Silicon detectors, lithium

Instrumentation. Traditional methods of alpha and beta spectrometry instrumentation have changed little over the past decade. Alpha spectrometric methods typically rely on semi-conductor or lithium-drifted silicon detectors (Si(Li)), or more historically gridded ion chambers, and these detection systems are still widely used in various types of uranium-series nuclide measurement for health, environmental, and... 

The most frequently used silicon detector is a small pellet of lithium drifted silicon, some 6 mm in diameter and 3-4 mm thick. It is good only for X-rays, in the energy range between 4 and 50 keV. In fact, there are some standard sizes of Si(Li) detectors, areas of 30 and 100 mm are considered normal, anything else is a detector made by specifications of the user. 

The x-ray fluorescence system consisted of a radioactive source as the excitor and a 200-ev resolution (FWHM) lithium-drifted silicon detector with standard electronics. Only 15 minutes were required to completely process a sample. 

Candelori, A. Bisello, D. Giubilato, R Kaminski, A. Litovchenko, A. Lozano, M. UUan, M. Rando, R. Wyss, J. 2004b. Lithium ion induced damage in silicon detector. Nuclear Instruments and Methods in Physics Research Section A, 518(l-2) 338-339. 

Candelori, A. Schramm, A. Bisello, D. Contarato, D. Fretwmst, E. Lindstbm, G. 2004c. Lithium ion irradiation effects on epitaxial silicon detectors. IEEE Transactions on Nuclear Science, 51(4)1 1766-1772. 

Semiconductor technology is still a rapidly developing field that has seen the introduction of new detector types in recent years. However, the standard detector type on which ED-XRF technology was founded is the lithium-drifted silicon detector, Si(Li). This is the detector type against which the performance of new types of semiconductor detector is evaluated. 

The situation is different if a semiconductor detector (lithium-doped silicon crystal) and the proper electronics are available. This setup can separate K a and K radiation, so that the beam does not have to be passed through a monochromator. The counter tube itself has nowadays become easier to operate, for the semiconductor crystal no longer has to be maintained at liquid nitrogen temperature—the problem has been solved electronically. Efforts continue to find broader applications for this type of detector, since replacement of the monochromator by electronics means that there is no longer a 50 % loss of primary intensity through diffraction by the monochromator crystal or absorption by the /( filter. 

Semiconductor transducers have assumed major importance as detectors of X-radiation. These devices are sometimes called lithium-drifted silicon detectors, Si(Li), or lithium-drifted germanium detectors, Ge(Li). 

Si(Li) DETECTOR (Pronounced silly ) A silicon detector created by lithium drifting. 

The resistivity of the silicon is increased by making the whole detector a semiconductor p-i-n junction which is reverse biased by a potential applied to a thin film of gold on the outer faces. The silicon is doped with a small concentration of lithium, and the whole detector is cooled to liquid nitrogen temperature (77 K). The current which passes between the (gold) electrodes is now very small until an X-ray enters the detector, and the resultant current pulse can be amplified and measured. 

The metals were coprecipitated with lead-ammonium pyrrolidine dithio-carbamate and detected by X-ray spectrometry following neutron activation. Magnetic fields deflect the p rays while the X rays reach the silicon (lithium) detector undeviated. The detectors have low sensitivity to y rays. The concentration of cobalt found by this method was 1.3 xg/l, about one-fifth of that measured previously, while that of copper, 2.0 xg/l, agreed with results obtained by some previous workers. The concentration of mercury was 1.2 xg/l. 

The alternative approach to detection and analysis incorporates a solid state detector and a multichannel pulse height analysis system. The crystals used are of silicon (of the highly pure intrinsic type), or the lithium drift principle (p. 463 etseq.) is utilized. All emitted radiations are presented to the detector simultaneously and a spectrum is generated from an electronic analysis of the mixture of voltage pulses produced. Chapter 10 contains a more detailed account of pulse height analysis and solid state detectors. Production of an X-ray spectrum in this way is sometimes known as energy dispersive analysis ofX-rays (EDAX) and where an electron microscope is employed as SEM-EDAX. 

Lithium dichromate, molecular formula, properties, and uses, 6 562t Lithium diisopropylamide (LDA), 15 148 Lithium-drifted silicon [Si(Li)] detector, 26 434... 

---