Poster

Secret nuclear meltdown? Measuring Cs-137 concentration from tree cores to determine radiation exposure from the Santa Susana Field Laboratory, Simi Valley, California

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Abstract

The Santa Susana Field Laboratory (SSFL) was a nuclear reactor development, rocket, and missile testing facility built ~48 km (30 miles) northwest of downtown Los Angeles in Simi Valley, CA. For two weeks in July of 1959, highly radioactive material was potentially emitted into the atmosphere following a secret nuclear incident. The meltdown was withheld from the public for three decades. The SSFL advisory panel, made up of researchers from the UCLA school of public health, estimate that up to 30% of the most toxic radionuclides were released from the reactor during the event. The spatial extent of the release and potentially affected regions are unknown because important information, including the duration, amount of material released, extent of damage to their cores, wind direction etc., has all been withheld by Boeing, the current site owner. In this study, we collect tree-cores of several species of the genus Quercus (Oak) from sites 5 - 10 km around SSFL to measure the radioactive isotope Cs-137, a common byproduct of nuclear fission with a half-life of ~30 years (i.e., ~25% original material still being present after the event). Tree cores from oaks are selected because previous studies deem them as reliable for age longevity and storage of radionuclides in their wood. All samples collected are divided into quinquennial growth, to correlate with the nuclear incident, and are measured for Cs-137 by a gamma-ray spectrometer. If radiation was released during a nuclear reactor failure and rocket engine testing at SSFL, then we should find measurable concentrations of Cs-137 in the surrounding ecosystem. This work will provide an estimate of if, when, and which surrounding communities were unknowingly exposed to radiation and the nuclear incident's magnitude.

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