Thanks for trying that Charles. The idea is to eliminate the 13.9 and 17.7 keV X-Rays from the exciter source before it even strikes the target. There is a sweet spot with absorbers (aluminum) that cause this to happen, leaving the 59.5 pretty much alone. I'll dig around in my notes to report the magic thickness I came up with by experimentation.
Someone better at math than I could probably go to the HVL (Half-Value-Layer) shielding charts and find that sweet spot thickness that way. Since there are 2+ "octaves" difference between the X-Rays and Gamma Ray, each added thickness will affect the lower one more than the upper one.
Now that you have these two scans "fit together" think about making a copy of each calling one Target, the other BG (for background). Import them back into DppMCA using the OPEN command under FILE.
Next go to the toolbar icon A+B and enter the expression Target-BG so that the program combines the two together, one being negative, feeding out a new scan that is just the TARGET altered to subtract the BG,
Once you have this newly fabricated scan you can import it back into your display program. I think you will be pleased with the results.
Geo
----- Original Message -----
From: Charles David Young <charlesdavidyoung@...>
To:
[email protected], Mike Loughlin <loughlin3@...>, Frank Roberts <froberts@...>
Sent: Wed, 29 Jan 2020 06:42:14 -0500 (EST)
Subject: [XRF] allanite-La using Am241 on Pb shield wrapped with Al foil
At George's suggestion I have been experimenting with wrapping the Am241 source with Al foil.? It seems to have improved the already very good results somewhat.
The target is an interesting specimen because it is one of the few non-radioactive rocks in my collection.? I bought it recently because it is labelled as allanite and I have many allanites in my collection but nothing from this locality.? Especially interesting is the claim that the allanites from
are allanite-La instead of the usual allanite-Ce.? I set out to prove this.
I tried different number of wraps of Al foil: 0, 2, 3, and 6 layers.? Frankly, it did not seem to make much difference except perhaps reduce the noise in the lower energies some.? So once I got to 6 layers I decided to do an overnight run and that is the first attachment.? I have plotted the Am241 leakage alongside to illustrate the peaks that can be attributed to the setup.? This helps me to pick out the peaks due to the target.
I have also attached the plots of the
0, 2, 3, and 6 layers runs.? One caveat is that the 0 layers (red) was done several days before I decided to try the Al foil experiment so it was allowed to run about 3x longer than the 2-hour runs of the others based on the size of the Fe peak.? So you have to extrapolate a little, but it seems like compared to the other runs the noise baseline of the lower energies is reduced by the foil.? At some point I may remove the foil to try that run again but for now I did not want to bother.
The bottom line regarding this mineral is that it indeed appears to have allanite-La since the La peak is a little larger than the Ce peak.
Charles
