This grant provides support for the acquisition of two Germanium gamma ray scintillometers for the analysis of short lived radioisotopes (e.g., 7Be T1/2 = 53 d and 210Pb T1/2 = 22.3 yr). As a result of their short half lives, these fallout radionuclides make excellent tracers of short term riverine bed load residence times. Both 7Be and 210Pb are reactive and readily adsorb to fine grained minerals (< 2 mm) common in fluvial bed loads. Given the differences in their half lives, the activity ratio 7Be/210Pb decreases with increased residence time of the sediments since last exposure to the atmosphere where it acquired its initial fallout activity. The transport of fine sediment (nominal diameter of less than ~2 mm) controls the sequestration of contaminants in fluvial environments. In addition, fine sediment is often a significant component of overall sediment flux, and thus can be an important agent of geomorphic change. The proposed equipment will be immediately employed in NSF-funded research by PIs at Dartmouth College to study the bed residence time of fine sediment in mixed-load rivers with relevance to understanding the effects of dam construction and removal on sediment dynamics and the transport and fate of particle reactive deleterious substances (e.g., trace metals, hydrocarbons). The proposed equipment would impact research and teaching in the Departments of Earth Sciences, Geography, and Environmental Studies at Dartmouth College. The equipment will support undergraduate and graduate student research in riverine sediment dynamics. The PIs plan to involve undergraduate women participating in Dartmouth's Women In Science Program - a program designed to encourage women to enter and continue in science, math, and engineering through mentoring and early hands-on research experience.
