Radon, thoron and their progenies measured in different dwelling rooms and reference atmospheres by using CR-39 and LR-115 SSNTD

ARTICLE IN PRESS

Applied Radiation and Isotopes 59 (2003) 273–280

Radon, thoron and their progenies measured in different dwelling rooms and reference atmospheres by using CR-39 and LR-115 SSNTD M.A. Misdaq* Nuclear Physics and Techniques Laboratory, Faculty of Sciences Semlalia, BP. 2390, University Cadi Ayyad, Marrakech, Morocco Received 4 October 2002; received in revised form 7 May 2003; accepted 27 June 2003

Abstract Detection efficiencies of the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) for a-particles emitted by radon, thoron and their decay products inside the air of different dwelling rooms and in various reference atmospheres were determined by using a Monte Carlo computer code. Alpha- and beta-activities per unit volume of air due to radon, thoron and their progenies were measured in the studied atmospheres by exploiting data obtained for the detection efficiencies of the SSNTD and measuring the resulting track density rates. Equilibrium factors between radon and its progeny and thoron and its daughters were evaluated in the studied atmospheres. r 2003 Elsevier Ltd. All rights reserved. Keywords: SSNTD detection efficiencies; Radon and thoron series; Alpha- and beta-activities

1. Introduction Radon, thoron and their decay products are alpha-, beta- and gamma-emitting nuclei. Inhalation of these radionuclides represents the main source of exposure to ionizing radiation for population in most countries . (Jonsson, 1988; Subba-Ramu et al., 1988; Papp and ! Daroczy, 1997; Misdaq et al., 2001a). Radon and thoron decay products have been measured in the air by betacounting using an end-window Geiger–Muller . counter ! (Papp and Daroczy, 1997). This technique has some limits and drawbacks. 208 Tl cannot be determined, the relative error of 218 Po and 212 Bi concentrations are much higher than that of the 214 Pb; 214 Bi and 212 Pb radionuclides and long duration counting is necessary to reach the maximum accuracy. Alpha-counting applied for measuring the concentrations of radon and thoron progenies presents some disadvantages such as the *Corresponding author. Tel.: +212-4-4434649; fax: +212-44436769. E-mail address: [email protected] (M.A. Misdaq).

absorption of alpha-particles and degradation of alpha-particle energy in the membrane filter of the counter. The use of gamma-ray spectrometry for measuring radon and thoron decay product concentrations in air suffers from some disadvantages such as low efficiency, high background and high cost. LR-115 type II solid state nuclear track detectors (SSNTD) utilized for measuring radon concentrations in houses in Sweden . (Jonsson, 1988) necessitates a calibration with known radon concentration sources. Solid state nuclear track detectors (SSNTD) have been intensively used for detecting charged particles during the last three decades (Fleischer et al., 1975; Durrani and Bull, 1987; Khan and Quereshi, 1994). In the present study, we use a SSNTD technique based on determining detection efficiencies of the CR-39 and LR-115 type II solid state nuclear track detectors for measuring alpha- and beta-activities due to the radon and thoron series inside different atmospheres. The relevant ranges of the emitted a-particles in air and SSNTD utilized, were calculated by means of a TRIM program (Biersack and Ziegler, 1998).

0969-8043/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0969-8043(03)00198-2

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thoron (four a-emitting nuclei: 220 Rn; 216 Po; 212 Bi and Po) series, registered on the CR-39 ðrCR G Þ and LR-115 II ðrLR Þ detectors are, respectively, given by (Misdaq G et al., 2002) " # 3 4 X pq2 X CR CR 0 0CR 0 rG ¼ Ac ðjÞKj ej Rj þ Ac ðjÞKj ej Rj ð1Þ 2Sd j¼1 j¼1

