natural radioactivity and radon exhalation in building materials used in italian dwellings

Journal of Environmental Radioactivity 88 (2006) 158e170www.elsevier.com/locate/jenvrad

Natural radioactivity and radon exhalation inbuilding materials used in Italian dwellings

Serena Righi*, Luigi Bruzzi

Centro Interdipartimentale di Ricerca per le Scienze Ambientali and Dipartimento di Fisica,

University of Bologna, via dell’Agricoltura 5, 48100, Ravenna, Italy

Received 1 April 2005; received in revised form 13 January 2006; accepted 26 January 2006

Available online 11 April 2006

Abstract

Forty-two samples of building materials commonly used in Italian dwellings were surveyed for naturalradioactivity. External (gamma), as defined and used by the European Commission, and internal (alpha)hazard indexes were calculated and radon specific exhalation rate and emanation fraction were measured.The accumulation method, by using the E-PERM electret ion chambers, was employed to determine spe-cific exhalation rates of 222Rn. Several of the materials had hazard indexes that exceeded the EuropeanCommission limit values. However, it was evident that limit values for internal hazard indexes set basedon Rn emanation should take into account the properties and use of the materials. For example, Rn em-anation from basalt and glazed tiles was substantially lower than the Rn emanation from other materialswith similar hazard indexes. Clearly there is need for improved guidelines and regulations in this area.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Building materials; Indoor exposure; Naturally occurring radioactive materials; Radon exhalation;

Emanation fraction; Hazard indexes

1. Introduction

Knowledge of ionising radiation levels in buildings is clearly of fundamental importance inthe assessment of population exposure, as the majority of individuals spend most time indoors.Normally, the two main routes of indoor exposure are terrestrial gamma-ray irradiation andradon isotope inhalation.

* Corresponding author. Tel.: þ39 0544 937306; fax: þ39 0544 937303.

E-mail address: [email protected] (S. Righi).

0265-931X/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvrad.2006.01.009

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159S. Righi, L. Bruzzi / J. Environ. Radioactivity 88 (2006) 158e170

In massive houses made of brick, concrete or stone, the building materials act as attenuatorsof gamma rays emitted outdoors, therefore the indoor absorbed dose rate depends mainly on theconcentration of radioactive substances occurring in the construction materials. It has beendemonstrated in various studies (Mjones, 1986; Pinnock, 1991; Thomas et al., 1993; Ahmadet al., 1998a; Stoulos et al., 2003; Arafa, 2004) that, if building materials with high natural ra-dioactivity concentration are employed, dose rates indoors will be elevated accordingly. Theratio of indoor-to-outdoor dose rates from terrestrial gamma rays varies from 0.8 to 2.0, withan average of 1.3 (UNSCEAR, 1988). This relatively narrow range of indoor-to-outdoordose ratios reflects the fact that building materials are generally of local origin and that theirradioactive contents are similar to those in the ground.

Radon gas enters the indoors from different sources, such as soil or rock under or surround-ing the buildings, building materials, water supplies, natural gas and outdoor air. The mainmechanisms of radon entry are diffusion and advection from the ground and building materials.However, it is not possible, on a general basis, to correlate radon levels in a building only to theradium content of the ground and building materials. Actually, radon emanation from a materialdepends on many factors: where radium atoms are situated in the grain; the texture, size andpermeability of the grain; the material porosity; and the environmental temperature and pres-sure changes (Akerblom and Wilson, 1981; Colle et al., 1981; Durrani and Ilic, 1997).

The European Commission published two recommendations regarding indoor exposure tomembers of the public from natural radiation. The first is the guideline on advisory levelsfor radon in residential dwellings (EC, 1990). The second one states the radiological protectionprinciples for natural radioactivity in building materials (EC, 1999). In spite of recent intereston indoor exposure, these recommendations are not yet being properly implemented in manyMember States; consequently nowadays there is a lack of legislative protection against ionisingradiation in dwellings. In Italy, for example, there are no regulations on the radioactivity ofbuilding materials.

This study assesses the radioactivity of some common building materials, taking into ac-count the above-mentioned guidelines (EC, 1990, 1999). In particular, the following activitieshave been carried out: (1) characterization through g-spectrometry of various building mate-rials used in Italy; (2) calculation of their external and internal hazard indexes; and (3) deter-mination of their radon exhalation and emanation fraction.

