Alpha Particle Kinetic Energy: Explained

[Manel]

i'm struggling to understand this:
an alpha particle is emitted with a kenetic energy 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

 

[mfb]

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

 

[Manel]

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

 

[mfb]

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.

 

[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?

 

[mfb]

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.

 

[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?