The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2C
ASSESSING THE RISK OF RADON PROGENY ACCEPTABLE LEVEL
EXCEEDING IN LIVING QUARTERS
I.YU. SILACHYOV. A.ZH.TU LEUSHEV , V .N .GLU CH SHENKO
Institute o f N uclear Physics o f N ational N uclear Centre o f the R epublic o f K azakhstan, Alm aty, the R epublic o f Kazakhstan, silachyov@ inp.kz
Close attention is paid in the w orld over last decades to the effect o f radon isotopes and radon progenies (RP) on population health. RP concentration o f die air is m ostly m easured in th e units o f “w orking level”, b u t in R ussia and K azakhstan “equivalent equilibrium volum e activity” (EEVA) is u sed defined as w eighted sum o f short-lived radon and thoron progenies: E E V A ^ ^ R n ) =
0 .1 0 V ™ +
0 .5 2 V ,»
+ 0 .3 8 V ™ “ ><* E E V A J “ «Rn) =0.91V ™
+0 .0 9 V ,,,.
The acceptablelevel (P) is EEVA average annual o f radon isotopes: EEVARn+ 4.6 EEVATn. F or instance, this value being m easured in the exploited living quarter air m ust not exceed 200 B q/m 3. Such an approach supposes carrying out long-term and expensive m easurem ents o f radon EEVA average annual values using integrating m easuring m ethods.
A ssum ing instant RP m easurem ents in hum an settlem ents are described by a sm ooth distribution function, prelim inary survey can be restricted b y assessm ent o f the risk o f P
The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
exceeding. Since in this case indoor radon tem poral variations are not so im portant, im m ediate R P m easurem ents can b e used thus enabling to reduce essentially the cost o f survey.
Presenting all possible R P values in a hum an settlem ent as a continuous variate X, risk is probability P o f p exceeding * , = * * > , w here f(x) is a differential distribution function. I f only RP are m easured, thoron progeny contribution can b e accounted according to m ean w o rld statistical data: EEVATn = 0.1 EE V A ^. In this case the acceptable level o f radon isotope EEVA 200 Bq/m 3 corresponds to the m easured RP value o f 137 B q/m 3.
Risk assessm ent w as m ade b y the results o f instant RP m easurem ents (“TN -IR -21” , Thom son& N ielson Electronics Ltd.) in the course o f sam ple radiation survey o f the living quarters in hum an settlem ents o f four K azakhstan oblasts in sum m er period, 2002-2007. R adon EEVA distributions were approxim ated by lognorm al, exponential and, W eibull functions. A pproxim ation quality by the first tw o w as checked w ith the help o f non-param etric K olm ogorov-Sm im ov test, by the last one - using standard “probability-probability” plots. P p values corresponding three f(x ) types w ere calculated in STATISTIC A 6.0, StatSoft, Inc.
■ r * 9 M i s 1 ■. * ■ * * ! * # > **' --- . —... .....J • ...\ ... ... , ' 1 ... 1 | j ’■ i_______ 1. ■ i...,. ... . ... - ... - 1 ---- -- ... 20 40 60 80 100 120 RP mean value». Bq/n? 140 160
Fig. Dependence between RP mean values and risk assessments (%)
Stochastic dependences between risk assessments and some parameters ofRP empirical distributions (mean, geometric mean, median) were revealed. With 222Rn mean values not greater than 150-200 Bq/m3 these dependences can be assumed as linear ones confirmed by high correlation coefficients > 0.94. The closest relationship is observed between mean values o f radon EEVA and values calculated with f(x) approximation by lognormal function (Fig.). This dependence is of a certain practical importance allowing high-reliable risk assessment using the results of indoor RP
instant m easurem ents. The suggested approach does not require protracted m easuring and thus can be recom m ended in the course o f prelim inary radiation survey o f hum an settlem ents.