2. Materials and methods

2.1. Sampling and sample preparation

Samples of building materials weighing from 1.0 to 2.0 kg were collected from quarries and local sup-pliers. The following materials were selected: 13 structural materials (bricks, concrete, and mortar), and 29covering materials (tiles, plaster coats and natural tiling stones). Structural building materials are used inbulk amounts while covering building materials have a restricted use. Structural materials, tiles and plastercoats were purchased from commercial companies and local suppliers located in the regions of northernItaly. Three types of natural tiling stone were imported: black gabbro from South Africa, white granitefrom Norway and one pink granite from Spain. The remaining types were collected from quarries locatedin regions of central and northern Italy.

All samples were pulverized and dried at 105 �C in order to eliminate any water content. For g-spec-trometric measurements, the homogenized samples were transferred to 450-mL Marinelli beakersand weighed. Samples were sealed and stored for at least 30 days to capture 222Rn gas (T1/2¼ 3.8 d)and ensure secular equilibrium between 226Ra (T1/2¼ 1.60� 103 y) and measured daughters 214Pb and

160 S. Righi, L. Bruzzi / J. Environ. Radioactivity 88 (2006) 158e170

214Bi (T1/2¼ 27 and 20 min, respectively). In order to determine the radon specific exhalation rate, anamount of about 150 g of sample was used for each measurement.

2.2. Natural radioactivity concentration

Measurements of radioactivity concentration in building materials were carried out using g-spectrom-etry by means of an n-type coaxial HPGe detector with an active volume of about 110 cm3 connected toa multichannel analyser. The considered energy range was 200e1500 keV and, in this interval, the spec-trometer resolution ranged from 1 to 2 keV. The detection system was calibrated for energy and efficiencyusing a multi-nuclide source supplied by the CEA (Commissariat a l’Energie Atomique e France)containing 57Co, 60Co, 85Sr, 88Y, 109Cd, 113Sn, 139Ce, 137Cs, and 241Am. More details are given by Bruzziet al. (2000) and Righi et al. (2000).

The spectrum analysis was performed using the software Gamma 2000 Silena v. 2.0. If several peaksbelonging to the same radionuclide are used to determine the activity value, the software calculates theweighted mean of the individual values. The software also provides the statistical errors of the activityconcentration. These are combined with the uncertainty of the efficiency through the root-sum-of-squaresrule to give the overall uncertainty (s overall (Ai)) for the activity concentration of each radionuclide asfollows:

s overallðAiÞ ¼ Ai

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi"sðAiÞ2

Ai

þ sð3Þ2

3

#vuut ð1Þ

where s(3) is the uncertainty of the efficiency. The last one is given by the statistical error due to the un-certainty in the counting rates and the systematic error due to the uncertainty in activities of the standardsource used for efficiency calibration of the detector (Silena, 2000).

The limits of detection (LD) are calculated by the software at the 95% confidence level according to:

LD ¼ hNi þ 3:29sðNÞ ð2Þ

where hNi is the expected value of the number of counts and s(N ) is the standard deviation of the ob-served value of the number of counts (Silena, 2000).

Short-lived daughters with more easily measured gamma-ray emissions such as 214Pb, 214Bi, 228Ac and212Pb were used for proxy determinations of the activity concentrations of their respective parents 226Raand 232Th. Gamma-ray peaks of 609.32 and 1120.28 keV (214Bi), 295.21 and 351.92 keV (214Pb), 338.40,911.07 and 968.90 keV (228Ac), and 238.63 keV (212Pb) were used. The 1460.83 keV gamma-ray peakwas used to determine 40K concentration. The detection limits of 228Ac, 214Bi, 212Pb, 214Pb and 40Kwere 7� 10�4, 4� 10�4, 3� 10�4, 4� 10�4 and 5� 10�3 Bq g�1, respectively.

Prior to sample measurement, the environmental gamma background at the laboratory site was deter-mined with an empty Marinelli beaker under identical measurement conditions. It was later subtractedfrom the measured g-ray spectra of each sample. Samples were counted for about 24 h. Measurementtimes were sufficiently long to ensure that the overall uncertainty was, generally, less than 10% at the95% confidence interval.

