Environmental Technology Letters, Vol. 5, pp. 81-88

© Science and Technology Letters, 1984

ASSESSMENT OF NATURAL RADIOACTIVITYLEVELS IN BUILDING MATERIALS AND

EVALUATION OF INDOOR RADIATION EXPOSURE

V. S. Londhe, S. R. Rao and K. C. Pillai*Environmental Studies Section

Health Physics DivisionBhabha Atomic Research Centre

Bombay 400 085 India

(Received 14 September 1983; in final form 6 January 1984)

ABSTRACT

Building mater ia l s used i s some cement houses in Greater Bombay and nearby areaswere analysed gamma speotrometr ical ly using a bulk mater ia l gamma counter, having 20 cm(dia) x 10 cm ( thickness) NaI (T1) de tec to r . Radium-226 was determined through Bi-214(1.76 MeV) and Thorium-232 through T1-208 (2.61 MeV) while Potassium-40 by i t s 1.46 MeVgamma photons. Average Ra-226 content in cement was found to be t he highest (60.4 Bq,Kg - 1) and t h a t in g ran i t e the lowest (10.7 Bq. Kg - 1 ) . Ra-226 gives 'Q' the Radon-222emanation r a t e from which Rn-222 concentration i s ca lcu la ted . From Rn-222, indoori n t e r n a l exposure in mWLM Y-1 and from Bi , T1 and K indoor a i r dose in urad h-1 ins idea model room t h a t can be bu i l t from such ma te r i a l s has been computed. I t i s 3.9 urad h - 1

(0.04 uGy h - 1 ) and i s comparable with values obtained by actual measurements in othercountr ies ( 1 ) .

• INTRODUCTION

Indoor exposure t o na tura l r ad ia t ion i s mainly through ( i ) whole body exposure tohigh energy gamma rad ia t ions from Potassium-40 (1.46 MeV) and some nuolides l i keBismuth-214(1.76 MeV) and Thall.ium-208 (2.61 MeV) of Uranium-238 and Thorium-232 se r i e sr e spec t ive ly and ( i i ) exposure of lung t i s s u e s t o Radon-222 and i t s alpha emitt ingsuccessors .

Certain recent prac t ices such as ( i ) use of f lyash (a waste product from thermalpower s t a t i o n ) to produce Portland poazolana cement (PPC) and ( i i ) use of phosphogypsum(a by-product of rock phosphate processing indust ry) in place of natural gypsum orcalcium carbonate during manufacture of cement, cause enhancement of indoor exposure.High l eve l s of Ra-226 in f lyash , phosphogypsum and calcium carbonate sludge have been

v reported e a r l i e r ( 1 , 2 , 3 ) . Incidences of enhanced indoor exposure to na tu ra l radia t ionhave been repor ted where waste s lag of a rock phosphate processing industry had beenused for house construct ion (4) and in a case where walls were l ined with Uraniumglazed f lagstone ( 5 ) .

Indoor occurrence of Rn-222, the decay product of Ra-226 can be mainly due to( i ) Diffusion from wal l s , f loor and c e i l i n g of the room and ( i i ) use of water, conta i -ning na tu ra l Ra-226. The l i t e r a t u r e study (6) revea l s tha t exposure to natura l r a d i a -t i on i s comparatively higher in cement houses than in wooden or br ick houses. No suchcomparative study however has been made for d i f ferent types of houses in India .

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This study presents resul ts of estimation of natural radioéléments l ike Rn-222,Th-232 and K-40 in a limited number of samples of building materials which are used inGreater Bombay and nearby areas. The values obtained are used to assess the possibleindoor exposure inside a room that.Trill be buil t out of these materials.

METHODOLOGT.

E x p e r i m e n t a l :

Sampling» 1 to 2 Kg samples were collected from some construction s i t e s and fromlocal dealers from Greater Bombay and nearby areas . Granite samples were collected fromquarries -which supply the material t o a large number of construction s i t e s and hencerepresent the quali ty of the material used foreonstruction in the area of study.

