Silicon drift detector

Fig. 4.9. Block diagram (left) and assembly image (right, also with cap removed) of a silicon drift detector (SDD) module, including electronics [4.30],...

Silicon drift detectors (SDD, Figs 4.8 and 4.9) now also provide sufficient resolution (FWHM = 0.175 keV) above a sample spot sized 2 x 2 to 100 x 100 mm, and enable high-speed operation (> 10 counts s ). SDD can be combined with microelectronics and applied in portable TXRF models for microanalytical applications [4.30]. They must be cooled by a Peltier element. 

Tab. 4.1. Certain elements whose Ka peaks interfere with escape peaks of other elements using solid state detector SSD or silicon drift detector SDD [4.16].

Solid-state detectors based on silicon- or germanium-diodes possess better resolution than gas counters, particularly when cooled with liquid nitrogen, but they allow only very low count rates. PIN diodes have also recently become available and have been developed for the instruments used in the examination of Martian soils (Sects. 3.3 and 8.3). A very recent development is the so-called silicon-drift detector (SDD), which has very high energy resolution (up to ca. 130 eV) and large sensitive detection area (up to ca. 1 cm ). The SNR is improved by an order of magnitude compared to Si-PIN detectors. Silicon drift detectors may also be used in X-ray florescence spectroscopy, even in direct combination with Mossbauer spectroscopy (see Sects. 3.3 and 8.3). 

Fig. 3.24 Left. Energy resolution of the silicon-drift-detectors (SDD) at 5.9 keV ( Fe radioactive source) as a function of temperature. Middle-. One segment (out of four) of SDDs composed of two individual chips with front-end electronics. The dimensions of the A1 housing are cm x 4 cm x 7 cm. In the center the opening of the radiation collimator can be seen. Right MIMOS IIA SDD segment (1/4 of the complete detector ring a 10 -cent coin is shown for comparison)...

Silicon drift detectors (SDD) are now available in some PXRF they have a higher energy resolution and count rates,... 

All Mars rovers to date have carried alpha-particle X-ray spectrometer (APXS) instruments for chemical analyses of rocks and soils (see Fig. 13.16). The source consists of radioactive curium, which decays with a short half-life to produce a-particles, which then irradiate the sample. Secondary X-rays characteristic of specific elements are then released and measured by a silicon drift detector. The Mars Pathfinder APXS also measured the backscattered a-particles, for detection of light elements, but the Mars Exploration Rovers measured only the X-rays. 

The major differences in the choice of a detection system for this application between Si(Li) and Silicon drift detector is the Peak-to-Background (PfS) ratio, wMch typically is better using a Si (Li) detection system. Future developments in the SDD technology show that P/B ratios are improving. 

Figure 8.17 (a) Schematic drawing of a TXRF system. From left to right is the X-ray source, the synthetic multilayer monochromator (Section 8.2.3.2), the thin sample on a support, the silicon drift detector (SDD) above the sample, and finally a beam stop, (b) A commercial TXRF spectrometer, the Bruker S2 PICOFOX with its laptop computer. The displayed spectrum shows the high S/N ratio. ( 2013 Bruker, Inc. www.bruker.com. Used with permission.)... 

Two type of detectors are used in commercially available units proportional detectors and semiconductor detectors such as silicon PIN, Si(Li), Ge(Li), and silicon drift detectors. The detectors used in EDXRF have very high intrinsic energy resolution. In these systems, the detector resolves the spectrum. The signal pulses are collected, integrated, and displayed by a multichannel analyzer (MCA). 

In energy dispersive analysis, semiconductor crystals such as the PIN-diode, Si(Li), Ge(Li), and silicon drift detector (SDD) are generally used as X-ray detectors. They allow the count of an amount of photons and determination of the energy of the photon. An introduction of recent progress in X-ray detection... 

The EDS detector is a crystal, usually Si (Li)—although most current systems use SDD ( silicon drift detector )—which absorbs the energy of the X-ray, generated by elements of the sample, producing electrical pulses corresponding to the characteristic X-rays. In a typical microanalysis characteristic X-rays, it generates an EDS spectrum (energy-dispersive X-ray spectroscopy) [15, 16]. 

With the development of faster silicon-drift detectors (SDDs) for EDS, the acquisition of a set of elemental maps can be done within a couple of minutes, in contrast to at least a few hours with older technology. Fully quantifiable spectral maps (a map where the full EDS spectrum is recorded at each pixel) of 1024 x 768 pixels can be recorded in under an hour. Two examples using the combination of BSE and EDS are illustrated in the following. 

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