2.3. Gamma-index

A number of indexes dealing with the assessment of the excess gamma radiation originating frombuilding materials (frequently called ‘‘gamma-indexes’’ or ‘‘external-indexes’’) have been proposed (Kri-siuk et al., 1971; Stranden, 1976; Krieger, 1981; Swedjemark, 1986; Bruzzi et al., 1992). In this study, thegamma-index was calculated as proposed by the European Commission (EC, 1999). The Commission sug-gests that building materials should be exempted from all restrictions concerning their radioactivity if theexcess gamma radiation originating from them increases the annual effective dose of a member of the


public by 0.3 mSv at the most. On the contrary, doses higher than 1 mSv should be accepted only in somevery exceptional cases where materials are used locally.

The gamma-index (Ig) proposed by the European Commission (EC, 1999) is calculated using the fol-lowing formula:

Ig ¼CRa

300 Bq kg�1 þCTh

200 Bq kg�1 þCK

3000 Bq kg�1 ð3Þ

where CRa, CTh, CK are the 226Ra, 232Th and 40K activity concentrations (Bq kg�1), respectively, in thebuilding material. The index shall not exceed the values given in Table 1, depending on the dose criterionand the way and amount the material is used in a building. For more information about parameter valuesused in deriving this gamma-index, see the work of Markkanen (1995).

2.4. Alpha-index

Also several indexes dealing with the assessment of the excess alpha radiation due to the radon inha-lation originating from building materials (called ‘‘alpha-indexes’’ or ‘‘internal-indexes’’) have been de-veloped (Krieger, 1981; Stoulos et al., 2003). In the present work, the alpha-indexes were determinedthrough the following formula:

Ia ¼CRa

200 Bq kg�1 ð4Þ

where CRa is the 226Ra activity concentration (Bq kg�1) in the building material. When the 226Ra activityconcentration of a building material exceeds the value of 200 Bq kg�1, it is possible that the radon exha-lation from this material could cause indoor radon concentrations exceeding 200 Bq m�3. On the contrary,when the 226Ra activity concentration is below 100 Bq kg�1 it is unlikely that the radon exhalation fromthe building materials could cause indoor radon concentrations exceeding 200 Bq m�3 (Nordic, 2000).The recommended exemption level and recommended upper level for 226Ra activity concentration are100 Bq kg�1 and 200 Bq kg�1, respectively, in building materials as suggested by the Radiation ProtectionAuthorities in Denmark, Finland, Iceland, Norway and Sweden (Nordic, 2000). The upper level is inagreement with the action level given by the ICRP in Publication 65 (1994) and by the European Com-mission (EC, 1990).

2.5. Radon exhalation

As reported in the summary of Stranden (1988), a variety of methods for determining radon exhalationhave been developed. The procedure used in this work involved the E-PERM electret ion chambers andconsisted of determining the 222Rn activity accumulated in a vessel after a given build-up time (Kotrappaand Stieff, 1994; Colle et al., 1995). The ‘‘accumulator method’’ is a common technique for radon exha-lation rate measurements in building materials (Petropoulos et al., 2001).

The growth of 222Rn activity concentration CRn (Bq m�3) as a function of time t within a closed ac-cumulation vessel may be given in approximate form as:

Table 1

Gamma-index values suggested by the European Commission (1999) taking into account typical ways and amounts in

which the material is used in a building

Dose criterion 0.3 mSv y�1 1 mSv y�1

Materials used in bulk amounts, e.g. bricks Ig� 0.5 Ig� 1

Superficial and other materials with restricted use: tiles, boards, etc. Ig� 2 Ig� 6


CRn ¼Eð1� e�lRn tÞ

VlRnmþC0

Rn e�lRn t ð5Þ

where E is the specific exhalation rate (Bq kg�1 h�1) from the sample, lRn is the decay constant for 222Rn(h�1), V is the volume of the accumulation vessel (m3), m is the mass of the sample (kg) and C0

Rn (Bq m�3)is the 222Rn activity concentration in the accumulation vessel at the start of an accumulation time (t¼ 0).

