Cosmogenic radionuclides in Antarctic H chondrites and radiocalcium developments in accelerator mass spectrometry
Abstract
The cosmogenic radionuclides $\rm\sp{10}Be\ (t\sb{1/2} = 1.5$ Myr), $\rm\sp{26}Al\ (t\sb{1/2} = 0.71$ Myr), and $\rm\sp{36}Cl (t\sb{1/2} = 0.30$ Myr) have been measured by accelerator mass spectrometry in 15 H chondrites from Allan Hills, Antarctica. The suite has unusually high natural thermoluminescence levels ($>$100 krad) and two samples have terrestrial ages $<$2.3 kyr, calculated from $\sp{14}$C activities. Terrestrial ages for the entire suite, determined from $\sp{36}$Cl activities are $<$78 kyr. Cosmogenic noble gas contents indicate two exposure ages at 6-7 Myr and 3-4 Myr. When production rate models are used together with $\rm\sp{10}Be,\ \sp{26}$Al, and $\rm\sp{22}Ne/\sp{21}$Ne contents, a complex exposure explains the data well. Results suggest the chondrites originate from a single genomict source, $\rm60 \leq r \leq 120$ cm, and experienced a recent change in perihelion to $<$1.0 A.U.
Cluster analysis was performed on 15 trace elements measured by radiochemical neutron activation analysis in 12 martian meteorites. It has been demonstrated through various population tests, the Ward's hierarchical cluster analysis is a robust method to study various multivariate meteorite populations. Ward's method provides a means to study classifications within the martian meteorite suite based on their trace elemental compositions. Clusters are very similar to those groups obtained using major refractory elements and mineralogic/petrographic characteristics. A method was developed to measure $\sp{41}$Ca at Purdue's PRIME Lab facility using the molecular ion CaH$\sb3\sp-$. The method is sensitive to $\rm\sp{41}Ca/\sp{40}Ca$ levels in the 10$\sp{-12}$ range with background $\rm\sp{41}Ca/\sp{40}Ca$ levels estimated at 10$\sp{-13}$. The first $\sp{41}$Ca measurements at the PRIME Lab facility were performed using 4 high density concrete samples from a decommissioned nuclear reactor biological shield in Manitoba, Canada. A depth profile was constructed to determine radionuclide contents and activity distributions within the biological shield.
Degree
Ph.D.
Advisors
Lipschutz, Purdue University.
Subject Area
Radiation|Analytical chemistry
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