Observation of x-ray resonant Raman scattering: The early days Page: 1 of 14
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OBSERVATION OF X-RAY RESONANT RAMAN SCATTERING:
THE EARLY DAYS
CULLIE J. SPARKS
Oak Ridge National Laboratory, P.O. Box 2008
Oak Ridge. TN 37831-6118, USA
My early observation of resonant Raman scattenng came as a serendipitous by-product of our
efforts to achieve the best possible signal for x-ray fluorescent analysis. We were also
investigating the x-ray spectrum produced by a monochromatic x-ray beam striking metal
targets which might contribute to the inelastic background. This background could contaminate
the very weak diffusely distributed elastically scattered radiation associated with defects in the
perfect periodicity of crystals. Energy analysis of the x-ray spectra created by monochromatic
Cu Ka and Mo K. radiation impinging on highly pure metal targets showed an inelastically
scattered intensity related to the energy difference between the exciting radiation and the nearest
bound state. Confirmation of these observations and availability of synchrotron radiation has led
to wide application of this new x-ray spectroscopy in atomic physics including its use as a probe
of the unoccupied density of states
1. - The Early Experiment
The discovery of radiative resonant Raman scattering1,2 occurred while we were
researching the radiative contributions to background when measuring very weak
and diffusely distnbuted x-ray scattering. The weak diffusely-scattered radiation
from crystalline Cu bearing alloys irradiated by monochromatic Cu Ka x rays was
slightly too intense to be accounted for by the known elastic and inelastic
(Compton) scattering processes- Trace impurities could contribute fluorescent
radiation which was not discriminated against by our scintillation and proportional
counters. Funding for environmental science led to a research program to
determine the minimum detectable limit for trace elemental contaminants by x-ray
fluorescent analysts. A recently developed Si(Li) solid state detector to analyze
the radiation spectrum excited by Cu Kit and Mo Ka radiation was central to the
1.2 Experimental Set-up
Our experiment was optimized to detect weak diffuse scattering associated with
measurements of short-ranged atomic arrangements and atomic-size
displacements in crystalline solid solution alloys3.4 as shown schematically in
Fig. 1. A large solid angle of characteristic Cu Ka radiation from a sealed Cu
anode x-ray tube was intercepted by a doubly-bent highly oriented graphite
monochromator and focused to a line at the sample.5 A Ross balanced filter pair
was used to remove the tremsstrahlung subharmonic x-ray energies diffracted by
the monochromator 6 High-purity Al covered all surfaces to reduce background
contamination by scattered or fluorescent radiation from other sources around
the sample. A drawing of the x-ray gontometer is shown in Fig. 2. The angle 0
defined in Fig t is the same as tme goniometer angle 29 of Fig. 2. Details are
given in Ref. 7.
DISTRIRUTION OF ThIS DOCUMENT i the submited manuscnX has been authored by a citractor
of ihe U.S. Government under contract t No. DE-AC s5-
960822464. Accoidngy. the U.S. Government retains a
noubsied oroy-fr ia cn et u ish or r ter o dc so.ho
I.s Goverrment purposes."
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Sparks, C.J. Observation of x-ray resonant Raman scattering: The early days, article, December 31, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc668529/m1/1/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.