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MINISTRY OF EDUCATION AND TRAINING

VIETNAM ACADEMY
OF SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY

----------------------------

SONEXAY XAYHEUNGSY

PROJECT NAME: ASSESSMENT OF NATURAL
RADIOACTIVITY IN SOME BUILDING MATERIALS
USED IN LAOS PDR

Major: ATOMIC AND NUCLEAR PHYSICS
Code: 9440106

SUMMARY OF DOCTORAL THESIS OF MATERIALS SCIENCE

HANOI - 2019



The doctoral thesis was completed at Institute of Physics, Graduate
University of Science and Technology

Supervisors: Prof. Dr. Le Hong Khiem
Reviewer 1: ……………………
Reviewer 2: ……………………
Reviewer3: ……………………

This doctoral thesis will be defensed at Graduate University of Science and
Technology, Vietnam Academy of Science and Technology on … hour…,
date…. month … year…

The dissertation can be referred at: National Library of Vietnam


LIST OF PUBLISTIONS
1.

2.

3.
4.

5.

6.

7.

Sonexay Xayheungsy, Le Hong Khiem. Measurement of natural radioactivity in some
cements of Lao PDR by using NaI(Tl) gamma-ray spectrometer, Advance in
applied and engineering Physics IV, Publishing House for Science and
Technology,2016, 231
Sonexay Xayheungsy, Le Hong Khiem, Phương pháp xác định hoạt độ của
các nguyên tố phóng xạ tự nhiên bằng phổ kế gamma dùng detector NaI(Tl),
Advance In Applied And Engineering Physics V, Publishing House for
Science and Technology, 2018, 295
S. Xayheungsy, L.H. Khiem, L.D. Nam, Radiation dose estimation of cement
samples used in Lao PDR, Communications in Physics, 27, No. 3, 2017,193-203.
Sonexay Xayheungsy, Le Hong Khiem, Le Dai Nam. Assessment Of The
Natual Radioactivity And Radiological Hazards In Lao Cement Samples.
Radiation Protection Dosimetry, 2018, Vol. 181, No. 3, 208–213.
Sonexay Xayheungsy, Le Hong Khiem. Natural Radioactivity In The Soil Of
Thoulakhom District In Vietiane Province, LaoPDR, Tạp Chí Phát Triển Khoa
Học Và Công Nghệ- Đại Học Quốc Gia TP. HCM, ngày 21 tháng 3 năm 2018.
X.Sonexay, L.H.Khiem, L.D.Nam, Assessment of Natural Radioactivity
Levels and Radiation Hazards of Building Materials of Lao PDR.
International Journal Of Modern Engineering Research (IJMER), 14.04.2018
Sonexay Xayheungsy1,3, N.C.Thanh2, L.D.Nam2, V.H.Giang2 and
L.H.Khiem2,3*, Measurement of natural radioactivity in some sand and brick
in Vietiane province, Lao PDR. IJRDO - Journal of Applied Science,
Volume-4, Issue, 11, Nov, 2018.


INTRODUCTION
1. Thesis necessity
There are various sources that contain radiation, especially in the earth, rocks with
different amounts. An amount of radiation that is higher than the safety threshold can be a
cause of many diseases including cancer, which is dangerous for people.
Building materials such as cement, brick, sand, soil, etc. are mainly made
from raw materials such as soil and rock. As a result, they can break down into
radioactive gas radon. According to statistics of the UN, a person spends 70% his
lifetime in-door (houses, offices, or public buildings, etc.). If the construction
materials contain an extremely high amount of radiation, it will be hazardous.
For the safety of humankind, The United Nations Scientific Committee on
the Effects of Atomic Radiation (UNSCEAR) has given a radiation safety
threshold for building materials. In most countries, it is mandatory to check
radioactivity of the materials for construction before they are used. In Laos PDR ,
up to now there has not been any inspection of radiation carried out (due to lack of
skilled personnel).
Laos has officially become a member of the IAEA since 2011. Since then,
Lao government have requested Vietnam to give a hand in training highly qualified
personnel in the field of radioactive control in construction materials. The objective
of this thesis is to understand the method of assessment of natural radioactivity in
some building materials for better implementation of constructions in Laos.
2. Objectives of the study
The objectives of the thesis is:
- Determination of the concentration of the Naturally Occurring Radioactive
Materials (NORM) in some building materials commonly used in Lao PDR such as
cement, sand, etc. by gamma spectrometers using NaI(Tl) and HPGe detectors.
- To assess the radiological hazard associated with the natural occurring
radioactive isotopes in the building materials used in Laos PDR.
These data are extremely important for the radiation dose assessment for
residents, and making proper warning and necessary recommendations to
production facilities so that they can make necessary adjustments to ensure the
absolute safety in radioactive aspects for construction materials used in the market.
3. Main research contents of the thesis
- The research is to analyze the amount of concentration of natural
occurring radioactive isotopes including 238U, 235U, 232Th and 40K in the
building materials used in Laos PDR by using gamma-ray spectroscopy technique.
For our measurements, both NaI(Tl) and HPGe detectors have been used for
gamma-ray detection.
- For analyzing the gamma-ray spectra obtained with NaI(Tl) detector, a
mathematical method has been used for determining the areas of overlapping spectral
regions due to the poor energy resolution of NaI(Tl) detector.
- To evaluate the radiological hazard of the natural radioactivity, the radium
equivalent activity, the air absorbed dose rate, the annual effective dose rate, the
representative index and the values of both external and internal hazard indices


