Oddo-Harkins effect

A principal difficulty in handling and comparing data for the lanthanides has been the so-called odd-even effect, in which the even-numbered lanthanides are more abundant than those with odd atomic numbers. Thus, La is almost always less abundant than Ce, a consequence of the inherent stability of even-numbered nuclides compared to those of odd mass number (the well-known Oddo-Harkins effect). These variations are shown in fig. 2. 

Various normalising procedures have been adopted to overcome the complexity induced by the Oddo-Harkins effect in comparing data. These have included plotting odd- and even-numbered elements separately, normalising to La, or Yb, and so on. All these methods are of historical interest only, and the Coryell—Masuda (Masuda, 1962, Coryell et al. 1963) method of normalising the lanthanide data is now universally used. This method consists of forming a ratio of one lanthanide pattern to another, commonly a chondritic abundance pattern (fig. 2). This procedure has several advantages ... 

Fig. 2. (a) Raw lanthanide abundance data for Australian shales and Cl chondritic meteorites, showing the inherently higher concentrations of even-numbered elements (the Oddo—Harkins effect, due to the greater stability of even-numbered nuclides), (b) The lanthanide pattern resulting from normalising the Australian shale abundance data to the Cl chondritic values. This normalisation illustrates both the relative abundance and fractionation of the lanthanides compared to values typical of the primordial solar nebula. (Data are from table 4.) ... 

The absolute concentrations of REE in geological materials follow the Oddo-Harkins, or odd-even, effect such that even atomic number elements are of higher concentrations than their adjacent odd atomic number counterparts. Since REE concentrations and relative distributions are also highly variable among rocks and minerals, it is difficult to compare absolute abundances graphically. Accordingly, it is customary to display REE data as a plot of normalized... 

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