Preprints
Filtering by Subject: Cosmochemistry
Causation of Late Quaternary Rapid-increase Radiocarbon Anomalies
Published: 2019-05-07
Subjects: Astrophysics and Astronomy, Cosmochemistry, Earth Sciences, Physical Sciences and Mathematics
Brief (<100 y) rapid-increase anomalies in the Earth’s atmospheric 14C production have previously been attributed to either gamma photon radiation from supernovae or to cosmic ray particle radiation from exceptionally large solar flares. Analysis of distances and ages of nearby supernovae (SNe) remnant surveys, the probable gamma emissions, the predicted Earth-incident radiation, and the [...]
Introduction to Geochronology
Published: 2017-12-29
Subjects: Cosmochemistry, Earth Sciences, Geochemistry, Physical Sciences and Mathematics
These lecture notes cover the first half of an Isotope Geology module at University College London that deals with the geochronological aspects of the subject. The notes introduce the basic principles of radioactive decay, mass spectrometry and isotope dilution before discussing the most common geochronometers in use today, including radiocarbon, Rb-Sr, Sm-Nd, U-Pb, Pb-Pb, K-Ar, Ar-Ar, U-Th-He, [...]
Isotopic composition (238U/235U) of some commonly used uranium reference materials
Published: 2017-11-05
Subjects: Chemistry, Cosmochemistry, Earth Sciences, Geochemistry, Inorganic Chemistry, Physical Sciences and Mathematics
We have determined 238U/235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, and HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U–236U double spike to accurately correct for mass fractionation. Total uncertainty on the 238U/235U determinations is estimated to be <0.02% (2σ). These [...]
238U/235U Systematics in Terrestrial Uranium-Bearing Minerals
Published: 2017-11-05
Subjects: Chemistry, Cosmochemistry, Earth Sciences, Geochemistry, Inorganic Chemistry, Physical Sciences and Mathematics
The present-day 238U/235U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision 238U/235U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. [...]