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Re: X-ray peaks



Bernard Cleyet mentions that alpha and beta designate which is most
intense and second most intense. I believe that was originally the
intent in the low-resolution days, and it still is the end result for
low-resolution spectra, but the assigning of a "Siegbahn Notation" to
x-ray transitions is now made by beginning/ending orbitals rather than
intensities.

Bernard is correct that x-ray spectroscopists tend to designate where
the electron hole moves rather than where the electron moves. For
example, when a vacancy (hole) exists in the n=1 orbital (K), the
vacancy might get filled by an n=2 (L) electron. I am inclined to say
we had an electron transition from n=2 to n=1 or an L to K transition.
The x-ray folks are more inclined to say the vacancy moved from n=1 to
n=2 and we therefore had a K to L transition (for the vacancy).

Either way, this is called a K-alpha x-ray. But with our better
technology we can distinguish whether the vacancy moved from the n=1 to
the (n=2,l=0) or (n=2,l=1) or (n=2,l=2) orbital. If the vacancy moved
to the (n=2,l=2) we call it K-alpha-one. If it moved to (n=2,l=1) we
called it K-alpha-two. If the vacancy moved from n=1 to (n=2,l=0) we
call it K-alpha-three. This latter transition is actually forbidden,
but it does occur a small but measurable fraction of the time for
elements with Z greater than about 40.

If we don't have the resolution to resolve the K-alpha-1,2,3 from each
other, then we just lump them together as K-alpha.

Likewise, K-beta transitions generally move the vacancy from n=1 to n=3,
but a few transitions labeled as K-beta are actually transition of a
vacancy from n=1 to n=4. So K-beta x-ray notation is pretty complicated
with 5 distinct transitions currently recognized, (labeled K-beta-one
through K-beta-five.) In very low resolution these are all lumped into
K x-rays. In higher resolution these are lumped into K-beta. In
higher-yet resolution they are lumped into K-beta-one-prime and
K-beta-two-prime. In very high resolution they are separated. In the
primed cases, KB1+KB3+KB5 are the KB1' and KB2+KB4 are the KB2'.

Probably more than anyone wants to know, but I think that is the state
of x-ray notation right now.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.