Compton Cosmic rays

The cosmic ray electrons which are responsible for the radio-halo and relic synchrotron emission inevitably Compton scatter the CMB (as well as other local background) photons which will then gain energy and emit at higher energy E ss 2.7 keV (E/GeV)2. Electrons with E E a few GeV produce emission in the HXR range, while electrons with E < 400 MeV produce soft X-rays and UV emission. There is actually evidence for an excess of emission w.r.t. the thermal bremsstrahlung emission by the hot IC gas in about 20 nearby clusters... 

X-rays, gamma, and cosmic rays are similar except for the fact that gamma and cosmic rays are natural. They ionize matter by photoelectric effect, Compton effect, and pair production (electron and positron). These radiations are of very high energy and therefore more penetrating. They cause injury to the tissues of the whole body. Therefore, they are more damaging to the living tissues. 

The previously cited sum peaks occur for two or more coincident gamma rays, for example, at 2505 keV for °Co. Interactions outside the detector commonly are detected as a peak at 511 keV due to annihilation radiation and at about 200 keV due to Compton scattering at 180°. Gamma rays produced by cosmic-ray interactions in or near the detector are observed as discussed in Section 8.2.2. 

Active background reduction is a means of reducing that continuum. I will discuss two aspects of this reduction in the Compton continuum within the spectrum and reduction of the cosmic ray continuum discussed above. Both involve additional detectors to detect gamma-rays that are either leaving the detector, in the case of Compton suppression, or might be about to enter the detector, in the case of background suppression. 

A Compton suppression shield should be chosen only after some thought. It is likely to be satisfactory only for the detection of gammas that are not in cascade. A veto guard detector will reduce cosmic ray events, being especially useful with high energies. 

All of the peaks due to the nuclides mentioned above will be sat on a continuum due to Compton scattering of the gamma-rays and backscattering and bremmstrahlung due to direct interaction of cosmic particles. This will be discussed further in Section 13.4.6. 

To observe a cosmic gamma ray, one must first devise a means to stop it (or at least to slow it down in some measurable way) within a detecting medium. In the gamma-ray regime, the primary interaction mechanisms of photons with matter are the photoelectric effect, the Compton effect, and pair production. Extensive analyses are available of these fundamental interaction processes. Here, we only briefly review their basic physical characteristics. 

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