# Homework Help: Electric Dipole Transition

1. Feb 25, 2010

### Fluffy86

Hey
have another problem with one of my exercises
1. The problem statement, all variables and given/known data
Make a crude estimate for the mean life of an electric dipole transition

in a atom $$E_\gamma = 10 eV$$
in a nucleus $$E_\gamma = 1 MeV$$

2. Relevant equations
$$W_{\alpha \beta} &=& \frac{4}{3} \frac{e^2}{\hbar^4 c^3} E_\gamma^3 |<\beta|\vec{x}|\alpha>|^2 \ &=& \frac{4}{3} \frac{\alpha}{\hbar^3 c^2} E_\gamma^3 |<\beta|\vec{x}|\alpha>|^2$$
with the first \alpha beeing the fine structure constant $$\alpha = \frac{e^2}{\hbar c}=\frac{1}{137}$$

3. The attempt at a solution
I am not quite sure how to estimate the last factor in the equation. Since we just have to do a crude estimate i dont think we have to calculate it with real wavefunctions(dont know if there are even wavefunctions for nuclei)
So my first thought was since $$|<\beta|\vec{x}|\alpha>|^2$$ has the dimension of a length^2 I inserted the typical lengthscales of an atom, the Bohr radius, and for the nucleus 1fm.
For the atom I get W= 1.1 10^9 1/s and for the nucleus 3.82 *10^14 1/s.
The lifetime is just the inverse of these. But I think the lifetime is then too small, I have something like 10^(-8) in my mind for the atom.
Anyone has a idea how to estimate it in a better way?

Bye
Fluffy

2. Feb 25, 2010

### kuruman

Crude estimates of this type are usually handled with the Uncertainty principle.