Compared to xenon, argon is cheaper and has a distinct scintillation time profile which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to 39
Ar contamination, unless one uses underground argon sources which has much less 39
Ar contamination. Most of the argon in the Earth’s atmosphere was produced by electron capture of long-lived 40
K (40
K + e− → 40
Ar + ν) present in natural potassium within the earth.