Gamma-ray activity determination in large volume samples with a Ge-Li detector

A method for the determination of the γ-ray activity of large volume sources is described and discussed. The efficiency of the detector is expressed as the product of an intrinsic, a geometrical, and a self-absorption factor. The first and the second terms are determined experimentally while the last is evaluated theoretically. The method has been applied to the determination of the γ specific activity of natural potassium and natural lanthanum. For potassium a value of 3.21 +- 0.01 γ/s g of K was obtained, while for 138La the partial half-lives for the photons of 789.1 and 1435.8 keV turned out to be 3.68 +- 0.14 x 1011 y and 1.99 +- 0.03 x 1011 y, respectively