Thanks for the interesting subject. It is really informing and very helpful to improve instrumental resolution. P.S. Julian, ever tried additional SAXS experiments changing several parameters to optimize your setup? Did you get same data on Synchrotron or taking neutron diffraction patterns with the same angles range, and setup? May it improve your results? As far as I see you are at the ILL so I guess won't be a problem to try these comparisons too. In my experience, Sometimes at low angles, commercial instruments just won' t get much improvement nonetheless the accuracy of the setup used. At low angles SAXS instruments are better than XRD in peak to noise ratio, in my experience
On Sunday, 6 March 2016, iangie <ian...@126.com> wrote: > 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 <http://u.163.com/signature> > On 03/06/2016 19:46, Julian Richard Tolchard > <javascript:_e(%7B%7D,'cvml','julianrichard.tolch...@sintef.no');> 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 > <javascript:_e(%7B%7D,'cvml','rietveld_l-requ...@ill.fr');> [ > rietveld_l-requ...@ill.fr > <javascript:_e(%7B%7D,'cvml','rietveld_l-requ...@ill.fr');>] on behalf of > Shay Tirosh [stiro...@gmail.com > <javascript:_e(%7B%7D,'cvml','stiro...@gmail.com');>] > *Sent:* 06 March 2016 10:51 > *To:* rietveld_l@ill.fr > <javascript:_e(%7B%7D,'cvml','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 > <javascript:_e(%7B%7D,'cvml','stiro...@gmail.com');> > _________________________________________________ > > -- Sent from Gmail Mobile
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