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Re: Stainless Steel XRF

Dude All Messages By This Member #673 开云体育 Geo, You use XRF filters to remove tube artifacts, Brem, ?and fine tune low energy response. The filters are used in conjunction with the tube voltage and the filter material is tailored for the absorption edge for the analytes you are interested in. ?Putting a 4.8mm block of Al will reduce the 50 kV intensity by a factor 0.6, at 30 kV the beam is attenuated down to 0.2. At 20 kV its gone at 0.012.? The only thing it’s doing is killing your beam intensity (count time) and shape resulting in excitation only by the highest energies.? For looking at a broad band range of elements don’t use a filter. When looking to reduce noise select a filter and beam kV tailored to that material of interest.? Filters are used to maximize the sensitivity to different groups of elements.? They are not thick, they are thin, a couple of um to mils, and are single or layered composite of Al , Ti, Cu, C, Pd, In, etc.? Filters are used to tailor the excitation ?energy range. The filter is designed to absorb x-rays with energies immediately above the absorption edge of the filter material.? Lower energy x-rays and the much higher energy x-rays will make it ?through.? This reduces the Brem just above the absorption edge.? For an Al filter (not a 4.8 mm! but a mil or so), the absorption edge of Al is 1.56 keV so the Ka of the lower Z elements Mg (1.2 keV) and Na (1.0 keV) will be absorbed by filter while the region just above that will have a very low background allowing better sensitivity to elements from Si (1.7 keV) to Ca (3.7) due to the lower brem. Above that the higher energies are unaffected.? The filter is used to help pull up the sensitivity in energy ranges defined by the element’s Z. The ?only thing you are doing with the Al block is reducing the total excitation flux rate, lowering the low energy flux rate and killing the low energy element sensitivity while increasing the count time. Take the Al filter out. ?If you’re getting Sum peaks then attenuate the beam but use the beam current first. ? Dud ? ? toggle quoted message Show quoted text From: [email protected] [mailto:[email protected]] On Behalf Of GEOelectronics@... Sent: Wednesday, February 5, 2020 10:24 AM To: [email protected] Subject: Re: [XRF] Stainless Steel XRF ? " Geo,Why is there ?4.8mm of Al attenuator in the beam path? " ? Two reasons, the first is to selectively block the lowest energies from the tube (to help the detector see less noise at the area of interest below 15keV, then the top layer is to control beam spreading and provide a clear path (1mm hole) for the beam I want to strike the target. ? Some of the same thought went into the Am_X8 to reduce the 13.9 +17.74 but leave the 59.5 pretty much unaffected flux-wise. ? Geo ? ----- Original Message ----- From: Dude <dfemer@...> To: [email protected] Sent: Wed, 05 Feb 2020 00:25:05 -0500 (EST) Subject: Re: [XRF] Stainless Steel XRF ? Geo, Why is there ?4.8mm of Al attenuator in the beam path? ?What is the no collimated diameter of the micro-focus beam on the target? Is it well aligned with the 1mm collimator, if it’s not you’ll have ?a lot of attenuation.? Collimation usually uses 2 ?separated collimators and sometimes one on the detector. ?Start simple, no collimator, no attenuators. Look at the beam diameter at the target plane. Set up the collimation to get the beam diameter you want at the target plane. ?Then move the Detector close to the target say about 1 – 2cm. ?Take a shot using the lowest beam current and look at Dead Time. You should be able to count at 40Kcps and have good resolution and count time.? Play with the beam current. Play with Detector distance to target. Your comment “…allows the sensor to be considerably close to the center of the chamber. Not that? it maters very much” ?What is considerably closer? It matters very much. The beam will expose a small circle on the target that will fluoresce over a solid angle. The flux in is proportional to the flux out. The percentage of that signal your detector will get is directly dependent on the distance from the target and that solid angle. Close up its 1/r, at a distance it falls as 1/r2.? Remember the time distance shielding thing ?Do a sensitivity analysis. What gets the best signal? What changes things the most? – where do I optimize my effort? Is it Distance, geometric angle between beam and detector, collimation, need for attenuator, what size beam spot do I want on the target, what s that get me in count time etc. The problem here is not the difference between a SDD and a SI-PIN it’s the set up geometry and the shield system limiting you to very poor performance. Dud KK7IF ? ? From: [email protected] [mailto:[email protected]] On Behalf Of GEOelectronics@... Sent: Tuesday, February 4, 2020 7:32 PM To: [email protected] Subject: Re: [XRF] Stainless Steel XRF ? ? Yes, the exciter flux is very low. Only 20 uA and in the beam port right now are 3 ea. 1.6mm Aluminum plates (solid) and then a 4.75mm plate with a 1mm hole in the center. I'm please with the clean patterns, even tho slow. This is a Si-PIN, not an SDD.? ? I did machine a new part the other day that connects the Al and Pb? cylinders together, that allows the sensor to be considerably close to the center of the chamber. Not that? it maters very much, as the beam can be positioned anywhere on the floor of the chamber. ? Also today, a trip to the garage yielded a good thick aluminum part that can be turned on the lather to make the lid-liner, With luck, the lid will be finished tomorrow and work on the permanent collimator started. Geo _._,_._,_

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#673

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