Echo
reducing tube power just reducing intensity which reduces your peak height 
together with the background level. It won't help on the peak to background 
ratio.


What you need to improve is the beam path. When    I was checking the low angle 
beam path, I measured the stage/goniometer dimensions and draw the beam path in 
AutoCAD. And I can calculate the footprint length of illuminated sample 
FP=Rα/Sinθ, where R=goniometer radius; α=divergence slit angle in rad; θ is 
half 2theta. With this equation I can calculate what divergence slit width 
should I use at what θ angle to make sure the beam is not exceed the sample 
area.
If you have a motorised divergence slit, it is highly recommended to use the 
variable divergence slit mode which gradually opens the beam divergence 
(theta-compensating) and guarantees that the FP on sample is constant. With 
this mode, you won't have directe beam on detector.


As Julian mentioned, a knife edge hovering above sample could largely reduce 
air scattering. Anti-scattering slit is not that useful at low angle for PSD.


Cheers,
Tony


发自 网易邮箱大师
On 03/06/2016 19:46, Julian Richard Tolchard wrote:
Shay,

Can we assume you are working with a reflection mode instrument?

You have two primary sources of background - the primary beam hitting the 
detector directly, and x-rays scattering from the air rather than the sample.

The first of these you control with the divergence slits, but really shouldn't 
be a problem until you go below 4-5 degrees. If you do scan from those sorts of 
angles, set the divergence slits to ~0.1 degrees to keep the beam on the 
sample. I haven't tested it myself, but you could also try reducing the 
detection window on the LynxEye if you want to go to really low angles (<2 
degrees).

The air scatter can be reduced with a special screen/knife that you should have 
received with the instrument, and correctly aligned it will reduce a lot of the 
background increase you see below 10-15 degrees 2-theta. There should be some 
instructions in the instrument manual about this. Using a smaller divergence 
slit (and a receiving slit if you have the option) will also reduce the 
background from airscatter.

I don't think that lowering the tube power will help very much,


jools






 

From:rietveld_l-requ...@ill.fr [rietveld_l-requ...@ill.fr] on behalf of Shay 
Tirosh [stiro...@gmail.com]
Sent: 06 March 2016 10:51
To:rietveld_l@ill.fr
Subject: Aking for Advice - reduce the current to X-ray tube to avoid director 
saturation at low angels


Dear Rietvelders


I would like to avoid director saturation (we have a LYNXEYE detector) when I 
work at low angles (lower then 10deg).
I thought it would be good to lower the current tube to reduce the current. say 
to 35mA instead of 40mA.
Can you please comment on problems it should encounter?
Can I correct problems by slowing down my scanning time?


Thank you from advance
Shay



--

_________________________________________________
 
Dr. Shay Tirosh
Institute for Nanotechnology & Advanced Materials
Bar Ilan University 
Ramat Gan, 52900
Israel
Phone: +972-(0)30-531-7320
Mobile: +972-(0)54-8834533
Email: stiro...@gmail.com
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