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x-ray intensity Essentially all x-ray meas-
urements are made by photon counting tech-
niques but the results are seldom converted to
X radiant flux or irradiance or radiant exposure.
The term photon flux would be appropriate if
the measurements were corrected for detector
efficiency but this is seldom done for x-ray chem-
ξ ξ ξ- (xi-) A symbol used to denote unknown ical analysis. Therefore, the term x-ray inten-
configuration at a chiral center. sity, I, is commonly used and expressed as
photons/unit time detected. Likewise the term
xanthophylls A subclass of carotenoids relative x-ray intensity, I , is used to mean the
r
consisting of the oxygenated carotenes.
intensity for the analyte in an unknown specimen
divided by the intensity for a known concentra-
xenobiotics Manmade compounds with
tion of the analyte element.
chemical structures foreign to a given organism.
xenon lamp An intense source of ultravio- x-ray level An electronic state occurring as
let, visible, and near-infrared light produced by the initial or final state of a process involving
electricaldischargeinxenonunderhighpressure. the absorption or emission of x-ray radiation. It
represents a many electron state which, in the
xerogel A term used for the dried out open purely atomic case, has total angular momentum
structures which have passed a gel stage during (J = L+S) as a well-defined quantum number.
preparation (e.g., silica gel); and also for fried out
compact macromolecular gels such as gelatin or
rubber. x-ray photoelectron spectroscopy (XPS) Any
technique in which the sample is bombarded with
XPRESS-MP A mathematical program- x-rays and photoelectrons produced by the sam-
ming modeling system and solver. ple are detected as a function of energy. ESCA
(Electron Spectroscopy for Chemical Analysis)
XPS See photoelectron spectroscopy. refers to the use of this technique to identify ele-
ments, their concentrations, and their chemical
x-radiation Radiation resulting from the state within the sample.
interaction of high-energy particles or photons
with matter.
x-ray satellite A weak line in the same
x-ray escape peak In a gamma or x-ray energy region as a normal x-ray line. Another
spectrum, the peak due to the photoelectric effect name used for weak features is non-diagram
in the detector and escape, from the sensitive part line. Recommendations as to the use of these
of the detector, of the x-ray photon emitted as a two terms have conflicted. Using the term dia-
result of the photoelectric effect. gram line as defined here, non-diagram line
may well be used for all lines with a different
x-ray fluorescence The emission of charac- origin. The majority of these lines originate from
teristic x-radiation by an atom as a result of the the dipole-allowed de-excitation of multiply ion-
interaction of electromagnetic radiation with its ized or excited states, and are called multiple-
orbital electrons. ionization satellites. A line where the initial
state has two vacancies in the same shell, notably
x-ray fluorescence analysis A kind of the K-shell, is called a hypersatellite. Other
analysis based on the measurement of the ener- mechanisms leading to weak spectral features
gies and intensities of characteristic x-radiation in x-ray emission are, e.g., resonance emission,
emitted by a test portion during irradiation with the radiative auger effect, magnetic dipole, and
electromagnetic radiation. electric quadrupole transitions and, in metals,

c

© 2003 by CRC Press LLC
© 2003 by CRC Press LLC