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Detecting and evaluating minimal traces of radioisotopesin environment and foods
No full textDuring 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
Utilizzo di Image Plate per la dosimetria personale e ambientale
No full textPurpose: A few years ago one of the largest manufacturers of photographic dosimeters has announced the discontinuation of production of this material, so the dosimetry services have had to find an alternative. We have begun to investigate the use of material based on photostimulable phosphors entirely similar to that used in computed radiography commonly referred to as Image Plate. In order to enable the use of new dosimeters phosphors we had to characterize the material, build the systems for reading and implementing the management software. After a few years of activity, we can say that the phosphor dosimeters combine the advantages of photographic dosimetry and TLD.
Methods and materials: The use of materials similar to the image plate for the dosimetry of ionizing radiation has been proposed for several years and in all experiences was highlighted the extreme sensitivity on the one hand and on the other hand that the fading is the typical problem of these materials [1]. The material we used, mainly the IP Fuji model VI, presents a fading with two decay times of the signal, there is a very rapid reduction of the signal in the early hours, then the residual signal remains at nearly constant values for very long times, this allows the use in personal and environmental dosimetry that have cycle times of the order of one or more months. For the sequential read of hundreds of dosimeters has been designed and developed a scanner that can identify each dosimeter via a barcode and then capture an image that is stored in a file in DICOM format. The dose is evaluated on the basis of a calibration performed with radiation beams of variable energy between 40 and 1250 keV. The advantage of having images easily transferable in electronic form allows users to verify the actual irradiation conditions.
Results: After a period of intense activity with the phosphor dosimeters we can say that there are numerous advantages compared to the photographic dosimetry and the TLD. The new method eliminates all chemical processes for the development of films that involve physical fatigue and problems for waste collection, you get a picture in digital format which allows a better evaluation of the dose and the ease in storing and transmitting data, finally, the sensitivity of the dosimeters phosphors is so high that can be used for measuring the environmental background.
Conclusion: The availability of passive dosimeters similar to image plates has made significant improvements in radiation protection, has improved the sensitivity, linear response, the dynamic range but above all it is simple to archive the dosimeter image in the form of a file in DICOM format that can be easily transmitted through the network web.
References:
[1] D. Mouhssine, A. Nourreddine, A. Nachab, A. Pape, F. Fernandez : A new environmental dosimeter with imaging plates for the fast neutron monitoring, Nuclear Instruments and Methods in Physics Research B 227 (2005) 609–61
Realizzazione di uno strumento a matrice di fotoresistori per la mappatura di fasci di radiazione
No full textStudio dosimetrico di un applicatore ginecologico per sorgenti di Co60 mediante l'impiego di un elaboratore
No full textIL PROGETTO LABORAD 2005 : UN LABORATORIO FAI DA TE PER LA RIVELAZIONE DELLA RADIOATTIVITA’ NATURALE
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Correlazione tra la radioattività naturale e la composizione chimica e mineralogica dei materiali da costruzione
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