1


have been calculated based on obtained concentration of the natural occurring
radioactive isotopes of the investigated of the building materials.
- Several computer programs have been developed for automatic analysis of
gamma-ray spectra obtained with NaI(Tl), HPGe detectors and for routinely determining
the values of the quantities related to radiological hazard due to the natural occurring
radioactive isotopes in the building materials.
CHAPTER 1.
OVERVIEW OF NORM IN BUILDING MATERIAL
1.1. Origin of natural radiation and its connection to building materials
1.1.1. The decay series of natural radioactive isotopes
Naturally occurring radioactive materials, under certain conditions, can
reach radiologically hazardous levels. The natural radioactivity in soil comes mainly
from the radionuclides in the U-238 and Th-232 series, and K-40. The radiological
implication of these radionuclides is external radiation exposure by gamma rays and
internal exposure due to inhalation of radon and its daughters. The decay schemes of
these series are listed below.
a) The uranium series 238U
Beginning with naturally occurring uranium-238, this series includes the
following elements: astatine, bismuth, lead, polonium, protactinium, radium,
radon, thallium, and thorium. All are present, at least transiently, in any natural
uranium-containing sample, whether metal, compound, or mineral. The series
terminates with lead-206. The decay scheme of this series is presented in
Figure 1.1
238
(1)
U 4,468×109 y năm
↓α
(2) 234Th
24,1 ngày
↓β
234
(3)
Pa 1,17 phút
↓β
234
(4)
U 2,455×105 năm
↓α
230
(5)
Th 7,538 ×104 năm
↓α
226
(6)
Ra 1600 năm
↓α
222
(7)
Rn
3,8232 ngày
↓α
218
(8)
Po
3,094 phút
↓α
214
(9)
Pb 26,8 phút
↓β
214
(10)
Bi 19,9 phút
↓β
214
(11)
Po
162,3 giây
2


210

↓α

22,3 năm
↓β
210
(13)
Bi 5,013 ngày
↓β
210
(14)
Po
138,4 ngày
↓α
206
Pb
Figure 1.1. The decay scheme of the 238U series. Nuclides underlined are
measurable by gamma-ray spectrometry.
b) The actinium series - 235U
Beginning with the naturally-occurring isotope U-235, this decay series
includes the following elements: actinium, astatine, bismuth, francium, lead,
polonium, protactinium, radium, radon, thallium, and thorium. All are present, at
least transiently, in any sample containing uranium-235, whether metal, compound,
ore, or mineral. This series terminates with the stable isotope lead-207. The decay
scheme of this series is shown in Figure 1.2.
235
(1)
U 1,7×108 năm
↓α
231
(2)
Th
25,52 giờ
↓β
231
(3)
Pa 3,276 ×104 năm
↓α
227
(4)
Ac 21,772 năm
↓β
227
(5)
Th
18,718 ngày
+ α (1,38 %) to 223Fr 22 phút then β
↓α
223
(6)
Ra
11,43 ngày
↓α
219
(7)
Rn 3,96 giây
↓α
215
(8)
Po 1,781 giay
↓α
211
(9)
Pb 36,1 phút
↓β
211
(10)
Bi
2,14 phút
↓α
207
(11)
Tl
4,77 phút
+ β (0,273%) 211Po 516 giây then α
↓β
207
Pb
Figure 1.2. The decay scheme of the 235U series. Only 235U is measurable by
gamma-ray spectrometry.
(12)

