Full text of DOI:10.1093/oxfordjournals.rpd.a006659

Radiation Protection Dosimetry
Vol. 97, No. 2, pp. 187–191 (2001)
Nuclear Technology Publishing
THORIUM DETERMINATION IN INTERCOMPARISON
SAMPLES AND IN SOME ROMANIAN BUILDING
MATERIALS BY GAMMA RAY SPECTROMETRY
A. Pantelica†, I. I. Georgescu‡, M. D. Murariu-Magureanu‡, I. Margaritescu‡ and E. Cincu†
†“Horia Hulubei” National Institute of Physics and Nuclear Engineering (IFIN-HH)
PO Box MG-6, 76900 Bucharest, Romania
‡“Politehnica” University, Faculty of Industrial Chemistry
Polizu Street 1, 78126 Bucharest, Romania
Abstract — Thorium content in zircon sand, thorium ore and
a thorium liquid sample (EU Laboratories Network
Intercomparison), as well as in some Romanian building materials: sand, wood, tufa, asbestos-cement, cement mill dust, coal fly
ash, bricks, and tile (28 samples) was determined by gamma ray spectrometry. For the building materials, 226Ra, 40K and 137Cs
specific activities were also measured. The results were compared with the Romanian legal norms concerning the highest admiss-
ible levels for 232Th, 226Ra, and 40K radioactivity, and to Th, U, and K concentration values previously determined in our laboratory
on similar types of samples.
INTRODUCTION
brick, and coal fly ash)(6,7). Fission and/or alpha track
methods were applied to determine U concentration in
The paper presents the results our laboratory has
obtained in thorium analysis by gamma ray spec-
trometry on some mineral samples. 232Th activity con-
wood building materials (tree and rush)(8)
.
centration was calculated from its decay products 228Ac, EXPERIMENTAL
212Pb,212Bi, and 208Tl, assuming radioactive equilibrium
Thorium nitrate solution containing 232Th in equilib-
rium with its decay products and two thorium minerals
(an ore and zircon sand) without any prior treatment
were prepared as test samples by the Centre for Ionizing
Radiation Metrology at the UK National Physical Lab-
among all 232Th decay chain isotopes. By comparison,
it should be mentioned that radioactive equilibrium does
not exist within biological samples such as tissues
because of the different metabolic behaviour of 232Th
decay radionuclides (e.g. 224Ra and 228Ra are largely
transported from the liver to the bone, while 220Rn
oratory (NPL), Teddington, England(2)
.
Building materials (28 samples) were collected from
different factories in the southern half of Romania: coal
fly ash from Deva and Paroseni (sub-bituminous coal-
fired power plants), cement mill dust from Hoghiz and
Fieni, and the other types of investigated building
materials from Horezu, Targu Jiu, Rovinari, Slatina, and
Craiova. The samples were collected during the summer
of 1999, except for the cement mill dust from Hoghiz
(April 1994) and Fieni (May 1995), as well as the coal
fly ash from Deva (March 1995).
enters the general circulation)(1)
.
Zircon sand, thorium ore and a thorium liquid sample
were analysed in the framework of the European Com-
mission Project ‘Thematic Network on the Analysis of
Thorium and its Isotopes in Workplace Materials’ coor-
dinated by the Health and Safety Laboratory (HSL),
Sheffield, United Kingdom(2). Sand, wood, tufa, asbes-
tos-cement, cement mill dust, coal fly ash, tile, red and
autoclaved cellular concrete (ACC) bricks collected
from building material factories in different zones of
Romania were investigated for natural and artificial
radioactivity. The results were compared to the Roman- Sample preparation
ian legal norms for maximum permissible 232Th, 226Ra,
Zircon sand and thorium ore intercomparison samples
of 5.7326 0.0003 g and 5.2800 0.0003 g, respect-
ively, were maintained inside sealed glass vessels of
2.5 cm diameter and 6 cm height. The liquid thorium
intercomparison sample (10 ml in 2 M nitric acid
solution) was diluted to 100 ml and put into a polyethyl-
ene pot (Sarpagan type, 7.2 cm diameter and 4 cm
height).
The bulk building materials were air-dried, except for
the wood samples which were dried in an oven at 60°C.
Brick, tile, tufa and asbestos-cement samples were then
ground and homogenised, while cement and coal fly ash
powder, as well as the sand samples were only hom-
and 40K activity concentrations in building materials(3)
.
