Commutivity of track formation and surface preparation in BP-1 track-etch detectors

Abstract

Using the Trek detector, an array of barium phosphate glass track-etch detectors deployed on the Russian space station Mir from 1991 to 1995, we have measured the abundances of elements with Z>70 in the galactic cosmic-rays (GCRs). Trek consisted of stacks of individually polished thin BP-1 glass detectors. The next generation BP-1 cosmic-ray detector, the Extremely heavy Cosmic-ray Composition Observer (ECCO), will be capable of measuring the age of GCR nuclei using the extremely rare actinides (Th, U, Pu, Cm) as clocks. ECCO will be a very large instrument (23–30 m 2 in area, depending on spacecraft), but will achieve both excellent resolution and low cost through use of a novel detector configuration. An essential feature of the new configuration is that detector surfaces are ground and polished after exposure on orbit. Naively, one might expect post-flight surface preparation to have a deleterious effect on detector signal. Here we show that, in BP-1 detectors, post-exposure surface preparation has no measurable effect on either the amplitude or the dispersion of the detector signal – in other words, latent nuclear track formation and detector surface preparation commute. This property of BP-1 enables ECCO to be effectively pointable, and also dramatically reduces the costs of pre-flight detector construction and post-flight detector processing.