Pb

3


c) The thorium series 232Th
Beginning with naturally occurring thorium-232, this series includes the following
elements: actinium, bismuth, lead, polonium, radium, radon and thallium. All are present,
at least transiently, in any natural thorium-containing sample, whether metal, compound,
or mineral. The series terminates with lead-208. The decay scheme of this series is shown
in Figure 1.3.
232
(1)
Th 1,405 ×109 năm
↓α
228
(2)
Ra 5,75 giờ
↓β
228
(3)
Ac 6,15 giờ
↓β
228
(4)
Th 1,9127 năm
↓α
224
(5)
Ra 3,627 ngày
↓α
220
(6)
Rn 55,8 giây
↓α
216
(7)
Po 150 giây
↓α
212
(8)
Pb 10,64 giờ
↓β
212
(9)
Bi 60,54 phút
↓ β (64,06%) ↓ α (35,94%)
208
Po 0,3 giây
Tl 3,06 phúg
↓α
↓β
206
Pb
Figure 1.3. The decay scheme of the 232Th series. Nuclides underlined are
measurable by gamma-ray spectrometry.
1.1.2. Radon loss
1.1.3. Natural disturbance of the decay series
1.2. Effects of radiation hazards from building material to health body
1.3. Research condition of radiation in building material in the world
In most countries, the inspection and assessment of the level of
radioactivity in building materials are mandatory. To understand more about this
issue, we have listed some recent works about natural radioactivity in different
types of building Materials conducted by scientists in some countries in the world.
The available data of specific radio-activities of some common building materials
in some countries taken from literatures are presented in the tables numbered as
1.1, 1.2 and 1.3 below.

(10)

212

4


Table 1.1. The activity concentration (Bq.kg-1) Portland cement samples for
different countries in the world.
Activity concentration (Bq.kg-1)
Countries
References
226
232
40
Ra
Th
K
Greece
92
31
310
[12]
Austria
26.7
14.2
210
[13]
Bangladesh
60.5
64.7
952.2
[14]
China
56.50
36.50
173.2
[15]
Egypt
134
88
416
[16]
Pakistan
31.3
26.8
51.3
[17]
Turkey
40.5
26.1
267.1
[18]
Ghana
61.63
25.96
451.30
[19]
India
37.0
24.1
432.2
[20]
Malaysia
34.7
32.9
190.6
[21]
Brazil
61.7
58.5
564.0
[22]
Lao PDR
41.12
16.60
141.48
[23]
Table 1.2. Comparison between the activity concentrations of our building
materials with that of other countries of the world
Activity concentration (Bq.kgRaeq
S.
1
)
(Bq.kg-1) References
Countries materials
No
226
232
40
Ra
Th
K
brick
41
89
681
220,71
[24]
1 Australia
[24]
Soil
62.9
162.8
403.3
326.76
[24]
Sand
3.7
40
44.4
64.32
brick
124.7
28.9
390.2
196.07
[25]
2
China
[26]
Soil
44.6
86.7
352.8 
195.75
[15]
Sand
40.7
21.5
302.6
96.4
brick
24
24.1
258
78.33
[27]
3 Egypt
Soil
13
6
433
54.92
[28]
Sand
9.2
3.3
47.3
17.56
[29]
brick
16.2
70
76
122.15
[30]
4
Brazil
[31]
Soil
30
67
112
134.43
[30]
Sand
35.3
74
315
165.38
brick
43.2
53.7
631.2
168.59
[17]
5
Pakistan
[17]
Soil
42.4
56.2
565.3
166.29
[17]
Sand
21.5
31.9
519.6
107.13
brick
63.74
38.6
313.71
143.09
[32]
6
India
Soil
116.1
43.51
300.07
201.44
[32]
Sand
90.27
101.67
280.71
257.27
[32]
brick
35
30
400
[33]
World7
Soil
35
30
400
[33]
wide
Sand
35
30
400
[33]
5


Table 1.3. The specific radio-activities of 40K, 226Ra and 232Th in building
materials used in Ha Noi
Activity concentration
S.
Building materials
No.
K-40
Ra-226
Th-232
1
Black sand
515 ± 23
24.4 ± 1,4
36,2 ± 1.0
2
khuyến lương Sand
483 ± 15
53,5 ± 3,7
46 ± 3.6
3
yellow sand
651 ± 21
25,5 ± 0,9
32,3 ± 0.6
4
Hà Bắc yellow sand
357 ± 2
12,4 ± 2,5
20 ± 2,4
5
Hải Phòng cement
73 ± 9
28,6 ± 2,5
32,3 ± 2,8
6
Hoàng Thạch cement
196 ± 2
65,9 ± 3,7
27,8 ± 2,8
7
X77 cement
205 ± 2
69,6 ± 3,7
32,2 ± 2,8
8
Gravel
389 ± 8
23,5 ± 5
23 ± 4
9
Rock
46 ± 21
25,5 ± 5
19 ± 4
10
Brick
665 ± 0
84,0 ± 15
85 ± 4
11
Tiles
385 ± 5
39 ± 8
34 ± 4
12
Plaster
525 ± 5
44 ± 4
37 ± 4
13
Rock dust
< 10
12,4 ± 2,5
6,8 ± 2,4
14
Tro xỉ hồ chứa
626 ± 3
122 ± 9
100 ±
15
Fly ash
788 ± 7
164 ± 13
126± 1
1.4. Investigation of Radioactivity in the building materials in Laos PDR
In recent years, the economy of Laos has continuously grown and
developed in a stable speed, with GDP increasing by an average of 7.6%; Per
capita income has reached nearly 1,700 USD in the period 2013-2014. These
achievements facilitate the Lao Government to successfully implement the 7th
Socio-Economic Development Plan this year as well as the Millennium
Development Goals. Along with economic development, the demand for
construction is rising significantly, leading to the establishment of various
construction materials companies. Nevertheless, because the scientific level of the
Lao People's Democratic Republic is still at a very modest level and lack of human
resources to undertake, the inspection of natural radioactivity in construction
materials so far has not been conducted. The researchers were also encouraged to
choose any topic that is related to natural radioactivity survey in Building
Materials, which aims to widely expand this research direction in Laos PDR. This
thesis may be considered as the first work in this direction in Laos PDR.

