Available online at www.sciencedirect.com

Variation of indoor radon progeny concentration and

ear inubse-eragelationra de-elatedyle on

www.elsevier.com/locate/jenvradJournal of Environmental Radioactivity 99 (2008) 539e545

its role in dose assessment

Manmohan Singh a,*, Kulwant Singh a, Surinder Singh a, Z. Papp b

a Department of Physics, Guru Nanak Dev University, Amritsar, Punjab, Indiab Department of Environmental Physics, University of Debrecen, PO Box 51, Debrecen 4001, Hungary

Received 15 October 2006; received in revised form 17 July 2007; accepted 9 August 2007

Available online 30 October 2007

Abstract

Instantaneous measurements of equilibrium equivalent concentration of radon (EECRn) were taken over a period of 1 y2004 in a typical house at Amritsar city, located in the northwest part of India. A method based on absolute beta counting squent to grab aerosol sampling was used. During that year, EECRn varied between 1.56 Bq m�3 and 22.77 Bq m�3 with avvalue of 8.76 Bq m�3. EECRn decreased with the transition from winter to summer and vice versa, having a negative correwith outdoor temperature. The use of mechanical ventilation, under normal living conditions during summer, caused an extcrease in the concentrations. The variations with temperature and mechanical ventilation are discussed. Some major issues rto the uncertainties in dose calculations caused by the lack of knowledge of equilibrium factor and ignoring the effect of life stthe radon and its progeny concentrations are discussed.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Radon; EECRn; EECTh; Mechanical ventilation; Dose assessment

1. Introduction

is the000).loca-thods

ent.sure,

e in-adon

Numerous worldwide studies of radiation exposure show that inhalation of radon (222Rn) and its progenydominating contributor to the total collective radiation exposure of world’s population (UNSCEAR, 1993, 2Nevertheless, investigations are still being carried out for the following reasons: (1) introducing data from newtions into the database, (2) revising the existing data with that obtained using more reliable instruments and meand (3) updating the previous information to account for the continuous interference of humans to the environmHowever, there remain some issues regarding the complex relationship of radiation dose with radiation expowhich are still needed to be resolved satisfactorily (Muirhead, 2002).

The main aim of the present work is to estimate the mean annual radon progeny concentrations and effectivhalation radiation dose in a typical indoor environment of India and to study the parameters affecting the indoor rprogeny concentrations, such as the seasonal variation of temperature and mechanical ventilation.

* Corresponding author. Tel.: þ91 183 225 7007; fax: þ91 183 225 8820.

E-mail address: manmohan_heer@yahoo.com (M. Singh).

0265-931X/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvrad.2007.08.023

2. Site description and sampling circumstances

art of. Then thely in-boveremes fall

ounderage

540 M. Singh et al. / Journal of Environmental Radioactivity 99 (2008) 539e545

Radon progeny concentrations were measured in a typical house at Amritsar city, located in the northwest pIndia in the State of Punjab in 2004. The house was double-story, made of clay bricks, concrete, gypsum and limetypical layout on both floors includes a kitchen, two bathrooms, a living room, and two bedrooms. The rooms ofirst floor were in the same position as on the ground floor. The immediate vicinity around this site is completehabited. This house was about 9 km away from the center of the city, towards the west. The height of Amritsar asea level is about 234 m and it lies at 31� 350N and 74� 560E, which falls in Seismic Zone IV. Amritsar has an extclimate with very hot summers and very cold winters. In summers temperatures rise beyond 40 �C and in winterbelow 0 �C.

All the measurements were performed in a bedroom on the ground floor at a height of 1.5 m above the grsurface. Measurements were confined to the time 9:00e10:00 AM, which is the best representative of the avconcentrations of the daily variations for the Indian environment (Nagaraja et al., 2003).

