Electron-positron pair production

Electron penetration, of aluminum, 176 of x-ray target, 8, 9 Electron-positron pair production, 290 Element determinations,. bibliography, 328-331... 

In his intervention Blackett treated the discovery of the positron in cosmic rays by C. D. Anderson in 193246 and its confirmation by Blackett and Occhialini,47 who had introduced, for the first time, the technique of triggering a vertical cloud chamber by means of the coincidence between two Geiger counters, one placed above, the other below the chamber. Blackett also discussed a number of papers by Meitner and Philipp, Curie-Joliot, Blackett, Chadwick and Occhialini, and Anderson and Nedder-meyer,48 all appearing almost at the same time, on the production of positrons in various elements irradiated with the -/-rays of 2.62 MeV energy of The. These were the first observations of electron-positron pair production. He also pointed out that the observed production of positrons has a cross section larger than the nuclear dimensions, and therefore, most probably, does not originate from a nuclear process. 

Table 1.1 Cross-sections for free electron-positron pair production. Collision energies are given in units of GeV per nucleon (GeV/u).

Electron-positron pair production is rather unaffected by the charge distribution. It is sufficiently well described by assuming point-like nuclei. The tiny effects caused... 

The linear attenuation coefficient is the sum of the probabilities of interaction per unit path length by each of the three scattering and absorption processes photoelectric effect, Compton effect, and electron-positron pair production. The reciprocal of p is defined as the mean-free path, which is the average distance the photon travels in an absorber before an interaction takes place. 

The hmiting factor in the a-(i theory appears to be the time of 700 seconds required to turn half the available neutrons into protons for deuterium production. As a possible remedy it was suggested that electron-positron pair production at T > 10 °K t < 2s) could speed up the formation of protons by the fast process... 

Temperature > 10 K. This was the temperature during the first few minutes after the Big Bang. At this temperature the thermal motion of the protons and neutrons is so violent that even the strong nuclear forces cannot hold them together. Electron-positron pairs appear and disappear spontaneously and are in thermal equilibrium with radiation. (The threshold for electron-positron pair production is about 6 x 10 K.)... 

Example 9.1 At a temperature T, the average energy hv of a thermal photon is roughly equal to kT. As discussed in Chapter 2, at high temperatures electron-positron pairs will be spontaneously produced when the energy of photons is larger the than the rest energy 2mc of an electron-positron pair (where m is the mass of the electron). Calculate the temperature at which electron-positron pair production occurs. 

Hubbell, J.H. (2006) Electron positron pair production by pbotons a historical overview. Rad. Phys. Chem., 75,614. 

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