Low-energy conversion electron detection in superfluid 3He at ultra-low temperature

We report on the first results of the MACHe3 (MAtrix of Cells of Helium 3) prototype experiment concerning the measurement of low-energy conversion electrons at ultra-low temperature. For the first time, the feasibility of the detection of low-energy electrons is demonstrated in superfluid 3He-B cooled down to 100μK. Low-energy electrons at 7.3 keV coming from the K shell conversion of the 14.4 keV nuclear transition of a low-activity 57Co source are detected, opening the possibility to use a 3He-based detector for the detection of Weakly Interacting Massive Particles (WIMPs) which are expected to release an amount of energy higher-bounded by 5.6 keV.