Thorium content in ores (monazite) was previously
analysed in our institutes by emanation, autoradiography
with nuclear emulsions, and gamma spectrometry
methods(4). Moreover, Instrumental Neutron Activation
Analysis (INAA) was used to determine Th and U con-
centration in Romanian zircon samples(5) and in some
building materials (raw material for cement production,
cement, furnace slag, phosphogypsum, cold compacted
Contact author E-mail: apantelȰifin.nipne.ro
187

A. PANTELICA, I. I. GEORGESCU, M. D. MURARIU-MAGUREANU, I. MARGARITESCU and E. CINCU
ogenised in a mortar. Wood material was cut in pieces for 228Ac, 212Pb, 212Bi, and 208Tl radionuclides of the
less than 5 mm each. Building material (30–150 g and natural 232Th series. The 208Tl gamma ray emission
80–150 cm3) was placed within Sarpagan polyethylene probability in this table has been corrected for the 212Bi
pots.
All samples were kept tightly closed in the pots for
about one month to avoid losses of the gaseous 222Rn its decay products 228Ac, 212Pb, 212Bi and 208Tl in inter-
238U series) and 220Rn (232Th series) in order to re- comparison samples (in Bq.kg−1). The presence of the
decay branching ratio (BR A = 35.94%)(2)
Table 2 includes the 232Th activity concentration by
.
(
establish radioactive equilibrium from their precursors same radionuclides, save for 212Bi, in building materials
226Ra and 224Ra, respectively.
is given in Table 3. Tables 2 and 3 also contain the cor-
responding thorium mass concentration in mg.kg−1 (1 g
Th yields 4057.2 Bq(2)).
Sample analysis
The activity concentrations of 226Ra (by 214Pb and
Gamma ray spectrometry was carried out using a 214Bi decay products), 40K, and 137Cs measured in build-
HPGe (EG&G Ortec) detector of 2.3 keV FWHM at ing materials are given in Table 4.
1332.5 keV of 60Co, and 30% relative efficiency,
Overall uncertainty values in all the tables are calcu-
mounted in a low background shielding. Counting time lated as squared roots of the sum of squared type A and
varied between 4 and 27 h.
type B components (k = 1). Type A uncertainties stem
As calibration standards, water equivalent solid vol- from sample and standard statistical counting; type B
ume sources (133Ba, 137Cs, 152Eu, and 241Am) of 100 uncertainty values correspond to detection efficiency
and 150 cm3 prepared by the Radionuclide Metrology calibration (2–5%), self-absorption (Ͻ3%), and activity
Laboratory (RML) of IFIN-HH(9,10)
, as well as concentration certified for calibration standards (1.5–
Th(NO3)4.5H2O (p.a. Merck, Germany) for zircon sand 5%). Detection limits (3␴) for the non-measured
and thorium ore samples (2.6306 g and 4.4748 g, elements are also shown in the tables.
respectively) were used. RML is legally, metrologically
As can be seen from Tables 2 and 3, a rather good
authorised to supply reference materials that are directly agreement between the activity values was obtained for
traceable to the national activity standard.
the measured 232Th decay products in every investigated
In addition, appropriate IAEA Reference Materials of sample. 232Th activity concentration was calculated as
geometry and densities similar to those of the investi- arithmetic (unweighted) mean of its progeny’s activities.
gated building materials were chosen as calibration stan-
For the intercomparison samples, the 232Th results
dards. They consisted of: IAEA-373 (Chernobyl grass) determined (Table 2) are in good agreement with the
for wood; IAEA-300 (Baltic Sea sediment) for ACC NPL target values of 551 21 Bq.kg−1 in zircon sand,
brick, coal fly ash, and tufa; IAEA-135 (Irish Sea 2494 32 Bq.kg−1 in thorium ore, and 10716
sediment) for red brick and tile, sand, cement, and 102 Bq.kg−1 in thorium nitrate solution (analyst/NPL
asbestos-cement samples.
Detection efficiency calibration curves were calcu-
ratios of 1.045, 0.99 and 0.97, respectively).
For the building materials, Th, U, and K concen-
lated for different building materials using certified trations obtained in the present work (Tables 3 and 4)
activity concentration values of 134Cs, 137Cs, and 40K in are similar to those previously determined by INAA in
all the calibration standards considered and also of cement, a cold compacted brick, and coal fly ash
241Am and 232Th in IAEA-135(11–13). The self-absorption samples(6,7), as well as by fission and/or the alpha track
correction factors for samples relative to the calibration method in wood(8) (Table 5). It was taken into account
standards were determined by transmission measure- that 1 g of U and 1 g of K yield 12,358 Bq 238U and
ments of gamma ray point sources.