3. Methods and materials

basedr. Theation

ABC)g, thethods

itablyssageplinge firstend-holdwithfrom

ide ofk wasback-

A new grab sampling method was employed for the determination of radon progeny concentrations in air. This method ison gross beta counting of a filtered aerosol sample over successive time intervals by an end-window GeigereMuller counteevaluation of the activity concentrations was based on: (1) the analysis of the measured complex decay curve and (2) the evaluof the individual beta-counting efficiencies for the progeny using the Defined Solid Angle Absolute Beta Counting (DSAmethod, taking the effect of the flow rate of the air, the duration of the sampling, the delay between sampling and countinbackground and dead time of counter, the counting geometry and filter parameters into account. The details of these meare discussed elsewhere (Papp, 1997; Papp and Daroczy, 1997; Papp and DezsT, 2006).

Aerosol samples were collected by drawing air through a glass-fiber filter (Whatman, GF/A), which was held with a sudesigned sampling head, at a rate of 0.05 m3/min, using a suction pump. The effective filter surface, available for the paof air was 2.6 cm in diameter. The duration of sampling was 10e15 min. After a short time removing the filter from the samhead and placing it under the detector, gross beta counts were recorded over successive time intervals of 1 min duration for thhour, 2e5 min for the next 2 h and 10e30 min for a few more hours. The dead time, window thickness and diameter of thewindow GeigereMuller tube were 2.4� 10-4 s, 1.3� 10�3 g cm�2 and 3.0 cm, respectively. A plexi-glass stand was used tothe tube, facing downward, inside a thick, cylindrical lead shield. The filter was fixed on a plexi-glass sample holder platea circular opening at its center. This opening in the plate was in order to avoid any backscattering of beta particles emittedthe filter, which otherwise may create difficulties while evaluating their exact contribution to the count-rate. The clean sthe filter faced downward. The distance between the filter and the window was 0.8 cm. A plastic sheet 0.012 g cm�2 thicused to cover the detector window to absorb alpha particles. The number of counts was corrected for coincidence loss and theground events.

4. Results and discussion

con-puted

ð1Þ

The parameter of interest in evaluating radiation exposure from radon progeny is the equilibrium equivalentcentration of radon (EECRn). Therefore, results in the present study are represented in the form of EECRn, comaccording to the following formula (NCRP, 1988):

EECRn ¼ 0:105C1þ 0:516C2þ 0:379C3;

value

where C1, C2 and C3 are the activity concentrations of 218Po, 214Pb and 214Bi, respectively.

EECRn values, measured over a period of 1 year, varied from 1.56 Bq m�3 to 22.77 Bq m�3 with the average

Thisents003;ur ofs are, etc.

il and

of 8.76 Bq m�3, with a standard deviation 4.56 Bq m�3. The frequency distribution of EECRn is shown in Fig. 1.distribution of EECRn looks log-normal in nature and has also been observed by many other authors for measuremof radon and as well as its progeny concentrations (Marenny et al., 1996; Duenas et al., 1996; Al-Jarallah et al., 2Abumurad and Al-Tamimi, 2005; Diyun et al., 2005). This log-normal distribution indicates the dynamic behavioradon and its progeny concentrations, with either time or space. The parameters responsible for temporal variationtemperature, moisture content, wind direction and speed, rainfall, ventilation of the different parts of the buildingand spatial variations are caused by parameters, such as 238U concentration and radon exhalation rate from the so

building materials (UNSCEAR, 1982; Duenas et al., 1996; Ortega and Vargas, 1996; Man and Yeung, 1999; Marley,

vari-ECRn

fromtionsed inationor airoveswas

r, thehole

ainlygenyinds,s the

0

5

10

15

20

25

30

2 4 6 8 10 12 14 16 18 20 22 24

EECRn (Bq m-3)

Freq

uenc

y

Fig. 1. Frequency distribution of EECRn.

541M. Singh et al. / Journal of Environmental Radioactivity 99 (2008) 539e545

2001).