The accumulation measurements were performed with screw-capped and gasketed glass jars that area component part of the E-PERM radon-in-water measurement test kit (Kotrappa and Jester, 1993).The E-PERM system is based on the electrical potential reduction of an electrostatically charged teflondisk held within a chamber, caused by the ions generated by radon decay. To determine radon concentra-tion, an integrated measurement with a 210-mL chamber configured with a short-term electret was ap-plied. The following formula was used to calculate the radon concentration, CRn, in Bq m�3:

CRn ¼�Vi �Vf

�CF T

�BG ð6Þ

where Vi and Vf are the measured initial and final electret voltages, respectively; CF is the calibration fac-tor in units of V per Bq m3 d; T is the exposure period in days; and BG is the radon concentration equiv-alent of natural g radiation background. The calibration factor was calculated for each measurement usingEq. (7).

CF¼ 0:04589þ 0:0000155

�Vi þVf

�2

ð7Þ

Use, characteristics and performance of the E-PERM system have been extensively described by Kotrappaet al. (1988, 1990). A survey on the accuracy of the E-PERM device for radon emanation measurementswas carried out by Kotrappa and Stieff (1994).

The total accumulation volume after subtracting the excluded volume for the E-PERM chamber is3.8 L, as carefully measured by Kotrappa and Stieff (1994). Therefore, considering that measurementswere carried out on an amount of about 150 g of sample and taking into account that the bulk densityof investigated materials ranged from 1.5 to 2.5 kg L�1, the volume of the measured samples was morethan 10 times less than the volume of the container. Under these circumstances, the ‘‘back diffusion’’ ef-fect has no influence on radon exhalation rate measurements (Krisiuk et al., 1971; Poffijn et al., 1984).

The jars were left in a low radon area (outside environment) so that the contribution from the residual ra-don in the jar was minimised before starting the accumulation. The electret ion chamber and the sample werepositioned one at a time in the jar: the sample was placed on the bottom and the chamber was suspendedthrough a hook attached to the screw cap. The jar lid was then sealed with a special rubber collar that wasclamped with metal bands. Each sample was left in the vessel for about 10 days. At the end of the exposuretime, the electret ion chamber was taken out and the reduction in electrical potential was measured.

According to Appendix A, the specific exhalation rate, E, was determined by Eq. (A.4) using the av-erage concentration over the accumulation time, CRn, of the sample. Since in the present case the 222Rnconcentration in the accumulator at the start of the experiment cannot be negligible, the blank reading wassubtracted from the total 222Rn concentration in order to find the net 222Rn concentration. The blank read-ing was determined by introducing E-PERM chambers into empty jars equal to those used for the exper-iments. These E-PERM chambers were exposed for the same time that was used for experimental ones.

The detection limit (3s of the background) was estimated to be 0.0015 Bq h�1 for an exposure time of240 h.

The emanation fraction f, i.e. the fraction of radon that reaches the external atmosphere by means of thediffusion process, was determined through the following equation:

f ¼ E

CRalRn

ð8Þ

where CRa is the 226Ra activity concentration (Bq kg�1).


3. Results and discussion

3.1. Natural activity concentration

The activity concentrations of 226Ra, 232Th and 40K in building materials used in bulk and inrestricted amounts are shown in Tables 2 and 3. The natural radioactivity levels measured in thesamples are comparable to those measured over a nationwide (Sciocchetti et al., 1983; CamposVenuti et al., 1985; Carrera et al., 1997) and worldwide scale (Ingersoll, 1983; Mustonen, 1984;Beretka and Mathew, 1985; Pakou et al., 1994; Ahmad et al., 1998b; Al-Jarallah, 2001; WalleyEl-Dine et al., 2001; Stoulos et al., 2003). As it can be seen in the tables, the measured min-imum value of 226Ra activity concentration was 0.53 Bq kg�1 in the sample of red marble,whereas the maximum activity concentration was 280 Bq kg�1 in a volcanic tuff. The minimumobserved 232Th activity concentration was 0.25 Bq kg�1 in the travertine sample and the max-imum was 360 Bq kg�1 in the red granite sample. 40K activity concentration varied from5.4 Bq kg�1 in the travertine to 1900 Bq kg�1 in a volcanic tuff. Volcanic tuffs are effusivemagmatic rocks typical of the central regions of Italy, characterized by natural activity concen-trations considerably higher than other natural building materials. Moreover, intrusive mag-matic rocks (such as granites) are generally characterized by a natural radioactivity relativelyhigher than other natural building materials.

