[Critical aspects in determining total radioactivity of biological samples]

During measurements of radioactivity in some milk samples with liquid scintillation counter (about one year after the nuclear accident of Chernobyl) we have observed an increase of the values of scintillation fluid with the passing of time. Although this enhancement is absolutely small (about 2 c.p.m. in 500 min), it is very important for an exact measurement of samples at low counting, as those tested. Our protocol of measure provides for insertion of alternate blanks and samples in the automatic sample-holders of liquid scintillation counter. The values of measurement of samples are taken during the increase phase subtracting the value of blank interpolated on the increasing straight line from c.p.m. of sample. Finally, we report the collected values of the whole radioactivity in some milk samples: at least 5-6 nCi/L contrary to about 1 nCi/L of 137Cs reported by USL. In our opinion it is important to consider the whole radioactivity as measure of the overall biological danger of radioactive samples. In fact, this measurement takes into account also biologically very dangerous radionuclides as 3H, 14C, 90Sr.