natural radioactivity in zambian building materials collected from lusaka

J.RADIOANAL.NUCL.CHEM.,LETTERS 199 (3) 229-238 (1995)

NATURAL RADIOACTIVITY IN ZAMBIAN BUILDING MATERIALS COLLECTED FROM LUSAKA

P. Hayumbu, M.B. Zaman, N.C.H. Lubaba*, S.S. Munsanje, D. Muleya**

Nuclear Analytical Laboratory, National Council for Scientific Research,

P.O. Box 310158, Lusaka, Zambia

*Buildinq and Industrial Minerals Research Unit, National Council for Scientific Research, Zambia

**Radiation Protection Services, Ministry of Health, Zambia

Received 12 September 1994 Accepted 24 September 1994

Samples of natural and manufactures building materials collected around Lusaka have been analyzed for natural radionuclides using y- spectrometry. A simple comparison of the specific radioactivities of primordial radionuclides in these materials to the world av- erages for soil (25 Bq kg-1 238U, 25 Bg kg-1 232Th, 370 Bq kg -I 40K and 89 Bq kg-1Raeq ) shows that, of the nine types of samples analyzed, only burnt clay bricks (for 238U, 232Th and 4UK), cement roofing tiles (for 238U), building and river sands (for 232Th and 40K) have greater activities than does soil. Radiological evaluation of specific radioactivities in these materials indi- cates that all materials meet the external y-ray dose limitation of 1.5 mSv y-l, that is, all samples have a radium equivalent activity of less than 370 Bq kg -1.

229 Elsevier Science S. A,, Lausanne Akad~miai Kiad6, Budapest

HAYUMBU et al.: NATURAL RADIOACTIVITY IN BUILDING MATERIALS

INTRODUCTION

Knowledge of radioactivity levels in building and

ceramic materials is vital in the assessment of possible

radiological hazards to human health. It is required for

setting up manufacturing standards and guidelines for

the use of these materials. Thus specific radioactivity

of natural building materials and those derived from

industrial wastes and by-products have been reported in

many countries I-4

Levels of natural radioactivity in Zambian building

materials have hitherto not been measured. With this

preliminary task unsolved, it is no wonder that at the

moment Zambia has neither standards nor guidelines pre-

senting the acceptable levels of radioactivity in these

materials.

This paper presents results of a y-spectroscopic de-

termination of 238U, 232Th and 40K in major building

materials used in Lusaka, the Capital of Zambia (where

about 10% of the total population, that is, 25% of the

urban population of the country resides). The results,

on a qualitative basis, are compared to the world aver-

age natural radioactivity levels in soil and are further

discussed on the basis of a criterion formula for accept-

able radiation dose rates attributable to building mate-

rials in developed countries I . This work is part of an

ongoing program for radioactivity monitoring in food and

environmental samples being undertaken by the National

Council for Scientific Research and the Radiation Pro-

tection Services.

230


TABLE I

Samples of building materials analyzed and their sources

Sample Sample name Source No.

I

2

3

4

5

6

7

8

9

Portland cement

Stone aggregates

Stone aggregates(b)

Concrete blocks

Burnt clay bricks

Cement roofing tiles

Asbestos roofing sheets

Building sand

River sand

Chilanga Cement Ltd.

Crushed Stones Ltd.

United Quarries Ltd.

United Quarries Ltd.

Brick and Tile Ltd.

Ital-Terrazo Ltd.

TAP Ltd.

Kasisi

Kafue

EXPERIMENTAL

Materials

The materials analyzed were river sand, aggregate

stones, cement, roofing tiles, asbestos sheets, burnt

clay bricks, concrete blocks and building sand (Table I).

There is little or no utilization of industrial wastes

in s Zambian construction industry, unlike in the case

of developed countries. This is because the industrial

infrastructure outside the mining centers is rather

small and wastes thereof are not major building materi-

als.

Samples after collection were crushed, pulverized to

a fine powder (<300 mesh) and homogenized in preparation

for spectral collection. A weighed quantity of powdered

sample sufficient to fill a 250 ml cup was used for y-

231


ray counting. The cup was sealed and left to stand

alone for a month to let the sample attain radioactive

equilibrium 5'6. Spectra of samples were collected using

a high resolution y-spectrometry system described pre- 7

viously .

Methods

The significant primordial radionuclides in building

materials are 238U, 232Th and 40K. Since 98.5% of the

radiological effects of the uranium series are produced

by radium and its progeny, the contribution of 238U and

the other 226Ra precursors are normally ignored 1. The

226Ra (or 238U for samples assumed to be at radioactive

equilibrium like in this work) and 232Th radioactivities

were estimated from 609.3 keV and 583.1 keV y-lines of

214Bi and 208TI, respectively 7. Alternatively, one could

use the 214pb (351.9 keV) and 228Ac (911.1 keV) y-lines.