Gamma Spectrometry; The samples were analysed by a bulk sample counter which i sused for environmental surveillance (7) of a wide var ie ty of samples. I t has a BicronNal (Ti) solid type detector (20 cm dia. i 10 cm thickness) coupled to a 1024 channelpulse sorter and Hewlett Packard Digi tal recorded. Background counting was carriedoutonce in a week using an empty sample container. The counting time of 1200 minutes waskept constant throughout, for samples as well as background. Known ac t iv i ty of Ra-226in the form of Uranium ore (in radioactive equilibrium), homogeniously mixeà with200 mesh s i l i c a powder and sealed in a PVC sample container was used as a source forthe standardisation of the instrument. The photo peak efficiency of instrument forRa-226 was found to be 8.6?S. For 600 g sample the minimum detection limit for Ra-226was 4.07 Bq IÇg"' (0.11 pCi g~1) of sample. Containers used were f l a t and a i r t i gh t ,fabricated specially from P7G mater ia l . Sample thickness was only 2 cms. when conta i -ners were f i l l ed to capacity. This minimised self scat ter ing and attenuation of gammarays by sample.

Calculations: Ra-226 content of sample was calculated through Bi-214 isotope emitt-ing \6f» gamma photons of 1.76 lie? energy per dis integrat ion. Counts obtained between1.625 MéV and 1.930 MeV energy range were summed together. The counter and the comptonbackground counts for the same energy range were taken into account for subtractionfrom the. gross counts.

RSSUUTS AND DISSUSSION

Figure 1 gives typical gamma spectra of different building mater ia ls .

X ENERGY (keV)

Y COUNTS

PHOSPHOGYPSUM

WHITE WASHPLASTERFLY ASHCEMENT

BRICKGRAVEL

2SUGRANITE

BACXGROUND

FIG. 1-GAMMA RAY SPECTRA OF DIFFERENT BUILDING MATERIALSUNOER IDENTICAL EXPERIMENTAL CONDITIONS

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Table 1 gives ranges as wel l as average va lues of Ra-226 content of major bu i ld ingm a t e r i a l s . The average value of Ra-226 for cement i s highest 60.4 Bq Kg"1 (1.63 pCig-1) and t h a t for Granite i s lowest 10.7 B<i Kg~1 (0.29 pCi g " 1 ) . Bricks 47 .8 Bq Xg-1(1.29 pCi g" 1 ) and sand 21,8 Bq Kg"1 (0.59 pCi g~1) a r e in between. Ea-226 concentra-t i o n for an Indian g r a n i t e sample col lec ted from loca t ion other than Bombay a l so hasbeen repor ted to be low as 33.3 Bq Kg"1 (0 .9 pCi g~1) ( 8 ) .

TABLB 1

S r .Ho.

1.

2 .

3.

4.

Cement

Bricks

Sand

Granite

Radium-226 content of ma.ior building

Location of samplecollection

Greater Bombay, Thane(one imported variety)

Greater Bombay and Thane

Greater Bombay and Thane

Çuaries in GreaterBombay and Thane

So, ofsamplesanalysed

'9

5

3

2

materials

Radium-226 Ba

Bange

49.6 - 91.8(1.34 - 2.48)

39.6 - 88.5(1.07 - 2.39)

19.6 - 22.9(0.53 - 0.62)

7.0 - 14.1(0.19 - 0.38)

Er"1

Averagevalue

60.4(1.63)

47.8(1.29)21.8

(0.59)

10.7(0.29)

* Figures in parenthesis are pCi g-1

Table 2 gives Ra-226 content of plaster , lime, flyash and phosphogypsum. lime isused for -white-wash while flyash and phosphogypsum are sometimes used as admixture incement. Lime sample also has shown significant Ra-226 content«

TABES 2

ST.No.

1.

2 .

3 .

4 .

RAÍdum-226 content of some of the

Sample

Plaster

Tfaite washmaterialFlyash

Phospho-gypsum

Location ofsample collection

Greater Bombay

Greater Bombay

Thermal power stationsin India

F.R. Germany

Orissa (India)

U.K. (1)

U.S.A. (1)

associated building materials

No. of Radium-226* Bq Ssamples Rangeanalysed

1

1

9* 150-554(4.04 - 14.97)

28

1

6

— —

Averagevalue

356.3(9.62)

375.2(10.13)

342(9.23)

211(5.70)1507

(40.69)

778(21.01)

1431(39.99)

* Figures in parenthesis under Ra-226 heading are pCi g.-1

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Table 3 gives K-40, Ra-226, U-238, Th-232 content of major building materials fromdifferent countries (9, 10) along with those obtained in the present work. I t can beseen that Ra-226 content of granite used in other countries i s comparatively an orderof magnitude higher than the values obtained in th i s work.

TABLB 3

¿adioactivitv in

Ho.

1.

2 .

3 .

4 .

