Hydrogen isotope biogeochemistry reactors in 1988, but nuclear weapons testing in the 1950s added large spikes of radioactive elements to the atmosphere, especially radiocarbon and tritium. This complicated measurements for geologists using radiometric dating of carbon. However, some oceanographers benefited from the tritium increase, utilizing the signal in the water to trace physical mixing of water masses. In biogeochemistry, scientists focused primarily on the stable isotope of deuterium as a tracer for environmental processes, especially the water cycle. The American geochemist Harmon Craig, once a graduate student of Urey's, discovered the relationship between rainwater's hydrogen and oxygen isotope ratios. The linear correlation between
High Flux Isotope Reactor monitoring and enables individual inspectors to obtain large numbers of samples in the hopes of finding required evidence. By screening those samples, the very high costs of destructive analysis are required only for those samples deemed interesting. Delayed neutron analysis is becoming increasingly useful for these studies. A recent application involves the irradiation of programmable memory devices that have been coated with a small amount of a fissile isotope. The fission events induced upon irradiation may be tracked spatially by comparing the values in memory with those assigned to memory initially; areas of differences are attributed to damage caused by