**7. Acknowledgements**

Thanks are due to my granddaughter Laura Calinoiu for the revision of the text and to my colleagues from IFIN-HH, Radionuclide Metrology Laboratory: Dr. E.L. Grigorescu, Mrs. A.C. Wätjen, Dr. A. Luca, Dr. C. Ivan, Mr. A. Antohe for our common work.