6


CHAPTER 2
GAMMA SPECTROCOPY USING EITHER HPGe AND NaI(Tl)
SCINTILLATION DETECTOR
2.1. Physics foundation of gamma-ray detection with scintillation and HPGE Detectors
2.1.1. Interaction Of Gamma Radiation With Matter
2.1.2. Photoelectric effect
2.1.3. Compton Scattering
2.1.4. Pair Production
2.1.5. Attenuation of Gamma Radiation with matter
2.2. Configuration and gamma ray spectroscopy of NaI(Tl) and HPGe
detector principles
2.3. HPGe Detector: Gamma-ray spectrum structure
2.3.1. Operational principles of HPGe detectors
2.3.2. Configurations of HPGe detectors
2.3.3. Gamma ray spectroscopy with HPGe detector
2.4. Scintillation detector: Gamma-ray spectrum structure
2.4.1. Configuration of Scintillation detectors
2.4.2. Gamma ray spectroscopy with Scintillation Detector
CHAPTER 3
EXPERIMENTAL METHODS
3.1. Selection of sampling point of building materials
Four kinds of building materials commonly used in Laos PDR including cement,
sand, brick and soil have been chosen in this thesis.
3.1.1. Cement samples collection

Figure 3.1. The map of Lao PDR showing the local famous cement factories in
Lao PDR (from which the cement samples were collected).

7


S.
No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

Table 3.1. The labels of the analyzed cement samples.
Position
Type of
Symbol
Map icon
Latitude (°N)
Longitude
cement
(°E)
1V1
1V2
1V3
Porland
1V4
cement
(1V)
1V5
1V6
1V7
A
18°56'7.6"N
102°27'7.0"E
2V1
2V2
2V3
Mixed
2V4
cement (2V)
2V5
2V6
2V7
1VT1
Mixed
1VT2
cement (1VT)
1VT3
2VT1
B
18°6'27.3"N
102°47'7.9"E
2VT2
Porland
cement (2VT)
2VT3
2VT4
1K1
Porland
1K2
cement
1K3
(1K)
1K4
C
17°24'19.8"N 105°12'58.2"E
2K1
2K2
Mixed
cement (2K)
2K3
2K4
1SV1
Porland
1SV2
cement
1SV3
(1SV)
1SV4
D
15°50'39.1"N 106°23'16.4"E
2SV1
2SV2
Mixed
cement (2SV)
2SV3
2SV4
8


3.1.2. Soil sample selection

Figure 3.2. The map of Lao PDR showing the Thoulakhom district and the soil
and sand sampling locations were indicated as P1, P2, …, P10.
Table 3.2. The labels of the analyzed soil samples.
Position
S.
Symbol
Village
No
Latitude (°N)
Longitude (°E)
1
1P1
2
1P2
Ban Dong (P1)
18°16'52.5" N
102°40'51.5"E
3
1P3
4
2P1
5
2P2
Ban PhaThao (P2)
18°19'40.5" N
102°39'56.5"E
6
2P3
7
3P1
8
3P2
Ban Nam Ang (P3)
18°22'23.9" N
102°36'5.4"E
9
3P3
10
4P1
Ban Nanokkhoum
11
4P2
18°17'18.2" N
102°41'35.8"E
(P4)
12
4P3
13
5P1
Ban Phonmouang
14
5P2
18°20'15.7" N
102°40'51.4"E
(P5)
15
5P3
16
6P1
17
6P2
Ban NaKang (P6)
18°20'42.0" N
102°39'40.4"E
18
6P3
19
7P1
20
7P2
Ban Naxanglek (P7)
18°21'54.5" N
102°37'48.8"E
21
7P3
22
8P1
Ban Keun (P8)
18°21'51.2" N
102°35'13.3"E
9


