Question

A particle and its antiparticle are at rest relative to an observer and annihilate (completely destroying both masses), creating two γ rays of equal energy. What is the characteristic γ-ray energy you would look for if searching for evidence of proton-antiproton annihilation? (The fact that such radiation is rarely observed is evidence that there is very little antimatter in the universe.)

(a)938MeV
(b)1GeV
(c)1.022MeV
(d)511keV

Answer 1

The characteristic γ-ray energy one would look for in proton-antiproton annihilation is 938 MeV; much greater than the 0.511-MeV energy from electron-positron annihilation due to the proton's larger rest mass.

Step-by-step explanation:

When a particle and its antiparticle annihilate, they convert their entire rest mass into energy in the form of γ rays. For proton-antiproton annihilation, each γ ray would carry an energy equivalent to the rest mass energy of the proton (or antiproton), which is approximately 938 MeV.

Therefore, the characteristic γ-ray energy you would look for if searching for evidence of proton-antiproton annihilation is (a) 938 MeV. This energy release is significantly higher than the 0.511-MeV energy associated with electron-positron annihilation, which occurs because the rest mass of a proton is much greater than that of an electron.