¹J.R.Lyons
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.05.001]
¹School of Earth & Space Exploration, Arizona State University, PO Box 871404, Tempe, AZ 85287, United States
Copyright Elsevier

Isotope fractionation due to photochemical self-shielding is believed to be responsible for the enrichment of inner solar system planetary materials in the rare isotopes of carbon, nitrogen, and oxygen relative to the Sun. Self-shielding may also contribute to sulfur isotope mass-independent fractionation in modern atmospheric sulfates, although its role in the early Earth atmosphere has not yet been convincingly established. Here, I present an analytical formulation of isotopic photodissociation rate coefficients that describe self-shielding isotope signatures for 3 and 4-isotope systems broadly representative of O and S isotopes. The analytic equations are derived for idealized molecular spectra, making an analytic formulation tractable. The idealized spectra characterize key features of actual isotopologue spectra, particularly for CO and SO2, but are applicable to many small molecules and their isotopologues. The analytic expressions are convenient for evaluating the magnitude of isotope effects without having to pursue involved numerical solutions. More importantly, the analytic expressions illustrate the origin of particular isotope signatures, such as the previously unexplained large mass-dependent fractionation associated with photodissociation of optically-thick SO2. The formulation presented here elucidates the origin of some of these important isotopic fractionation processes.

¹Rhiannon G. Mayne,²Catherine M. Corrigan,²Timothy J. McCoy,³James M. D. Day,²Timothy R. Rose
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13478]
¹Oscar E. Monnig Meteorite Collection, Texas Christian University, Fort Worth, Texas, 76109 USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, 20013‐7012 USA
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, 92093‐0244 USA
Published by arrangement with John Wiley & Sons

Qarabawi’s Camel Charm was acquired from Abdullah Qarabawi of the Ababda tribe of eastern Egypt. The charm consists of a chain with four links and an ~6.5 cm diameter flattened disk with the Arabic inscription “Allahu Akbar,” which translates as “God is Greatest.” Belief in the evil eye is prevalent among the Ababda, even to the modern day, and as men identify camels and the cultural objects and activities related to them as one of their most important possessions, charms and amulets are often used to ward off its influence. Nondestructive analyses of the disk and metallographic examination of the distal link reveal a deformed medium octahedral pattern, confirming the meteoritic origin of the Camel Charm. Major, minor, and trace element compositions are consistent with classification as a IIIAB iron. Combined heating to modest temperatures (~600 °C) and cold working were used in the manufacture of the Camel Charm. Although compositionally similar to the Wabar IIIAB irons, chemical differences, the significant distance between Wabar and eastern Egypt, and the lack of established trade routes suggest that the Camel Charm source material was a meteorite unknown as an unworked specimen. This meteorite has been given the name Wadi El Gamal, the name of a National Park in the Ababda homelands.

¹Juraj Beno,¹Robert Breier,¹Jozef Masarik
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13487]
¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Commenius University Bratislava, Bratislava, SK‐842 48 Slovakia
Published by arrangement with John Wiley & Sons

The solar activity can be quantified by solar modulation parameter Φ that affects the heliospheric magnetic field. This activity influences the intensity of the galactic cosmic ray (GCR) particle flux within the solar system, and consequently, the differential primary particle spectra depend on the solar modulation parameter Φ (MeV). The modulation parameter Φ shows spatial and temporal variations (Leya and Masarik 2009). Some of the solar activity variations are cyclic and result in measurable effects as for example the 11‐year solar cycle. Variations in solar activity only induce small effects on the production of long‐lived cosmogenic radionuclides. This is due to the fact that activities measured in meteorites usually correspond to saturation values and represent long‐term average values. Long‐lived radionuclides often require millions of years of irradiation by GCR to reach saturation and therefore activity cycles average out. In contrast, one can expect strongly pronounced variations for saturation values caused by primary flux intensity variations, if short‐lived radionuclides with half‐lives ranging from days to a few years are investigated. Short‐lived cosmogenic nuclides were the subject of many experimental and theoretical investigations (e.g., Evans et al. 1982; Spergel et al. 1986; Neumann et al. 1997; Komura et al. 2002; Laubenstein et al. 2012). The aim of this work is to develop formulae for calculating production rates of radionuclides with short half‐life, taking into account temporal variations in the primary cosmic ray intensity. The developed formulae were applied to the Kosice and Chelyabinsk meteorites. The results for the Košice meteorite were already published (Povinec et al. 2015). Here, we give a full explanation of underlying model.