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

  • Context: Undergrad 
  • Thread starter Thread starter dRic2
  • Start date Start date
  • Tags Tags
    Rules Selection rules
Click For Summary

Discussion Overview

The discussion revolves around the selection rules in beta decay and electron capture (EC), particularly focusing on the conditions under which certain transitions are allowed or forbidden. Participants explore the implications of angular momentum and parity changes in these processes, as well as the differences between beta decay and EC selection rules.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why direct decay to the ground state is considered absolutely forbidden, suggesting that a first-order forbidden transition with l = 3 could allow for parity change and conservation of angular momentum.
  • Another participant notes that while direct decay is not impossible, it is so unlikely that it has not been measured.
  • A participant elaborates on the transition rules, stating that the ground state of 152Eu (3−) to 152Gd (0+) involves a change of Δ J = 3 and a change of parity, categorizing it as a third-order forbidden transition.
  • There is a discussion about the selection rules for EC and whether they are the same as those for beta decay, with one participant affirming that the questions posed are valid.
  • A participant acknowledges a mistake in their earlier explanation regarding the order of forbidden transitions.

Areas of Agreement / Disagreement

Participants express differing views on the nature of forbidden transitions, with some uncertainty about the implications of angular momentum and parity changes. The discussion does not reach a consensus on the specifics of the selection rules for beta decay and EC.

Contextual Notes

Participants reference specific transitions and their orders without resolving the underlying assumptions or definitions that may affect the discussion. There is an acknowledgment of potential errors in earlier statements, but no final resolution is reached.

Who May Find This Useful

This discussion may be of interest to those studying nuclear physics, particularly in understanding beta decay and electron capture processes, as well as the associated selection rules and their implications.

dRic2
Gold Member
Messages
887
Reaction score
225
Schermata 2020-10-18 alle 16.37.18.png

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
 
Physics news on Phys.org
It's not impossible but apparently so unlikely that people haven't measured it yet.
 
  • Like
Likes   Reactions: dRic2
dRic2 said:
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.
 
  • Like
Likes   Reactions: vanhees71 and dRic2
bobob said:
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 :)
 

Similar threads

  • · Replies 32 ·
2
Replies
32
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 4 ·
Replies
4
Views
5K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
2
Views
2K