What is the lowest beta energy that SEI’s units can detect? Posted on April 18, 2018July 3, 2019 The 10 keV mentioned in some of our specifications is specific to gamma/x rays. For beta particles, it is a bit different. For example, the detector used in The Ranger and Abacus units has an “Areal density” listed as 1.5 to 2.0 mg/cm^2. Looking this up on a beta particle range/energy curve, this thickness will stop all betas up to about 35 keV. Therefore the ABSOLUTE minimum beta energy that can be detected is about 35 keV, not taking into account any other physical factors (distance, self-absorption, the grill over the detector, etc.).