Pulse Height Distribution

Another important property of PMTs is the pulse height distribution. The amplification of individual photoelectrons by the PMT is a stochastic process that causes variations in the gain of individual photoelectrons. As a result significant jitter in the amplitude of the output pulses is observed, see Fig. 3.6. These pulse height variations can be more than a factor of 10. The lowest pulse heights mainly consist of (thermal) noise, indicated by the dashed line in Fig. 3.6. The pulse height distribution exhibits a peak corresponding to detected photons. The threshold level of the... 

Fig. 3.6. The pulses produced by PMTs show a distribution in pulse heights. The lowest pulses are caused by noise (dashed line) and the higher pulses are due to detected photons. The vertical line indicates the position of the valley in the pulse height distribution. This position would correspond to the optimal setting for the discriminator.

Weber, R. J M. R. Stolzenburg, S. N. Pandis, and P. H. McMurry, Inversion of Ultrafine Condensation Nucleus Counter Pulse Height Distributions to Obtain Nanoparticle (— 3—10 nm) Size Distributions, J. Aerosol Sci, 29, 601-615 (1998). 

These are amplified and sent to a pulse height analyzer which sorts out the pulses and displays a pulse height spectrum. A particular gamma ray shows up as a fairly sharp peak in this pulse height distribution. 

In the pulse-height distributions of Compton interactions of y-rays in scintillation detectors there are two prominent features usually present (1) the Compton edge, which corresponds to the maximum energy that can be transferred to an electron by the y-ray, and (2) the backscatter peak, which corresponds to the absorption of a photon which has been scattered through 180° in the material surrounding the detector. 

A pulse height distribution shifts toward a lower pulse height. 

A probe has been developed to measure two important phytoplankton characteristics in situ and while underway in marine waters. The unit consists of a shipboard laser source and signal processor that are connected to a submerged sensory unit by an optical fiber cable. The submerged unit consists of two sensors one measures particle size from the intensity of individual fluorescence pulses and the other obtains excitation spectra for chlorophyll a emission. The submerged unit is towed by a ship, and the measured data, such as the fluorescence pulse-height distribution and the excitation (emission) spectra, are obtained aboard ship. 

Method of Data Processing. The amplitude of the signal pulses depends on the size of the phytoplankters, their trajectory, and their position in the measured volume because of the nonuniformity of the irradiated intensity and the characteristics of the collecting optics (Figure 6). This section presents our method to obtain size information of the particles from the raw data of the pulse-height distribution. 

If the pulse-height distribution is denoted by 8(7 ), where the pulse height is in the ith channel, and the size distribution of the ph)4 oplankton is denoted by N r), then the relation between S Ii) and N r) is expressed by... 

Equations 2-4 assume that the pulse-height distribution has m divisions, the size distribution has n divisions, and the Ar is the bin width of the size classification. In our actual calculations, we had 20 divisions. 

Figure 8, Pulse-height distribution for system calibration (green algae). (Reproduced with permission from Ref. 2. Copyright 1983, Japan Association of Automatic Control Engineers.)...

Figure 14. Pulse-height distribution (field data).

Figure 15. Particle-size distribution from pulse-height distribution shown in...

Fig. 7-19 Pulse-height distribution curves for three kinds of counter. Incident radiation isMn/fa(A = 2A0k,hv - 5.90keV) and Mn = 1.91 A,Av = 6.50 keV). Frankel and Aitken [7.14].

Fig. 7-22 Pulse-height distribution curves showing escape peaks (ep) in proportional counters for (a) Mo Kol radiation incident on a krypton counter and (b) Cu K

Figure 5. Pulse height distribution of a tandem pair of MCPs each having L/d - 80.1 and A - 12.5 pm. Conditions (top) gain, 106 and FWHM, 58%. Conditions (middle) gain, 1.9 106 and FWHM, 41%. Conditions (bottom) gain, 4.6 106 and FWHM, 32%.

The two-dimensional position of the incident photon can be extracted from the centroid of the induced pulse-height distribution in the two cathode planes. There are two main methods for position determination, the delay line method and the amplifier per wire method. 

THE RELATIONSHIP BETWEEN PULSE-HEIGHT DISTRIBUTION AND ENERGY SPECTRUM... 

Since the relationship between pulse-height distribution and energy spectrum depends on these three requirements, it is important to discuss them in some detail. 

As a result of incomplete energy deposition and the statistical nature of the events that take place in the detector, the shape of the pulse-height distribution is different from that of the source energy spectrum. In other words, two spectra are involved in every measurement ... 

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