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61.
at an even mass number- From this, one can understand the fact that the odd 4
abundance curve is much more smoothed out than that for the even A species.
Otherwise the difference in the abiujdancea of tbe even and odd nuclear species
nay be only a qualitative nature o
As expressed by Haricin's rule, there is alsT&ys one even A isobar at each
mass number trith an abundance greater ttianthe geometric mean of the respective
odd A neighbor So
The difference in the even and odd abundances, 1. e», the
even odd effect of the abundances, decreases with increasing mass nutdbers and
disappears for several mass numbers around A » 170 and 190o
The even odd effect of the abundances, as expressed by Harkin's rule can
not bo a sinple conaeqxience of the difference in the binding energies between
the even and odd A nuclei, as was assuned for many years-
The effect does
not follow fron ttisneutron captmre theory of the formation of the aleaaents, but
a nunber of refinomsitts and additional assun^ptions are possible which could
explain the effect within the frame of this theory in a satisfactory way-
For
exainple, tt^ rate of the processes in a beta decay series is on the average
SOTiewhat greater for odd than for even mass mudbers so that odd A si^cies formed
on the neutron-rich slope of the energy valley will decay into speeies tdth a
lower neutron exe«