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57o
In the corresponding region proceeding the shell closure at W equal to
50 no conclusive indications of a similar pattern are found-
The data, however, indicate a small laaxiDBum for nuclei
containing 50 neutrons and a minimum preeeeding that region-
Our adopted values
show this behaviour, although a more regular pattern may also be possible©
A breaJc that cannot be smoothad out by any roeansjoscurs in the abundance
curves at A equal to 120 and 121a
The break, associated with a change in the character
of isotopic abundance distribution occurs at a point where the iranber of
neutrons in Hie nuclei reaches 70o
The break at this nui*er is \ms3qoected, but
the conclusion seems inevitable that tte high spin of the rtsutrons in the 6 hii/2
shell must in scans way t© connected wi.th this irregularityo
At the corresoonding
place for 112 neutrons a slight change in the character of tire abundance
disti^bution mi^t be disscemed, butt a break in the abundance curves, which m5.^t
possibly exist at A. equal to 186 and lfl7, can be smoothed out without difficulty©
Probably the filling of the 7 1 x3/2 neutron shell begins l^fore the nuaiber of
neutrons reaches 112-
Other irregularities in the hi^er mass range are less impressive and not
as firmly established-
Uncertainties in the relative abundamses of the rare
oarth eleu^nts make it impoaalble to recognize in a quantitative way an irregulailty
irtiich apparently exists in the A equal to 170 region, and to see what pattern
may be correlated with the fact that the odd A hafniim isotopes do not show abun-