Question

Classify the following transitions (the spin parity, J^P, of the nuclear states are given in brackets):- 

¹⁴O →¹⁴N^∗ + e⁺ + ν(0⁺ → 0⁺) 

⁶He → ⁶Li + e⁻ + ν (0⁺ → 1⁺)

Why is the transition 

¹⁷F → 17O + e⁻ + ν (5/2⁺ → 5/2⁺) 

called a super-allowed transition?

Answer 1

The selection rules for allowed transitions in β-decay are:

where I is the nuclear spin and π is the parity. In view of the above selection rules the first transition is Fermi transition, the second one Gamow–Teller transition. The third one occurs between two mirror nuclei ¹⁷F and ¹⁷O in which the proton number and neutron number are interchanged.The configuration of nucleus is very much similar in such nuclei, consequently the wave functions are nearly identical. This leads to a large value for the overlap integral. The log ft value for such transitions is small being in the range of 3–3.7. These are characterized by 

ΔI = 0,±1 and Δπ = 0. The given transition ¹⁷F →¹⁷O is an example of super allowed transition.