<p> A new dating method has been developed which
uses fission product xenon in a manner similar to
radiogenic argon in the 40Ar - 39Ar method.
Measurable quantities of spontaneous fission xenon
accumulate with time in rocks and minerals containing
approximately 1 ppm or more of uranium as a result of
the spontaneous fission of 238u. In the past, attempts
have been made to date this type of sample by measuring
the absolute amount of fission product xenon and the
uranium content. In the new method a sample is irradiated
in a thermal neutron flux to implant xenon from
the neutron induced fission of 235u in amounts
proportional to the uranium content. After a short
cooling period (before radioactive 133xe has decayed)
the sample is placed in a high vacuum system and the
xenon is released by heating in a series of temperature
steps. For each step the isotopic composition of the
xenon is measured using a high sensitivity mass spectrameter
and the ratio of spontaneous fission xenon to
neutron fission xenon is calculated. Fission xenon ages
for all steps are then calculated from the spontaneous to neutron fission xenon ratios and the measured integrated neutron flux. </p> <p> The method has several advantages over the conventional U - Xe technique. {a) The measurement of isotope
ratios is inherently more precise than the measurement of
absolute quantities. (b) Whereas the conventional U - Xe
technique measures the sample date only once, the method
described in this thesis measures the sample date several
times. (c) If a geological disturbance has caused loss
of fission xenon a valid date can still be obtained using
the low mobility xenon released at high temperatures.
(d) In some samples disturbed dates as well as initial
formation dates can be measured. </p> <p> The method was developed and evaluated by a series
of experiments which dated four zircon samples, one sphene
sample, and a carbonatite sample. The zircon and sphene
samples had been dated in other laboratories by the conventional
u - Th - Pb and Rb - Sr methods. Fission xenon dating
of these samples provided valuable new geochronological
information. The experiments also showed that in addition
to the advantages mentioned, the new method appears to be
better able to see past metamorphic events than other
methods. </p> / Thesis / Candidate in Philosophy
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20368 |
| Date | 06 1900 |
| Creators | Teitsma, Albert |
| Contributors | Clarke, W. B., Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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