Low-level measurement of alpha-particle emitting nuclei in ceramics and lead

Abstract

Nearly all natural materials contain trace quantities of uranium (U) and thorium (Th) and their daughter nuclides, many of which emit α-particles in their decay. Lead, at the end of the U-decay chain, typically contains some radioactive²¹⁰Pb which is chemically inseparable from the other Pb isotopes. α-particle emission from these decays can affect sensitive electronic components, such as memory chips or processors. Measurement of α-particle emitters can be accomplished by direct detection of the α-particles (which typically provides no positive identification of the emitting isotope because of energy loss in the sample) or by low-background γ-ray spectroscopy (which does provide positive identification via characteristic γ-rays.) The latter is by far the best method for screening kg-sized samples of materials like ceramics, aluminum, iron or copper. The difference between α counting and γ-ray spectroscopy is less for measuring²¹⁰Pb in Pb since the 46.5 keV characteristic γ-rays directly following the²¹⁰Pb decay are strongly absorbed and both methods are limited to thin layers. This paper discusses these two cases and concludes that a large n-type germanium γ-ray spectrometer is probably the best overall system for both measurements.