KING SAUD UNIVERSITY
COLLEGE OF SCIENCE
DEPARTMENT OF PHYSICS AND
ASTRONOMY
Radioecological Aspects of Hail Region:
Behavior of Some Radionuclides in Soil
Submitted in Partial Fulfillment of the Requirement
for the Master's Degree in the Department of Physics and Astronomy
at the College of Science, King Saud University
By
ABDULKAREEM SALEM AL-SAIF
Supervised By:
Dr. Ashraf E. M. Khater
Dr. Hamed A. AL Sewaidan
Associate Professor
Assistant Professor
Principal Supervisor
Co-Supervisor
Physics and Astronomy Department College of Science,
King Saud University
January 2009
KING SAUD UNIVERSITY
COLLEGE OF SCIENCE
DEPARTMENT OF PHYSICS
AND ASTRONOMY
Radioecological Aspects of Hail Region:
Behavior of Some Radionuclides in Soil
By
ABDULKAREEM SALEM AL-SAIF
This thesis was defended on 2 /2/1430 H; 28 /1/2009 G and approved by
the following committee
Dr. Ashraf E.M. Khater
Physics & Astronomy Department –
College of Science,
King Saud University
Supervisor
Signature:………………
Dr. Hamed A. Al-Sewaidan
Physics & Astronomy Department –
College of Science,
King Saud University
Signature:………………
Examiner
Prof. Abdulrasoul Al-Omran
Department of Soil Sciences,
College of Food and Agricultural
Sciences, King Saud University
Examiner
Signature:…………….
Prof. Samir Ushah El-Khamisy
Physics Department,
College of Science,
Ain Shams University,
Egypt
Examiner
Signature:…………….
Dr. Safar AL-Ghamdi
Physics & Astronomy Department –
College of Science,
King Saud University
Signature:………………
Examiner
‫إهداء‬
‫‪To ..‬‬
‫إلى والدي حفظهما هللا‬
‫‪To my parents‬‬
‫إلى زوجتي حفظها هللا‬
‫‪to my Beloved wife‬‬
‫إلى كل من ساندني جزآهم هللا‬
‫خيرا‬
‫‪To all who supported me‬‬
Acknowledgement
The author would like to take this opportunity to thank the
Principal supervisor Dr. Ashraf E. M. Khater for the immense time and
advice. Without his guidance and supervision this thesis could not have
been completed.
The author would like to give my sincere thanks to Dr. Hamed A.
Al-Sewaidan for his great support and encouragement.
It is with sincere gratitude that the author would like to
acknowledge the following people Dr. Hanan Diab (Egyptian Atomic
Energy Authority, Cairo- Egypt), Mr. Abdulaziz AL Ghamdi (King Saud
University), Eng. Nabil Namir (King Saud University) and Eng. Ahmed
Radwan (HADCO). The help and support of these people has made my
thesis a reality as they have guided me to a valuable conclusion.
The author was also greatly assisted by Department of soil science,
College of Food and Agricultural Sciences, King Saud University
and HADCO Company both of which allowed me to use their facilities.
In particular, I would like to express my appreciation to the Physics
department where I have spent many hours developing my ideas and
discussing issues with my colleagues.
Finally, I acknowledge the financial support of King Abdul Aziz City for
Science and Technology, Saudi Arabia (KACST) (14-69 At) to our study,
which is much appreciated.
