Detecting and evaluating minimal traces of radioisotopesin environment and foods

During the August 2012, 12 children from Japan have spent their holidays in Italy When they arrived we collected their urine and we found traces of Cs-137 and Cs-134. We again collected the urine before they leave Italy. In the first measurement we have found a clear sign of contamination by Cs-137 and Cs-134. The cesium is eliminated slowly. The daily amount of cesium excreted in urine is approximately 1% of the total cesium incorporated. The biological mean-life time of cesium is about 100 days. As a first ipothesys we can assume that the cesium contamination occurred during the first days after the accident in Fukushima. This assumption has been proved false by the final measurement after 25 days. At the end of the holidays we did a second measurement and we found a significant reduction in the activity not compatible with the hypothesis of acute contamination. Most likely the children have eaten contaminated food in the period prior to their departure from Japan, so we must assume a chronic contamination. The cesium in food is partly absorbed in the body and partly excreted daily in the urine. After a short time, an equilibrium condition is reached and the amount of cesium in the body remains constant, thus the amount of cesium which is excreted daily corresponds to the amount of cesium ingested daily with food. We measured the cesium excreted on the first day of arrival of the children, then we have an estimate of the amount of cesium taken daily with food. When the children started to eat uncontaminated food the equilibrium conditions were modified. In the urine there was only a fraction of cesium accumulated into the body. We know approximatively the fraction of cesium excreted daily (it about 1%) and we have measured it at the end of holidays, so we can calculate the total amount of cesium accumulated in to the boby. The first measurement can be used as an extimation of the cesium content in the food eaten daily. As a conclusion: there is still a contamination by Cs-137 and Cs-134 in environment and food in Japan, but the risk for the health is minimal in comparision with the most important natural radioisotope the Potassium 40. The european regulations fix a limit of 2 microgram per liter of Uranium in the mineral water used by new borns and children. This limit value (2 ppb) can be evaluated with a standard device like an ICP-MS. But often in our region the Uranium concentration is a thousandth of the limit value, just some ppt, so we need a more sensitive device: the Alfa spectroscopy. After a many-step chemical process the uranium has been fixed as a mono atomic layer on a steel plate. We use a Silicon Surface Barrier Detector to detect every single alfa particle and find the emitting radioisotope.