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 in the matrix which is going to determine
what gets excited and what gets absorbed. ?What is the gamma activity of
the Cerite? What¡¯s the mass. Is this a big boy or a chip?
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 both the Fe and Y.? But the biggest
problem is just what are you exciting and where is it ¨C on the surface,
deep inside just a small xtal?
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 and then measured.? It makes for a
homogenous mixture removing the ambiguity of what the matrix effects are.
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
?
?
?
?
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 it.....
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 far as the elements at the surface and a
little further inside are concerned, it is much more "exciting" than
the stuff coming from deep inside and spread over the entire surface of the
rock.
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 are from Np or U atoms, or both.
-----
Original Message -----
From: Charles David Young <charlesdavidyoung@...>
To: [email protected], Mike Loughlin <loughlin3@...>
Sent: Fri, 07 Feb 2020 17:12:15 -0500 (EST)
Subject: [XRF] The case of the missing elements
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 careful to keep the
same spot on the rock even though it looked quite uniform.
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 compared to the internal
radiation.? It is kind of a pain to weed through the Am241 background
peaks but it appears that I may not get a complete picture with the internal
radiation alone.
