is too broad then it might be hitting the sample holder and you will get scattering from that and cause the low angle background to rise. As has been mentioned by Weiran Zheng slit size and count time will indeed have an effect on the base level.
Tell us more about your system, post some diffractograms.
Apart from above expert (Dr Ian and Dr Weiran):
For same instrument configuration than it came from ur sample (bulk or powder, amorphous content, fluorescence, chemical compound, particle size etc).
For same sample and same instrument configuration than it's ur scan time; the longer the scan time the higher the intensity.
For instrument configuration; intensity is related to tube power (usually current), div. slit size, soller slit size, beam mask size, stage mode (reflection or transmission), anti scatter slit size, receiving slit size, monochromator, beta filter thickness, absorber thickness and detector mode.
The size of the sample may make a difference as well as the exposure time. Also in cases where a binder is used to hold the sample particles together its effect on the scattering will vary the base line intensity.
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