Hi Robert Exactly! If installed properly, it doesn't affect anything except the background. I had a nice spreadsheet setup to give me knife heights vs divergence vs maximum 2T value to make sure that I don't run into forbidden teritory.
I dispute your assertion that a knife wouldn't be necessary if the optics worked properly. As far as I know, the only way to get rid of air scatter would be to evacuate the beam path. I'm currently doing some experiments with an old knife setup on a D8, and I'm getting some funny bumps at low angle, but in my experience with a newer know setup, that is due to a divergence that is too big. I'll see if I can put something together. Matthew On 30 Jul 2015 2:04 pm, "Dr. Robert Möckel" <r.moec...@hzdr.de> wrote: > Hi Matthew, > > what you mentioned earlier is not completely correct: > > An anti-air scatter (or beam knife) does not only reduce background > (mainly at low angles), but also cuts intensity at higher 2theta values, if > not installed correctly. It does not result in a sample displacement error, > it just cuts intensity as it cuts off the beam like you mentioned. > This is also an relatively easy issue to modell, I even managed to put it > into an excel-file to calculate the max. 2theta angle that can be measured > at a certain knife height and detector length. BGMN "handles" this properly > as well. Nowadays, there are even knifes available that move vertically, > depending on the actual 2theta value. > > In general, a beam knife would not be necessary if the optics worked > properly, i.e. the optical path is not disturbed or diffracted or > fluorescence would not be generated somewhere in the beam path. Basing on > our experience, the main source of these unwanted X-rays are within or > close to the tube itself, making it hard to suppress it effectively. > All these things result in some strange background phenomena at low angles > (bumps/edges...). We discussed these issues with Reinhard Kleeberg and > others for a while. It seems to be a serious problem in modern devices, as > we experienced this on our own PANalytical and other (Bruker) devices from > colleagues. > > Regards, > > Robert > > > > , 30 Jul 2015 11:53:15 +0800 schrieb Matthew Rowles <rowle...@gmail.com>: > >> Hi Jilin >> >> You could probably add a note to your input file. >> >> Not everything you use in your hardware can be either properly modelled, >> or >> influence the pattern significantly. Do you need to model the anti-scatter >> slits? They help reduce background. >> >> One thing that could happen is that if the knife is set up incorrectly, it >> will cut off the beam, shifting the centroid of diffraction. That may >> mimic >> a sample displacement type error. >> >> Re your comment about double-digit results. Are you talking about the >> quant >> results given in the GUI? The actual answer is going to be a lot less >> precise than that. >> >> >> Matthew >> >> >> >> >> >> >> >> >> >> On 30 July 2015 at 09:19, ji zhang <jilin_zhang_hous...@yahoo.ca> wrote: >> >> >>> >>> Matthew >>> >>> I was thinking shouldn't we be able to input some parameters to reflect >>> this hardware configuration in the program? >>> >>> I forgot that I had asked the same question in2007 in this list. Nobody >>> seemed to care enough except Dr Bergmann. Then I went to do log analysis, >>> and this thing is completely forgotten. >>> >>> Currently we have topaz where I can't find a way to circumvent this yet >>> or >>> to handle this as I called it. I am thinking we may need a copy of bgmn. >>> Certainly both give double digit results (albeit not the same) and both >>> look accurate. >>> >>> >>> >>> Sent from Yahoo Mail for iPhone <https://yho.com/footer0> >>> >>> On Jul 29, 2015, 5:56:41 PM, Matthew Rowles wrote: >>> >>> Hi >>> >>> What do you mean by "handle it"? >>> >>> If the knife edge is correctly set up, the only thing that should change >>> is the background. >>> >>> Matthew Rowles >>> On 30 Jul 2015 3:04 am, "ji zhang" <jilin_zhang_hous...@yahoo.ca> wrote: >>> >>> >>>> About ten years ago, I was working on a D4 with lynx eye, had to put an >>>> air scatter blocker 1 or 2 mm above the powder sample. In the >>>> beginning, I >>>> had to put simple geometry into the bgmn configuration sav-file until Dr >>>> Bergmann put a parameter airscatter=#. >>>> >>>> Now I came back to the business with a D8 with lynx eye; is there >>>> anybody >>>> here willing to share the experience of handling it in TOPAZ? >>>> >>>> thanks >>>> >>>> Jilin zhang >>>> >>>> Sent from Yahoo Mail for iPhone <https://yho.com/footer0> >>>> >>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>>> Please do NOT attach files to the whole list >>>> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body >>>> text >>>> The Rietveld_L list archive is on >>>> http://www.mail-archive.com/rietveld_l@ill.fr/ >>>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>>> >>>> >>>> >>>> > --- > Dr. rer. nat. Robert Möckel > Diplom-Mineraloge > Helmholtz-Institut Freiberg für Ressourcentechnologie > Tel.: +49 (0) 3731 39 2079 > Helmholtz-Zentrum Dresden-Rossendorf > Halsbrücker Str. 34 | 09599 Freiberg > http://www.hzdr.de/hif | r.moec...@hzdr.de > Vorstand: Prof. Dr. Dr. h. c. Roland Sauerbrey | Prof. Dr. Dr. h. c. Peter > Joehnk | VR 1693 beim Amtsgericht Dresden >
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