2. Method of study

212

2.1. Determination of alpha- and beta-activities per unit volume due to radon, thoron and their decay products in the air of different dwelling rooms Disc-shaped pershore Mouldings CR-39 (500 mm thickness) and Kodak LR-115 II (12 mm cellulose nitrate on 100 mm polyster base) SSNTD films of radius q ¼ 2 cm have been separately placed in the air of different rooms built by the same materials (cement, bricks) for 24 h as shown in Fig. 1. During the exposure time, aparticles emitted by radon, thoron and their progenies bombarded the SSNTD films. After the irradiation, the exposed films were etched in the NaOH solution (2:5 N at 60 C for 120 min for LR-115 films and 6:25 N at 70 C for 7 h for the CR-39 sheets). After this etching treatment the track densities registered on the CR-39 and LR-115 II SSNTD were determined by means of an optical microscope. For our experimental etching conditions, the residual thickness of the LR-115 type II SSNTD is 5 mm which corresponds to the lower ðEmin ¼ 1:6 MeVÞ and upper ðEmax ¼ 4:7 MeVÞ energy limits for the registration of tracks of alpha-particles in the LR-115 II films (Misdaq et al., 2000). All a-particles emitted by the radon and thoron series that reach the LR-115 II detector surface under an angle lower than its critical angle of etching with a residual energy between 1.6 and 4:7 MeV are registered as bright track-holes. The CR-39 detector is sensitive to all a-particles reaching its surface under an angle smaller than its critical angle of etching. The global track density rates ðtracks cm2 s1 Þ; due to a-particles emitted by radon (three a-emitting nuclei: 222 Rn; 218 Po and 214 Po) and

and rLR G

" # 3 4 X pq2 X LR 0 0LR 0 ¼ 0 Ac ðjÞKj ej Rj þ Ac ðjÞKj ej Rj ; ð2Þ 2Sd j¼1 j¼1

where Sd and Sd0 are, respectively, the fields surface areas (for a given microscope magnitude) of the CR-39 and LR-115 II films, Ac ðjÞ ðBq cm3 Þ is the a-activity of the jth a-emitting nucleus, Rj and R0j are the ranges, in air, of an a-particle of index j and initial energy Ej emitted by the nuclei of the radon and thoron series, respectively, Kj and Kj0 are, respectively, the branching ratios corresponding to the disintegration of the nuclei of the 0CR radon and thoron groups, and eCR ; eLR and e0LR j ; ej j j are, respectively, the detection efficiencies of the CR-39 and LR-115 II detectors for the emitted a-particles. The activities of a jth nucleus Ac ðjÞ and its ðj þ 1Þth daughter Ac ðj þ 1Þ of the radon and thoron series are related by (Swedjemark, 1983; Jacobi, 1972; Planinic et al., 1997) Ac ðj þ 1Þ ¼ Mðj þ 1ÞAc ðjÞ

ð3Þ

where Mðj þ 1Þ ¼

lðj þ 1Þ : lðj þ 1Þ þ F ðj þ 1ÞDa þ ð1  F ðj þ 1ÞÞDu þ V

ð4Þ

Ceiling

Wall

222

Rn 220

ψ

Air volume Vj

I

Q1

P'

xj θ P

Rn

O 1' t

SSNTD

t

r

Rj

O1

Rn 220

Rn 222

222

Rn

Fig. 1. Arrangement of the solid state nuclear track detector of radius q ¼ 2 cm placed in a dwelling room. Vj ¼ pq2 Rj is the air volume.

ARTICLE IN PRESS M.A. Misdaq / Applied Radiation and Isotopes 59 (2003) 273–280

Here lðj þ 1Þðs1 Þ is the disintegration constant of the ðj þ 1Þth daughter, F ðj þ 1Þ is the ratio of the concentration of the attached ðj þ 1Þth daughter on aerosols to the total concentration of the attached and unattached radon or thoron daughters (Planinic et al., 1997), Da ¼ 7:5  105 s1 (Planinic et al., 1997) is the deposition rate of the attached radon and thoron decay products, Du ¼ 8:33  103 s1 (Planinic et al., 1997) is the deposition rate of the unattached radon and thoron decay products, and V ðh1 Þ is the ventilation rate. Values of the F ðj þ 1Þ; lðj þ 1Þ and Mðj þ 1Þ parameters for radon and thoron progenies are given in Table 1. We have developed a new calculational method, adapted to the experimental conditions, for evaluating,

