Compton scattering event

A number of special techniques have evolved to increase the detection sensitivity in y-ray counting. One of the most important is the suppression of the Compton scattering events in the y-ray spectrum by the use of anticoincidence annulus around the central y-ray detector. The idea behind a Compton suppression spectrometer is that most events in which the incident photon undergoes one or more Compton scattering events in the central detector will result in partial energy deposition in the detector with a low-energy photon escaping the detector. 

The relative values of absorption and transmission of adjacent elemental ray paths in an x-ray beam provide the contrast in a projected image. The associated interaction of the x-rays with the material body can be defined in terms of collision cross sections that describe the probability of particular events occurring along the ray path. Here, the principal effects, for x-ray energies below 1 MeV, are identified in Sec. 26.2 as the photoelectron event and the Compton scattering event. These effects are combined to define a linear attenuation coefficient pj(x) that describes the variation of photon intensity along the ray path x according to the exponential relation = o... 

Of course, any real detector represents a case somewhere between the above two extremes. We can expect that some Compton scattering events and even some pair production events might be followed by complete absorption of the residual gamma-ray energy or, more likely, by a greater partial absorption. There are other specific possibilities (Figure 2.10) which give rise to identifiable features in... 

In order to reduce errors resulting from the detection of Compton scattered photons (which can be as high as 35%[ 1), which lead to anomalous positioning of annihilation events, energy selection of the photons is... 

A further effect which is evident in Fig. 1(a) is that of scattering out of passive material. The modelled detector contains about 25% dead area which is mostly the Aluminium support structure. Above a few hundred keV all of the interactions in A1 are Compton scatters, and it is highly likely that the scattered photon will interact in the active pixels. The effect of scattered events can be removed by plotting the photopeak IPR efficiency... 

Fig. 3 On-line display of a Compton scattered y-ray event (1 274MeV), showing the digitized wavefonns induction signals and anode signal...

AE Between the single escape and double escape peaks there are events from Compton scattering of both escaping 511 keV photons, which leave the sensitive volume. Their... 

Figure 2.11 Spectra expected from detectors of different sizes. The larger the detector, the higher the proportion of events resulting in complete absorption PE, photoelectric effect CS, Compton scattering PP, pair production...

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