the determination of yttrium in the presence of large amounts of the rare earths by the thermal neutron reaction ( 89 ) y ( n , gamma ) ( 90 ) y is complicated because of frequent problems of sample self-shielding from major constituents of the sample , and the difficulty of separating ( 90 ) y , a pure beta-emitter , from other elements which are very similar chemically .
C0025556
rare earths
C0013879
elements