“…Of the 819 natural background level measurements, almost 550 measurements were extracted from studies reported in the literature (Black 1956, Radford and Hunt 1964, Taylor et al 1964, Glöbel et al 1966, Kuroda 1967, Holgye 1969, De Boeck et al 1971, Ladinskaya et al 1973, Bale et al 1975, Eakins and Morrison 1975, Novakova et al 1975, Okabayashi et al 1975, Juan and Ballelos 1976, Holtzman et al 1971, 1979, Spencer et al 1977, Helmkamp et al 1979, Clemente et al 1980, Okabayashi 1982, Irlweck 1982, Mancini et al 1984, Fenzi 1986, Azeredo and Lipsztein 1991, Hunt and Allington 1993, Santos et al 1994, 1995, 2000, Naumann et al 1998, Thomas et al 2001, Lipsztein et al 2003, Samavat and Seaward 2004, Schafer et al 2005, Al-Arifi et al 2006, Hunt and Rumney 2007, Kirchner and Kröger 2008, Gjelsvik et al 2009, Puerta et al 2009, Manickam et al 2010, Gascó et al 2011. The additional 269 measurements were contributions of previously unpublished data.…”