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Dictionary

Astronomical X-ray sources

X-ray astronomy is the study of X-rays that originate from outside the Earth’s atmosphere. As with all cosmic rays they are either solar or galactic in origin. Bremsstrahlung and synchrotron radiation emitted by electrons from cosmic rays are supposedly one of the physical processes responsible for cosmic X-rays. As they penetrate the atmosphere only to a limited extent, it is necessary to detect them from balloons, rockets, or satellites. Photons with energies larger than usual X-rays are called gamma rays regardless of their origin.

Auger electrons

Just as the emission of internal conversion electrons is an alternative to gamma-ray emission from a nucleus, there is an alternative decay mode to an atom’s X-ray emission. The excitation energy of the atom in this alternative arising as a result of the vacancy created in an inner shell is transferred directly to an outer electron. This Auger electron is finally ejected. The emission of Auger electrons occurs primarily for elements of low atomic number, and therefore the energy is typically only a few keV.

AXAS

The KETEK detector system where the complete analog electronics are integrated into a compact housing (Analog X-ray Acquisition System).

CERN

European center for elementary particle research (Conseil Européene pour la Recherche Nucléaire) in Geneva, Switzerland. CERN is the word’s largest center for high energy physics (elementary particle physics).

CCD

Charge Coupled Devices are used as electronic elements for storing and transfering charges and as optical sensors (like in digital cameras). They are also used as particle detectors in elementary particle physics. pn-CCDs for particle and X-ray detection have been developed within an international collaboration including KETEK GmbH. In contrast to SDDs, pn-CCDs deliver spatial and spectral information about the incoming radiation.

DESY

German electron synchrotron (Deutsches-Elektronen-Synchrotron) is a German research center for particle physics and synchrotron radiation. It is located in Hamburg with an institute in Zeuthen near Berlin.

Detector

A device that detects (traces) particles and/or radiation. Most detectors also resolves the energy of the incoming particles or radiation. Detector systems used in high energy physics are composed of several detection and recording devices, because many different kinds of particles are produced by the collisions.

EDX

Energy Dispersive X-ray analysis. In principle every analysis method that measures X-rays and distinguishes the incoming spectrum by energy is called EDX. This method allows the determination of a sample’s composition by measuring the characteristic X-rays it emitts. The excitation sources are usually X-ray sources or electron beams.

Electron Volt (eV)

A energy unit used in nuclear and elementary particle physics. 1 eV is the energy gained by a single electron when it is accelerated by a potential difference of 1 Volt. 1 eV = 1.6 x 10-19 J and 1 keV = 1000 eV.

EMPA

Electron Microprobe Analysis. Energy dispersive X-ray analysis inside a SEM (Scanning Electron Microscope) or a TEM (Transmission Electron Microscope) where X-rays are excited by a focused electron beam with a diameter of about 1 nm (SEM) or even 0.1 nm (TEM).

Energy resolution

The capability of resolving (discern) different energies. The energy resolution of KETEK spectrometers are measured with a radioactive iron source ( 55Fe) that emits X-rays at a fixed energy of 5.9 keV (the Mn Kα line). The energy resolution is specified as the full width at half maximum (FWHM) of the peak height of the Mn Kα line. A low value of the width in FWHM corresponds to a high energy resolution. The higher its energy resolution, the better is the device’s capability of separating adjacent lines.

HERA

The Hadron Electron Ring Installation (Hadron-Elektron-Ring-Anlage) at DESY in Hamburg is the world’s only electron-proton collider.

LEP

Housed at CERN, the LEP (Large Electron-Positron Collider) is one of the largest particle accelerator in the world. Its tunnel, which is 27 km in circumference, is buried 100 m underground. At four separate points the four gigantic detector systens ALEPH, DELPHI, OPAL, and L3 measure collisions between electrons and positrons.

LHC

Large Hadron Collider at CERN. LHC will be the largest and the most powerful particle accelerator and is planned to start-up in 2007. It is installed in the same tunnel as the LEP to save costs for a new tunnel.

MIS (MOS)

A metal – insulator – semiconductor structure, more frequently referred to as metal – oxide – semiconductor structure, since the most common insulator in silicon technology is silicon oxide. The MOS structure forms the basis of most CCDs. It also forms the essential part of MOS transistors, which are the building blocks of the most widely used microelectronics technology.

Photons

Photons are the quanta of the electromagnetic fields. They mediate the electromagnetic interactions and posses neither mass nor charge.

SDD

Silicon Drift Detector. An energy dispersive spectrometer for X-rays and charged particles. The electrons produced by incoming radiation are drifted to the readout node by an electric field.

SEM-EDX

Scanning electron microscopy energy dispersive X-ray analysis.

Synchrotron radiation

Synchrotron radiation is emitted by a beam of fast electrons which are deflected by magnetic fields. Synchrotron accelerators give intense, highly collimated beams of radiation mainly in the X-ray energy region.

TXRF

Total reflection X-ray fluorescence. The fluorescence radiation is created by a total reflected X-ray beam resulting in a reduced background compared to standard XRF. The method is used for impurity analysis in the semiconductor industry and often referred to as VPD-TXRF if the residue of a droplet that was used to collect impurities from a large area is analyzed.

X-Rays

High energy photons (about 0.1 – 100 keV) which are non-nuclear in origin. X-rays are generated when an electron fills a vacancy in an atom’s inner shell, the vacancy being previously created by a disruption caused by excitation. These excitations come either from accelerated electrons in cathode rays or other external radiation (alpha, beta, gamma radiation or even X-rays) or from the radioactive decay of the central nucleus of the atom concerned. A convenient X-ray source excited by radioactive decay entails the electron capture process. This leaves an inner (usually K) shell vacancy in the atom, which, when filled, leads to X-ray emission characteristic of the atom produced. Internal conversion also leads to X-ray production because of the vacancy created in the inner shell by the ejected electron.

XRF

X-ray fluorescence. XRF is a mode of energy dispersive X-ray analysis. A sample is irradiated by an X-ray beam and the atoms inside are excited to emit characteristic X-ray. This secondary radiation is detected and allows the determination of the sample composition. The method is widely used in science and industry to determine compositions and find traces of elements and contaminations.