Metrološki problemi određivanja radionuklida u uzorcima iz životne sredine

Abstract

U radii se razmatraju problemi odredivanja aktivnosti radionuklida 11 uzorcima iz zivolne sredine obzirom na metode sakupljanja uzoraka. metode za odredivanje aktivnosti radionuklida, tehnicke karakteristike i kalibraciju merila i opste usiove merenja. Ukazano je na prednost metode reprezentativnog uzorka i bioindikatora za odredene radionuklide u odnosu na metodu slucajnog uzorka. U opstem slucaju. radiohemijske metode imaju veci procenat gubitaka radionuklida u toku pripremc uzorka i samog merenja ali su cesto osetijivije. dok se kod spektromctrijc gama zracenja isti stepen osetljivosti postize produzenjem merenja i povecanjem mase uzorka. Ovo s druge strane moze predstavijati znacajan svega prirodnih vremena izvor greske, posebno kod merenja niskih aktivnosti, pre r radionuklida zbog varijacija nivoa prirodnog zracenja u toku merenja. Znacajni izvori gresaka mogu poticati i od nehomogenosti uzorka i geometrije merenja, jei su neke geometrije merenja pogodnije u datim uslovima merenja, obzirom na specificnu guslinu matriksa (nosaca radionuklida) i nivo aktivnosti radionuklida. Hemijski sastav i geometrija referentnih standardnih materijala u odnosu na sastav i geometriju merenja uzorka mogu predstavijati dodatni izvor greske. Minimizacija Likupne greske merenja postize se standardizacijom merila i metoda merenja u okviru postupaka interkalibracije i interkomparacije.

The paper reviews some of the basic problems in radionuclide activity determination in environmental samples. Problems arise from procedures ' sampling and sample preparation, technical characteristics and calibration or measuring instruments, data processing and presentation. Advantages of the representative sample method and bioindicators over the random sample method accentuated with regard to certain radionuclides. Significant errors in radiochemical methods occur due to losses during sample preparation and measurement. In general, radiochemical methods are more sensitive than gamma radiation spectrometry methods. The same level of sensitivity is achieved by prolonging the measurement period and/or by increasing the sample mass which can be a significant source of error particularly in low activity measurements of natural radionuclides because of natural radiation level variations during measurements. Significant error sources can also stem from non-homogeneity of the sample and measurement geometry. Some measurement geometries are more suitable than others which depends on the specific density of their matrix (radionuclide carrier) and the activity level of radionuclides. Differences in the chemical composition and the geometry betw'een reference materials and the sample can additionally generate errors. Total measurement error is minimized by the standardization of instruments and measurement methods resulting from intercalibration and intercomparison procedures. The importance of Quality Control and Quality Assurance program implementation is emphasized. are