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Concentrations of 222Rn and its short-lived decay products at a number of greek radon spas
537
Nuclear Instruments and Methods in Physics Research B17 (1986) 537-539 North-Holland, Amsterdam
CONCENTRATIONS OF ‘**Rn AND ITS SHORT-LIVED AT A NUMBER OF GREEK RADON SPAS P. KRITIDIS
DECAY PRODUCTS
and P. ANGELOU
Environmental Rodiooctiuity Laboratory, Department of Nuclear Technology, Nuclear Research Center “Democritos’: Aghia Poroskeui, Attiki, Greece
A series of measurements has been performed in 9 radon therapy centers in order to determine its decay products in the air and to assess the related personnel and patient annual doses.
1. Introduction Concentrations of “*Rn of the order of 1 MBq mm3 have been measured in waters of certain Greek spas. The therapy centers using these waters present a typical example of “technologically enhanced” natural radioactivity caused by the release of significant amounts of 222Rn in the indoor air. This results in elevated air concentrations of radon decay products (RDP: accumula*tspo *14Pb *r4Bi, 214Po). Their prolonged tion in the lung can result in considerable local irradiation. A series of measurements has been performed in 9 radon therapy centers of Loutraki and Kammena Vourla (Greece) in order to determine the concentration levels of RDP in air and to assess the related personnel and patient annual doses. The concentrations of ***Rn in the water used have been determined as well. The present report concentrates on the methods used, while the results and dose estimates have to be further confirmed and analyzed.
2.I. 222Rn concentrations in the waters The concentrations of ***Rn in the water have been determined with the well established laboratory method of partial radon transfer to the measuring chamber (here - a Lucas cell [l]) in a closed air loop (fig. 1). A number of measures have been applied to improve the accuracy and reliability of the method: - The use of vacuum sampling. The glass samplers are evacuated in the laboratory and are able to keep sufficient under-pressure for days. Thus sampling is possible even under very unfavourable field conditions, where the alternative “syphon” sampling cannot be applied. - The combined sampler/extractor construction al0168-583X/86/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
levels of radon
and
lows the direct connection of the sampler to the extraction air loop, without any loss-potential water transfer. - Air circulation extraction of radon is used instead of vacuum. It can be shown [2] that this leads to lower overall uncertainty in the case of low chamber-to-sample volume ratio. The duration of air circulation is 20 min with a flow rate of 0.3 1 min -’ and at controlled water temperature of = 20°C. - Volume and temperature corrections are applied in the form of “normalization” of each result (including calibrations) to the nominal values of V, V, and T (fig. 1). The correction coefficient is given by C,, = 1 - (L3I$/W) -(SK/ST)
AV-
(SK/SK)
Av,
AT,
(1)
where
is the equilibrium part of radon in the measuring chamber and S(T) is the solubility coefficient of radon in the water as given by the empirical relation [3]: S(T)
2. Methods
concentration
= 0.106 + 0.405 e.& -O.O52T(“C)],
(2)
AV, AV, and AT are the respective differences between the actual and the nominal values; AV is known for each sampler, A V, is determined volumetrically and AT is controlled during the radon extraction. The system has been calibrated by use of = 100 Bq 226Ra solutions in radioactive equilibrium with 222Rn. The calibration coefficient is equal to 102 Bq m-3/cpm. The background counting rate is = 1 cpm. The 95% confidence detection level is 45 Bq me3 for a 30-min measurement at the 3rd hour after the end of air circulation, when equilibrium between 222Rn and its shortlived decay products has been established [4]. 2.2. RDP concentrations in air The concentrations of RDP in air have been determined by use of two field variants of the three VI. NATURAL RADIONUCLIDES
538
P. Kriridis,
P. Angelou
of “‘Rn
/ Concentrations
al some rudon spav
l-
Sampler/extractor:
2 -
Sample: Vs= 250 ml
3 -
Water bath: T = 20 oC
V = 380 ml
4 - Thermometer 5 -
Air pump
Total parasitic
6-
Filter/dryer
? -
Measuring
a-
ZnS(Ag)
9-
Photomultiplier
I volume VP= 200 ml
chamber:
V,= 170 ml
layer
Fig. 1. Schematic diagram of the laboratory system for determination of 222Rn concentrations in water samples. Air flow rate: 0.3 I/min; air circulation lasts 20 min; measurement made 3 hours after the end of circulation.
