Observation of x-ray resonant Raman scattering: The early days Page: 3 of 14
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SI(L) DETECTOR NOISE
0 25 50 100 '25 5.0 175 200
ENERGr I hVI
Fig. 3. Spectrum generated in a SitL detector by a doubly diffracted monochromatic source of Mo Ka x
rays shows the tarmiiar S( Ka escape Deai. Au fluorescence from the voltage contacts on the Si diode, and
the typical flat background associated with insufficient charge collection in the Si diode.
which a residue from evaporated water and air samples was deposited. Bragg
diffraction from the wafers was avoided by cutting the crystal so that there were no
lattice planes parallel to the surface. The Si substrates excited with either Cu or
Mo Ka radiation gave the expected K fluorescent and scattered incident radiation
and a featureless background like that shown in Fig. 3. Spectra from Ge
substrates excited with Cu Ka radiation gave the expected scattered Cu Ka
radiation and Ge K fluorescence excited by multiple x-ray energies selected by
the higher-order graphite Bragg reflections from the bremsstrahlung produced in
the x-ray tube from 40 keV electrons.
An unexpected asymmetric broad maximum - 1.2 keV below the energy
of the incident Cu Ka radiation impinging on a Ge target is shown in Fig. 4. This
broad maximum starting at - 7.0 keV and extending below 5 keV was not caused
by the multiple x-ray energies passed by the monochromator as verified by taking
the difference between the two measurements made with the Ni and Co filters.
Their thicknesses are chosen to match their photoelectric linear absorption
coefficients at twice the energy of the 8 04-keV Cu Ka radiation. The spectra of
Fig. 4 are offset in energy to show that the filters are balanced in that the Ge Ka
fluorescence excited by radiation having energies above the Ge K edge is the
same in both spectra. The intensity difference between the two measurements is
the scattered radiation from x rays diffracted by the monochromator between the
Co K absorption edge at 7 71 keV and the Ni K edge at 8.33 keV and brackets
the 8.04-keV Cu Ka radiation A similar measurement on the Ge sample with
monochromatic Mo Ka raoiataon and yttrium oxide-Zr Ross balanced filter pair did
not produce the broad maxima near 6.8 keV found with Cu Ka excitation.
Therefore. the maxima was not the usual fluorescence from impurities. A
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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/m1/3/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.