40K radioactivities were determined using the 1.46 MeV

y_line 1,8,9

Spectral analysis was done using GANAAS I0 whose pro-

gram modules end with a report of activities of radio-

nuclides evaluated according to Eq. (I).

C a

A : -- (I) a s

Y

where A a - is the activity of the radionuclide (Bq),

- is the detector efficiency for the analyti-

cal y-line,

P - is the absolute transition probability of Y

y-decay through the analytical y-line, and

C - is the count rate of the radionuclide for a the analytical y-line (cts s-l).

~2 ~2


Specific activities of radionuclides in analyzed

samples result when activities derived from Eq. (I)

are divided by.the mass of the sample as shown by

Eq. (2). A a

A = s M s

(2)

where A s

M s

- is the specific activity of the sample (Bq kg 1)-

and

- is the mass of the sample (kg).

In order to radiologically compare the specific radio-

activities of building materials which contain Ra, Th and

K, a common index called the radium equivalent activity

Ra was used I . The radium equivalent activity is a eq

weighted sum of activities of the above three radio-

nuclides based on the estimation that 370 Bq kg -I 226Ra,

259 Bq kg -I 232Th or 4810 Bq kg -I 40K produce the same

y-ray dose rates given by Eq. (3).

Raeq = 370 + + 4810 (3) or

Raeq = ARa + (AThX 1.43) + (AKX 0.077) (3a)

where232Th ARa,40ThA and A K are the activities of 226Ra,

and K, respectively, in Bq kg -I.

RESULTS AND DISCUSSION

Table 2 lists the measured activities of 238U, 232Th

and 40K for the collected samples (serial numbers I to

9) along with Raeq calculated using Eq. (3). The Table 2

233


TABLE 2

-I Specific activities of building materials (Bk kg )

Sample Sample name 238 u 232Th 40 K 226N~ N o . eq

I. Portland cement

2. Stone aggregate

3. Stone Aggregate(b)

4. Concrete blocks

5. Burnt clay bricks

6. Cement roofing tiles

7. Asbestos roofing sheets 15•

8. Building sand 25•

9. River sand

10. Clays bricks 12 12

11. Tiles

12. Sand bricks 12

13. Cement plaster 12

14. Unmixed cement 12

15. Carbonate rock 11

16. Soil 11

23• 32• 134• 79•

6• 6• 111• 8 23•

5• 12• 37• 8 25•

7• 10• 43• 8 25•

32• 81• 412• 180•

55• 21 • 116• 94•

24• 149• 8 61 • 5

26• 714• 7 117•

16• 44• 971• 154•

59• 96•

52• 81•

44• 44•

48• 26•

11 26

2 8 74 19

25 25 370 89

includes, for comparison, values of radioactivities in

similar samples (serial numbers 10 to 16) reported in the

literature. Although two samples, especially if they are

from different locations, are unlikely to be identical,

it may be seen that values of radioactivities found by

us are comparable to reported results. For example, the

activities of 238U and 232Th in our Portland cement

(serial number I) are within the range of values reported

for cement plaster (serial number 13) and unmixed cement

(serial number 14). Cement being a mixture of minerals,

the radioactivities in different cement samples are

234


likely to vary, depending on the radioactivities of the

component minerals.

Table 3 has been compiled to show the radioactive

status of Zambian building materials in comparison to

those of other countries. As stated earlier and shown

in the table, the radioactivities in building materials

do vary from one place to the other. If we consider the

case of stone aggregates, the Ra value is 24 for Zambia eq

(Lusaka), 115 for Australia, 322 for Germany, 74 for

Norway, 141 for Sweden and 59 for U.K. It should be

stressed here that even these values are not the repre-

sentative values for the countries mentioned but for the

localities from where the samples had been collected I .

The ultimate objective of measuring radioactivities

in building materials is to make an estimate of radia-

tion dose likely to be delivered externally if a building

is constructed using them. To limit the radiation dose

from building materials to 1.5 mSv y-l, a number of mod-

els have been suggested by various workers. One such

model, proposed to serve as a criterion in the then Fed-

eral Republic of Germany at the beginning of the 1980s I,

was

IIARa ATh AK } ~7 -T6 +-T+ TT6 <1 (4)

This criterion, which only considers the.external

hazard due to y-rays corresponds to a maximum radium

equivalent activity of 370 Bq kg -I for the material.

From Table 2, it is apparent that Zambian materials meet

this criterion. Table 3 shows that building materials

used in Lusaka have comparable levels of radioactivity

to natural building materials used in other countries

calculated on the basis of Eq. (4).