total a-counts filter methods. A definite air volume is sampled with constant flow rate through a microporous, low self-absorption filter which is consequently counted during 3 given time intervals. The first, high sensitivity variant has been described in detail in [5]. The second, mostly used in the present work, is an express variant with sampling time of 1 min and measuring intervals of (l-5) (6-10) and (11-15) min after the end of sampling 16). The concentrations of 2’8Po (a,) 2’4Pb (u2) and 2’4Bi/2’4Po (a,) and their uncertainties are calculated according to a,+Aa,=(Qnr)-’ ~{~,~P,,c,,*[~,~Pac,)ll/i)~
(3)
where C, are the counts during the interval k, Q is the sampling flow rate, n and t are the sampling and counting efficiencies, while i {&,I=
: 3
k=l 22.22 11.74
2 - 51.87 - 56.21
3 30.24 50.33
- 8.60
34.60
- 22.35
Both methods have been applied with a modified portable radon monitor type EDA RDA-200 and a separate air pump. The filter has an active area of 7 cm2 similarly as the ZnS(Ag) detector, Q = 100 I min-‘, n = 0.8 and c = 0.31. The low self-absorption has been confirmed by high-resolution a-spectroscopy of selected filters. The background counting rate is = 0.3 cpm and the detection limit is = 20 Bq mm3 equilibrium equivalent - low enough for the given application. The short sampling time reduces the deposition of a-energy ab-
sorbing humidity on the filter, while the reduced overall application time makes possible up to 20 determinations per day.
3. Results and discussion The concentrations of 222Rn in the waters examined cover the range W-850 kBq m-3, the highest related to Kammena Vourla spas. Air concentrations of “*PO in bathrooms range between 0.4 and 45 kBq rnm3, while the equilibrium equivalent concentrations of RDP between 0.05 and 18 kBq m-‘. The values measured in adjacent premises are typically in the range 0.02-0.04 kBq me3 and depend strongly on ventilation rate, indoor architecture, duration and intensity of bath operation. Generally, higher air values are related to higher water concentrations of 222Rn, but the correlation is not strong. The air concentration averages, the occupation factors and the exposure/dose relations recommended in [7] have been used to assess the annual effective dose equivalents. The estimates for the personnel exceed in two cases the 5 rem/a category A limit and in 6 cases, the 10% of this limit. The estimates for patients are typically of the order of tens of mrem/a, except two cases in the range of 100-300 mrem/a.
4. Conclusion The dose estimates for the personnel indicate a radiation protection problem which could be faced by application of forced ventilation of the working areas. As
P. Kritidis. P. Angelou / Concentrations o/‘“‘Rn
for the patients, although the annual doses are relatively (for a moderate 10 h/a total exposure) the question of risk-to-benefit justification arises, as in any case of medical exposure to ionizing radiations. The benefit due to the balneological treatment is not questionable per se. The question is what part of this benefit can be associated with 222Rn and its decay products and the opinions on this point seem to differ strongly [8,9]. The methods described could be of use for obtaining further information related to the solution of the above problems. low
References
01 some radon spas
539
131 A.S. Serdiukova
and J.T. Kapitanov, in: Isotopes of Radon and their Decay Products in Nature (Atomizdat, Moscow, 1975) p. 184. I41 P. Kritidis and P. Angelou, DEMO 84/S Report (Athens, 1984). ISI P. Kritidis, I. Uzunov, and L. Minev, Nucl. lnstr. and Meth. 143 (1977) 299. (61 P. Kritidis and P. Angeiou, DEMO 84/7G Report (Athens, 1984). aspects of exposure to radon and thoron (71 Dosimetty daughter products, Report by a Group of NEA Experts. NEA/OECD (Paris, 1983). I81 1. Uzunov, F. Steinhausler and E. Pohl, Health Phys. 41 (1981) 807. 34 (1981) 49. 191 E. Broda, Naturw. Rundschau
[l] H.F. Lucas, Rev. Sci. Instr. 28 (1957) 68. [Z] P. Kritidis and P. Angelou, DEMO 83/14 Report (Athens, 1983).