275

respectively, the CR-39 and LR-115 II SSNTD detection 0CR LR efficiencies eCR ; ej and e0LR for a-particles emitted j ; ej j by the radon and thoron series inside the air atmosphere of a dwelling room (Fig. 1). An a-particle of index j and initial energy Ej generated from point P inside the air volume Vj (Fig. 1) at a distance xj from the detector which reaches the detector surface has range RjD in the CR-39 detector and a range R0jD in the LR-115 film (Fig. 2). The distance xj is given by t if q > O01 Q1 ; xj ¼ ð5Þ cos y where 2

O01 Q1 ¼ r2 þ t2 tg2 ðyÞ þ 2rt tgðyÞ cosðcÞ:

ð6Þ

Table 1 Values of the lðj þ 1Þ; F ðj þ 1Þ and Mðj þ 1Þ (for different ventilation rates V ðh1 Þ) parameters for radon and thoron decay products Radon decay products 218

Decay constant lðj þ 1Þ ðs1 Þ F ðj þ 1Þ Mðj þ 1Þ ðV ¼ 1 h1 Þ Mðj þ 1Þ ðV ¼ 0:5 h1 Þ Mðj þ 1Þ ðV ¼ 0:33 h1 Þ Mðj þ 1Þ ðV ¼ 0:32 h1 Þ Mðj þ 1Þ ðV ¼ 0:25 h1 Þ Mðj þ 1Þ ðV ¼ 0 h1 Þ

214

Po

3:8  103 0.90 0.76 0.79 0.79 0.79 0.79 0.80

Pb

4:3  104 1.00 0.55 0.66 0.72 0.72 0.75 0.85

E αj

θ E αjRes

Original film surface

Thoron decay products 214

Bi

5:86  104 1.00 0.62 0.73 0.78 0.78 0.80 0.88

214

216

Po

4:2  103 1.00 0.99 0.99 0.99 0.99 0.99 0.99

Po

4.4 0.90 0.99 0.99 0.99 0.99 0.99 0.99

212

212

Pb

1:8  105 1.00 0.05 0.08 0.09 0.09 0.11 0.20

Bi

1:9  104 1.00 0.35 0.47 0.53 0.54 0.57 0.71

212

Po

1:9  106 1.00 1.00 1.00 1.00 1.00 1 1.00

Air

P

θ

θ

θ

I h or h' 4

2

F

H

SSNTD film

1

3

Fig. 2. Trajectory of an a-particle of index j and initial energy Eaj inside the air of a dwelling room (reference atmosphere) ðPI ¼ xj Þ and SSNTD ðIF ¼ RjD Þ: EaRes is the residual energy of the a-particle at the point I: h and h0 are the removed thicknesses of the CR-39 j and LR-115 SSNTD.

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The calculation of the SSNTD detection efficiencies consists firstly on generating random numbers by using a program called random subroutine based on a congruential method and calculating the xj distances and RjD and R0jD ranges by using a program called ‘‘SSNTDDEfaM’’ which is represented schematically in Fig. 3. The uniform random sampling of the emission point P and emission direction is achieved by computing the distances from the center, the depth t; cos y (y between 0 and p=2) and c with four uniform random numbers (Misdaq et al.,1998): pffiffiffiffiffi r ¼ q x1 ; 0px1 o1; t ¼ Rj x2 ; cos y ¼ x3 ; c ¼ 2px4 ;

0px2 o1; 0px3 o1; 0px4 o1;

ð7Þ

xj oRj :

The considered a-particle is registered as a track on the SSNTD films when (Misdaq et al., 2002): RjD cos y > h