The major chemical components of IAEA-135 sedi-
33.11 Bq 40K, respectively.
Concerning the radioactivity levels in building
ment, are respectively the following: SiO2 61.7%; Al2O3 materials, higher (by about 1.3–2 times) values were
9.3%; FeO 4.4%; CaCO3 11.2% and CaO 3.6%(13). The found for 232Th in two of the red brick samples, and for
major contents of mineral building materials lie within 232Th, 226Ra, and 40K in almost all tile samples compared
the following ranges: SiO2 25–50% (coal fly ash, red with the Romanian legal norms. The accepted radioac-
brick and tile) and ෂ95% (sand); Al2O3 2–15%; Fe2O3 tivity levels are 53.3 Bq.kg−1 for 232Th, 100 Bq.kg−1 for
0.5–15% or Fe3O4 7–10% (cement); CaO 6–12% (coal 226Ra, and 832 Bq.kg−1 for 40K in red brick, as well as
fly ash, red brick and tile, ACC brick) and 35–40% 32.2 Bq.kg−1 for 232Th, 32.6 Bq.kg−1 for 226Ra, and
(cement)(14)
.
466 Bq.kg−1 for 40K in tile(3)
.
Cellulose is the main constituent of the cell walls of
plants and also of wood (beside the lignin).
CONCLUSIONS
The gamma ray spectrometry method could success-
fully be used in the thorium analysis of liquid and solid
RESULTS AND DISCUSSION
Table 1 shows the characteristic gamma rays taken mineral samples, provided that the radioactive equilib-
into account and their absolute emission probabilities rium between 232Th and its decay products can be estab-
188

THORIUM IN INTERCOMPARISON SAMPLES AND BUILDING MATERIALS
Table 1. Nuclear data for 228Ac, 212Pb, 212Bi, and 208Tl (232Th radioactive series)(2)
.
Radionuclide
228Ac
228Ac
212Pb
212Bi
208Tl
Energy (keV)
Gamma ray emission probability (%)
338.3
11.27
911.2
25.8
238.6
43.4
727.3
6.75
583.1
30.6
Table 2. 228Ac, 212Pb, 212Bi, 208Tl and 232Th activity concentrations (Bq.kg−1) and Th content (mg.kg−1) in intercomparison
samples.
Sample
228Ac
212Pb
212Bi
208Tl
232Th
(Bq.kg−1
)
(mg.kg−1
142
)
Zircon sand
Thorium ore
Liquid sample
541 18
2451 76
10520 569
595 18
2744 123
10429 643
568 41
2328 123
11006 596
599 37
2366 66
9787 535
576 14
3
2472 47
10435 294
609 12
2572 72
Table 3. 228Ac, 212Pb, 208Tl and 232Th activity concentrations (Bq.kg−1) and Th content (mg.kg−1) in building materials.
Sample
228Ac
212Pb
208Tl
232Th
(Bq.kg−1
)
(mg.kg−1
)
Red brick, Horezu
Red brick, Targu Jiu
Red brick, Rovinari
Red brick, Slatina
Red brick, Craiova
ACC brick, Targu Jiu
ACC brick, Slatina
ACC brick, Craiova
Tile, Horezu
38.3 3.4
87.4 7.9
117.5 8.5
49.5 3.7
50.1 4.0
14.7 3.7
11.7 3.5
10.8 1.8
60.4 3.0
52.3 5.3
65.1 3.3
58.1 4.0
17.0 3.6
16.6 3.7
10.1 3.0
10.7 1.5
13.8 3.1
103.9 7.8
70.6 8.4
23.4 4.2
30.5 2.4
38.2 4.6
16.5 2.2
12.6 1.5
12.9 3.6
Ͻ5.4
41.3 3.7
85.0 4.2
101.6 7.8
45.5 3.7
49.2 4.5
12.2 1.3
15.3 3.9
12.8 2.4
56.8 4.0
47.8 3.1
71.7 5.0
60.3 8.4
15.2 2.5
14.6 2.6
11.6 2.5
11.2 1.5
12.7 2.1
90.1 7.2
82.8 7.4
17.6 2.0
27.4 2.3
29.8 2.0
13.6 1.6
16.6 2.5
9.4 3.1
39.3 4.7
83.6 9.3
104.8 8.0
41.0 2.9
50.0 5.8
10.4 1.3
14.5 2.0
10.1 1.7
52.4 3.1
49.6 3.9