Contents
Pages
List of Figures
I
List of Tables
IX
Abstrac
XIV
Chapter 1: Introduction
1
1.1 Preamble
1
1.2 Objectives of this study
3
Chapter 2: Literature review
6
2.1 Introduction
6
2.2 Environmental radioactivity
7
2.3 Sources of natural radioactivity
8
2.4 Natural radioactivity in soil
13
2.5 Natural radioactivity in phosphate deposits and
fertilizers
17
2.6 Behavior of long-lived radionuclides in soil
20
Chapter 3 : Experimental techniques
26
3.1 Introduction
26
3.2 Area of study
26
3.3 Sampling and Samples Preparation
28
3.3.1 Soil sampling and sample preparation
28
3.3.2 Water sampling and sample preparation
28
3.4 Instrumentation and instrument set up
29
3.4.1 Gamma Ray Spectrometer
29
3.4.1.1 Setting Up Gamma Ray Spectrometer
32
3.4.1.2 Calibration
33
3.4.1.3 Error Calculation
39
3.4.1.4 Detection Limits
42
3.4 .1.5 Analytical Quality Control
43
3.4.2 Inductively coupled plasma-mass spectrometry,
ICP-MS
44
3.5 Theoretical calculations
44
3.5.1 Dose assessment
44
3.5.2 Radium equivalent index; (RaEq)
45
Chapter 4: Results and discussion
47
4.1 Introduction
47
4.2 Activity concentration of radionuclides in soil sample
47
4.2.1 Gamma Ray- Spectrometry
47
4.2.2 Inductively coupled plasma-mass spectrometry, ICP-MS
61
4.3 Soil properties
75
4.4 Activity concentration of radionuclides in water
87
samples
Summary and Conclusions
90
References
94
Arabic Summary
108
List of Figure Captions
Title
Page
Figure 2-1: A schematic diagram of the 238U series.
10
Figure 2-2: A schematic diagram of the 233Th series.
11
Figure 2-3:A schematic diagram of 235U radioactive decay series
12
(actinium).
Figure 2-4: Transfer of most important radionuclides and heavy
19
metals from rock phosphate to P-fertilizers and phosphogypsum
during the production process.
Figure 3-1:Main geological divisions of Saudi Arabia
27
Figure 3-2:Soil and water sampling locations, HADCO farmer
30
Figure 3-3: Block diagram of Gamma ray Spectrometer set up
32
Figure 3-4:The arrangement of the HP Ge detector with the lead
33
shield
Figure 3-5: Relative efficiency of
226
Ra and its daughter's gamma
37
energy lines.
Figure 3-6: Gamma Transitions of
and
137
238
U Series,
232
Th Series,
40
K
39
Cs shows approximate detection limits of all the
elements that can be detected.
Figure 4-1: Activity concentration of
226
Ra,
228
Ra,
40
K and Ra-Eq
55
value (D), in Bq/kg, in cultivated (inside), uncultivated
(outside) and all soil samples, and their world average (range).
Figure 4-2 : Correlation between activity concentration of 226Ra and
228
57
Ra in cultivated soil (A), uncultivated soil (B) and all soil
samples (C), and of 226Ra- 40K (D) in all soil samples
Figure 4-3: Activity concentration ratio of cultivated (I)/
uncultivated (O) soil of
226
Ra,
228
Ra,
40
58
K and Ra-Eq in
different locations (A), their average value (range) (b) and
their box chart (C)
Figure 4-4 : Activity concentration of
226
Ra (A),
228
Ra (B),
40
K(C)
and Ra-Eq value (D), in Bq/kg, in cultivated (inside) and
uncultivated (outside) soil samples (data point inside circles
59
were not considered in correlation)
Figure 4-5: Activity concentration ratio I/O (cultivated-I/
uncultivated-O) correlation between
226
Ra - 228Ra (A),
60
Ra –
226
radium equivalent (Ra-Eq) (B), and 226Ra – 40K (C)
Figure 4-6 : Box chart of activity concentration, Bq/kg dry weight,
67
of leachable (A) and total (B) 238U, 232Th and 40K in all (ALL),
cultivated (IN) and uncultivated soil samples
Figure 4-7: Box chart of activity concentration, Bq/kg dry weight,
68
of leachable 238U, 232Th and 40K in all (ALL), cultivated (IN)
and uncultivated soil samples .