ð9Þ

for the CR-39 detector and R0jD

yoy0jc ;

Nrj Noj

N dj = 0 I=1, No

Call random subroutine

Calculation of O'1Q1

q > O'1Q1

cos y > h0 ;

;

No

Res Calculation of xj and E α j

E αRes j < E αj

Emin oEjRes oEmax

Yes Calculation of R Dj and R 'Dj

θ < θcj ,

θ < θ 'cj

xj
ð10Þ

ð11Þ

No

E min < E αRes j < E max

j RD cos θ > h

for the LR-115 SSNTD. Here yjc and y0jc are, respectively, the critical angles of etching of the CR-39 and LR-115 type II SSNTD which are calculated by using a method developed by Misdaq et al. (Misdaq et al., 1999), h and h0 are, respectively, the removed thicknesses of the CR-39 and LR-115 type II SSNTD and EjRes is the residual energy of the a-particle on point I (Fig. 2). a-particles whose tracks development starts from the detector surface and which satisfy the RjD cos y > h and R0jD cos y > h0 conditions (cases 1 and 3 (Fig. 2)) are registered as etched through tracks if they satisfy the other conditions (Eqs. (8)–(10)). a-particles whose tracks development does not start from the detector surface and which satisfy the RjD cos y > h and R0jD cos y > h0 conditions (case 2 (Fig. 2)) are also registered as etched through tracks if they satisfy the other conditions. a-particles whose tracks development starts from the detector surface and which do not satisfy the RjD cos y > h and R0jD cos y > h0 conditions (case 4 (Fig. 2)) are not registered as etched through tracks even if they satisfy the other conditions. For a large number Noj ; of a-particles of index j and initial energy Ej the detection efficiency of the SSNTD is given by ej ¼

J=1, 7

ð8Þ

and

'j

Yes

where Rj is the range of an a-particle of index j and initial energy Ej in the air (Fig. 1). An a-particle of index j and initial energy Ej reaches the CR-39 and LR-115 II SSNTD when

yoyjc

j

Calculation of Rj, θ c and θ c

No

, R 'Dj cosθ > h ' Yes

N dj = N dj + 1

Calculation of εj , ε'j End

Fig. 3. Flow chart of the ‘‘SSNTDDEaM’’ fortran program which is used to calculate the solid state nuclear track detectors detection efficiencies for a-particles emitted by the nuclei of the radon and thoron series inside the air of a dwelling room (reference atmosphere). We employ the same symbols as in the text. It is therefore self-explanatory.

where Nrj is the number of a-particles which reach and are registered as tracks on the SSNTD. By calculating first the detection efficiencies of the CR-39 (eCR and e0CR ) and LR-115 type II (eLR and e0LR ) j j j j SSNTD for a-particles emitted by the radon and thoron series inside a room by using the ‘‘SSNTDDEaM’’ Fortran program and secondly by measuring global track density rates ðtracks cm2 s1 Þ registered on the LR CR-39 ðrCR G Þ and LR-115 type II ðrG Þ; one can evaluate 222 the radon Ac ð RnÞ and thoron Ac ð220 RnÞ alpha activities ðBq cm3 Þ and consequently alpha activities of the radon and thoron decay products (Eq. (3)) in the air of a given room by using a method described in detail

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2.2. Evaluation of alpha- and beta- activities per unit air volume due to radon and thoron series inside different reference atmospheres

by Misdaq et al. (2002). Indeed, we have Ac ð220 RnÞ Ac ð222 RnÞ LR ¼ ðSd =Sd0 ÞðrCR G =rG Þ 218 K1 eLR PoÞK2 eLR 1 R1 þ Mð 2 R2 214 214 214 218 þMð PoÞMð BiÞMð PbÞMð PoÞK3 eLR 3 R3



!