Material

Cement

Sand(Gravel)

Granite(Stone)

Bricks

some building materials from

Country —

NorwayU.K.ÏÏ.S.S.RV. GermanyU.S.FinlandBombay - India(present work)

U.K.Ü.S.S.R¥ . GermanyU.S.FinlandBombay - India(present work)

U.K.U.S.S.R.V. GermanyU.S.FinlandBombay - India(present work)

HorwayU.K.U.S.S.R.¥ . GermanyFinlandBombay - India

' (present work)

K-40

241.7155.0148.1222.0126.0241.0107.4 •

370.4259

<259259

1034233

111114811259

——

48.1

1058703.0666.7673.0962129.6

India and other countries

Radioactivity in Bq KeT1

U - 238

40.7-—

40.7--

7.4--

11.1-—

222-----

111----

Ra - 226

30.022.025.925.9

-44.459.2

7.4<14.8 - 37.0

14.8-

37.022.0

89.0111.0104.0

_-

11.1

104.052.055.559.0

778.048.1

(9) (10)

Th-232

18.518.014.822.214.826.014.8

3.714.818.511.143.09.3 '

8.15167.080.0

-7.4

62.044.037.067.062.025.9

Radium-226 content of plaster appears rather high possibly due to contributionfrom lime and this needs further confirmation. However quantities involved aresmall and i t s contribution to radiation exposure i s not significant.

EVALUATION OF IMDOOR INTERNà-L EXPOSURE INSIDE THE MODEL ROOM

Dimensions and other details

The 'model room' for which indoor exposures are calculated i s assumed to be above

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ground floor and is constructed out of building materials sampled. It is 3.05 m x3.05 m x 3.05 m in dimensions. It has got reinforced concrete ceiling and columns.Two out of four brick walls are 23 cm thick and the other two are 12 cm thick. Thebrick work and the columns are covered with 1 cm thick cement sand mixture and thensmoothened with plaster work about 1mm thick. The room is white washed. One of i t stwo doors is 2.05 m high and 1.05 m wide while the other door is 2.05 m high and 0.9 mwide«. One window 1.2 m in height and 0.9 m in width.

Formula developed by Krissiuk (10) and others was used to find Radon emanationrate '<*'.

4 = C„ . nX d p . 10"8 Ci/m"2 s~1

"k6*6 CL » specific activity of Ra-226 in pCi g"1

n - Radon emanation factor (dimension-less)

>. = Radon decay constant; 2.1 x'10 S

d = wall or floor half thickness in cm

p = material density g cm

•Qf value obtained is Used to find Rn-222 concentration 'X, ' in curies per l i t re ofair by using the formula» n

K = air change rate (no. changes h )2

S = . surface area of the room in m7 = volume of room in m

Internal exposure calculations

Value of 'n1 is assumed 0.04 for the type of construction under study (1O). The*Q* value becomes maximum as i t is presumed that a l l the Radon that would be produ-ced in the pore spaces diffuses completely in the room air .

Internal exposure values are calculated in Working Level Month (WLM) as recommendedby ICRP-32 (11 ) . Working level (WL) is defined as any combination of the short liveddecay products of Rn-222 in one l i t r e of-air that will result in ultimate emission of1.3 x 10^ MeV of alpha particle energy during decay up to Lead-210. One WL is equiva-lent to 100 pCi of Rn-222 per l i t r e of air in equilibrium with i t s short lived decayproducts. One WLM is defined as exposure (occupational) to a Rn-222 decay productsconcentration of one WL for one month (170 hours).

•Quantities of cement, sand, bricks and stones required for model room were calcula-ted from the standard construction data. îrom the values obtained for Ra-226 contentin the building materials, the 'Q1 value was calculated and then used to get Rn-222concentration per l i t r e of air in the room. Prom Rn-222 values exposure rates werecomputed.

Table 4 gives Rn-222 concentrations inside the model room under different ventila-tion conditions. It can be seen that in poorly ventilated room the radon concentrationis about 100 times more than that of the normal ventilated room (one air change per hour).

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TABLE 4

3adon-222 concentrations inside the model room under different ventilation conditions

No. of air changes per hour

Ventilation condition

Rn-222 Bq L~1 of a i r

1.0

Normal

0.0029

0.5 •

Medium

0.0059

0.1

îîedium

0.029

0.01

Poor

0.29

The drop in radon concentration in normal ventilated room i s possible because theemanation rate does not supply radon fast enough to replace the amount removed, -Aileradon concentration inside a poor ventilated room, goes on increasing since the venti-lation is not efficient enough to remove radon fast enough as i t i s produced throughemanation.