23
8P2
24
8P3
25
9P1
26
9P2
Ban Hatnoi (P9)
27
9P3
28
10P1
Ban Boungphao
29
10P2
(P10)
30
10P3
3.1.3. Sand samples preparation

18°22'58.6" N

102°33'52.5"E

18°20'49.3" N

102°33'59.6"

Figure 3.3. Map of Vientiane capital showing the Mekog river and locations of
sand samples discussed in this preliminary study

Figure 3.4. Photo of river sand in Mekong driver in Vientiane capital

Figure 3.5. River sand Namngeum in Thoulakhom district, Vientiane province.
10


S. No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33

Table 3.3. The labels of the analyzed cement samples.
Position
Symbol
Village
Latitude (°N) Longitude (°E)
1NK1
1NK2
Ban HuayYai
1NK3
18°56'7.6"N
102°27'7.0"E
(NK1)
1NK4
1NK4
2Nk1
2NK2
Ban
18°6'27.3"N
102°47'7.9"E
HuayHom(NK2)
2Nk3
2Nk4
3NK1
3NK2
Ban
17°58'22.7"N
102°30'8.9"E
NongDa(NK3)
3NK3
3NK4
4N1
4NK2
Ban Don
17°57'57.0"N
102°35'47.3"
Chan(NK4)
4NK3
4NK4
5NK1
5NK2
Ban Hom1(NK5)
17°50'10.8"N
102°35'58.8"
5NK3
5NK4
6NK1
6NK2
Ban Hom2(NK6)
17°51'16.5"N
102°35'37.8"
6NK3
6NK4
1NG1
1NG2
Ban Keun (P11)
18°21'30.7"N 102°34'19.3"E
1NG3
NG4
2NG1
2NG2
Ban Pakchan (P12) 18°22'15.1"N 102°32'10.7"E
2NG3
2NG4

11


Figure 3.6. Square flame of 100cm × 100cm.
3.1.4. Brick sample selection
3.2. Preparation of sample for analysis
Before analysis, the collected samples have to be prepared for
measurement. The sample preparation procedure is presented below in figure 3.6.

Figure 3.6. The schematic of the process of sample preparation.
Figure 3.7 is a picture for illustration of the sample preparation process. A
mortar and pestle for crushing and homogenizing and a standard sieve of 0.2 mm
mesh size have been used for sample preparation. The prepared building materials
finally were filled in the beakers sealed with plastic tape to prevent the escape of
airborne radionuclides. The pictures of some prepared samples are presented in
figure 3.8.

12


Figure 3.7. A mortar and pestle for crushing and homogenizing. A standard sieve
of 0.2 mm mesh zize.

Figure 3.8. A prepared building materials were filled in the beaker sealed with
plastic tape to prevent the escape of airborne radionuclides.
3.3. Reference materials

Figure 3.9. Picture of Three reference materials, obtained from the International
Atomic Energy Agency (IAEA: RGU-1, RGTh-1 and RGK-1).
For determination of the specific radioactive concentrations of the
materials, the relative method has been used. For this, the reference materials
obtained for IAEA have been used. The picture of these reference materials
including RGU-1, RGTh-1 and RGK-1 is shown in figure 3.9 together with their
data listed in Table 3.4.
Table 3.4. The table shows the data of reference material used.
Sample
Mass (g)
Density (g/cm3)
Mass acivity (Bq/kg)
IAEA-RGK-1
340,91
1,8
14000±400
IAEA-RGU-1
378,82
1,94
4940±30
IAEA-RGTh-1
309,01
1,736
3250±90

13


3.4. Method of Determination of activity concentrations of natural
radionuclides from gamma-ray spectra with Scintillation detectors
Figure 3.10 is the pictures of the gamma-ray spectrometers used in our work. On
the left panel is the spectrometer using NaI(Tl) detector while on the right panel is
the spectrometer using HPGe detector.

Fig. 3.10. Picture of gamma-ray spectroscopy using Scintillation Detector.
For determination of activity of the naturally occurring radioactive
isotopes using NaI(Tl) detector, we have used a method for overcoming the poor
energy resolution of NaI(Tl) detector. The method is based on the characteristics of
the IAEA reference materials used in our investigation. Firstly, we need to measure
the spectra of background, RGU-1, RGTh-1 and GRK-1 reference samples. These
spectra are presented in figure 3.11.

Fig. 3.11. a) Background Spectrum, obtained in a collecting time for 52700
second. b) Spectrum of IAEA RGU-1 was collected for 13942 second. c) Spectrum
of IAEA-RGTh-1 was collected for 18190second. d) Spectrum of IAEA-RGK-1
was collected for 17215 second.
Based on these spectra, we defined the energy region of interest (ROI) for
our interested isotopes, which is written in table 3.5.

