# Energy of a gamma particle

1. Apr 27, 2015

### Ethan_Tab

1. The problem statement, all variables and given/known data

Fluorine-18 is an isotope of fluorine often used in positron emission tomography, as it undergoes beta negative decay.
1. a) Determine the decay equation for fluorine-18.

2. b) If the positron emitted collides with an electron, it annihilates the electron and emits 2 gamma particles in the opposite direction. Determine the energy that one gamma particle has as a result of this collision. m(electron/positron) = 0.000549 u
2. Relevant equations
E=mc^2

3. The attempt at a solution

1) 189F---->188O+e-1

2) Im not too sure about this one. Im assuming it has something to do with e=mc^2 but I'm not sure how to approach it

2. Apr 27, 2015

### SteamKing

Staff Emeritus
There's a couple of inconsistencies in the stated problem and your solution:

1) If fluorine-18 is used in PET, shouldn't it give off beta+ particles (positrons) instead of beta- particles (electrons)?

2) This is not how a beta decay reaction works:
189F---->188O+e-1

http://en.wikipedia.org/wiki/Beta_decay