Position-Sensitive Semiconductor Detectors

Most of the position-sensitive semiconductor detectors determine the position of the incident particle by employing the method of resistive-charge division To illustrate the method, consider the detector in Fig. 13.25. The detector is a reverse-biased p-n junction with electrodes on both front and back. The front electrode with considerable resistivity has two electrical contacts a distance L apart. The back electrode has low resistivity and provides a good electrical contact to the base material. When a particle enters the detector, electrons and holes are created that move under the influence of the electric field. If the resistivity of the front electrode is homogeneous, and charge-sensitive low-impedance amplifiers are used, the charge collected at one of the two contacts of the front electrode is proportional to the distance between the point of impact 

The detector described above is of the continuous type. Position-sensitive detectors of the discrete type have also been developed. They consist of individual semiconductor elements all placed on the same base material, with each element connected to its own preamplifier-amplifier system. Two-dimensional detectors of the continuous type as well as of the discrete type have 

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The first magnetic spectrometers used photographic plates for the detection of the deflected particles. Today, position-sensitive semiconductor detectors or multiwire proportional chambers are used (see Sec. 13.10). These detectors are better than photographic plates because they have the capability of on-line data collection, provide time information for coincidence experiments, and measure the energy of the particle. 

Figure 13.25 A position-sensitive semiconductor detector using resistive-charge division (from Ref. 71).

A typical detection setup at the focal plane of a kinematic separator includes transmission time-of-flight detectors followed by a stopping position-sensitive semiconductor detector. The time-of-flight detectors are used to tag energy signals... 

Successful detection of S3P-labeled molecules separated by capillary electrophoresis using the above detection schemes, in which a sensor was positioned external to the separation channel, was made possible by several factors. These included (1) the large energy associated with 0 decay of S3P (1.7 MeV), (2) the high sensitivity and small size of commercially available semiconductor detectors, (3) the availability of efficient solid scintillator materials and sensitive photomultiplier tubes, (4) the short lengths of fused silica (capillary wall thickness) and aqueous electrolyte through which the radiation must pass before striking the detector, and (5) the relatively short half-life of S3P (14.3 days). 

Semiconductor detectors have supplanted all other point detectors during 1980s, soon to be superseded by position-sensitive detectors (PSDs) alias area detectors, which can... 

This second edition includes an account of new developments made possible by the semiconductor detector and pulse-height analysis, namely, energy-dispersive spectrometry and diffractometry. Applications of position-sensitive detectors are also described. 

A, Bragg scattering angles 2d in SAXS reach up to about 5°. The detection of the scattered intensity is usually realized with electronic detectors as, for example, proportional counters, scintillation counters, or semiconductor-based counters. Point detectors and position-sensitive devices are common. 

In the simplest version of AFM, called contact mode or normal force mode, the tip is brought into hard contact with the sample surface such that the cantilever bends due to the tip-sample repulsion (Fig. 3A). The cantilever deflection can be measured in several ways, but the most common is the optical beam method. In this approach, a laser beam from a semiconductor laser is focused on the back side of the cantilever, as shown in Fig. 2A. The reflected light hits a position-sensitive detector that produces a voltage indicating how much the cantilever has deflected up or down. In some cases, the detector also produces a... 

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