Other materials which showed relatively high radioactivity concentrations were porcelainstoneware tiles and some bricks. The high concentration of 226Ra observed in porcelain stone-ware tiles can be explained through the presence of zircon mineral, having a relatively high ac-tivity concentration of uranium. However, the average values of activity concentration ofinvestigated materials for 226Ra (60 Bq kg�1), 232Th (58 Bq kg�1) and 40K (600 Bq kg�1) arein the ranges of the corresponding typical world averages of 50, 50 and 500 Bq kg�1, respec-tively (UNSCEAR, 1993).

In general, activity concentrations of 226Ra and 232Th were rather low in all the samples. InFig. 1, the frequency distribution of 226Ra and 232Th concentrations in samples is shown. Therange of 1e100 Bq kg�1 includes most of the samples (83% and 88% for 226Ra and 232Th,

Table 2

Natural activity concentrations of 226Ra, 232Th and 40K (Bq kg�1) and gamma- and alpha-indexes in samples of

materials used in bulk amounts for building construction

Code Samples

(building material type)

226Ra (M.V.� s) 232Th (M.V.� s) 40K (M.V.� s) Ig Ia

1 Brick 110� 9 97� 8 380� 30 0.98 0.55

2 Brick 96� 8 90� 7 160� 10 0.82 0.48

3 Brick 20� 2 25� 2 410� 30 0.33 0.10

4 Brick 35� 3 36� 3 560� 50 0.48 0.18

5 Brick 34� 3 40� 4 680� 60 0.54 0.17

6 Brick 76� 6 33� 3 590� 50 0.61 0.38

7 Brick 32� 3 39� 3 530� 50 0.48 0.16

8 Concrete 18� 2 12.3� 1.5 230� 20 0.20 0.09

9 Concrete 12.9� 1.2 20� 2 390� 30 0.27 0.06

10 Mortar 22� 2 25� 2 490� 40 0.36 0.11

11 Mortar 7.0� 0.6 7.7� 0.7 130� 10 0.10 0.03

12 Mortar 13.4� 1.2 15.0� 1.6 400� 40 0.25 0.07

13 Lime mortar 16.4� 1.5 21� 2 400� 30 0.30 0.08

M.V.� s¼mean value� standard deviation.


respectively). Only 4.8% and 9.5% of all samples had 226Ra and 232Th activity concentrationsabove 200 Bq kg�1, respectively. As shown in the logelog plot of Fig. 2, the 226Ra were sig-nificantly correlated with 232Th concentrations (r¼ 0.77, n¼ 42, P< 0.05%). Thorium anduranium are concentrated in crustal rocks in an average Th/U activity ratio of about 1 (UN-SCEAR, 2000). The constancy of this value among different igneous rock types indicatesthe general lack of fractionation of the two elements during magmatic processes (Gascoyne,1992). Assuming the radioactive equilibrium between 238U and 226Ra, the observed correlationreflects that the original Th/U ratio is preserved from stone materials to end products. Signif-icant deviations from this correlation are noted in the sample number 6 (brick), 17 (plastercoat), 21 and 22 (porcelain stoneware), 24 (red granite), and 39 and 40 (limestone). Theyare probably related to the natural genesis of raw materials or original rock.

Gamma- and alpha-indexes of the samples are also shown in Tables 2 and 3. Gamma-index(Ig) ranged from 0.10 to 0.98 and from 0.01 to 2.92 in building materials used in bulk and inrestricted amounts, respectively. No exceedance of the recommended upper limit was noted, butseven samples exceeded the recommended exemption level for exposure to external gamma ra-diation. The average relative contribution to gamma-index due to 232Th was 37%, followed by

