Measurements of iridium and the meteoric impact hypothesis at cretaceous end

Details Measurements of iridium and the meteoric impact hypothesis at cretaceous end Measurements of iridium and the meteoric impact hypothesis at cretaceous end

Dec 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986ipespreptr....s&link_type=abstract

M.S. Thesis Instituto de Pesquisas Espaciais, Sao Jose dos Campos (Brazil).

Physics

Extinction, Geochronology, Hypervelocity Impact, Hypotheses, Iridium, Meteorite Collisions, Flux (Rate), Gold, Irradiation, Meteorites, Tellurium

Scientific paper

Both instrumental and radiochemical neutron activation analysis methods were developed for trace-element determination, such as iridium and gold, for application in cosmochemistry. The magnitude of the determined concentrations is in the range of parts per billion. In the instrumental method 1.5 grams of sample were submitted to irradiation by 10 to the 13th power thermal neutrons/sq cm/s during 32 hours. The gamma spectrometry is carried out with 10 to 12 hours counting time after 40 days of decay. In the radiochemical analysis a method of radiochemical separation of noble metals based on tellurium coprecipitation is implanted for iridium and gold determinations. As an application of the instrumental neutron activation analysis, preliminary iridium concentrations are measured for the first time in sedimentary rocks collected on Brazilian territory. These techniques for the determination of iridium content will be useful to check the asteroid impact hypothesis, supposedly the cause of the great Cretaceous/Tertiary mass extinction, using samples collected in the Southern Hemisphere.

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