63.4 3.2
59.8 8.9
16.1 3.0
16.8 2.0
10.6 3.0
10.4 1.9
13.9 2.0
96.1 14.2
76.8 5.4
17.4 2.3
28.7 2.5
28.4 3.0
13.8 1.6
12.5 1.6
7.1 2.3
Ͻ4.0
39.6 2.3
85.3 4.3
108.0 4.7
45.3 2.0
49.8 2.8
12.4 1.4
13.8 1.9
11.2 1.1
56.5 2.0
49.9 2.4
66.7 2.3
59.4 4.3
16.1 1.8
16.0 1.6
10.8 1.6
10.8 0.9
13.5 1.4
96.7 5.9
76.7 4.1
19.5 1.7
28.9 1.4
32.1 1.9
14.6 1.1
13.9 1.1
9.8 1.8
9.8 0.6
21.0 1.1
26.6 1.2
11.2 0.5
12.3 0.7
3.1 0.3
3.4 0.5
2.8 0.3
13.9 0.5
12.3 0.6
16.4 0.6
14.6 1.1
4.0 0.4
3.9 0.4
2.7 0.4
2.7 0.2
3.3 0.3
23.8 1.5
18.9 1.0
4.8 0.4
7.1 0.3
7.9 0.5
3.6 0.3
3.4 0.3
2.4 0.4
0.42 0.35
0.71 0.44
0.42 0.35
Tile, Targu Jiu
Tile, Rovinari
Tile, Slatina
Cement mill dust, Hoghiz
Cement dust, Fieni
Asbestos-cem., Horezu
Asbestos-cem., Targu Jiu
Asbestos-cem., Craiova
Coal fly ash, Deva
Coal fly ash, Paroseni
Sand, Horezu
Sand, Targu Jiu
Sand, Rovinari
Sand, Slatina
Sand, Craiova
Tufa, Horezu
Wood, Horezu
Wood, Targu Jiu
Wood, Craiova
1.7 1.4
1.8 1.3
1.7 1.4
1.7 1.4
2.9 1.8
1.7 1.4
3.9 3.4
Ͻ5.6
Ͻ3.6
Ͻ4.7
189

A. PANTELICA, I. I. GEORGESCU, M. D. MURARIU-MAGUREANU, I. MARGARITESCU and E. CINCU
lished. The method also makes it possible to analyse Thorium concentrations determined by gamma ray
uranium and potassium contents in mineral samples spectrometry of thorium minerals and of some Roman-
(building materials, in particular) by measuring 238U (in ian building materials are found to lie in a range from
equilibrium with its radioactive progeny) and 40K radio- 0.42 0.35 mg.kg−1 in wood to 24.4 0.8 mg.kg−1 in
activity.
red brick, and 643 13 mg.kg−1 in thorium ore samples.
Table 4. 226Ra, 40K, and 137Cs activity concentrations in building materials (Bq.kg−1).
Sample
226Ra
40K
137Cs
Red brick, Horezu
Red brick, Targu Jiu
Red brick, Rovinari
Red brick, Slatina
Red brick, Craiova
ACC brick, Targu Jiu
ACC brick, Slatina
ACC brick, Craiova
Tile, Horezu
25.2 2.4
55.7 5.0
104.9 4.1
21.7 2.2
30.0 2.1
6.2 1.6
5.0 1.4
12.4 1.1
37.7 2.5
29.9 2.2
59.2 2.8
55.4 5.2
Ͻ3.5
588 48
727 51
760 30
615 25
655 26
233 13
279 17
279 14
892 33
706 35
826 37
742 52
633 30
209 23
46.5 9.3
46.6 6.5
56.6 9.0
729 55
617 37
410 21
662 26
592 21
501 18
370 22
180 27
140 34
40.9 33.7
44.3 35.4
14.5 1.7
1.7 0.8
Ͻ0.8
Ͻ0.8
1.4 0.6
4.3 0.8
Ͻ0.8
4.1 0.7
8.0 0.4
Ͻ0.9
Tile, Targu Jiu
Tile, Rovinari
Tile, Slatina
Ͻ1.1
Ͻ1.6
Cement mill dust, Hoghiz
Cement mill dust, Fieni
Asbestos-cement, Horezu
Asbestos-cement, Targu Jiu
Asbestos-cement, Craiova
Coal fly ash, Deva
Coal fly ash, Paroseni
Sand, Horezu
Sand, Targu Jiu
Sand, Rovinari
Sand, Slatina
Sand, Craiova
3.9 0.7
1.7 0.6
7.6 0.5
0.9 0.5
7.7 1.0
3.3 1.6
Ͻ2.1
1.3 0.5
1.9 0.4
3.2 0.6
2.7 0.3
1.1 0.3
9.6 0.9
3.8 0.8
14.3 1.3
9.7 1.4
Ͻ4.2
7.6 1.8
4.3 1.1
8.9 1.2
121.5 8.0
113.7 7.3
5.5 0.9
12.4 0.7
10.9 1.5
3.4 1.8
Ͻ1.6
Tufa, Horezu
Wood, Horezu
Wood, Targu Jiu
Wood, Craiova
10.5 2.4
Ͻ6.7
Ͻ4.8
Ͻ3.3
Table 5. Th, U, and K contents in building materials by INAA and by fission and/or alpha track method (mg.kg−1).
