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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