The half- life of a positron is very short. it reacts with an electron, and the masses of both are converted to two gamma-ray photons:

(0e+1)+ (0e-1)---> 2?

(the 0 in front of e is the mass # and behind it is the atomic #)

(? stands for the photons)

This reaction is called an annihilation reaction. the mass of an electrion or positron is 9.109 * 10^-31 kg

a) Calculate the energy produced by the reaction between one electron and one positron.( in Joules)

change in E= ______J

b)Assuming that the two ?-ray photons have the same frequency,calculate this frequency.

? photon=_____Hz