# Alpha emission

1. Nov 10, 2014

### Manel

i'm struggling to understand this:
an alpha particle is emitted with a kenetic enery T, if we know the value of the depth of the nuclear potential well V, we find the kenetic energy of the alpha particle inside the nuclei by substructing V-T , would you please explain this to me? Thank's

2. Nov 10, 2014

### Staff: Mentor

"substructing" is subtracting?
I think this should be T-V. Or T+V, depending on the sign definition of "depth".

3. Nov 10, 2014

### Manel

the depth is postive,the problem is that i don't get why? i found V-T?

4. Nov 10, 2014

### Staff: Mentor

Well, the particle needs an energy E to get out. So if it has T outside, it had T+E inside. Now you can identify E with + or - V.

5. Nov 10, 2014

### Manel

so it's not V-T (because i couldn't get why) but if it's V+T i accept it, i thought that the particle can get out even if it has an energy lower than the potential well because of tunneling effect!! according to what you said it must have an energy greater or equal to it! is that right?

6. Nov 10, 2014

### Staff: Mentor

Wait... I always used the energy difference between "inside the nucleus" and "far away from it". The potential wall in between is something different.
If the alpha particle would have an energy larger than the potential wall, the nucleus would not exist at all (no bound state). All alpha decays are via tunneling.

7. Nov 11, 2014

### Manel

ok, i get that, so if we say: the energy outside is equal to T+V (taking V positive) we will get an energy for the alpha particle greater than the potential wall..in other words V is negative?