Charge sensitive amplifier

Figure 8 Schematic of the optical system used to perform the Raman FID and echo experiments. P = Polarizer (D)BS = (dichroic) beamsplitter MD = manual delay line SD = computer-scanned delay line CSA = charge sensitive amplifier CH = chopper PH = pinhole S = sample F = bandpass and neutral density filters PD = photodiode A/D = analog-to-digital converter PC = computer PMT = photomultiplier X/2 = half-wave plate. (From Ref. 6.)...

For a spectrometry silicon surface-barrier detectors are most suitable. They are operated at room temperature in a vacuum chamber to avoid energy losses. The a particles are stopped within a thin depleted region of the detector and the number of electron-hole pairs is directly proportional to the energy of the a particles. The charge pulses are integrated in a charge-sensitive amplifier. Some a emitters used as a. sources for the purpose of calibration are listed in Table 7.4. 

The charge measured due to electrons is one half of the total charge deposited by the ionizing particle. The other half is transferred by the positive ions which are not detected by the charge-sensitive amplifier. Equation 119 describes a parabola with its apex at t. When impurities are present, the electron current is given as... 

Munoz et al. (1986) studied the electron pulses obtained from a Am-a-source as a function of field strength. The source was deposited at the center of the cathode and the anode was connected to a charge-sensitive amplifier. A pulse height spectrum obtained for isooctane at two different field strengths is shown in Figure 9, while the electron yield as a function of field strength is depicted in Figure 10. 

Another example is the matrix ionization chamber system (vanHerk, 1991 1992). The ionization chamber consists of two printed boards which enclose a thin liquid film. Each plate carries a system of 256 parallel conducting strips. The principle is shown in Figure 8. The strips of one plate are connected to 256 charge-sensitive amplifiers. Voltage pulses are applied successively by a multiplexer to the 256 strips of the other plate. This way, 256 x 256 = 65,536 crossing points exist which function as mini-ionization chambers. The sensitive volume is irradiated continuously by X-rays and the ionization produced in each minichamber is read out. Such a device has been applied as a portal imaging device in radiation therapy (Meertens et al., 1990). 

Small amounts of organic compounds of low ionization potential (see Section 4.2) can be dissolved in liquefied rare gases. The solubility increases from argon to xenon. The scintillation light leads to single photon ionization from which electron/ion pairs originate. The electrons are detected in the usual manner with a charge-sensitive amplifier (see Section 2.10). This way the sensitivity and resolution of rare gas liquid detectors can be improved. Another method uses the scintillation photons to eject electrons from a photocathode (Aprile et al., 1994). 

BJTs, on the other hand, have low input impedances which makes them unsuitable for applications such as charge-sensitive amplifiers in which it is necessary to sense a voltage with little or no disturbance to the system, or in systems such as digital watches or other applications where the flow of current must be held to a minimum. 

Photoelectrons or holes can be collected under charged metal electrodes that form the pixels in a CCD video camera. By manipulating the voltages on the electrodes, these charges may be transferred serially in a shift register to a charge-sensitive amplifier to produce an analog video output. 

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