Lavi, N., Groppi, F. and Alfassi, Z. (2004) On the Measurement of 40K in Natural and Synthetic Materials by the Method of High Resolution γ Ray Spectrometry. Radiation Measurements, 38, 139-143.
http://dx.doi.org/10.1016/j.radmeas.2003.11.005

has been cited by the following article:

• TITLE: Radioactive Contamination Factor (RCF) Obtained by Comparing Contaminant Radioactivity (137Cs) with Natural Radioactivity (40K) in Marine Sediments Taken up from Mexican Sea Waters

  AUTHORS: Manuel Navarrete, Miguel A. Zúñiga, Guillermo Espinosa, José I. Golzarri

  KEYWORDS: Radioactive, Contamination, Factor, Sea, Sediments

  JOURNAL NAME: World Journal of Nuclear Science and Technology, Vol.4 No.3, July 30, 2014

  ABSTRACT: Radioactive contamination at planet scale started in 1945 when the first nuclear taste was performed in Alamo Gordo, New Mexico, followed by two war actions in Japan, a second test in Bikini, and more than 2000 tests were performed all over the world by different countries since then on. In this context, 10 main accidents in power and research nuclear reactors seem to be negligible in the general radioactive contamination at planet scale, which can be measured by comparing radioactivity of fission product 137Cs with that of natural 40K, both detected from marine sediments taken up at different places and depth. This paper shows 9 results obtained from Gulf of Mexico samples and one from Pacific North ocean, confirming the fact that this simple method works well enough to keep watching the process of radioactive contamination on earth, whatever may be the cause, to prove if it remains constant for a time, by equilibrium between contamination and decaying of 137Cs, it is decreasing at same rate than 137Cs radioactive decaying, or by the contrary, it is growing up and approaching at some extent the natural radioactivity from 40K.