14


Table 3.5. Energy windows for determination of concentration of naturally occurring
radioactive isotopes using the gamma spectrometer with NaI(Tl) detector.
Parent
Gamma ray energy
Energy window
Daughter isotope
isotope
(keV)
(keV)
238
214
1
U
Bi
1764,49
1632 – 1897
232
208
2
Th
Tl
2614,53
2418 – 2811
40
40
3
K
K
1460,8
1351 - 1570
The following algorithm was used to determine the concentration of
radioactive isotopes, which is explained below. The net count rate
in the ith
Roi of a calibration standard j (with i and j equal to 1, 2 and 3 denoting the ROIs, and
the calibration standards of K, U and Th, respectively) is proportional to the activity
An,j of each investigated nuclide n (n=1,2 and 3 for 40K, 238U and 232Th,
respectively) according to:


(3.1)

Where
is the counting efficiency in the ith. ROI for the nuclide n. the net
count rate is given by



i, j

N
t



i, j

 Ri , b

(3.2)

j

Thus, AK, ATh và AU can be obtained by solving the system of simultaneous
equations:

 e A e A e A
 e A e A
 e A e A
K

U

K

1,1

U

2, 2

Th

2, 3

U

3, 2

From the RGK-1 standard, on has:


e

1,1

U

1, 2

1,3

Th

(3.3)

Th

3,3


A

1,1

Th

(3.4)

1,1

From the RGU-1 standard:

e

1, 2


A





1, 2
2, 2

e

2, 2

(3.5)

2, 2

A

2, 2

And from the RGTh-1 standard:

e1,3 



1, 3





1, 2

A
A

A

2,3

2, 2

3, 3

15

(3.6)


e



2,3





2,3



2, 2

A

2,3

A
A

2,3

3, 3

The other constant can be obtained by combining the count rates for the U and Th
standards in the third ROI:

e

3, 2





3, 2

A

 A A
e 
A
2, 2

(3.7)

3, 2

2,3

3, 3

2, 2

3, 3

3, 3

Giá trị của các hoạt độ trong các mẫu chuẩn của IAEA là: A11=9869 Bq,
A12=129.55 Bq, A13=0.07 Bq, A22=3527 Bq, A23=18 Bq và A33=2298 Bq.
Table 3.6. Counting efficiency values, determination from spectrum of reference materials
(IAEA)
e11
e12
e13
e22
e23
e32
e33
7,216327 x 1,033662 x -2,413112 x 7,927624 x -4,421488 x -2,433944 x 1,29643
10-4
10-4
10-4
10-4
10-4
10-5
x 10-3

The concentration of
following equations:

238

232

U,

Th and

40

K isotopes are calculated using the

 
e e
A e e

e e
 e
A   A
e e
e
 e
A   A A
e e
e
U

Th

2, 2

3, 2

2,3

3, 3

2, 2

3, 2

Th

U

2,3

2, 2

2, 2

U

Th

1, 2

K

K

1, 3

U

1,1

Th

1,1

(3.8)

(3.9)
(3.10)

1,1

The standard uncertainty on the activity values, can be calculate as

 A  e N  tR 
1
 A  e N  t R 
1

1/ 2

1

K

1,b

t

1,1

1/ 2

U

2, b

3

 t R3,b

(3.11)

2, 2 t

1
 A  e N
Th

2

3, 3t



1/ 2

A computer program has been written to determine these coefficients. Its flow
chart is shown in the in Figure 3.12.

16


Fig. 3.12. Computer flow chart showing the automatic determination of activity
concentrations of natural radionuclides from gamma-ray spectra with NaI(Tl) detector.
3.5. Determination of activity concentrations of natural radionuclides from
gamma-ray spectra with HPGe detectors
Two method for measurement of radioactive concentration: Relative method and
absolute method. Before measurement of radioactivity concentration in the
samples, we have to perform some calibration including energy, resolution and
efficiency calibrations.
3.5.1. Data analysis when used relative method of determination of the specific
activity for the natural radioactive isotopes

17


3.5.2. Relative method of Determination of the Specific Activity of the naturally
occurring radioactive isotopes
The activity concentrtion of the naturally occurring radioactive isotopes in the
investigated samples is given by the following equation [72]:
(3.20)
where: Am and AS are the activity concentrations of the cement and reference
samples in Bq.kg-1;
Cm and CS are the count rates obtained under the corresponding peak of cement
sample and reference samples in counts.s-1;
Mm and MS are masses of the cement and reference samples in kg;
tm and tS are the measuring live times for the cement and reference samples (s);
T1/2,i is the half-life of the radionuclide.
The error of the specific activities is calculated using the following formula:
√(

)

(

)

(

)

(

)

(

)

(3.21)