4.1. Seasonal variations

In the present study, the measurements were carried out at a fixed location in a bedroom. Therefore, spatialations in EECRn were minimal. However, the results show temporal variations in EECRn. Monthly variations in Eas well as the ratio of each month to the previous month and to the next month are shown in Table 1. It can be seenthis table that EECRn gradually decreased with the transition from winter to summer and vice versa. These variaare attributed to variations in outdoor radon and its progeny concentrations. These outdoor variations are discussour previous publication (Singh et al., 2005). Outdoor air enters and leaves a house by infiltration, natural ventiland mechanical ventilation and therefore regularly replaces the indoor air. Infiltration is caused by flow of outdointo the house through joints and cracks in walls, ceilings, and around windows and doors. However, air mthrough opened windows and doors in natural ventilation. In the present study, the ventilation of the housevery poor. The single door to the bedroom was facing towards the living room inside the house. Moreovemain entry to this house itself was not exposed directly to open air but, rather, through a long corridor. The whouse remained closed most of the time, even in summer. Because of these circumstances, air exchange was mvia infiltration. When measurements are performed over a long time, as in our case, variations in radon and its proare caused by deterministic variables (temperature) and in that case the influence of random variables (rainfalls, wetc.) is removed from the average values (Garzon et al., 1986). Fig. 2 shows that as outdoor temperature increase

Table 1

Monthly variation of EECRn

Month Average EECRn (Bq m�3) Ratio of EECRn to previous month Ratio of EECRn to next month

January 16.16 1.25

February 12.96 0.80 1.28

March 10.16 0.78 1.54

April 6.61 0.65 1.29

May 5.09 0.77 1.20

June 4.25 0.83 1.09

July 3.89 0.91 0.80

August 4.84 1.24 0.75

September 6.49 1.34 0.67

October 9.64 1.49 0.81

November 11.91 1.24 0.81

December 14.62 1.23

indoor EECRn value decreases. This has been explained by numerous investigators (Garzon et al., 1986; Porstendorfer,

fromfromr, theril iswereper-l de-

erageven-ber,

ECRn

sses:wallsadon

wing

0

2

4

6

8

10

12

14

16

18

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

EE

CR

n (B

q m

-3)

0

5

10

15

20

25

30

35

Tem

pera

ture

(o C

)

EECRn

Temperature

Fig. 2. Monthly variation of temperature and EECRn.

542 M. Singh et al. / Journal of Environmental Radioactivity 99 (2008) 539e545

1994; Marcazzan et al., 1995; Marcazzan and Persico, 1996; Sheets and Lawrence, 1999).

4.2. Ventilation effect

The other interesting part of this study is the effect of mechanical ventilation on EECRn values. As can be seenTable 1, EECRn decreases with an almost constant rate from January to March and increases with the same rateOctober to December. This is caused by the slowly changing seasonal temperature, as discussed above. Howeveratio of EECRn in March to that of April is comparatively much greater. The sudden decrease in EECRn in Apbecause of a change in life style of the residents of this house. Summer occurs in April in India and fansused during this period. From April to September, this variation is random as sometimes measurements wereformed with fans ON and sometimes with fans OFF. The mechanical ventilation due to fans caused an additionacrease in EECRn. This effect is more clearly shown in Table 2. When mechanical ventilation was ON, the avEECRn is lower by a factor of 1.56 compared to the average EECRn value measured in the absence of mechanicaltilation. The minimum value of EECRn was observed in July, which is the mid-summer month in India. In Septemthe use of mechanical ventilation was very rare and completely stopped in October, which resulted in increased Evalues. The variations in EECRn due to mechanical ventilation are possibly caused by the following proce(1) continuous removal of indoor air due to higher exchange rate of air, (2) deposition of radon progeny on theand ground surface due to the downward flow of air from the ceiling fan and (3) a decrease in exhalation rate of rfrom the walls and the floors with the higher pressure on their surfaces caused by the fan.

4.3. Dose estimation

The annual inhalation dose due to radon and progeny concentrations is estimated according to the folloformula (UNSCEAR, 2000):

Table 2

EECRn with mechanical ventilation ON and OFF (AprileSeptember)

Parameter EECRn (Bq m�3)

Mechanical ventilation ON Mechanical ventilation OFF

Number 36 32

Minimum 1.56 2.83

Maximum 6.94 11.4

Average 4.07 6.35

Median 4.14 6.46

Standard deviation 1.36 1.94

DAðmSvÞ ¼ Tð0:17CRnþ 9EECRnÞ � 10�6; ð2Þ

its ofe the

543M. Singh et al. / Journal of Environmental Radioactivity 99 (2008) 539e545

where T is the time in hours a person spends at a particular location and CRn is the concentration of radon gas in unBq m�3. The factors of 0.17 and 9 are the effective dose coefficients for radon and EECRn, respectively, which hav

yeartion:

