Reducing unwanted X-Rays with filters. ISOTOPE EXCITERS
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In medical X-Ray imaging, it was long ago discovered that the lowest energies coming from the X-Ray generator did nothing at all to improve the image on the film, but rather, instead of penetrating the target, they were needlessly absorbed by the skin and upper layers of the body In the early days these unwanted rays became known as "burning rays" and for good reason. ALL medical X-Ray generators today have? aluminum filters.In the science lab, the low powered X-Ray tubes don't have filters, so they must be added, if needed.X-Rays from isotopes are also a nuisance especially in the area of XRF detection. So many of these X-Rays interfere and simply clutter up the scan, causing all sorts of interpretation problems in the analysis stage.Am- is particularly bad for this because the daughter Np has X-Rays right in the middle of our range of interest, the worst being 13.9 and 17.74.
Borrowing the aluminum filter idea from our medical colleagues, an experiment was conducted to determine if filtering could perhaps clean up our exciters.
Using the Spectrum Techniques RAS absorber set, all of the aluminum filters were sequentially placed between the business end of an? Am_X8 exciter, pointing directly at the CdTe detector. CdTe was chosen for these tests because it gives a truer representation of the 59.5 energy, although the resolution is much poorer than the Si-PIN.
The Al absorbers were labeled G (0.20" or 129 mg/Mm^2) through P (0.125" or 849 mg/CM^2), the others in the set being made of plastic and lead.
A ideal goal was set to chase, 90% reduction of said interfering X-Ray, while retaining 90% of the 59.5.
Enough data was gathered to make a full blown report, but here are the highlights in picture form.
First scan, source directly illuminating the detector with NOTHING but air between them.
Then scan repeated with the 0.20" filter and all the others in sequence, one at a time.
0.40 was determined to be a very good end point, but the test was continued all the way to 0.125" to see what happens. The final result, while not being much use to use directly set off yet another experiment with really thick aluminum (inches) to examine what was noticed and guessed to be scattering or channeling within.
Test Zero- NO FILTER NOTE: The outline of this test remains on all others as a reminder of the original levels.
Test-G-0.020"Aluminum = 129 mg/cm^2
Test-J 0.40 Aluminum= 258 mg/cm^2 looked good, but not quite to the ultimate goal 90%/10%
Test-M - First to break over 90% reduction @ 17.74, and then some! 0.080" = 516 mg/cm^2
Have fun,
Geo>K0FF
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