The flux of ionizing radiation from cosmic background sources has been measured as a function of altitude using a compact Geiger counter aboard a high altitude balloon. The payload was developed by researchers from University of Tsukuba and flown under the auspices of the Utah State Get-Away-Special (GAS) team. Dose rate, temperature, pressure, humidity, altitude and position data were acquired during a ~4 hour flight up to an altitude of 32 km in August 2016. The altitude reached by this balloon was more than 5 times the height of that reached by Victor Hess’ experiment in 1912, which later won him the Nobel Prize in 1936. At this altitude the dose rate increased by a factor of ~300. Data from a second flight in October 2016 will be corrected for the temperature and pressure dependence of the efficiency of the Geiger counter. Both the magnitude and non-monotonically increasing profile of the dose curve with altitude were found to agree well with numerous other previous measurements and with theoretical predictions based on the production of showers of daughter products generated by interactions with the atmosphere of high energy protons, alpha particles, electrons and higher mass nuclei that originate primarily from outside the solar system.

# Partially funded by Japan Student Services Organization (JASSO), and University of Tsukuba
* Support for the USU Get Away Special (GAS) team comes from the Office of the Vice President for Research at USU and the USU Space Dynamics Laboratory (SDL).