Optimizacija merenja koncentracije radona u zatvorenom prostoru metodom ugljenih filtera

Abstract

Merenje koncentracija radona u zatvorenom prostoru metodom ugljenih filtera se sprovodi duže od 30 godina. Postoji više varijanti ove metode, a varijanta koja se zasniva na otvorenim kanisterima i gama-spektrometrijskim merenjima (EPA metoda) ima relativno nizak prag detekcije i koristi se za kraća merenja, ali je osetljiva na promenu uslova tokom izlaganja kanistera. U ovoj tezi su metoda i njena primena detaljno opisane i izvršen pregled dostupne literature, a posebna pažnja je posvećena određivanju krivih kalibracionog faktora i faktora podešavanja i diskutovani su alternativni načini kalibracije. U dostupnoj literaturi postoji vrlo malo podataka o određivanju merne nesigurnosti EPA metode. Na osnovu merenja u školama i stanovima, određen je jednostavan model merne nesigurnosti, koji je primenjiv za najveći broj izlaganja kanistera. Takođe su određena optimalna podešavanja za gama-spektrometrijska merenja, uzevši u obzir mernu nesigurnost, jednostavnost merenja i potrebno vreme. U laboratorijskoj zgradi u INN “Vinča” je sprovedena dugotrajna kampanja merenja koncentracije radona i pokazano je kako se ova metoda može koristiti za određivanje srednjih mesečnih i godišnjih koncentracija i sezonskih korekcionih faktora. Tokom izlaganja kanistera, kontinuirano su praćeni temperatura i relativna vlažnost vazduha, što je omogućilo da se proveri uticaj ovih parametara na masu adsorbovane vode u recikliranim kanisterima i uporedi sa rezultatima ostvarenim sa novim kanisterima tokom kalibracije. Pošto su primećene značajne razlike u ponašanju kanistera, predložena je korekcija. Poređenje rezultata ostvarenih EPA metodom sa drugim metodama, kao i sa drugim laboratorijama koje takođe koriste EPA metodu, pokazalo je da je podudaranje rezultata u većini okolnosti zadovoljavajuće, ali da to nije uvek slučaj. Takvi nalazi su zahtevali da se ponovo preispita budžet merne nesigurnosti, kao i zahtevi za način postavljanja kanistera. Dodatnim merenjima i detaljnom analizom postojećih rezultata, kao i analizom dostupnih literaturnih podataka, identifikovan je niz doprinosa mernoj nesigurnosti koji nisu razmatrani u literaturi niti u prethodnim merenjima u INN Vinča. Ovi doprinosi su kvantifikovani i određene su preporuke za postavljanje kanistera u cilju smanjenja merne nesigurnosti i optimizacije metode...

Indoor radon concentrations have been measured by means of charcoal canisters for over 30 years. There are several variations of this method. Variant of the method with open-faced canisters and gamma spectrometric measurements (EPA method) is relatively sensitive and is used for short time measurements, but is susceptible to change in conditions during canister exposure. The method and its application are described in detail in this thesis and an overview of available literature is presented. Special attention is given to determination of calibration factors and adjustment factors. Alternative calibration procedures are also discussed. In the available literature, there is very little information about measurement uncertainty of EPA method. A simple measurement uncertainty budget is presented, based on the measurements performed in schools and dwellings. This budget is applicable for most of the canister exposures and is easy for application. Optimum settings of the range of interest in gamma spectrum are determined, having in mind measurement uncertainty, ease of application and needed time. Long term measurement campaign was conducted in a laboratory building in Vinča Institute. The results were used to show how EPA method can be used for determination of mean monthly and yearly concentrations and for calculation of seasonal correction factors. During the canister exposures, ambient temperature and relative air humidity were continuously monitored, which allowed the investigation of the influence of these parameters on the mass of adsorbed water in recycled canisters and comparison with the results for new canisters used for calibration. Significant differences were observed, and a correction was proposed. Comparison of results obtained by EPA method with other methods, as well as with other laboratories using the same method, has shown that there are no significant differences for most exposure conditions. However, in some cases, significant differences were observed. Such observations prompted reevaluation of uncertainty budget and the requirements for canister exposure. Additional measurements were conducted, the existing measurements analyzed and a detailed overview of available literature was conducted, which allowed to identify contributions to measurement uncertainty that are not discussed in available literature and not taken into account in previous measurements. These contributions were quantified and new recommendations for canister exposure are proposed, in order to optimize the method...