!,

218 R1 K1 eCR PoÞR2 K2 eCR 1 þ Mð 2



þMð214 PoÞMð214 BiÞMð214 PbÞMð218 PoÞR3 K3 eCR 3

20

1

0 216 0 K10 e0CR PoÞK20 e0CR 1 R1 þ Mð 2 R2

6B 4@

C A

0 þMð212 PbÞMð212 BiÞMð216 PoÞK30 e0CR 3 R3 0 þMð212 PbÞMð212 BiÞMð212 PoÞMð216 PoÞK40 e0CR 4 R4

LR ðSd =Sd0 ÞðrCR G =rG Þ

0 B @

277

13

0 216 0 K10 e0LR PoÞK20 e0LR 1 R1 þ Mð 2 R2 0 þMð212 PbÞMð212 BiÞMð216 PoÞK30 e0LR 3 R3 0 þMð212 PbÞMð212 BiÞMð212 PoÞMð216 PoÞK40 e0LR 4 R4

The same disc shaped CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) used in Section 2.1 were separately placed at a distance of 11 cm above different marble material samples in a hermetically sealed cylindrical plastic container for 24 h as shown in Fig. 4. Due to the radon and thoron emanation from the marble sample a reference atmosphere (gas volume) is formed (see Fig. 4). During the exposure time alpha-particles emitted by thoron, radon and their daughters bombarded the SSNTD films. After the irradiation, the exposed films were etched in the same NaOH solution used in Section 2.1. The resulting track density rates were evaluated as mentioned in Section 2.1.

C7 A5

ð12Þ and SSNTD

Ac ð222 RnÞ

α

α

2rCR Sd ¼ G2 pq 2

31 218 PoÞR2 K2 eCR R1 K1 eCR 1 þ Mð 2 6 7 6 þMð214 PoÞMð214 BiÞMð214 PbÞMð218 PoÞR3 K3 eCR 7 3 6 7 6 7 Ac ð220 RnÞ 0 0 0CR 6 7 216 0 0 0CR 6 þ 222 ½R1 K1 e1 þ Mð PoÞR2 K2 e2 7 : 6 7 Ac ð RnÞ 6 7 6 7 212 212 216 0 0 0CR þMð BiÞMð PbÞMð PoÞR K e 4 5 3 3 3 212 212 212 216 0 0 0CR þMð PoÞMð BiÞMð PbÞMð PoÞR4 K4 e4

ð13Þ

α

222

Rn

220

Plastic container

Rn

11 cm 222

Reference atmosphere

Rn

The equilibrium factors between radon, thoron and their corresponding decay products are defined by (Jacobi, 1972; Swedjemark, 1983) F 222 ¼ ½f ð218 PoÞAc ð218 PoÞ þ f ð214 PbÞAc ð214 PbÞ 214

þfð

BiÞAc ð

214

BiÞ þ f ð

214

214

PoÞAc ð

222

PoÞ =Ac ð

220

Rn

RnÞ ð14Þ

for radon ð222 RnÞ and F

220

216

¼ ½f ð

216

PoÞAc ð

222

PoÞ þ f ð

212

PbÞAc ð

212

Rn

222

Rn

220

Rn

PbÞ

þ f ð212 BiÞAc ð212 BiÞ þ f ð212 PoÞAc ð212 PoÞ =Ac ð220 RnÞ

1 cm

Marble sample

ð15Þ for thoron ð220 RnÞ; where f ð218 PoÞ ¼ 0:105; f ð214 PbÞ ¼ 0:516; f ð214 BiÞ ¼ 0:38; f ð214 PoÞ ¼ 5:25  108 ; f ð216 PoÞ ¼ 2:09  104 ; f ð212 PbÞ ¼ 0:91; f ð212 BiÞ ¼ 0:087 and f ð212 PoÞ ¼ 5:24  1012 :

Fig. 4. Arrangement of the solid state nuclear track detector films placed at a distance of 11 cm above a marble material sample in a hermetically sealed cylindrical plastic container of radius q ¼ 2 cm:

