When a high-energy photon passes near the nucleus of an atom, it may be converte

Question

When a high-energy photon passes near the nucleus of an atom, it may be converted into an electron and a positron (“pair production”), as seen in the figure shown above. That is, the photon is transformed into the electron and positron; the original photon ceases to exist. A positron has the same mass as an electron (9.1 × 1031 kg), but the opposite charge (electron charge= 1.6 × 1019 coulombs, positron charge= +1.6 × 1019 coulombs).

(a) A photon of energy 2.2 × 1013 J produces an electron-positron pair. When the electron and positron are 1.0 × 1014 m from each other, what is the total kinetic energy of the electron-positron system?

Explanation / Answer

apply from the law of conservation of eenrgy

change in KE + PE = 2.2 e -13

0.5 mv^2 + Kq1q2/r

so total KE = (2.2 e -13) - (9e9 * 1.6e -19 * 1.6 e -19)/(1e -14)

total KE = 1.96 e -13 Joules

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