Browsing by Author "Mayer, Adam John"

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    Measurement of the absolute isotopic composition and atomic weight of molybdenum by multiple collector inductively coupled plasma mass spectrometry
    (2012-10-03) Mayer, Adam John; Wieser, Michael
    Analytical techniques have been developed for measuring the absolute isotopic composition of molybdenum reference materials using multiple collector inductively coupled plasma mass spectrometry. A correction for instrumental mass bias was performed using a molybdenum double-spike prepared from gravimetric mixtures of 92Mo and 98Mo isotope spikes. Careful assessments of laboratory procedures and data were performed to analyze possible impacts on the nal results. The absolute isotopic composition of the SCP Science - PlasmaCal molybdenum reference material was determined to be: 92Mo=14.626(17), 94Mo=9.182(5), 95Mo=15.869(5), 96Mo=16.67(3), 97Mo=9.585(3), 98Mo=24.308(14), and 100Mo=9.758(11). The atomic weight of molybdenum in PlasmaCal was calculated as Ar=95.9508(16). Delta values (reported as 98=85Mo relative to PlasmaCal) were determined for: NIST SRM-3134, +0.37(14)‰; Johnson-Matthey pure molybdenum rod, -0.32(14)‰; BCR-2, +0.28(14)‰; and SDO-1, +1.5(5)‰. The total natural variation of molybdenum of -1.5‰ to +3‰ results in a calculated atomic weight of Ar=[95.948, 95.956].
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    Study of the decay of Zr-96 by isotope geochemistry and Penning trap mass spectrometry
    (2018-04-30) Mayer, Adam John; Thompson, Robert Ian; Wieser, Michael E.; Dilling, Jens; Sharma, Kumar; Nair, Rajeev Sasidharan; Hobill, David W.
    Double-beta ( ßß) decay measurements are a class of nuclear studies with the objective of detecting a neutrinoless decay process. 96Zr is of particular interest as a ßß decay candidate as it has one of the shortest ßß-decay half-lives and largest Q-values. In addition, it is also unstable against the fourfold unique-forbidden single ß decay, decaying via 96Zr->96Nb which then immediately decays to 96Mo. These properties thus designate 96Zr as a unique system to test nuclear theory. Prior to the work outlined in this thesis, two published measurements of the 96Zr half-life yielded quite different results. A geochemical measurement of the decay in ancient zircon samples resulted in a value of T(1/2)=0.94(32)x10^19 a. Conversely, a direct count rate measurement found the ßß-decay half-life to be T( 1/2,ßß)=2.35(21)x10^19 a. The geochemical measurement of the 96Zr half-life does not discriminate between the two decay channels and thus, in conjunction with ßß-decay count-rate data, could provide a way to measure the single-beta decay rate. The aim of this project was to study this system through a series of experiments combining nuclear physics and geochemical techniques. First, the single and double-ß decay Q-values were measured using the JYFLTRAP mass spectrometer. This measurement significantly improved the Q-value uncertainties over previous measurements, refining the underlying nuclear theory to improve understanding of the single-ß decay path of 96Zr->96Nb. A study of the geochemical measurement was then performed. Zircon can remain a closed system over its lifetime and is especially suitable for this investigation due to its high Zr content and low Mo content. A novel method for the separation of molybdenum from zirconium was developed to enable the detection of the small amount of accumulated decay product as an excess compared to the natural Mo isotopic composition. The 96Mo isotopic anomaly in a 2.68 Ga zircon sample was determined to be 107(40) ppm, which translates to a 96Zr half-life of (1.8(+0.7/-0.4))x10^19 a. With the 2νßß partial decay half-life known to be 2.35(21)x10^19 a, a lower limit for the single ß decay half-life was set at T(1/2,ß)=3.5x10^19 a.