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3. Results and discussion 3.1. Alpha- and beta-activities per unit volume due to radon, thoron and their decay products in the air of different dwelling rooms Alpha- and beta-activities per unit volume due to radon, thoron and their decay products have been measured inside various dwelling rooms in Morocco. Data obtained are shown in Tables 2 and 3. From the statistical error on track counting one can determine the error on track density rate and then evaluate the relative uncertainty of the radon, thoron and their progenies determination which is of 7%. We notice that alpha- and beta-activities due to the radon and its progeny are higher than those due to thoron and its daughters for the dwelling rooms studied. This is due to the fact that radon has a higher half-life ð3:82 dÞ than thoron ð55 sÞ: Alpha- and beta-activities per unit volume decrease when the ventilation rate V increases for rooms built with the same building materials (rooms M1, M2, M3, M5 and M6) (see Table 2). For a fixed ventilation rate, alpha- and beta- activities per unit volume are higher for rooms built with natural materials (clay bricks, limestone rocks) (rooms M5 and M6) than for those built with industrialized materials (cement+bricks) (rooms M2 and M3). This is due to the fact that the former materials contain more uranium (radon) than the latter

(Misdaq et al., 1997). Equilibrium factors between radon and its daughters F 222 and between thoron and its decay products F 220 were evaluated for the studied dwelling rooms (Tables 2 and 3). The F 222 and F 220 factors decrease when the ventilation rate V increases. These factors do not depend on the nature of the building material. 3.2. Alpha- and beta-activities per unit volume due to radon, thoron and their decay products inside various reference atmospheres Alpha- and beta-activities due to radon, thoron and their corresponding decay products were evaluated inside three different reference gas atmospheres by using the method described in Section 2.1 deleting the ventilation rate V since the system is well closed (Eq. (4)). Data obtained are shown in Table 4. The statistical relative uncertainty of the radon, thoron and their progenies determination is of 7%. 222 220 Radon ðAin RnÞÞ and thoron ðAin RnÞÞ alphaCð Cð activities per unit volume have been evaluated inside the same marble samples by using a method described in detail by Misdaq et al. (2001b). Data obtained are shown in Table 6. We notice that alpha- and betaactivities per unit volume due to radon, thoron and their decay products inside a reference atmosphere increase 222 220 when radon ðAin RnÞÞ and thoron ðAin RnÞÞ Cð Cð

Table 2 Data obtained for alpha- and beta-activities per unit volume due to radon and its decay products inside different dwelling rooms. F 222 is the equilibrium factor between radon and its progeny Dwelling room (building material)

V ðh1 Þ

Ac ð222 RnÞ ðBq m3 Þ

Ac ð218 PoÞ ðBq m3 Þ

Ac ð214 PbÞ ðBq m3 Þ

Ac ð214 BiÞ ðBq m3 Þ

Ac ð214 PoÞ ðBq m3 Þ

F 222

M1 M2 M3 M4 M5 M6

1.00 0.50 0.32 0.25 0.50 0.33

1371 2872 8076 6875 6473 10477

9.870.7 2271 6374 5372 5072 7775

5.470.3 14.370.8 4673 4072 3372 5674

3.470.2 10.470.6 3672 3272 2471 4573

3.370.2 10.370.6 3672 3272 2471 4573

0.40 0.50 0.54 0.56 0.50 0.54

(cement+bricks) (cement+bricks) (cement+bricks) (clay bricks) (limestone rocks) (limestone rocks)

Table 3 Data obtained for alpha- and beta-activities per unit volume due to thoron and its progeny inside various dwelling rooms. F 220 is the equilibrium factor between thoron and its daughters Dwelling room (building material)