Figure 4-8: Box chart of soil chemical properties; soluble cations
(Ca2+, Mg2+, Na+, K+) and soluble anion (CO32-, HCO3-, Cl-,
SO4-)
84
List of Table Captions
Title
Page
Table 2-1: Summary of the activity concentration of
232
Th (228Ra),
40
K and
137
238
U (226Ra),
15
Cs (Bq/kg) in soil samples
worldwide
Table 2-2: Activity concentration of
226
Ra,
238
U,
232
Th and
40
K,
19
and radium equivalent index in Bq/kg of phosphate ores from
different countries
Table 2-3: Activity concentration of
226
Ra,
232
K
21
Ra with its
38
Th (228Ra) and
40
(Bq/kg) in phosphate fertilizers from different countries
Table 3-1: Relative intensities of gamma-rays from
226
short-lived gamma emitting daughters (214Pb and 214Bi)
Table 3-2: Absorbed dose rate and dose equivalent rate; one meter
above
ground
surface
per
unit
activity
226
228
of
45
natural
radionuclides
Table 4-1: Activity concentration of
Ra,
Ra,
40
K and
137
Cs,
52
and radium equivalent index in Bq/kg dry weight of soil
samples, activity ratio of 226Ra/228Ra, and calculated absorbed
dose (D) in nGy.h-1 and effective dose equivalent (H) in
nSv.h-1
Table 4-2: Statistical summary of activity concentration of
228
Ra,
40
K and
137
226
Ra,
54
Cs, and radium equivalent index in Bq/kg
dry weight of soil samples, and calculated absorbed dose (D)
in nGy.h-1 and effective dose equivalent (H) in nSv.h-1
Table 4-3: Activity concentration ratios (I/O)* of 226Ra, 228Ra, and
40
K, and radium equivalent index (Ra-Eq), in Bq.kg-1, in soil
56
samples from the same location
Table 4-4: Activity concentration ratios (I/O)* of 226Ra, 228Ra, and
40
65
K, and radium equivalent index (Ra-Eq), in Bq.kg-1, in soil
samples from the same location: Leachable+ concentration of
uranium, thorium and potassium, and calculated leachable
activity concentration of
238
232
U,
Th and
40
K, Bq/kg dry
weight, in soil samples
Table 4-5: Total concentration of uranium, thorium and
potassium, and calculated total activity concentration of
232
238
U,
Th and 40K, Bq/kg dry weight, in selected soil samples
Table 4-6: Statistical summary* of activity concentration, Bq/kg,
of leachable (L) and total (T), and T/L activity ratio of
232
66
238
69
U,
Th and 40K
Table 4-7: Leachable (L), total (T) and L/T ratio for inside/outside
activity concentration ratio of
238
U,
232
Th and
40
70
K in soil
samples
Table 4-8: Leachable activity concentration ratio of
238
U/40K and
232
Th/40K, and inside/outside ratio of
238
U/232Th,
238
72
U/232Th
ratio
Table 4-9: Total activity concentration ratio of
238
U/40K and
232
Th/40K, and inside/outside ratio of
238
U/232Th,
238
73
U/232Th
ratio
Table 4-10: Calculated activity concentration ratios [226Ra/228Ra,
226
Ra/238U(L),
228
Ra/232Th(T)]
226
Ra/238U(T),
228
Ra/232Th(L)
74
and
Table 4-11: soil physical properties; saturation percentage (SP),
pH, electric conductivity (EC in mS/cm), and clay, silt, sand
80
and calcium carbonate (CaCO3) percentages
Table 4-12: Statistical summary of soil physical properties;
81
saturation percentage (SP), pH, electric conductivity (EC),
and clay, silt, sand and calcium carbonate (CaCO3)
percentages
Table 4-13: soil chemical properties; soluble cations (Ca2+, Mg2+,
82
Na+, K+) and soluble anion (CO32-, HCO3-, Cl-, SO4-) meq/L
Table 4-14: Statistical summary of soil chemical properties;
83
soluble cations (Ca2+, Mg2+, Na+, K+) and soluble anion
(CO32-, HCO3-, Cl-, SO4-) meq/L
Table 4-15: The Pearson correlation between soil properties and
85
activity concentration of natural radionuclides
Table 4-16: The Pearson correlation between soluble actions and
86
soluble anions, and activity concentration of natural
radionuclides
Table 4-17: Uranium, thorium and potassium concentrations, and
activity concentration of 238U, 232Th and 40K in water samples
88
Abstract
ABSTRACT
Soil is a significant part of the human environment that provides resources for
food production. It is a very dynamic ecosystem of particular importance since, once
contaminate, the soil acts as a potentially long-term source of environmental
contamination of food, water and air.
