# Homework Help: Pair production question,

1. Apr 19, 2010

### Kiwithepike

1. The problem statement, all variables and given/known data
If positron and electron have the same rest energy can pair production occur?

2. Relevant equations
E=hc/λ plancks equation
E=mc^2

3. The attempt at a solution
so i found the E of the photons using plancks equation
and found the photon E to be 6.83x10^-14 ( should I double this due to two photons required?)
so
for pair production the energy of the photons has to be at least the energy of mc^2
so i just added the positron and electrons masses and multiplied by c^2
and got 1.64x10^-13
did i do this correctly? so Ephoton < E of Positron and electron so no pair production can occur?
am i missing anything or do something wrong?

Last edited: Apr 19, 2010
2. Apr 19, 2010

### vela

Staff Emeritus
You still seem to be leaving out information. Could you please post the entire text of the problem?

3. Apr 19, 2010

### Kiwithepike

heres the first part
A. Use wiens law to determine the peak wavelength of blackbody photons where T = 10^9K
so λ= 2.9x10^-3 / 10^9
=> λ = 2.9x10^-12
then
B. use planck Eq to determine the energy of the photons
E = hc/λ => E = (6.6x10^-25)(3x10^8)/ 2.9x10^-12 => E = 6.83x10^-14

C. The positron and electron where created by pair production (ie. Photon + photon --> Positron + Electron). If Both positron and electron have the same "rest energy" show whether or pair production can occur.
I tried using E=mc^2
I know that the energy of the photns must be atleast the energy of the posi and electron.
so mc^2 is the energy of the electron and positron.
used m as (9.109x10^-31)x2 since the positron and electron have the same mass.

Last edited: Apr 19, 2010
4. Apr 19, 2010

### vela

Staff Emeritus
You need to include units on your numbers. You've calculated the individual energies correctiy. You just need to make sure the initial energy exceeds the minimum energy of electron-positron pair.

5. Apr 19, 2010

### Kiwithepike

ok il make sure to add units,
just for clarification is the E i calculated in step B the initial ? and if it's not larger they cant be formed right?

thanks for all the help!