Editing X-ray fluorescence (section)

===Energy dispersive spectrometry===
{{main|Energy-dispersive X-ray spectroscopy}}
In [[energy dispersive X-ray spectroscopy|energy-dispersive]] spectrometers (EDX or EDS), the detector allows the determination of the energy of the photon when it is detected. Detectors historically have been based on silicon semiconductors, in the form of lithium-drifted silicon crystals, or high-purity silicon wafers.

[[File:DmedxrfSiLiDetector.jpg|thumb|Figure 5: Schematic form of a Si(Li) detector]]

====Si(Li) detectors====
These consist essentially of a 3–5&nbsp;mm thick silicon junction type p-i-n diode (same as PIN diode) with a bias of −1000 V across it. The lithium-drifted centre part forms the non-conducting i-layer, where Li compensates the residual acceptors which would otherwise make the layer p-type. When an X-ray photon passes through, it causes a swarm of electron-hole pairs to form, and this causes a voltage pulse. To obtain sufficiently low conductivity, the detector must be maintained at low temperature, and liquid-nitrogen cooling must be used for the best resolution. With some loss of resolution, the much more convenient Peltier cooling can be employed.<ref>{{cite book|url=https://books.google.com/books?id=667SJf95AFAC&pg=PA559|page=559|title=Transmission electron microscopy: a textbook for materials science|volume=2|author=David Bernard Williams|author2=C. Barry Carter|publisher=Springer|date=1996|isbn=978-0-306-45324-3}}</ref>

====Wafer detectors====
More recently, high-purity silicon wafers with low conductivity have become routinely available. Cooled by the [[Thermoelectric effect#Peltier effect|Peltier effect]], this provides a cheap and convenient detector, although the [[liquid nitrogen]] cooled Si(Li) detector still has the best resolution (i.e. ability to distinguish different photon energies).

====Amplifiers====
The pulses generated by the detector are processed by [[pulse-shaping]] amplifiers. It takes time for the amplifier to shape the pulse for optimum resolution, and there is therefore a trade-off between resolution and count-rate: long processing time for good resolution results in "pulse pile-up" in which the pulses from successive photons overlap. Multi-photon events are, however, typically more drawn out in time (photons did not arrive exactly at the same time) than single photon events and pulse-length discrimination can thus be used to filter most of these out. Even so, a small number of pile-up peaks will remain and pile-up correction should be built into the software in applications that require trace analysis. To make the most efficient use of the detector, the tube current should be reduced to keep multi-photon events (before discrimination) at a reasonable level, e.g. 5–20%.

====Processing====
Considerable computer power is dedicated to correcting for pulse-pile up and for extraction of data from poorly resolved spectra. These elaborate correction processes tend to be based on empirical relationships that may change with time, so that continuous vigilance is required in order to obtain chemical data of adequate precision.

Digital pulse processors are widely used in high performance nuclear instrumentation. They are able to effectively reduce pile-up and base line shifts, allowing for easier processing. A low pass filter is integrated, improving the signal to noise ratio. The Digital Pulse Processor requires a significant amount of energy to run, but it provides precise results.

====Usage====
[[Energy-dispersive X-ray spectroscopy|EDX]] spectrometers are different from [[Wavelength dispersive X-ray spectroscopy|WDX]] spectrometers in that they are smaller, simpler in design and have fewer engineered parts, however the accuracy and resolution of EDX spectrometers are lower than for WDX.  EDX spectrometers can also use miniature X-ray tubes or gamma sources, which makes them cheaper and allows miniaturization and portability. This type of instrument is commonly used for portable quality control screening applications, such as testing toys for lead (Pb) content, sorting scrap metals, and measuring the lead content of residential paint. On the other hand, the low resolution and problems with low count rate and long dead-time makes them inferior for high-precision analysis. They are, however, very effective for high-speed, multi-elemental analysis. Field Portable XRF analysers currently on the market weigh less than 2&nbsp;kg, and have limits of detection on the order of 2 parts per million of lead (Pb) in pure sand. Using a Scanning Electron Microscope and using EDX, studies have been broadened to organic based samples such as biological samples and polymers.

[[File:dmwdxrfschematic.jpg|thumb|Figure 6: Schematic arrangement of wavelength dispersive spectrometer]]
[[File:XRFgoniometer manual.jpg|thumb|right|Chemist operates a [[goniometer]] used for X-ray fluorescence analysis of individual grains of mineral specimens, [[U.S. Geological Survey]], 1958.]]