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

• I
Gold Member I'm not very familiar with this topic so I quickly went through some introductory books on nuclear physcis 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

Related High Energy, Nuclear, Particle Physics News on Phys.org
mfb
Mentor
It's not impossible but apparently so unlikely that people haven't measured it yet.

• dRic2
bobob
Gold Member
View attachment 271120
I'm not very familiar with this topic so I quickly went through some introductory books on nuclear physcis 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.

• vanhees71 and dRic2
Gold Member
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 :)