Internal dose rate to K-feldspar grains from radioactive elements other than potassium

The concentrations of radioactive elements in K-feldspar grains were studied using electron micro-probe for potassium (K) content and inductively coupled plasma mass spectrometer (ICP-MS) for uranium (U), thorium (Th) and rubidium (Rb) contents. The K content of individual grains is 13-14%. The U, Th and Rb contents are sufficiently high to make significant contributions to the internal dose rate compared to the contribution from the K content. The U and Th contents are reduced, but not eliminated completely, by hydrofluoric (HF) acid etching.