All Problems

Elementary Particles

Problem 6.303

A positron with kinetic energy T=750keVT=750 \mathrm{keV} strikes a stationary free electron. As a result of annihilation, two gamma quanta with equal energies appear. Find the angle of divergence between them.

Reveal Answer
cos⁡(Θ/2)=1/1+2m/T, whence Θ=99∘\cos (\Theta / 2)=1 / \sqrt{1+2 m / T}, \text { whence } \Theta=99^{\circ}
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