STATISTICAL ANALYSIS OF RADON CONCENTRATION IN THE GROUND LAYER OF AIR IN TBILISI

Abstract

The results of statistical analysis of data on radon concentration in the ground layer of air in Tbilisi in 2010-2011 are presented. Radon concentrations were determined by measuring its nearest alpha decay products (radium A and radium C´). Air samples were collected into an AFA-RMP-20 filter for 5 minutes using a dedicated air pump. Alpha particles emitted from the filter were then counted using a BDZA receiver and a corresponding pulse counter. Measurements were taken four times daily: at 9:00, 12:00, 15:00, and 18:00 (at 17:00 in winter) at the third floor of the thermal chamber building (central Tbilisi, Kura River valley, a relatively unpolluted area, 8 meters above ground level, 41.754º N, 44.927º E, 450 m above sea level). Data analysis was performed without taking into account weather conditions.    
    Statistical characteristics of hourly, average daily, and monthly radon concentrations (C) in different periods and seasons of the year are presented. The following were studied: linear correlation (R) between hourly and average daily radon concentrations in different seasons of the year; repetition of hourly and average daily values of radon concentrations; intra annual distribution of mean monthly radon concentration; linear correlation and regression between intra annual distribution of radon concentration in 2010 and 2011.          
    In particular, the following results were obtained. According to annual data, the average radon concentration varied from 3.2 Bq/m³ at 17-18 h to 5.0 Bq/m³ at 9 h, with a daily average of 3.8 Bq/m³; the minimum C value was 0.4 Bq/m³ at 9 h, and the maximum was 19.6 Bq/m³, also at 9 h. The best correlations between hourly and average daily values ​​of C are observed in winter (0.73≤R≤0.95), the worst – in summer (0.08≤R≤0.82). For different seasons of the year and measurement time radon concentration distributions have one maximum within the range of C values >2÷4 Bq/m³  or>4÷6 Bq/m³. The intra-annual distribution of mean monthly radon concentration (C^*) is J-shaped: a decrease in C^* values ​​from January (first maximum value) to April-May (minimum), followed by an increase to maximum values ​​in December. These distributions have the form of a fifth-degree polynomial. Coefficient of linear correlation between intra annual distribution of C^* values in 2010 and 2011 change from 0.89 (for measurements at 9 hour) to 0.96 (for measurements at 12 hour). It is noted that the intra-annual distribution of C* values ​​for the period under study was quite stable.