Dartmouth College Department of Earth Sciences

 

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Short-lived Isotopes Laboratory

 

The Short-lived isotope laboratory in Department of Earth Sciences at Dartmouth College is equipped to measure the abundance of a variety of short-lived isotopes. We have three Canberra “Broad Energy” Intrinsic Ge Detectors, each equipped with a low-background lead shield for the determination of natural and anthropogenic radionuclides in soils and sediment. We specifically analyze for “fallout” Pb-210 (T 1/2 = 22.3 years), Cs-137 (T 1/2 = 32.1 years), Am-241 ( 241Pu daughter, 241Pu T 1/2 =14.4 years; 241Am T 1/2 = 432 years), and 7Be (T 1/2 = 53 days). Fallout radionuclides are useful for tracing physical processes (soil mixing, erosion, sedimentation) and geochemical processes occurring at the earth's surface on timescales of years to decades. We are also capable of analyzing for “geogenic” radionuclides, including K-40, Th-234, U-238 (via Th-234), Ra-226, Rn-222 (via Pb-214, Bi-214), Ra-228 (via Ac-228), and Th-228 (via 212Pb). Geogenic radionuclides can be used alone or in conjunction with fallout radionuclides to source sediment, quantify sedimentation processes, and investigate particulate dynamics in lakes, rivers, estuaries, and in the ocean. For example, radiocesium production and distribution is largely limited to the period since 1945, during which time aboveground nuclear testing spread Cs throughout the world. Thus, the presence of radiocesium at depth in a soil profile indicates that either physical mixing, or chemical transport has occurred on that timescale. Similarly, Pb-210 is produced from the decay of radon, and provides a useful tracer of surficial processes (both chemical and physical) that occur on time scales of hundreds of years.

 

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