VI. NATURAL
RADfONUCLIDES
Nuclear Instruments and Methods in Physics Research B17 (1986) 537-539 North-Holland, Amsterdam
CONCENTRATIONS OF ‘**Rn AND ITS SHORT-LIVED AT A NUMBER OF GREEK RADON SPAS P. KRITIDIS
DECAY PRODUCTS
and P. ANGELOU
Environmental Rodiooctiuity Laboratory, Department of Nuclear Technology, Nuclear Research Center “Democritos’: Aghia Poroskeui, Attiki, Greece
A series of measurements has been performed in 9 radon therapy centers in order to determine its decay products in the air and to assess the related personnel and patient annual doses.
1. Introduction Concentrations of “*Rn of the order of 1 MBq mm3 have been measured in waters of certain Greek spas. The therapy centers using these waters present a typical example of “technologically enhanced” natural radioactivity caused by the release of significant amounts of 222Rn in the indoor air. This results in elevated air concentrations of radon decay products (RDP: accumula*tspo *14Pb *r4Bi, 214Po). Their prolonged tion in the lung can result in considerable local irradiation. A series of measurements has been performed in 9 radon therapy centers of Loutraki and Kammena Vourla (Greece) in order to determine the concentration levels of RDP in air and to assess the related personnel and patient annual doses. The concentrations of ***Rn in the water used have been determined as well. The present report concentrates on the methods used, while the results and dose estimates have to be further confirmed and analyzed.
2.I. 222Rn concentrations in the waters The concentrations of ***Rn in the water have been determined with the well established laboratory method of partial radon transfer to the measuring chamber (here - a Lucas cell [l]) in a closed air loop (fig. 1). A number of measures have been applied to improve the accuracy and reliability of the method: - The use of vacuum sampling. The glass samplers are evacuated in the laboratory and are able to keep sufficient under-pressure for days. Thus sampling is possible even under very unfavourable field conditions, where the alternative “syphon” sampling cannot be applied. - The combined sampler/extractor construction al0168-583X/86/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
levels of radon
and
lows the direct connection of the sampler to the extraction air loop, without any loss-potential water transfer. - Air circulation extraction of radon is used instead of vacuum. It can be shown [2] that this leads to lower overall uncertainty in the case of low chamber-to-sample volume ratio. The duration of air circulation is 20 min with a flow rate of 0.3 1 min -’ and at controlled water temperature of = 20°C. - Volume and temperature corrections are applied in the form of “normalization” of each result (including calibrations) to the nominal values of V, V, and T (fig. 1). The correction coefficient is given by C,, = 1 - (L3I$/W) -(SK/ST)
AV-
(SK/SK)
Av,
AT,
(1)
where
is the equilibrium part of radon in the measuring chamber and S(T) is the solubility coefficient of radon in the water as given by the empirical relation [3]: S(T)
2. Methods
concentration
= 0.106 + 0.405 e.& -O.O52T(“C)],
(2)
AV, AV, and AT are the respective differences between the actual and the nominal values; AV is known for each sampler, A V, is determined volumetrically and AT is controlled during the radon extraction. The system has been calibrated by use of = 100 Bq 226Ra solutions in radioactive equilibrium with 222Rn. The calibration coefficient is equal to 102 Bq m-3/cpm. The background counting rate is = 1 cpm. The 95% confidence detection level is 45 Bq me3 for a 30-min measurement at the 3rd hour after the end of air circulation, when equilibrium between 222Rn and its shortlived decay products has been established [4]. 2.2. RDP concentrations in air The concentrations of RDP in air have been determined by use of two field variants of the three VI. NATURAL RADIONUCLIDES
538
P. Kriridis,
P. Angelou
of “‘Rn
/ Concentrations
al some rudon spav
l-
Sampler/extractor:
2 -
Sample: Vs= 250 ml
3 -
Water bath: T = 20 oC
V = 380 ml
4 - Thermometer 5 -
Air pump
Total parasitic
6-
Filter/dryer
? -
Measuring
a-
ZnS(Ag)
9-
Photomultiplier
I volume VP= 200 ml
chamber:
V,= 170 ml
layer
Fig. 1. Schematic diagram of the laboratory system for determination of 222Rn concentrations in water samples. Air flow rate: 0.3 I/min; air circulation lasts 20 min; measurement made 3 hours after the end of circulation.
