1. Andrews, J.N., 1979,Inert Gases in Ground Water from the Bunter Sandstone of England as Indicator of Age and Paleoclimatic Trends. Jour. Hydrology,41, p. 233.
2. Baldi, P., Ceccarelli, A., Bertrami, R., Friedman, I., Lomabardi, S.,Helium in Soil Gases in Geothermal Areas. Seminar on Utilization of Geothermal Energy for Electric Power Production and Space Heating. Florence (Italy), 14–17 May 1984.
3. Brady, B.T., Rice, R.S., 1977,Helium Determination as an Explorations Technique at the Ambrosia Lake Uranium District, Mc Kinley County, New Mexico. U.S. Dept. of Interior, Geological Survey, Open-File Report 77-669.
4. Bulaschevich Yu., P., Bashorin, V.N., Druzhinin, V.S., 1974,Helium in Ground Water along the Sverdlovsk Deep-seismic Traverse. Am. Geol. Inst Dokl. Acad. Sci. U.S.R.,208, pp. 15–17.
5. Carrara, E., Pinna, E., Rapolla A., 1983,Indagini geofisiche nelle aree vulcaniche italiane di interesse geotermico. Abst., Atti accad. Ponteiana, Nuova Serie,XXXI.