Naturally occurring radionuclides (NOR) such as
40
238
U series,
232
Th series and
K are wide spread in the Earth’s environment and are considered the main source of
human radiation exposure. In addition to that, human activities such as the production
and application of phosphate fertilizers increases the quantity of NOR and heavy
metals in agricultural soil .As a result of that a long-term application of phosphate
fertilizers, could be considered as a source of soil contamination.
This study aims at investigating the impact of agricultural activities on the activity
concentration levels of naturally occurring radionuclides such as
228
Ra and
40
238
U,
226
Ra,
232
Th,
K in soil, and their relationship to the soil’s physical and chemical
properties. Radiation dose assessment due to natural radionuclides in soil has also
been considered.
Twenty eight representative soil samples from 14 location (cultivated and
uncultivated) and 14 water samples were collected from HADCO farm in the Hail
region. Activity concentrations of
226
Ra,
228
Ra,
40
K and
137
Cs were measured in soil
samples using gamma-ray spectrometry based on the hyper pure germanium
detector(HPGe). Leachable and total concentrations of uranium, thorium and
potassium were measured in soil and water samples using inductively coupled
plasma-mass spectrometry (ICP-MS). Soil physical (pH, EC and soil texture) and
chemical properties (soluble cations and anions) were also analyzed. Based on the
analytical data, radium equivalent index (Ra-Eq), absorbed dose rate, effective dose
equivalent rate and activity ratios (226Ra/228Ra,
238
226
Ra/238U,
238
U/232Th,
228
Ra/232Th,
U/40K, 232Th/40K) were calculated.
226
Activity concentrations of
Ra,
228
Ra,
40
K and
137
Cs indicate their slight
increment in cultivated soil samples over that in uncultivated soil samples, which
could be correlated directly to agricultural fertilization for 226Ra and 40K. It is possible
to correlate the increment of
228
Ra and
137
Cs (man-made radionuclide) levels in
cultivated soil samples to the change of soil physical and chemical properties that
affect the behavior of radionuclide’s in soil. The average activity concentration ratio
of 226Ra/228Ra was less than one which could be because the average level of 228Ra is
lower than the level of 226Ra in the soil’s parent material.
Generally average leachable and total activity concentrations of uranium (238U),
thorium (232Th) and potassium (40K) did not show any indication of their activity
concentration increments in cultivated soil samples. The range of
238
U is much wider
for leachable concentration (8-20)Bq/kg than that of the total concentration
(22-25)Bq/kg. The average activity concentration ratio of leachable and total uranium
in cultivated to uncultivated soil of the same origins indicate slight increment in
cultivated soil samples, which is clearer for leachable concentration than the total
concentration. Uranium in soil has two origins, naturally occurring from the parent
soil materials and artificially occurring mainly from phosphate fertilization. Uranium
concentration in soil samples indicate the increase of leachable uranium with
increasing total uranium in uncultivated soil samples, while leachable uranium
increased with decreasing total uranium in cultivated soil samples.
Activity concentration ratios of
238
U/232Th were used as a significant parameter to
indicate the increment of uranium concentration in cultivated soil samples. The
average ratios
of
238
U/232Th indicate the increment of about 20% of leachable
uranium concentrations in cultivated soil samples to that uncultivated.
Soil physical and chemical properties and their correlations with the activity
concentrations of natural radionuclides were also investigated.
Finally, measurement on water samples showed the following :
Uranium was less than the maximum level recommended by the international
agencies, thorium was less than the minimum level of measurements, and potassium
was within the normal concentration of underground water. No indication was found
for the agricultural activation on water in the studied area which may be due to the
profound depth of the wells .