V ðh1 Þ

Ac ð220 RnÞ ðBq m3 Þ

Ac ð216 PoÞ ðBq m3 Þ

Ac ð212 PbÞ ð103 Bq m3 Þ

Ac ð212 BiÞ ð103 Bq m3 Þ

Ac ð212 PoÞ ð103 Bq m3 Þ

F 220

M1 M2 M3 M4 M5 M6

1.00 0.50 0.32 0.25 0.50 0.33

0.2370.01 1.0470.06 6.070.4 2.570.1 2.670.1 8.570.6

0.2370.01 1.0370.05 6.070.4 2.570.1 2.570.1 8.570.6

11.070.7 72.070.4 590740 273710 17779 883750

4.0170.30 3371 320720 15578 8374 440730

3.9770.28 3272 320720 15477 8274 440730

0.05 0.07 0.09 0.10 0.07 0.09

(cement+bricks) (cement+bricks) (cement+bricks) (clay bricks) (limestone rocks) (limestone rocks)

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Table 4 222 220 222 Data obtained for alpha-activities per unit volume due to radon and thoron inside (Ain RnÞ and Ain RnÞ) and outside (Aout RnÞ Cð Cð C ð 220 and Aout ð RnÞ) various reference atmospheres C Marble sample

222 Ain RnÞ Cð ðkBq m3 Þ

222 RnÞ Aout C ð ðBq m3 Þ

220 RnÞ Ain Cð ðkBq m3 Þ

220 RnÞ Aout C ð ðBq m3 Þ

Rose granite Gray granite Black granite

263710 241710 11674

1168756 539731 479728

21979 20578 7573

11579 6275 5874

Table 5 Data obtained for track density rates registered on the CR-39 and LR-115 SSNTD and alpha- and beta-activities per unit volume due to radon and its decay products inside different reference atmospheres. F 222 is the equilibrium factor between radon and its progeny Marble sample

rCR  103 ðtr cm2 s1 Þ

rLR  103 ðtr cm2 s1 Þ

222 RnÞ Aout C ð ðBq m3 Þ

218 PoÞ Aout C ð ðBq m3 Þ

214 PbÞ Aout C ð ðBq m3 Þ

214 BiÞ Aout C ð ðBq m3 Þ

214 PoÞ Aout C ð ðBq m3 Þ

F 222

Rose granite Gray granite Black granite

6:2670:25 3:7570:18 3:3570:16

1:8970:09 1:1470:06 1:0270:06

1168756 539731 479728

943745 435725 406723

803739 371721 345720

712734 329719 306718

712734 329719 306718

0.67 0.67 0.67

Table 6 Data obtained for alpha- and beta-activities per unit volume due to thoron and its progeny inside various reference atmospheres. F 220 is the equilibrium factor between thoron and its daughters Marble sample

220 RnÞ Aout C ð ðBq m3 Þ

216 PoÞ Aout C ð ðBq m3 Þ

212 PbÞ Aout C ð ðBq m3 Þ

212 BiÞ Aout C ð ðBq m3 Þ

212 PoÞ Aout C ð ðBq m3 Þ

F 220

Rose granite Gray granite Black granite

11579 6275 5874

11579 6275 5874

22.571.7 1271 11.370.9

16.271.3 8.770.7 8.270.6

16.271.3 8.770.7 8.270.6

0.19 0.19 0.19

alpha-activities inside the corresponding marble sample (source) increase. Values of the F 222 and F 220 factors (Tables 5 and 6) show that there exist a disequilibrium between radon and its decay products and between thoron and its daughters inside the considered reference atmospheres.

inexpensive, accurate, sensitive and does not need the use of standards for its calibration is a good tool for measuring radon, thoron and their progenies inside mining deposits, caves and factories.

References 4. Conclusion In this study, alpha- and beta-activities per unit air volume due to the radon and thoron series have been measured inside different dwelling rooms by using two different types of solid state nuclear track detectors (SSNTD). It has been shown that these activities are influenced by the nature of the building material utilized and ventilation rate of the studied dwelling rooms. A good airing is necessary to avoid any enhancement of exposure to radiation for population. It has also been shown that by using this SSNTD method one can prepare radon and thoron standard sources and measure the corresponding alpha- and beta-activities due to the radon and thoron groups. The SSNTD method developed which has the advantage of being simple,

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