Analyzer MCA

Fig. 3.3 Velocity control and synchronization of data recording by the multi-channel analyzer (MCA) operated in MCS mode with 512 channels. For the common triangular velocity profile shown here the spectrum is recorded twice, because each velocity increment is reached upon sweeping up and down. The sense of the velocity scales may also be opposite to that shown here, which means the MCA sweep may also start at...

Fig. 3.7 Pulse-height analysis (PHA) Function of the single-channel analyzer (SCA) and data recording by the multi-channel analyzer (MCA). The output (L) of the SCA yields a 5 V squareshaped pulse, a so-called TTL pulse for each y-pulse matching the voltage selection window. The SCA is set to select the Mossbauer pulses for the subsequent measurement...

The output from the TAC is an analog signal that is proportional to the time difference between the start and stop pulses. The next step consists of digitizing the TAC output and storing the event in a multichannel analyzer (MCA). After repeating this process many times, a histogram of the arrival times of photons is accumulated in the memory of the MCA. In fluorescence lifetime spectroscopy the histogram usually contains 512-2048 channels... 

Multichannel analyzer (MCA), 26 434 Multichannel detection, in concentric hemispherical analyzers, 24 106 Multiclient studies, 15 635-636 Multicollector-I CP-MS (MC-ICP-MS), archaeological materials, 5 743 Multicolor displays, LEDs in, 22 175 Multicompartment drum filters, 11 357 Multicomponent copolymerization, 7 619-620... 

The voltage pulse produced by the TAC is fed to the multichannel analyzer (MCA), and is stored in a specific channel according to its amplitude, and hence time, post-excitation. The probability of a single photon event being counted is high soon after excitation and decreases with time. Repetitive operation of the TAC produces a probability histogram for the detection of fluorescence photons, which is identical to the fluorescence decay curve. 

A multichannel analyzer (MCA) with a minimum of 4096 channels should be connected to a keyboard and display screen for input and output of data and interaction with a computer. Several kits are available for the conversion of personal computers (PCs) into MCAs. Basically there are three types of conversion kits. One makes use of board with an analogue-to-digital converter (ADC) that simply clips into the PC a second type uses a clip-in board with an external ADC and the third type uses a multichannel buffer (MCB) connected to the PC. All of these PC-based MCA systems are relatively inexpensive and are very suitable for use in germanium and sodium iodide y-ray spectrometry. 

Most laboratories involved in radiation measurements now use personal computers and commercially available software for the analysis of y-ray spectra. Some of these programs allow the user to control the multichannel analyzer (MCA), calibrate the detector for various geometries, and provide analysis results. The programs are easy to use and do not require the user to be an expert in y-ray spectrometry. 

The essential parts of an energy-dispersive spectrometer were shown in Fig. 15-l(b). It consists of a Si(Li) counter and a FET preamplifier, both cooled by liquid nitrogen, and a multichannel analyzer (MCA). It is mechanically simple, because it has no analyzing crystal, and electronically complex, because of the MCA. 

The multichannel analyzer (MCA) records and stores pulses according to their height. Each storage unit is called a channel. 

To measure an energy spectrum of a radioactive source means to record the pulse-height distribution produced by the particles emitted from the source, which is achieved with the use of an instrument called the multichannel analyzer (MCA). Multichannel analyzers are used in either of two different modes the pulse-height analysis (PHA) mode or the multichannel scaling (MCS) mode. 

A basic counting system for activation analysis consists of a detector [Ge or Si(Li)], electronics (i.e., preamplifier, amplifier), and a multichannel analyzer (MCA). Modern MCAs do much more than record the data. They are minicomputers or are connected to computers that store and analyze the recorded data. Examples are the ADCAM architecture offered by EG G ORTEC and the Genie-ESP VAX-based Data Acquistion and Analysis System offered by Canberra. 

A significant improvement to LS instrumentation was summing the pulses from each PMT for an output proportional to the total intensity of the scintillation event. This design for an LS system with pulse coincidence detection and summation (Fig. 8.5) has remained basically unchanged over the last forty years. More recently, instrument vendors have replaced a traditional three-channel system with a multichannel analyzer (MCA) and software for spectral analysis. 

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