Determinazione di tracce di terre rare nelle rocce e nei minerali mediante attvazione neutronica

Viene fornita una descrizione generale delle tecniche di analisi in attivazione neutronica ed una spiegazione dettagliata del metodo di determinazione delle terre rare. II metodo usato h quello puramente strumentale. The neutron activation analysis is a method particularly able to evaluate many smples whatfs useful in geochemical applications. The reactor used in our analysis is a Triga moflel of 250 MW of power. We employed a neutron flux of 1012 n/cm2sec for three irradiation for each sample. A 30 hours flux for the isotopes with ahalfperiod over seven days, a 30 minutes flux for the halflifes of about 3 hours and an irradiation of 5 minutes for the very short lifes. The first are counted aftera wefe.k, the seconds are counted after 2 or 3 days and the last just after the irradiation. These gamma counting are repeated periodically, expecially for the long-lived nuclides. The nuclear reactions considered for our gamma counting are reported at the end in the tables. We used a Ge/Li crystal and an equipment of LABEN to evaluate our results. The total amount of sample necessary to a complete analysis is just about 250 mg. The procedure employed are all instrumental neutron activation analysis: no separation procedures are considered in this work.