Title: Deposition of vaporized species onto glassy fallout from a near-surface nuclear test

Abstract

In a near-surface nuclear explosion where the resultant fireball can interact with the surface, vaporized materials from the nuclear device can be incorporated into molten soil and other carrier materials from that surface. This mixed material becomes a source of glassy fallout upon quenching and is locally deposited. Fallout formation models have been proposed; however, the specific mechanisms and physical conditions by which soil and other carrier materials interact in the fireball, as well as the subsequent incorporation of device materials with carrier materials, are not well constrained. We observe a surface deposition layer preserved at interfaces where two aerodynamic fallout glasses agglomerated and fused, and characterized 11 such boundaries using spatial analyses to better understand the vaporization and condensation behavior of species in the fireball. Using nanoscale secondary ion mass spectrometry (NanoSIMS), we identify higher enrichments of uranium from the device (235U/238U ratio >7.5) in 8 of the interface layers. Major element analysis of the interfaces reveals the deposition layer to be enriched in Fe, Ca, Mg, Mn, and Na-bearing species and depleted in Ti and Al-bearing species. Most notably, the Fe and Ca-bearing species are enriched approximately 50% at the interface layer relative to the average concentrations measuredmore » within the fallout glasses, while Ti and Al-bearing species are depleted by approximately 20%. SiO2 is found to be relatively invariable across the samples and interfaces (~3% standard deviation). The notable depletion of Al, a refractory oxide abundant in the soil, together with the enrichment of 235U and Fe, suggests an anthropogenic source of the enriched species or an unexpected vaporization/condensation behavior. The presence of both refractory (e.g., Ca and U) and volatile (e.g., Na) species approximately co-located in most of the observed layers (within 1.5 μm) suggests a continuous condensation process may also be occurring. These fallout formation processes deviate from historical models of fallout formation, and have not been previously recognized in the literature.« less

Authors:

Weisz, David G. ^[1]; Jacobsen, Benjamin ^[2]; Marks, Naomi E. ^[2]; Knight, Kim B. ^[2]; Isselhardt, Brett H. ^[2]; Matzel, Jennifer E. ^[2]; Weber, Peter K. ^[2]; Prussin, Stan G. ^[3]; Hutcheon, Ian D. ^[2]

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+ Show Author Affiliations

1. Univ. of California, Berkeley, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
3. Univ. of California, Berkeley, CA (United States)

Publication Date:

Sat Oct 29 00:00:00 EDT 2016

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); The Regents of the Univ. of California, Berkeley, CA (United States). Nuclear Science and Security Consortium

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation

OSTI Identifier:

1349786

Alternate Identifier(s):

OSTI ID: 1397814; OSTI ID: 1405147

Report Number(s):

LLNL-JRNL-684357
Journal ID: ISSN 0016-7037

Grant/Contract Number:  

AC52-07NA27344; NA0000979; JRNL-684357; NA0003180

Resource Type:

Accepted Manuscript

Journal Name:

Geochimica et Cosmochimica Acta

Additional Journal Information:

Journal Volume: 201; Journal Issue: C; Journal ID: ISSN 0016-7037

Publisher:

The Geochemical Society; The Meteoritical Society

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; nuclear fallout; condensation; fractionation; nuclear fireball; uranium isotopes; nanoSIMS; EPMA; 98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION