The use of in-situ produced cosmogenic helium to measure surface exposure ages has many applications in the earth sciences. Because 3He is stable and has a high production rate (by cosmic ray spallation), it can be used to measure the ages of both young (~ kyr) and old (~myr) surfaces. However, there are a number of important problems that must be addressed. Most important, it is critical to have accurate determination of the production rate as a function of latitude, altitude and depth and time. The acquisition of new data from young radiocarbon dated lava flows will help constrain the reason for the apparent 3He production rate changes during the last 10 ka (which may be partly due to dipole moment fluctuations). In addition, it is critical to know diffusion rates to assess the importance of diffusive helium loss. This proposal seeks funds to address these problems with new measurements of dated lava flows and glacial moraines, production rate experiments, and diffusion measurements. The combination of field work and laboratory experiments proposed is critical to evaluating the precision of the technique, the basic assumptions involved, and for developing surface exposure dating for use in geomorphology, glacial geology, volcanology, and archaeology.
