Cosmic ray tracks in astrophysical ices: Modeling with the Geant4-DNA Monte Carlo Toolkit

Abstract

Cosmic rays are ubiquitous in interstellar environments, and their bombardment of dust-grain ice mantles is a possible driver for the formation of complex, even prebiotic molecules. Yet, critical data that are essential for accurate modeling of this phenomenon, such as the average radii of cosmic-ray tracks in amorphous solid water (ASW) remain unconstrained. It is shown that cosmic ray tracks in ASW can be approximated as a cylindrical volume with an average radius that is mostly independent of the initial particle energy. Interactions between energetic ions and both a low-density amorphous (LDA) and high-density amorphous (HDA) ice target are simulated using the Geant4-DNA Monte Carlo toolkit, which allows for tracking secondary electrons down to subexcitation energies in the material. We find the peak track core radii, $r_{\mathrm{cyl}}$, for LDA and HDA ices to be 9.9 nm and 8.4 nm, respectively - somewhat less than double the value of 5 nm often assumed in astrochemical models.

arXiv comment19 pages, 7 figures, 1 table (accepted in ApJ)

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Cited by in corpus (4)

• Laboratory and Computational Studies of Interstellar Ices
• Ice mantles on dust grains: dramatic variation of thickness with grain size
• The sulfur plume in the Horsehead nebula: New detections of S${}_2$H, SH${}^{+}$, and CO${}^{+}$
• The Cosmic-Ray Induced Sputtering Process On Icy Grains