Non-destructive activation determination of gadolinium, holmium and erbium in geological samples by means of epithermal neutrons

The neutron activation determination of Gd, Ho and Er by means of thermal neutrons is connected with some difficulties, comming from the activity of great number of radionuclides obtained by (n, γ)-nuclear reactions with high cross-section. In the present work samples are irradiated with neutrons whose energy is greater than 8.5 eV. As filter a cadmium foil is used. The corresponding cadmium ratios have been determined. The irradiations are carried out with neutron flux 1,6.1012 neutrons/cm2sec for 1 hour and the measurements - after 2-4 hours cooling time by means of Li (Ge)-Detector and Multichannel Analyser-Computer ''Histomat''. The method is applied for the determination of Gd, Ho and Er in apatites, titanites and ortites from South-Bulgaria. The data obtained agreed with the established diminution in the content of rare earths from Gd to Er. (author)