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.
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