Assuming in a XRD system we have one sample, but two different sets of diffractometer (including X-ray source and detector). I am wondering, how will the results change (peak intensity, analysing time, etc.) if we increase/decrease the voltage/current of X-ray source?
Please review:
1. LI - http://www.linkedin.com/groupItem?view=&gid=2683600&type=member&item=266592537&qid=937146ab-d093-4560-b414-74702024c6e2&goback=%2Egna_2683600
2. RG - https://www.researchgate.net/post/Bloody_Murder_Why_is_there_nearly_such_a_visceral_response_to_any_disruption_to_alignment_of_existing_diffractometers_by_XRD_users_technicians
These are two images where two different diffractometers producing conventional linear diffractograms are compared:
Figure 1: http://www.flickr.com/photos/85210325@N04/10885954484/lightbox/
Figure 2: http://www.flickr.com/photos/85210325@N04/10888339173/lightbox/
http://www.flickr.com/photos/85210325@N04/10885954484/lightbox/
Qualitatively - no change, i.e. maxima will still have the same theta or d(hkl) values and approximately the same relative intensities.
Quantitatively, with increased I or U of source, intensity of the primary beam is also increased (approx. linearly with I, approx. quadratically with U). So with the same exposition/scanning rate I/sigma(I) will be better.
Quantifiable variables include i-Current (mA), V-Voltage (kV), I-Relative Intensity (A.U), SNR - Signal to Noise Ratio, BG-Back-Ground Signal, cps-count per second (Absolute Intensity).
Generally, as the Power Level (i.V) increases:
a. cps will increase.
b. BG would be elevated.
c. SNR will be enhances.
d. Contribution from fluorescence would be elevated.
e. Relative Intensity (I) would remain invariant in the diffractogram. This is the reason internal/external standards are recommended in general for precise XRD analyses.
f. Resolution will be enhanced in reciprocal space due to better SNR.
We would be much obliged if someone could post the relationship of i & V to cps when convenient.
http://www.flickr.com/photos/85210325@N04/10515372183/lightbox/
It would be important to identify the following variables for the source & optics/geometry used as they may affect the cps as well:
1. Diffractometer Diameter. Diffractometer axis to detector surface distance.
2. Incident Beam Conditioning apparatus. e.g., foil filter, monochromator, collimator, slit dimensions.
3. Detector characteristics, detector active input area, sensitivity, gain, dynamic range, slit dimensions etc.
4. Tube temperature. Cooling solution temperature/flow.
5. Target heat dissipation rate. Use of heat-sinks.
An example of micro-focus XRD apparatus and the factors involved:
http://www.linkedin.com/groupItem?view=&gid=3614857&type=member&item=153476690&qid=8ce98149-68ec-4c98-8ce9-15db48e4bb21&trk=group_items_see_more-0-b-ttl
http://www.nrl.navy.mil/media/news-releases/2013/nrl-researchers-discover-novel-material-for-cooling-of-electronic-devices?goback=%2Egde_2683600_member_189258615%2Egmr_2683600%2Egde_2683600_member_5810700387807698945%2Egmr_2683600%2Egde_2683600_member_5803264366392401921%2Egna_2683600#%21
Below are examples with a Panalytical X'Pert diffractometer system @ BNL:
1. GaAs (004) Symmetric Reflection XRD Rocking Curve for 40kV/20mA with 0.392 Arc Sec step & 40kV/17mA with 1.569 Arc Sec step, compared:
http://www.flickr.com/photos/85210325@N04/8446683472/sizes/l/in/set-72157632728949610/
http://www.flickr.com/photos/85210325@N04/8001095415/in/set-72157632729013664
Happy Thanksgiving! Goble.. Goble!
Uh oh! I smell the "basturi" (scalpel) of Matteo Leoni and I love it! I better work on improving my behavior besides my content.
I'll be posting details of how the data changes with various diffractometers, step sizes, kV, mA, sampling size, etc. and eagerly look forward to the "master basturist" to help me mold it in to shape.
http://animals.nationalgeographic.com/animals/birds/wild-turkey/
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