HALO-1kT prototype He-3 counters: background studies

Abstract

The last supernova near our galaxy was in 1987. HALO-1kT will be a low background galactic Supernova detector. HALO- 1kT needs to have low backgrounds to detect a supernova on the far side of the galaxy. A big source of backgrounds is the planned 4.3 km of helium-3 proportional counters. My research tested the prototype proportional counters to ensure their backgrounds are low enough to avoid regular false positives. The first way of testing them was to take the 4 counters underground at SNOLAB to collect 3-4 months of data as well as a 2-day calibration run to see what the base background rate is. Two of the counters were then attached to electrostatic counters and counted to determine the background of the wall material. Those results showed emanation rates of 0.137 Hz to 0.811 Hz in the wall material. While that is clean, it is not clean enough to meet HALO-1kT background goals.