total a-counts filter methods. A definite air volume is sampled with constant flow rate through a microporous, low self-absorption filter which is consequently counted during 3 given time intervals. The first, high sensitivity variant has been described in detail in [5]. The second, mostly used in the present work, is an express variant with sampling time of 1 min and measuring intervals of (l-5) (6-10) and (11-15) min after the end of sampling 16). The concentrations of 2’8Po (a,) 2’4Pb (u2) and 2’4Bi/2’4Po (a,) and their uncertainties are calculated according to a,+Aa,=(Qnr)-’ ~{~,~P,,c,,*[~,~Pac,)ll/i)~
(3)
where C, are the counts during the interval k, Q is the sampling flow rate, n and t are the sampling and counting efficiencies, while i {&,I=
: 3
k=l 22.22 11.74
2 - 51.87 - 56.21
3 30.24 50.33
- 8.60
34.60
- 22.35
Both methods have been applied with a modified portable radon monitor type EDA RDA-200 and a separate air pump. The filter has an active area of 7 cm2 similarly as the ZnS(Ag) detector, Q = 100 I min-‘, n = 0.8 and c = 0.31. The low self-absorption has been confirmed by high-resolution a-spectroscopy of selected filters. The background counting rate is = 0.3 cpm and the detection limit is = 20 Bq mm3 equilibrium equivalent - low enough for the given application. The short sampling time reduces the deposition of a-energy ab-
sorbing humidity on the filter, while the reduced overall application time makes possible up to 20 determinations per day.
3. Results and discussion The concentrations of 222Rn in the waters examined cover the range W-850 kBq m-3, the highest related to Kammena Vourla spas. Air concentrations of “*PO in bathrooms range between 0.4 and 45 kBq rnm3, while the equilibrium equivalent concentrations of RDP between 0.05 and 18 kBq m-‘. The values measured in adjacent premises are typically in the range 0.02-0.04 kBq me3 and depend strongly on ventilation rate, indoor architecture, duration and intensity of bath operation. Generally, higher air values are related to higher water concentrations of 222Rn, but the correlation is not strong. The air concentration averages, the occupation factors and the exposure/dose relations recommended in [7] have been used to assess the annual effective dose equivalents. The estimates for the personnel exceed in two cases the 5 rem/a category A limit and in 6 cases, the 10% of this limit. The estimates for patients are typically of the order of tens of mrem/a, except two cases in the range of 100-300 mrem/a.
4. Conclusion The dose estimates for the personnel indicate a radiation protection problem which could be faced by application of forced ventilation of the working areas. As
P. Kritidis. P. Angelou / Concentrations o/‘“‘Rn
for the patients, although the annual doses are relatively (for a moderate 10 h/a total exposure) the question of risk-to-benefit justification arises, as in any case of medical exposure to ionizing radiations. The benefit due to the balneological treatment is not questionable per se. The question is what part of this benefit can be associated with 222Rn and its decay products and the opinions on this point seem to differ strongly [8,9]. The methods described could be of use for obtaining further information related to the solution of the above problems. low
References
01 some radon spas
539
131 A.S. Serdiukova
and J.T. Kapitanov, in: Isotopes of Radon and their Decay Products in Nature (Atomizdat, Moscow, 1975) p. 184. I41 P. Kritidis and P. Angelou, DEMO 84/S Report (Athens, 1984). ISI P. Kritidis, I. Uzunov, and L. Minev, Nucl. lnstr. and Meth. 143 (1977) 299. (61 P. Kritidis and P. Angeiou, DEMO 84/7G Report (Athens, 1984). aspects of exposure to radon and thoron (71 Dosimetty daughter products, Report by a Group of NEA Experts. NEA/OECD (Paris, 1983). I81 1. Uzunov, F. Steinhausler and E. Pohl, Health Phys. 41 (1981) 807. 34 (1981) 49. 191 E. Broda, Naturw. Rundschau
[l] H.F. Lucas, Rev. Sci. Instr. 28 (1957) 68. [Z] P. Kritidis and P. Angelou, DEMO 83/14 Report (Athens, 1983).
VI. NATURAL
RADfONUCLIDES