3.6. Assessment of Radiological Hazard
3.6.1. Radium equivalent activity (Raeq)
The most widely used radiation hazard index is called the radium equivalent
activity Raeq, which is a weighted sum of activities of the 3 radionuclides 226Ra,
232
Th and 40K. It has been calculated by the following equation:
(

)

(

)

(3.22)
226

Where ARa, ATh and Ak are the activity concentrations of Ra,
232
Th, and 40K in Bq.kg-1, respectively.
3.6.2. External and internal hazard indexes (Hex and Hin)
A widely used hazard index (reflecting external exposure) called the external
hazard index Hex is defined as follows:
Ra
Th
(3.23)
370 259 4810
Radon and its short-lived product are also hazardous to the respiratory organs. The
internal exposure to radon and its daughter progenies is quantified by the internal
hazard index Hin, which is given by the equation:
ex

Ra

Th

259

4810

(3.24)
The values of the indices (Hex, Hin) must be less than unity for radiation hazard to
be negligible.
3.6.3. Absorbed dose rate in air (D)
The activity concentrations of 226Ra, 232Th and 40K were used to calculate the total
external absorbed dose rate DR in nGy.h-1 to the general public in outdoor air at 1 m
above the earth’s surface was calculated as follows:
(3.25)
18


The safe threshold value of DR is 80 nGy.h-1.
3.6.4. Annual effective dose equivalent (AEDE)
The annual effective dose equivalent (AEDE) resulting from the ingestion of the
radionuclides in the samples was estimated using following equation:
(3.26)

CHAPTER 4
EXPERIMENTAL RESULTS AND DISCUSSION
4.1. Energy calibration
The energy calibration of the gamma spectrometry set-up in the current
work was performed using four differnence sources: 22Na, 137Cs, 60Co and 152Eu.
The energy calibration curve can be calculated using the equation below :
(4.1)

Fig.4.1. The Spectrum and Gamma-ray effiency calibration: a), b) The Spectrum
and detector efficiency calibration (used 137Cs and 60Co, standard source) for
the NaI(Tl) detector. c), d). The Spectrum and efficiency calibration (used
152Eu standard source) for HPGe detector.
4.2. Experimental efficiency calibration for a HPGe detector
The absolute, full-energy peak efficiency can be defined as follows [4.2]:
(4.2)
The kit standard a reference sample which IAEA-RGU-1 have been used perform
the standard curve of efficieny for HPGe detector. It’s show 5 polynomial function
(4.3)

19


Figure 4.2. Detector Efficiency calibration susing IAEA-RGU-1 reference materials.
Table 4.2. Values and standard devirations of A0, A1, A2, A3, A4, A5
parameters
Value
Uncertainty
A0
0.0296
4.72E-04
A1
-8.16E-05
2.62E-06
A2
1.05E-07
4.95E-09
A3
-6.64E-11
4.20E-12
A4
2.03E-14
1.64E-15
A5
-2.41E-18
2.39E-19
4.3. Determination of activity concentrations of natural radionuclides in
building materials from gamma-ray spectra with HPGe detectors
The acquisition time is 72 000s for background, reference and samples
respectively. The activity concentration in Bq kg-1 of the natural radionuclides of
the collected cement samples were determined by a high resolution gamma-ray
spectrometry using a p-type high purity germanium (HPGe) detector model with
crystal diameter 53 mm, crystal length 54.7mm of the ORTEC company, and the
relative efficiency 20% and the energy resolution (FWHM) at 1332 keV ( 60Co) is
1.8 keV, which is connected to a spectroscopy amplifier model 572A (ORTEC)
and a computer based PCA-MR 8192 ACCUSPEC multichannel analyzer. The
MAESTRO-32 multi-channel analyzer emulation software was used for data
acquisition, storage, display, online and offline analysis of the gamma-spectra.
4.4. Activity concentration of building materials
4.4.1. The activity concentration results for the cement samples are measured by
gamma-ray spectra with HPGe detectors