ð3Þ

units of nSv/Bq h m�3. An average person spends time indoors with an occupancy factor of 0.8 averaged over 1(UNSCEAR, 1993). This gives T¼ 7008 h. In the present study, CRn is estimated according to the following rela

CRn ¼EECRn

;

ue ofpted

F

Using annual average EECRn¼ 8.76 Bq m�3 and equilibrium factor F¼ 0.4, CRn is calculated to the val21.9 Bq m�3. The annual dose, calculated using all these factors in Eq. (1) is 0.58 mSv. The value F¼ 0.4 is ado

gnif-t al.,

Rn is

ð4Þ

in this study because this is an average value from extensive worldwide studies (UNSCEAR, 1993). However, siicant deviation from this value may be observed while studying a particular location (Kojima, 1996; Winkler e2001).

If the exact value of F at a given location deviates by a factor of DF from the accepted value of 0.4 and only Cmeasured, then the percentage error in dose can be calculated using the following equation:

%DError ¼9DF

100;

d as:

3:77þ 9DF

If the dose is estimated only from measured values of EECRn, then the percentage error in dose can be calculate

ð5Þ

%DError ¼�0:43DF

100;

CRn

error

3:77þ 9DF

Comparing Eqs. (4) and (5), it can be seen that the error induced by estimating effective dose from measuredvalue is 21 times higher than that if the effective dose is estimated from measured EECRn values. The percentage

xpe-0.2,

same4. Aated.adonn andf notgas

rep-

in the dose, calculated from Eqs. (4) and (5) and taking the most probable values of DF that can be practically erienced, is shown in Figs. 3 and 4. It can be seen from Fig. 3 that the error in dose for a deviation (DF) merely of�calculated using the measured CRn value and predicted EECRn, is as large as �91%. However, the error for thevalue of DF, calculated from a measured EECRn value but predicted CRn value is only 4.4%, as shown in Fig.negative value of percentage error means that dose is overestimated and a positive value means dose is underestim

From this discussion it can be concluded that dose should be evaluated by measuring both radon as well as rprogeny concentrations under the same circumstances. However, the data on simultaneous measurements of radoits progeny are still scarce. Calculations from progeny concentrations can give good approximations with errors omore than 5%, which is acceptable in most cases. However, dose estimation from merely measured radonconcentrations at a particular location requires knowledge of the equilibrium factor for that location, rather than aresentative value obtained from literature or other locations.

60

-100

-80

-60

-40

-20

0

20

40

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

ΔF deviated from average accepted value F=0.4

Err

or in

dos

e (

)

Fig. 3. Error in dose calculation if CRn is measured and EECRn is predicted.

For more accurate dose assessment, however, not only the radon and its progeny concentrations but also humanchan-owerctors,adoncon-

com-ouslyudy.sure-adon

80.

diation

ts 39,

on and

e195.

S192.

diation

evel at

rosols.

ussia.

pheric

1225,

, 2003.

n and

talonia

-3

-2

-1

0

1

2

3

4

5

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

ΔF deviated from average accepted value F=0.4

Err

or in

dos

e (

)

Fig. 4. Error in dose calculation if EECRn is measured and CRn is predicted.

544 M. Singh et al. / Journal of Environmental Radioactivity 99 (2008) 539e545

activities should be considered. One example is shown in Table 2, where EECRn is significantly reduced by meical ventilation. Fans were used only when residents were present in the house. Therefore, they were exposed to lradon levels. Once they left the house (fans OFF), radon and progeny concentrations increased. Passive detewidely used for long-term measurements, continuously monitor radon and its progeny. Therefore, the high rlevels that occurred under normal conditions and to which residents are not exposed also contribute to averagecentrations measured over a long period and hence cause an overestimation of the radiation dose. This study remends the use of advanced radiation detectors, which can be switched ON and OFF without the loss of previrecorded data, so that measurements are recorded only when the residents are present in the dwelling under st

The results in this study are less representative for the actual dose as they are based only on short-term meaments. However, this study provides essential information and guidelines for relating any dose profiles with rexposure.

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