Genetically Engineered Mouse Models (GEMM)The Genetically Engineered Mouse Models Core (GEMM)provides a variety of mouse genetic engineering services.
These services include vector design and construction, gene targeting and blastocyst injection for the production of gene-targeted mice, as well as vector design and construction and DNA microinjection for the production of transgenic mice.
We make routine high precision measurements of U, Th, Sm, REE, Ca, and Zr for (U-Th)/He chronometry, and the instrument is also capable of analyzing a very broad range of trace and major elements in solutions and solids.
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This alpha-ejection correction ranges from about 20-40% of the measured age for zircon or apatite crystals with typical sizes.
Uncertainty associated with the correction depends on uncertainties in measurements of crystal dimensions, the correspondence of analyzed and original crystal morphologies, and the distribution of parent nuclides both within the crystal and within the ~20- m external environment during He accumulation in the rock.
This equation assumes secular equilibrium of U- and Th-series isotopes, though additional information can account for disequilibrium effects in young (He concentration of a sample is a function of both production (as above) and diffusive loss, and can be represented and modeled as a function of time and temperature (e.g., Wolf et al., 1998).
The properties governing diffusive loss are described by Arrhenius laws for thermally activated volume diffusion, with parameters specific to each mineral species, crystal or diffusion domain size, and, in some cases, composition or radiation dosage (e.g., Shuster et al., 2006).
Just to show you what I've been up to lately, here is a shot of some of my favorite secondary minerals from my favorite place in the world.
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It can arguably be interpreted as an allegory for the history of thermochronology in general, in which early, presumably nonsensical or inconsistent ages are later interpreted as geologically meaningful cooling ages in the context of additional kinetic and geologic constraints (e.g., see review in Reiners et al., 2005).