EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Cosmic ray muons as a proxy for in-cruise galactic cosmic ray protons in 3He gas proportional counters

Jack T. Wilson1, Patrick N. Peplowski1, Zachary W. Yokley1, David J. Lawrence1, and Richard C. Elphic2
Jack T. Wilson et al.
  • 1The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA.
  • 2NASA Ames Research Center, Moffett Field, CA 94035, USA

3He gas proportional counters have an extensive history in planetary neutron spectroscopy and several upcoming missions including Psyche, VIPER, MMX and Dragonfly will include this technology. In space, Galactic Cosmic Ray (GCR) protons deposit energy in the 3He gas in these detectors via ionization. This energy deposition constitutes a background on top of the neutron capture pulse-height spectrum that is particularly prominent at low energies. As planetary nuclear spectroscopy experiments are often count-rate limited using the full pulse height spectrum, including the proton and triton wall effect regions, has significant value. This will be particularly true for the upcoming VIPER mission that will explore the permanently shaded regions at the Moon’s south pole using the Neutron Spectrometer System (NSS).  The NSS does not include a neutron generator, so the count rates are low, and the rover will not spend long at any location.  However, using lower-energy parts of the spectrum requires understanding the GCR-originating background, which none of the previous missions were able to measure due to their low-energy cutoffs. GCR protons with mean energy around 400 MeV deposit similar amounts of energy to the 4 GeV mean-energy muons present at ground level as both represent minimum ionizing particles within the 3He sensors.  We therefore developed an experiment using a pair of plastic scintillators in coincidence with a 3He tube to measure energy deposition from muons while excluding room background gamma rays.  Here we will present results of this experiment to characterize the angular response to cosmic ray muons of a 3He flight spare detector from the VIPER NSS and explore the implications of these results for analysis of planetary neutron data sets.

How to cite: Wilson, J. T., Peplowski, P. N., Yokley, Z. W., Lawrence, D. J., and Elphic, R. C.: Cosmic ray muons as a proxy for in-cruise galactic cosmic ray protons in 3He gas proportional counters, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17421,, 2023.