20


Table 4.4. The results of the average activity concentrations of 238U, 232Th and 40K
in cement samples using spectrometry with HPGe detector.
Activity concentration in Bq kg-1
Sample
238
232
40
U (Bq.kg-1)
Th (Bq.kg-1)
K (Bq.kg-1)
1V
39.48±0.86
9.83±0.76
156.92±3.76
2V
38.94±0.86
9.47±0.75
61.76±2.66
1VT
33.28±1.26
17.21±1.35
131.93±5.48
2VT
29.41±1.05
20.96±1.23
168.70±5.08
1K
28.96±1.07
20.59±1.27
141.83±4.94
2K
25.76±1.16
16.20±1.19
111.28±4.63
1SV
53.19±1.24
7.73±0.98
45.22±3.64
2SV
49.52±1.24
4.74±0.86
39.32±3.50
Average value
37.32±0.3746
13.34±0.3673
107.12±1.4861
World average
35
30
400
4.4.2. Determination of activity concentrations of natural radionuclides in
cement samples using gamma-ray spectrometry with Scintillation detectors
Table 4.6. The average activity concentrations of 238U, 232Th and 40K in some
cement samples are measured using by NaI(Tl) detector and automatic
measurement using by computer program QB64
Activity concentration in Bq kg-1
Sample
238
232
40
U
Th
K
1V
63.22
12.06
157.43
2V
65.02
13.51
130.38
1K
49.58
47.11
114.03
2K
54.45
30.62
94.09
4.4.3. The activity concentration results for the soil samples were using
gamma-ray spectra with HPGe detectors
Table 4.7. Average activity concerntration (Bq kg-1) in soil samples
Activity concentration in Bq kg-1
Sample
238
232
40
U
Th
K
P1
11.28±0.90
7.43±1.05
40.52±3.88
P2
25.94±1.13
29.56±1.52
137.13±5.39
P3
30.06±1.17
44.47±1.70
581.52±8.09
P4
20.43±1.06
14.47±1.25
81.38±4.68
P5
15.73±0.99
15.10±1.27
68.63±4.47
P6
13.25±0.95
7.13±1.04
8.96±2.60
P7
29.01±1.16
37.77±1.62
88.31±4.78
P8
31.46±1.19
44.42±1.70
468.59±7.60
P9
28.61±1.16
39.58±1.64
415.23±7.34
P10
25.62±1.13
31.39±1.54
372.28±7.12
Average value
23.14±0.34
27.13±0.46
226.26±1.85
World average
35
30
400
21


4.4.4. The activity concentration results for the sand samples using gamma-ray
spectra with HPGe detectors
Table 4.8. Average activity concerntration (Bq kg-1) in sand samples in Mekong
and NamNgeum river
Activity concentration in Bq kg-1
Sample
238
232
40
U
Th
K
NK1
19.88±0.13
32.05±0.33
535.15±5.59
NK2
16.20±0.11
25.73±0.27
541.55±5.62
NK3
15.32±0.11
21.94±0.24
515.04±5.15
NK4
16.53±0.12
24.01±0.26
545.40±5.65
NK5
12.31±0.10
17.12±0.20
456.27±4.88
NK6
12.51±0.10
18.05±0.21
483.12±5.15
P11
9.47±0.08
9.54±0.13
229.57±2.96
P12
11.51±0.09
11.97±0.16
272.89±3.38
Average value
14.22±0.05
20.05±0.11
447.37±2.31
World average
35
30
400
4.4.5. The activity concentration results for the brick samples using gamma-ray
spectra with HPGe detectors
Table 4.9. Average activity concerntration (Bq kg-1) in Brick samples
Activity concentration in Bq kg-1
Sample
238
232
40
U (Bq.kg-1)
Th (Bq.kg-1)
K (Bq.kg-1)
1BG
42.46±2.23
54.03±3.10
589.74±14.08
2BG
43.77±2.25
54.84±3.11
598.94±14.14
3BG
41.17±2.21
54.43±3.11
628.26±14.34
4BG
40.38±2.20
53.92±3.10
610.59±14.22
5BG
37.66±2.16
55.98±3.13
634.82±14.38
6BG
44.08±2.26
55.53±3.12
625.25±14.32
Average value
41.59±0.91
54.79±1.27
614.60±5.82
World average
35
30
400
4.5. Estimation of radiation hazard in building materials

4.5.1. Evaluated dose and risk assessment for cement samples used in Lao PDR
Table 4.10. Evaluated dose and risk assessment for cement samples of Lao PDR
AEDE
Sample
Req (Bq.kg-1) D (nGy.h-1)
Hex
Hin
(mSv. y-1)
1V
65.62±1.42 30.72±0.63 0.151±0.01 0.18±0.01
0.28±0.01
2V
57.24±1.39 26.29±0.61 0.129±0.01 0.16±0.01 0.26±0.01
1VT
68.05±2.34 31.27±1.03 0.153±0.01 0.18±0.01 0.27±0.01
2VT
72.37±2.09 33.28±0.91 0.163±0.01 0.19±0.01 0.275±0.01
1K
69.32±2.14 31.73±0,93 0,156±0,01 0,19±0,01 0,27±0,01
2K
57,49±2,09 26,32±0,92 0,129±0,01 0,16±0,01 0,23±0,01
1SV
67,72±1,89 31,13±0,84 0,153±0,01 0,18±0,01 0,33±0,01
2SV
59,31±1,76 27,38±0,79 0,134±0,01 0,16±0,01 0,29±0,01
Average value 64,64±0,66 29,76±0,29 0,146±0,01 0,16±0,01 0,28±0,02
World average
370
57
0,41
1
1
22


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