Isotopic water composition amount effect

Many years of International Atomic Eneigy Agency netwoik data show that the average isotopic compositions of meteoric water correlates with mean snrface temperatures. This woiks particularly well when the mean surfaee temperature drops below 15°C. Above 15°C, something called the amount effect becomes dominant and the relationship between surface temperature and the isotopic composition of rain breaks down (Fig. 7). This latter scenario is more common in the tropics and summer storm activity such as monsoons. 

In fact, when either chloride ion or water is added to the reaction mixture, both the rate and the product composition change markedly. For example, the rate increases by fourteen times and the product composition changes from 9% of the N-coupled diazoamino compound to 79% of the diazoamino compound when the chloride ion concentration is increased from zero to 1.4 x 10" M. The amount of the N-coupled diazoamino product also increased at all three temperatures used in the study as the amount of amine (base) increased. On the basis of the base catalysis and the hydrogen-deuterium kinetic isotope effects and their studies of other diazo coupling reactions, the authors concluded that the N-coupling and the C-coupling reactions both proceed by an S 2 mechanism with the proton transfer from the cr-complex rate-determining. The results are best explained by the mechanism presented in Scheme 3. 

A series of experiments has been completed with plutonium obtained from extreme high burnup fuel to establish the combined effects of the various isotopes of plutonium on criticality. The isotopic composition of the plutonium, as measured on August 11, 1971, was Pu-0.2 wt%, Pu-41.4 Wt%, Pu-42.9wt%, Pu-10.8wt%, and Pu-4.7 wt%. A nonnegligible amount of Am also was present to the extent of 1.08 wt% of the total Pu. The experiments were performed in a 24-ln.-diam, water-reflected, cylindrical vessel. Ten data points were obtained with the critical heights and masses de rmined for various plutonium concentrations and nitric acid molarities in the plutonium nitrate solutions. Plutonium concentrations covered the range of about 40 to 140 g Phi/liter with nitric acid molarities ranging from about 1.5 to 5. 

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