Target Isotope Effects

The dichlorides of hafnocene and zirconocene were found by Hillman, Weiss and Hahne to have retentions of 15—60% and to show very strong isotope effects. The isotope effects were even larger in benzene solution than in the crystalline targets, reaching a value of 4.13 for the ratio of the retentions of "" Hf and Hf. 

Thus the counting rate should be sufficiently high to ensure a precision sufficient for isotope effect measurements a target precision of 0.1% is obtained for total counts of 106. Radiolabeled material used for isotope effect measurements usually has counting rates of 15,000 counts per minute (cpm). To achieve 0.1% precision such samples must be counted for 8 h or more. More often counting time is limited to several cycles of about 10 min each with a commensurate increase in the statistical error. 

This paper describes a new reaction which may yield useful amounts of the product isotope following neutron capture by lanthanide or actinide elements. The trivalent target ion is exchanged into Linde X or Y zeolite, fixed in the structure by appropriate heat treatment, and irradiated in a nuclear realtor. The (n, y) product isotope, one mass unit heavier than the target, is ejected from its exchange site location by y recoil. It may then be selectively eluted from the zeolite. The reaction has been demonstrated with several rare earths, and with americium and curium. Products typically contain about 50% of the neutron capture isotope, accompanied by about 1% of the target isotope. The effect of experimental variables on enrichment is discussed. 

Much of what is currently known about the Earth s climate comes from the application of stable isotopes collected from ocean drill cores in marine sediments (e.g., Zachos et al. 2001). These isotopic data sets provide detailed records of how the Earth s oceans have responded to changing climate and are extremely valuable in assessing global climate histories down to millennial scales. Similar detailed isotopic records for terrestrial systems are, however, uncommon and frequently continuous terrestrial climate records that span millions to tens of millions of years are not preserved in the terrestrial geologic record. With the advent of paleoaltimetry studies targeted directly at the coupled isotopic effects of changes in climate... 

However, cosmogenic reactions can also produce small variations in the abundances of stable isotopes. Such anomalies can be difficult to resolve from radic enic, nudeosynthetic, and stable isotope effects and, if undiscovered, can lead to erroneous data interpretations. Targeted measurements of isotopes that are generated at particularly high levels by such cosmogenic reactions (e.g., Sm, have... 

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