Nick Andrews
Fluorescence, emission of , usually visible , caused by of in a material, which then reemit almost immediately (within about 10?8 seconds). The initial excitation is usually caused by absorption of energy from incident radiation or particles, such as X-rays or electrons. Because reemission occurs so quickly, the fluorescence ceases as soon as the exciting source is removed, unlike , which persists as an afterglow. A fluorescent is coated on the inside with a powder and contains a gas; electricity causes the gas to emit , which then stimulates the tube coating to emit light. The of a television or computer screen fluoresce when electrons from an strike them. Fluorescence is often used to analyze molecules, and the addition of a fluorescing agent with emissions in the blue region of the to detergents causes fabrics to appear whiter in sunlight. X-ray fluorescence is used to analyze minerals.
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Re: Charles- cerium in minerals question. Geo
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On 2018/10/21 04:27 PM, Charles David Young wrote:
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Re: Hello! Lixi PS-500 unit
Picture of same model(?) that ran through the shop last year-
This one was in a cabinet unit version called the "Workstation" it lives at the Mayo Clinic as a "OS Table Top" unit now. The big cable coming out the back of the control unit carries HV from the controller to the tube head. Another version uses a much smaller control box and has the HV unit inside the head/tube assembly.? The former are much easier/cheaper to repair/replace just the tube. On the front end of the Image Intensifier, there is a round plate- this is the scatter shield. Those tube's nameplate might look like max I is 0-2mA but it is actually Max= 0.2 mA= 200 microamps. Normal use is less than 100 uA. Geo |
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Re: Charles- cerium in minerals question. Geo
Ok, keep in mind that all the minerals in my collection are radioactive and I am just measuring the secondary XRF stimulated by the internal radioactivity of these specimens.? I use no external xray source.? This technique obviously has its limitations but I want to find out what those limitations are.? Also, I am using a normal Scionix 38 B 57 PMT probe.? Eventually I want to be using a low energy probe and I am working on that with Geo. I just do a normal gamma scan but with higher
PMT
voltages (e.g. 850V) to make it more sensitive in the lower energies.? In fact, the highest energy I normally linearize is 295 keV because with that and the position of the peak around 240 keV I can tell whether a specimen has U or Th or both.? That is convenient if I am looking at an unknown mineral. The other thing I do is normalize my scans to the Pb XRF around 80 keV.? I have modified Theremino to count until a selected peak reaches a threshold count.? I typically will set that count to 10000.? That levels the region to the left of 80 keV, which in the absence of prominent XRF peaks tends to align pretty closely.? My theory is that this region consists primarily of Bremstrahlung from the 80 keV peak. Take for instance the 3 scans in the attached image that are red, lime, and blue.? Those are of thorite and thoriante crystals that are relatively pure.? The black is actually the average of these that forms a baseline against which I compare other more complex minerals. The other 3 scans are of monazite specimens from different localities.? They all share a prominent bump at the beginning of the Lanthanide series which is probably Ce and other Lanthanides by substitution. This Lanthanide bump is also present with allanite, chevkinite, and steenstrupine.? In fact, I have not found anything in my collection that is supposed to contain Ce that doesn't have this bump. I see a similar phenomenon with samarskite vs uraninite.? There is a fairly distinct bump around Ta.? See the other attachment. Anyway, this is a work in progress as I continue to refine my instrumentation and techniques.? I'll report more scans as I survey more of my collection. Charles El dom., 21 de oct. de 2018 a la(s) 10:53, <GEOelectronics@...> escribi¨®: Charles you mentioned possibly directly detecting cerium X-Rays in minerals? When you have a chance, would you explaining the method and reasoning? |
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Hello! Lixi PS-500 unit
I recently purchased a LIXI inspection system.? ?Waiting for them to ship it.? ?I hope it works,? as it would provide x-ray inspection capability for small stuff as well as being an excellent,? highly controllable source for XRF work.? It has an older CCTV type video camera installed but I will likely look to replace that with a nice cheap digital camera I can control remotely.? |
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