Single channel analyzers

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 X-ray powder diffraction pattern of niclosamide has been measured using a Philips PW-1050 diffractometer, equipped with a single-channel analyzer and using a copper Ka radiation. The pattern obtained is shown in Fig. 1, and the data of scattering angle (degrees 20) and the relative intensities (///max) are found in Table 1. 

The preamplifier amplifies the voltage pulse. Further amplification is obtained by sending the signal through an amplifier circuit (typically about 10 volts maximum). The pulse size is then determined by a single channel analyzer. Figure 10 shows the operation of a single channel analyzer. 

The single channel analyzer has two dial settings a LEVEL dial and a WINDOW dial. For example, when the level is set at 2 volts, and the window at 0.2 volts, the analyzer will give an output pulse only when the input pulse is between 2 and 2.2 volts. The output pulse is usually a standardized height and width logic pulse, as shown in Figure 11. 

Since the single channel analyzer can be set so that an output is only produced by a certain pulse size, it provides for the counting of one specific radiation in a mixed radiation field. 

By using a discriminator,the scaler can be set to read only the larger pulses produced by the neutron. A discriminator is basically a single channel analyzer with only one setting. Figure 12 illustrates the operation of a discriminator. 

The single channel analyzer/discriminator produces an output only when the input is a certain pulse size. 

A Princeton Gamma Tech Si (Li) solid state detector in conjunction with an EG G Ortec Model 673 Spectroscopy Amplifier and a Tennelec Model 450 Single Channel analyzer were employed to detect the characteristic Ru Ka... 

In pulse fluorometry, we take advantage of the fact that the amplitudes of the output pulses of the TAC are proportional to the times of arrival of the fluorescence photons on the photomultiplier. Selection of a given height of pulse, i.e. of a given time of arrival, is electronically possible (by means of a single-channel analyzer) and allows us to record the fluorescence spectra at a given time t after the excitation pulse. This is repeated for various times. The method described above for phase fluorometry can also be used in pulse fluorometry. 

Section 6.2.2) as follows because the excited-state lifetime is generally of a few nanoseconds, a single-channel analyzer is used in conjunction with a time-to-amplitude converter to process only the photons that are detected at times longer than 1 ns after the excitation pulse. 

Figure 3. Pulse height spectrum of gamma radiations. Window of single channel analyzer fixed to optimize intensity of 14.4-k,e,v, radiation...

Once we have the appropriate nuclide, we must separate the radiation of interest from all other radiation present. A typical gamma spectrum is shown in Figure 3 for cobalt-57 in palladium. The radiations which can be identified include the 6-k.e.v. x-ray, the 14-k.e.v. y-ray of interest, and a sum peak and palladium x-ray peak, both lying at about 21 k.e.v. If one now sets the single-channel analyzer window correctly, one observes essentially only the 14-k.e.v. peak, but all of this is not recoil-free radiation it includes other radiation which falls into the window from various gamma quantum de-excitation processes. 

Single-channel analyzer Shaped linear pulse Logic pulse if input amplitude lies within acceptance window... 

The second order Na K X-ray emission spectrum and the O X-ray emission spectrum were seen to overlap, the real intensity of the former being twice that of the lattes. Thirs, we eliminated the second order Na K X-ray using a single channel analyzer (SCA). 

The gamma ray scintillation spectrometer (Fig. 1) consisted of two single channel analyzers coupled to a common sodium iodide well detector, preamplifier, amplifier and scalers. By setting each analyzer for the appropriate energy the two isotopes were determined. 

Ultrafiltration was used to determine the extent of europium binding to humic acid. While stirring, Eu(III) + Eu- 152 tracer was added to a 10 ml solution of humate at pH 4.2 (ace tate buffer) in an Amicon model 8050 ultrafiltration cell. After a 500 /xL aliquot was withdrawn for counting, the cell was immediately pressurized. An Amicon YM2 filtration membrane (1000 molecular weight cut-off) would retain the humic acid plus the bound europium while unbound Eu(III) would elute. One ml of filtrate was collected and tested for the presence of humate by measuring the visible spectrum of the solution with a Milton Roy Spectronic 1201. On cessation of filtration, 500 /xL aliquots were removed from the filtrate and the residual solution above the membrane. The samples were counted for the presence of Eu-152 in a well-type Nal(Tl) crystal connected to a single channel analyzer. 

Discrete instruments may be designed to analyze samples for one analyte at a time. These are the so-called batch instruments, or single-channel analyzers. See Figure 23.3. However, those that analyze the samples in parallel, that is. 

Figure 1.7 Typical commercial NIMs (Continued)-, (c) single-channel analyzer, (d) scaler, (e) timer (made by Canberra and Tennelec).

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