235

H A Y U M B U e t al . : N A T U R A L R A D I O A C T I V I T Y I N B U I L D I N G M A T E R I A L S

,-.t

-,-t

O ~ 0

5 - , , t : : a~

0 0 -~0

I1)

-,-4 0

m O ol

.,-4 -~

O m

~ -,..t -,.-t ~

r~

0

0 ffl

.,-t

0

~400

0 r 0"~ O~ ~1 ~ I ~

I.~ ~ 0") ~'~ ~ ~.0 ~ ~l ~ ~

0 0 L~

~ ~ ~ ~ ~ 0

t.r ~.o o oo

t~ ~.o

-I~ �9 m ,-~ ,--I t~ 0 -,--I

,-'4 .;-I 4a

0 O~ l~ ~ ~ 0 ul

0 --4 ~ l:l ~ ~ "0 4a ~ 0

4-4 0

.IJ o

0

I

,Q

r~

0 t~

0

0

0 0

o

0

,nl m

,--4 t0 �9

r~

0 - , - I

~ . q .,-I 0

o O

o 0 ~

-,-I o ~4

4-) �9 o~ D~

.,-4 0

2 3 6


It should, however, be pointed that addressing the

radiation hazard to respiratory organs due to radon and

its progeny requires reduction of the acceptable maximum -I

Ra to at most 185 Bq kg (Refs (I)-(3)). It is note- eq

worthy thatthis limitation coincides with our qualita-

tive comparison of activities of building materials to

the world average for soil which has an Ra of 89 -I eq

Bq kg (Table 2). In this work we do not discuss inter-

nal exposure because radon concentrations in dwelling

places depend on many factors such as air-flow patterns,

air changes, types and porosity of materials used.

CONCLUSION

The results show that of the nine samples of building

materials analyzed, six of them had Ra activities less eq

than, or comparable to the value calculated for world

average in soil (89 Bq kg-1). The material with the

highest Raeq activity (burnt clay bricks) has twice the

world average value. The results also show that Zambian

building materials meet the criterion limiting the radia-

tion dose from building materials to 1.5 mSv y I (Ref.

(I)). Follow-up studies of direct radon measurements as

well as those using dose limitation models in dwellings

built with these materials will be carried out in order

to ascertain internal radiation exposure.

The authors acknowledge with thanks the companies

which supplied the building materials used in this study.

We would also like to thank the Secretary General of

NCSR for his support during the course of this work.

237


REFERENCES

I. J. Beretka, P.J. Mathew, Health Phys.~ 48 (1985) 87.

2. G.A. Swedjemark, Health Phys., 51 (1986) 569.

3. W.F. Passchier, Klijn, Van der Heijde, Health Phys., 51 (I 986) 661.

4. A.S. Paschoa, R.R. Pinho, D.A.C. Binns, Monitoring Radon and Environmental Gamma Radiation Indoors and Outdoors at PUC/RJ, Brazil; Proceedings of the Inter- national Workshop on Radon Monitoring in Radioprotec- tion, Environmental Radioactivity and Earth Sciences, (Eds by L. Tommasino, G. Furlan, H.A. Khan, M. Monnin) ICTP, Trieste, Italy, April 3-14, 1989, 381.

5. A. Canet, R. Jacquemin, Methods of Measuring Radium Isotopes: Gamma Spectrometry; Technical Report Series No. 310, Environmental Behaviour of Radium, Vol. I, IAEA, Vienna, 1990, p. 196.

6. G. Smithson, Sampling and Selection of Analytical Methods for Radium; Technical Report Series No. 310, Environmental Behaviour of Radium, Vol. I, IAEA, Vienna, 1990, p. 267.

7. M.B. Zaman, P. Hayumbu, S.S. Munsanje, Int. J. Bio- ChemiPhysics, 2 (1993) 143.

8. Technical Report Series No. 295, Measurement of Radionuclides in Food and Environment, IAEA, Vienna, 1990, p. 63.

9. F. Steger, Final Report: Setting up a Radiation Pro- tection Laboratory for Environmental, Foodstuff and Internal Monitoring at the Radiation Protection Ser- vices, IAEA, Vienna, 1990, p. 11-12.

10. Computer Manual Series No. 3, Nuclear Analysis Soft- ware; Part 2: Gamma Spectrum Analysis, Activity Cal- culations and Neutron Activation Analysis (GANAAS), IAEA, Vienna, 1991.

11. P. Linsalata, Radiat. Phys. Chem., 34 (1989) 241; Int. J. Radiat. Appl. Instrum., Part C.

12. R.H. Mahat, Y.M. Amin, J. Radioanal. Nucl. Chem., Lett., 144 (1990) 375.

238

natural radioactivity in zambian building materials collected from lusaka

Documents