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Re: The case of the missing elements
¿ªÔÆÌåÓýA Pellet press is commonly used for FTIR, LIBS and XRF. It¡¯s expensive to get set up though. I am just getting set up with a 12 ton press and the die¡¯s for my LIBS system. ?The problem is you can¡¯t use a powder sample for ?LIBS as the laser pulse blows the sample all over the place. ?It needs to be a tough solid pellet. I use either an iron or ceramic mortar and pestle for pulverizing
the small samples. ? From: [email protected]
[mailto:[email protected]] On Behalf Of GEOelectronics@...
Sent: Saturday, February 8, 2020 9:13 AM To: [email protected] Subject: Re: [XRF] The case of the missing elements ? " How would you prepare a sample like that? Taking a piece off with a Dremel or even a cheese grater might introduce contamination. Do you know how labs do it, and can we do this in the home lab? I have some samples I can use so I am willing to give it a try. ? Steve" ? Take that a step further Steve, and compress the powder into a standard pellet, and you have the perfect sample for XRD, or X-Ray Diffraction. Using that method the phase of the mineral can be determined as well as the elements. ? Crushing- I use a cast iron mortar and pestle, available in different sizes from any mining outfitter. ? Geo ? ? ? ? ? -----
Original Message ----- ?
?
?
? ? From: [email protected] <[email protected]> on behalf of Dude
<dfemer@...> ? Good
points here Geo. However we¡¯re all doing this all wrong and comparing apples to
oranges.? The
excitation sources have widely different energies and source strength and
exposure is from within or on the surface.? Worse yet we have no idea of
the elemental distribution The
excitation energy from the Th is going to be very high while the Am is lower in
energy and has the Np x-rays which are closer and stronger to excite the
absorption edges of To
properly compare these measurements the rock should be pulverized down to 200 u
or so (Charles just cringed) ?mixed and homogenized and put into a XRF cup
with a mylar cover I think Geo is right in the density- thickness problem and the different source ?strengths. Charles, I have an external ?higher activity natural ?source that I think you might like to try, give me a call Dud ? ? ? From:
[email protected] [mailto:[email protected]]
Hi Charles, cool observation. If I may guess at it: ? We know from experience that an atom will make XRF if excited by energy from alpha, beta (or electron stream) Gamma, X-Rays etc. Probably many other ways too. ? So if you rely on internal energy to do this, it will do so in response to the available radiation from the rock. Some have LOTS, some have very little, some almost none. ? One advantage to that way
is all the atoms, even those deep within a big rock are being excited. If those
XRF rays can get out depends only on the energy of the ray and the overburden. ? Rays above 50 keV have little problem penetrating silicon-calcium-oxygen atoms. This goes for adding external energy or gathering internally generated XRF. ? So your method might show up something that an external exciter misses. ? But a good exciter will
work on a rock that has no discernable radioactivity, the thing is how
radioactive is the rock and how radioactive is does the external exciter have
to be to equal or better ? The pro units have a need
for speed so they have X-Ray tubes, blasting the sample with as much as the law
allows. We don't actually have a need for speed so we can use tiny little
exciters, but as ? In other words it may be small, but it is concentrated where it counts, we substitute long run times to get the results we need. ? Say on another note, do
you have enough Trinitite to do some Gamma Spec runs on it with your Si-PIN?
You could precisely calibrate the detector with Am, the see if the X-Rays
coming from Trinitite ? Geo ? ? ----- Original Message
----- ? I recently picked up a specimen of melanocerite-Ce at the mineral show and did a scan without Am241 by depending on the internal radiation.? I was not surprised to see Th La Ce and Nd in the blue plot. ? Then I wanted to see if I
got the same results using Am241 as an additional exciter.? So I carefully
moved the specimen just far enough from the detector to allow me to slide in
the Am241 jig.? I was ? Curiously I am now getting additional strong Fe and Y peaks in the red plot.? What could account for this?? I am not surprised that the La Ce Nd are lit up as they are. ? I have also attached both
.mca files in case one wishes to analyze them.? However, I am not really
asking for that.? I would just like to understand why the Am241 lights up
the Fe and Y so strongly ? Charles ? ? ? ? ? ? ? ? |