Elem.
Cement(6)
Brick(6)
Coal fly ash(7)
Wood(8)
Th
U
K
(4.7 0.1) − (5.9 0.3)
(1.6 0.1) − (3.9 0.2)
15.9 0.5
7.4 0.4
18.7 0.9
7.7 0.7
21100 1100
na*
0.006 − 0.25
na
(3900 400) − (6500 400) 11700 500
*na–not analysed.
REFERENCES
1. De Goeij, J. J. M. and Rasmussen, C. E. Thorium Determination in a Liver Autopsy Sample via Direct ␥-spectrometry and
Neutron Activation Analysis. J. Radioanal. Nucl. Chem. Lett. 175(5), 325–332 (1993).
2. Howe, A. M. and Butler, O. T. Thematic Network on the Analysis of Thorium and its Isotopes in Workplace Materials:
Report on the 3rd Intercomparison Exercise. (Health and Safety Laboratory, Sheffield S3 7HQ, United Kingdom) Report
IEAS/01/01 (2001).
3. Gheorghe, R., Milu, C., Modoran, G., Gheorghe, D. and Dobrescu, E. Natural Radioactivity of Classic Building Materials
in Romania. In: Proc. Int. Congress on Radiation Protection, Vienna, 2, 2 (1996).
190

THORIUM IN INTERCOMPARISON SAMPLES AND BUILDING MATERIALS
4. Georgescu, I. I., Ciohodaru, L. and Cojocaru, V. Determination of Thorium in Different Monazite Ore Samples. Rev. Roum.
Phys. 10(7), 755–767 (1965).
5. Salagean, M. N., Pantelica, A. I., Znamirovchi, V. and Motiu, A. Neutron Activation Analysis of some Zircon Samples from
the Apuseni Montains (Romania). In: Proc. First Balkan Conf. on Activation Analysis, Varna. pp. 149–151 (1985).
6. Salagean, M. N., Pantelica, A. I., Georgescu, I. I. and Muntean, M. I. Neutron Activation Analysis of some Building Materials.
Czech. J. Phys. 49/S1, 355–358 (1999).
7. Salagean, M. N., Pantelica, A. I., Georgescu, I. I. and Barca, F. Environmental Pollution Elements in Fly Coal Ashes on
Industrial Filters Determined by INAA. In: Proc. Int. Workshop on Neutron Activation Analysis on Environment, Dubna,
Russia, 18–20 Sept. 1990. D14–93–325 pp. 416–420 (1993).
8. Murariu-Magureanu, M. D., Georgescu, I. I., Oprica, H. M. I., Ciubotariu, M. and Danis, A. Uranium Content Measurements
in Building Materials using Track Detection. J. Radioanal. Nucl. Chem. 224(2), 41–44 (1997).
9. Sahagia, M. and Grigorescu, E. L. Water-equivalent Solid Standard Sources. Nucl. Instrum. Methods Phys. Res. A 312,
236–239 (1992).
10. Sahagia, M., Grigorescu, E. L., Popescu, C. C. and Razdolescu, A. C. National Comparison of Environmental Sample Activity
Measurement. Nucl. Instrum. Methods Phys. Res. A 339, 38–42 (1994).
11. Report of the Intercomparison Run IAEA-0373, Radionuclides in Grass. IAEA/Al/073 (February 1996).
12. Report of the Intercomparison Run IAEA-300, Radionuclides in Marine Sediment. IAEA/Al/046 (September 1994).
13. Report of the Intercomparison Run IAEA-135, Radionuclides in Irish Sea Sediment. IAEA/Al/063 (August 1993).
14. Barca, F. “Politehnica” University, Faculty of Industrial Chemistry, Bucharest, Romania (private communication).
191

192