particle physics calculations

The annihilation of an electron and a positron may produce a pair of gamma photons. Calculate the mininum energy of each photon and the minimum frequency of the gamma radiation. Ive used E = mc^2 and E = hf and got 8.2x10^-14 J and 1.24x10^20Hz which i dont think is right.
Also,
To overcome proton-proton repulsion, nuclei need energies in the order of 110keV. Use this value to estimate the temperature needed for a proton to hve this amount of thermal energy - i just dont know how to do this :confused:

Can anyone help please?
Katie x

Reply 1

Little_Button

anyone?? would i be able to use 1/2 mv^2 = 3/2 kT for the 2nd question?

Reply 2

teachercol

You dont need the 1/2 mv^2 part.

3/2 kT = 100keV = 100 x 1000 x 1.6E-19 J

Reply 3

Mehh

teachercol

You dont need the 1/2 mv^2 part.

3/2 kT = 100keV = 100 x 1000 x 1.6E-19 J

Yea. Additionally since its an estimate question just do it to order of magnitude. Forget the 3/2 or 1/2 or 5/2 or 7/2 or whatever it is. Its really just the structure of the equation that counts.