Table 3

Natural activity concentrations of 226Ra, 232Th and 40K (Bq kg�1) and gamma- and alpha-indexes in samples of mate-

rials used in restricted amounts for building construction

Code Samples


226Ra (M.V.� s) 232Th (M.V.� s) 40K (M.V.� s) Ig Ia

14 Red clay roofing tile 23� 2 30� 3 540� 50 0.41 0.12

15 Red clay roofing tile 24� 2 36� 3 590� 50 0.45 0.12

16 Plaster coat 22� 2 23� 2 470� 40 0.35 0.11

17 Plaster coat 34� 3 1.7� 0.2 25� 3 0.13 0.17

18 Terracotta tile 12.0� 1.1 9.1� 1.2 150� 13 0.14 0.06

19 Ceramic glazed tile 48� 4 42� 4 460� 40 0.52 0.24

20 Ceramic glazed tile 56� 5 43� 4 440� 40 0.55 0.28

21 Porcelain stoneware 230� 20 76� 6 650� 60 1.36 1.15

22 Porcelain stoneware 150� 15 56� 5 410� 40 0.92 0.75

23 Green granite 57� 5 49� 4 560� 50 0.62 0.32

24 Red granite 153� 13 360� 30 1600� 100 2.84 0.77

25 Pink granite 147� 13 200� 18 1200� 100 1.89 0.74

26 Pink granite 33� 3 44� 4 1000� 90 0.66 0.16

27 Pink granite 61� 5 79� 7 1200� 100 1.00 0.31

28 White granite 37� 3 42� 4 830� 70 0.61 0.19

29 Black gabbro 11.7� 1.0 19� 2 240� 20 0.22 0.06

30 Basalt 41� 4 26� 2 340� 30 0.38 0.21

31 Trachyte 41� 3 41� 3 1100� 100 0.71 0.21

32 Porphyry 40� 3 48� 4 950� 80 0.69 0.20

33 Porphyry 41� 4 57� 5 1050� 90 0.77 0.21

34 Volcanic tuff 92� 8 138� 11 1200� 100 1.40 0.46

35 Volcanic tuff 190� 20 210� 20 1900� 200 2.32 0.95

36 Volcanic tuff 280� 20 270� 20 1900� 200 2.92 1.40

37 Sandstone 33� 3 32� 3 530� 40 0.45 0.17

38 Sandstone 13.6� 1.2 12.8� 1.2 230� 20 0.19 0.07

39 Limestone 65� 5 6.1� 0.5 46� 4 0.26 0.33

40 Limestone 76� 6 8.0� 0.7 47� 4 0.31 0.38

41 Travertine 0.75� 0.07 0.25� 0.04 5.4� 0.7 0.01 0.004

42 Red marble 0.53� 0.08 3.9� 0.7 20� 3 0.03 0.003


the contributions due to 40K and 226Ra (33% and 30%, respectively). This means that generally226Ra, 232Th and 40K contributed similarly to external exposure; only in few cases did one ofthese radionuclides play a predominant role.

Alpha-index (Ia) ranged from 0.03 to 0.55 for building materials used in bulk, and from0.003 to 1.40 for those used in restricted amounts. All the samples measured, except for oneporcelain stoneware tile (Ia¼ 1.15) and one volcanic tuff (Ia¼ 1.40), showed values belowthe recommended upper level. Only five samples exceeded the recommended exemption levelfor internal exposure.

To sum up, about 25% of samples exceeded the recommended exemption level and 5% ex-ceeded the recommended upper level for external and/or internal radiation exposure. These re-sults highlight the need to execute controls on the radioactivity of building materials.

However, it is important to point out that there is no distinction between materials used inbulk amounts and materials with restricted use in the alpha-index determination. There is ev-idence that in some cases, 200 Bq kg�1 of 226Ra in building materials is a very conservativevalue. Studies of Bruzzi et al. (1991), for instance, suggest that values exceeding 200 Bq kg�1of

0

1

2

3

4

5

6

7

8

9

0-9

30-39

60-69

90-99

120-129

150-159

180-189

210-219

240-249

270-279

300-309

330-339

360-369

Activity concentration (Bq kg-1

)

Freq

uen

cy

(n

° o

f sam

ples)

Ra-226Th-232

Fig. 1. Distribution of activity concentration of 226Ra and 232Th in the samples.

0

1

10

100

1000

0 1 10 100 1000226

Ra activity concentration (Bq kg-1

)

232T

h activity co

ncen

tratio

n (B

q kg

-1)

Fig. 2. 232Th activity concentration as a function of 226Ra activity concentration of samples.