I t can be seen thorn Table 5 that the indoor exposure i s dependant on the timespent indoors by invividuals.

TABLB 5

Computed Indoor Exposure from Rn-222 andexperienced by different categories of

Category of person *»££»*

Outdoor worker

Indoor murker

Aged person

12

20

24

Occupancyfactor

0.50

0.83

1.00

Present•work

- 20-34

- 40- .

daughterspersons

Exposure rnïïLU Y

• Calculated valuesfrom l i t e r a u t r e (10)

18.0430.0636.07

* These values are obtained on the basis of representat ive levelof 0.7 nWL of radon daughter concentration and occupancy factor .

UVAHÛ.TION OP AIR DOSE DISIDE THE MODEL ROOM

E-40, Bi-214 and Tl-208 concentrations in different building materials are usedin the Hultquist ' s modified (lO) formula to evaluate D, the a i r dose r a t e within theroom.

D = 4.37 x 10~3 Cg + 5.11 x 10"2 CR& + 7.82 x 1O~2 C ^ urad h"1 in a i r

»here C i s in Bq Kg" .On substitution of C , R„ and C_ values in the above formula, indoor air dose

•works out to be 3.9 urad ¿M. This calculated indoor air dose inside the model room i scomparable with those found by some actual dose measurements in similar houses inother countries as can be seen in Table 6.

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TABLE 6

Indoor air dose 1 m above floor level in cement house

lío. Country Indoor air dose uGy h"

1 ' l e s t Germany (1) 0.062 East Germany ( i ) 0.043 Poland ( i ) • 0.054 Bombay - India (calculated value - present -work) 0.04

Exposure comparison

I t appears from t h i s study that the indoor in terna l exposure to Radon from bui ld -ing material samples under study are similar to the values reported elsewhere ( i ) .The lower exposure due to use of granite of low Ea-226 content i s offset by higherradium content of cement.

I t i s proposed to measure the actual 'Indoor a i r dose1 and ' In ternal exposure' insome of the newly constructed houses using the type of building materials described int h i s work.

R5FERENCSS

1. 'Sources and effects of ionising r ad i a t i on ' ,UMSCEAR - 1982 Report to General Assembly with annexes, United Nations.

2 . Londhe V.S. , P i l l a i K.C. and Soman S.D.,'Technologically enhanced radiation exposure from some non-nuclear sources ' ,Bullet in of Radiation Protection, 2 (3 ) , 1979.

3 . Paul A.C., londhe V.S. and P i l l a i K.C.,'Radium-228 and Radium-226 levels in a r iver environment and i t s modification byHuman A c t i v i t i e s ' , Natural Radiation Environment, DOE Symposium Series 51, 1980.

4 . Mehl J.,'External Radiation .Exposure of the public in Federal Ministry of Interior, Bonn',IV International Congress of the International Radiation Protection Association(IRPA), Paris, 1977.

5. Ludwieg F. and Kunz H.,Radioactivity and Radiation exposure from U-glazed flagstone lining of Walls',Proceedings of VIII Annual meeting of the Fachverband fur Strahlenschutz,Helgoland, 1974.

6. Eadie G.G.,'Radioactivity in construction materials, a l i t e ra ture review and bibliography',U.S. Protection Agency, ORP/LP-75-1, 1975.

7 . Rao S.R., Londhe V.S. and P i l l a i K.C.,'Low Level radioactivity measurements using gamma ray speetrometry',Bulletin of Radiation Protection 6,, Vol. 2, 1983.

8. M.R. Menon, U.C. Mishra, B.T. L a u t , V.K. Shukla and T.V. Ramachandran,'Uranium, thorium and potassium in Indian rocks and o re s ' ,Proceedings of the Indian Academy of Sciences (Barth and Planetary Sciences)Vol. 91, No. 2, July 1982, pp 127-136.

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9. Harley J.H.,'Radioactivity in building materials',Health and Safety Laboratory, U.S. Energy Research and Development Administration,New York, N.Y.

10. Report by a group of Experts of the Kuclear Energy, OECD on 'Exposure to radiationfrom the Natural Radioactivity in Building materials', May 1979.

11. ICRP Publication 32,'Limits for Inhalation of Radon Daughters by Workers'Vol. 6, Ho. 1, Pergamon Press, Oxford, 1981.

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