Unexpectedly narrower track diameter at site of fission event

Abstract

Fission events in minerals create a damage track, which provides critical information for events that occur over a wide range of time scales, ranging from nuclear fission events (10−20 to 10−12 seconds) to track formation (10−17 to 10−9 seconds) and geological processes (millions of years). However, the site where fission occurs has never been identified along a fission track, as it is long (∼20 μm), thin (diameter <10 nm), and randomly oriented in the mineral matrix. Here, we, for the first time, observe an unexpectedly narrower track diameter (∼1 nm), rather than the conventionally assumed largest diameter, near the fission-event site by a novel technique that confines fission events to the sample surface. The low-charge states of fission fragments produce the narrower track nearest the fission site due to the instantaneous partitioning of negatively charged electrons between two positively charged fission fragments, roughly scaling to their proton numbers. Because a narrower fission track is easier to anneal, the nanostructure nearest the fission site provides spatial information necessary for understanding the atomic-scale mechanisms of track formation and track annealing, with significant implications for fission track thermochronology.