Understand selection rules in ##\beta##-decay/EC

[dRic2]

I'm not very familiar with this topic so I quickly went through some introductory books on nuclear physics and read the chpater about beta decay. What I don't understand looking at this graph is the following:
Why is the direct decay to ground state absolutely forbidden ? If you take a 1st order forbidden transition with $l = 3$, then parity can change and conservation of angular momentum can be assured by requiring the electron and neutrino to have opposite spin (S = 0). Yet you don't see this.

An other question I have is: are EC selection rules the same ones I have in $\beta$-decay? (I have zero background in nuclear physics so I apologize if my question is stupid)

Thanks Ric

 

[mfb]

It's not impossible but apparently so unlikely that people haven't measured it yet.

 

[bobob]

View attachment 271120
I'm not very familiar with this topic so I quickly went through some introductory books on nuclear physics and read the chpater about beta decay. What I don't understand looking at this graph is the following:
Why is the direct decay to ground state absolutely forbidden ?

The groundstate of 152Eu is 3− and the groundstate of 152Gd is 0+. That's a change Δ J=3 and a change of parity. That's at least a third order forbidden transition.

If you take a 1st order forbidden transition with l=3, then parity can change and conservation of angular momentum can be assured by requiring the electron and neutrino to have opposite spin (S = 0). Yet you don't see this.

A first forbidden Fermi transition has a Δ J of 0,1. A first forbidden GT transition has a Δ J of 0,1,2. Both have a change of parity. You have to go to a third order forbidden transition to get Δ J = 3 with a change of parity.

An other question I have is: are EC selection rules the same ones I have in β-decay? (I have zero background in nuclear physics so I apologize if my question is stupid)

Yes and none of those questions were stupid in any way.

 

[dRic2]

You have to go to a third order forbidden transition to get Δ J = 3 with a change of parity.

Yes, sorry. I was writing in a rush and didn't notice. Thank you for spotting my mistake :)