Chemistry Reference
In-Depth Information
After World War II, the first complete X-ray spectrometers became availa-
ble, developed for example, by Philips, The Netherlands, by Siemens,
Germany, and by ARL, Switzerland. In the 1960s, the spectrometers were
equipped with hardwired controllers, servo transmitters, switching circuits, and
electronic registration [4]. In the 1970s, X-ray spectrometers became computer-
controlled and automated for a high throughput of samples. They were used for
production and quality control in several branches of the metallurgical indus-
try. Furthermore, X-ray spectrometers were applied in the exploitation of
mineral resources and also in environmental protection. At this time XRF-
spectrometers filled a whole lab, but in the 1980s the lateral dimensions
decreased. In the decades since, XRF has developed into a powerful method
of spectrochemical analysis of materials. However, classical XRF is not suitable
for ultratrace analyses and it is notorious for producing matrix effects that may
lead to systematic errors. Extensive efforts have been made to overcome these
drawbacks, for example by matrix separation, thin-film formation, and mathe-
matical corrections. Nevertheless, the new techniques of optical atomic spec-
trometry have surpassed conventional XRF in many respects.
From the start in 1895, X-rays were immediately applied to medical and
dental diagnosis and later on for security checks at airports, for material
analysis, ore mining, and pollution control. Furthermore, X-rays in astronomy
have enlarged our view of the universe. In 1932, the“German Röntgen
Museum”was founded at Röntgen's birthplace in Lennep, 50 km away
from Dortmund, Germany. Today it is a global center of the life, research,
and impact of Wilhelm Conrad Röntgen and presents numerous valuable
original objects of the discovery, development, and application of X-rays [9].
1.2THENEWVARIANTTXRF
Simultaneously with the invention of semiconductor devices in the“silicon
valley”after 1970, a new kind of an X-ray detector was developed. It could not
only count the individual X-ray photons but could also determine their energy.
Such a Si(Li) detector was called“energy-dispersive”instead of the“wave-
length-dispersive”spectrometers used so far. The novel detectors were small
and compact, did not need a goniometer with an analyzing crystal, and could
collect the whole spectrum simultaneously in a very short time.
1.2.1RetrospectonitsDevelopment
Additional important progress in XRF was made 50 years after the discovery of
total reflection of X-rays by Compton. In 1971, Yoneda and Horiuchi [10]
evolved an ingenious idea of using total reflection for the excitation of X-ray
fluorescence. They proposed the analysis of a small amount of material applied
on a flat, even, and totally reflecting support. An energy-dispersive Si(Li)
detector, developed shortly before, was placed directly above the support for
Search WWH ::
Custom Search