226Ra in ceramic tiles could be accepted because the solid matrix of the tile is highly condensedand gives little possibility for radon to escape; moreover the external surface of a tile is, gen-erally, covered by a vitrified layer representing an efficient barrier against the radon release.Therefore, it is hoped that, as for the gamma-index, the European Commission will set limitvalues for the alpha-index also taking into account typical ways and amounts in which the ma-terial is used in a building.

3.2. Radon exhalation

Tables 4 and 5 list the 222Rn specific exhalation rate (Bq kg�1 h�1) and the emanation frac-tion (%) in building materials used in bulk and in restricted amounts, respectively. The 222Rnspecific exhalation rate ranged from less than the detection limit to 0.25 Bq kg�1 h�1. The meanvalue was 0.029 Bq kg�1 h�1. The emanation fraction varied from ‘‘not quantifiable’’ to 23%(mean value 6.6%).

The maximum rate of radon exhalation was observed in the red granite sample. By contrast,the samples of roofing tiles, marbles, and ceramics did not show detectable radon exhalation.This evidence confirms the hypothesis previously mentioned about the difficulty for radon toescape condensed solid matrices. Generally, it was found that the stones of magmatic origin(such as granites, porphyries and volcanic tuffs) are the more significant sources of radon em-anation. Nevertheless, the levels of radon exhalation rate from magmatic rock samples showeda wide dispersion, with values scattered over two orders of magnitude. In these samples the ex-halation rate varied from less than the detection limit to 0.25 Bq kg�1 h�1 with an average of0.051 Bq kg�1 h�1. The emanation fraction from magmatic rocks also presented a wide rangeof values, ranging from ‘‘not quantifiable’’ to 21% with an average of 5.3%. A similar behav-iour has been observed in other classes of building materials (such as bricks and mortar). Theresults are in good agreement with the corresponding values that were measured at a worldwidescale (Ingersoll, 1983; Savidou et al., 1996; Al-Jarallah, 2001; Rizzo et al, 2001; Petropouloset al., 2002; Stoulos et al., 2003).

Our results support the theory that radon exhalation rates are not predictable from the radiumcontent only, as reported in Section 1. Although, for instance, basalt has a similar 226Ra

Table 4

Radon specific exhalation rate (Bq kg�1 h�1) and emanation fraction (%) in samples of materials used in bulk amounts

for building construction

Code Samples


Specific exhalation

rate (M.V.� s)

Emanation fraction

(M.V.� s)

1 Brick 0.0137� 0.0003 1.65� 0.04

2 Brick 0.0164� 0.0011 2.3� 0.2

3 Brick 0.0276� 0.0013 18.3� 0.8

4 Brick 0.007� 0.002 3.5� 0.3

5 Brick 0.008� 0.002 1.8� 0.2

6 Brick 0.009� 0.004 2.5� 0.2

7 Brick 0.0071� 0.0012 1.60� 0.12

8 Concrete 0.0089� 0.0007 6.6� 0.5

9 Concrete 0.016� 0.003 16� 3

10 Mortar 0.015� 0.002 9.1� 1.5

11 Mortar 0.0123� 0.0009 23� 2

12 Mortar 0.0128� 0.0002 12.6� 0.2

13 Lime mortar 0.0040� 0.0005 2.9� 0.2


concentration as trachyte, the radon exhalation rate is much lower. It is also very interesting tonote that regardless of the value of 226Ra concentration, ceramic tiles have no detectable radonexhalation. This might be caused, as mentioned before, by a reduction of the microporosity ofthe grain or by the glazed layer created on the tile surface during the manufacturing process,which blocks radon emanation.

4. Conclusions

From this study, the natural radionuclide content, internal and external hazard indexes, radonspecific exhalation rate and emanation fraction of some building materials commonly used inItalian dwellings were determined. The average activity concentrations for 226Ra (60 Bq kg�1),232Th (58 Bq kg�1) and 40K (600 Bq kg�1) in these samples of building materials are in goodagreement with the corresponding typical world averages of 50, 50 and 500 Bq kg�1, respec-tively. The results indicate that magmatic rocks are generally characterized by higher naturalradioactivity than other natural building materials.

