introduction-weak-interaction-volume-one

which has the limiting form s
h(Q) --- (1/30) Q5 , Q. >> 5 (3 .4 .15 )
(the Sargent rule), and
h(Q) (2/105) Q7 , Q < 0.5 , (3 .4.16 )
the logarithmic term being unimportant at high energies . Experimentally ,
the 'comparative half-life' ,
ht = (h(Q)) Ti , (3 .4 .17 )
of beta-emitters is often measured, and, by substituting values fo r
EO
in (3 .4 .14), this may be used to give information concerning matri x
elements . We now append a table giving the values of log10ht for a few
typical beta decays : (30)
Parent nucleus JP Product nucleus JP lo ,lOh t
n 4 1H ;- 4 3 .0744
3x
- 3He 3 .03
6He 0+ 6Li 1 + 2 .77
39A 7 /2 39Kr 3/2 1- 9 .0 3
380l 2 38A 0 + 8 .1 5
22Na 3 +
2 e 0 + 11 .9
,Table 3 . 1
We see that the beta decay matrix elements vary over
a wide range of
values, but that transitions with large amplitudes all involve
J = * 1, 0 . (3 .4 .18 )
Obviously the electron and antineutrino carry away zero angular momentu m
if they are emitted with their spins antiparallel, corresponding to th e
Fermi selection rul e
DJ = 0 , (3 .4 .19a )
and unit angular momentum if with their spins parallel, according t o
the Gamow-Teller rul e
~J = ± 1 . (3 .4 .19b )
In neither of the cases (3 .4 .19) does the decay involve
a change in
intrinsic parity . When beta decay matrix elements were first measured ,
it was thought that only transitions of the pure Fermi type (3 .4 .19a)