Table 5

Radon specific exhalation rate (Bq kg�1 h�1) and emanation fraction (%) in samples of materials used in restricted

amounts for building construction

Code Samples


Specific exhalation

rate (M.V.� s)

Emanation fraction

(M.V.� s)

14 Red clay roofing tile <LLD N.Q.

15 Red clay roofing tile <LLD N.Q.

16 Plaster coat 0.0171� 0.0002 10.26� 0.12

17 Plaster coat 0.0031� 0.0006 1.2� 0.2

18 Terracotta tile 0.0065� 0.0008 7.1� 0.9

19 Ceramic glazed tile <LLD N.Q.

20 Ceramic glazed tile <LLD N.Q.

21 Porcelain stoneware <LLD N.Q.

22 Porcelain stoneware <LLD N.Q.

23 Green granite 0.082� 0.005 19.1� 1.2

24 Red granite 0.25� 0.03 21� 2

25 Pink granite 0.129� 0.004 11.6� 0.4

26 Pink granite 0.0122� 0.0004 4.89� 0.15

27 Pink granite 0.069� 0.007 15.0� 1.5

28 White granite 0.0043� 0.0005 1.5� 0.2

29 Black gabbro 0.007� 0.001 7.4� 1.2

30 Basalt <LLD N.Q.

31 Trachyte 0.032� 0.002 10.4� 0.7

32 Porphyry 0.0068� 0.0006 2.2� 0.2

33 Porphyry 0.038� 0.002 12.4� 0.7

34 Volcanic tuff 0.041� 0.004 5.8� 0.7

35 Volcanic tuff 0.103� 0.002 7.2� 0.9

36 Volcanic tuff 0.17� 0.02 7.9� 1.1

37 Sandstone 0.014� 0.002 5.7� 0.8

38 Sandstone 0.0099� 0.0010 9.3� 1.0

39 Limestone 0.036� 0.003 7.4� 0.5

40 Limestone 0.034� 0.003 5.8� 0.9

41 Travertine <LLD N.Q.

42 Red marble <LLD N.Q.

<LLD¼ less than the lower detection limit.

N.Q.¼ not quantifiable.


Calculations of alpha-(Ia) and gamma-(Ig) indexes showed that about 25% of the samplesexceeded the recommended exemption level and 5% exceeded the recommended upper levelfor external and/or internal radiation exposure. This strengthens the need for regulation of theradioactivity of building materials. The study also highlights the need for improved alpha-indexes that take into account typical ways and amounts in which the material is used in a building.

Finally, the results confirm that the radon exhalation rates are not predictable from the radiumcontent only and that the emanation rate cannot be presumed to be constant within a given class ofbuilding materials or from one class to another with approximately the same radium content.

Acknowledgements

This research would not have been possible without the technical support of the HealthPhysics Service of Ravenna Hospital. The authors would also like to thank Dr. A. Albertazziof the Ceramic Centre of Bologna for her help in preparing the samples, and Dr. R. Capozziand Prof. V. Simoncini for their valuable comments and contributions.

Appendix A

If the 222Rn activity concentration (ARn) in the accumulator at the start of the experiment isassumed to be neglected, then the 222Rn activity concentration at any time T after the start of theaccumulation is given by Kotrappa and Stieff (1994):

ARn ¼fCRa

�1� eð�lRnTÞ�

VA

ðA:1Þ

where f is the emanation fraction, CRa is the activity concentration of 226Ra, VA is the air vol-ume of the accumulator, and lRn is the decay constant of 222Rn. The 222Rn concentration variesfrom zero at the start of the accumulation to the concentration obtained by the Eq. (A.1) at theend of the exposure time T. The quantity fCRa is defined as ‘‘effective radium’’ content and rep-resents the amount of the produced radon from the grains that finally enters by recoil effect anddiffusion process in the porous system of the material.

The time-integrated concentration of 222Rn (TICRn) can be calculated by integrating Eq.(A.1) as follows:

TICRn ¼Z T

0

�fCRa

�1� eð�lRntÞ�

VA

�dt ðA:2Þ

If the time-integrated concentration of 222Rn is divided by the accumulation time T, the av-erage concentration CRn over the time T is obtained, namely:

CRn ¼fCRa

VA

�1� 1� eð�lRnTÞ

lRnT

�ðA:3Þ

Finally, the specific exhalation rate, E, can be determined as:

E¼ ðCRnVAlRnÞ=m

1� ð1� eð�lRnTÞÞ=ðlRnTÞ ðA:4Þ

where m is the sample mass.


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