SEDIMENTATION RATE AT SETIU LAGOON USING NATURAL

RADIOTRACER 210

Pb TECHNIQUE

NURLYANA BINTI OMAR

UNIVERSITI TEKNOLOGI MALAYSIA

ii

SEDIMENTATION RATE AT SETIU LAGOON USING NATURAL

RADIOTRACER 210

Pb TECHNIQUE

NURLYANA BINTI OMAR

A thesis submitted in fulfillment of the

requirements for the award of the degree of

Master of Science (Physics)

Faculty of Science

Universiti Teknologi Malaysia

DECEMBER 2012

iv

For the nation

v

ACKNOWLEDGEMENTS

Alhamdulillah. First and foremost, I would like to express my gratitude to Prof.

Dr. Noorddin bin Ibrahim for his guidance, discussion, kind and useful advice

throughout this project.

I also would like to take this chance to express my deepest appreciation to my

parents, En. Omar Osman and Pn. Norhayati Jelani and also my siblings for their

constant believe and support to me.

Special thanks to En. Joseph from Institut Osenografi (INOS) Universiti

Malaysia Terengganu and also staff of INOS for helping me in the sampling process in

Setiu Lagoon.

I am also indebt especially to Afifah, Aezal, Nabilah Solehah, Nurul Farah Ain,

Zati Hani and to all my friend who helped me continuously along the way.

Not to forget, the staff of Perpustakaan Sultanah Zanariah (PSZ) for helping me

in locating many of journals and references that I needed in the process of completing

this project.

Lastly, to the entire individual that contributed their help, directly or indirectly in

this project, thank you for your influence and help.

vi

ABSTRACT

This study was conducted to determine the sedimentation rate of soil at Setiu

Lagoon by using natural radiotracer 210

Pb. The area covers a 10 km length lagoon

involving 5 sampling stations of approximately 2 km apart. The sediment samples were

collected using a corer box comprising of a meter long transparent PVC plastic pipe

inserted manually into the sediment bed 2 m below the water surface. The sediment core

extracted were then cut into several 5 cm interval, labeled and stored in a close beaker.

A total of 24 samples were collected from the 5 sampling stations. The measurement of

210Pb activity was made using Hyper Purity Germanium (HPGe). The total activity of

210Pb was measured from gamma ray peak of energy 46.5 keV and supported

210Pb by the

weighted average decay of 226

Ra daughters at 295, 351 and 609 keV. Unsupported 210

Pb

was calculated as the difference between the total and the supported 210

Pb activity. Two

models were used in this study to calculate the sedimentation rate; the Constant Initial

Concentration (CIC) and Advection-Diffusion Equation (ADE) model. The results show

that, there are differences in sedimentation rate values of each model for each station.

The sedimentation rates obtained using CIC model varies from 0.08 to 0.37 cm/yr

whereas ADE model varies from 0.43 to 0.93 cm/yr.

vii

ABSTRAK

Kajian ini dijalankan untuk menentukan kadar pemendapan tanah di Setiu Lagun

menggunakan radionuklid 210

Pb semulajadi. Kawasan ini meliputi 10 km panjang lagun

yang melibatkan 5 stesen persampelan yang jarak antara satu sama lain adalah

dianggarkan 2 km. Sampel sedimen telah diambil dengan menggunakan corer box yang

terdiri daripada paip PVC plastik lutsinar sepanjang satu meter yang telah yang

dimasukkan ke dalam sedimen yang jaraknya 2 m di bawah permukaan air. Teras

sedimen yang diekstrak kemudian dipotong 5 cm, dilabel dan disimpan dalam sebuah

bikar ditutp rapat. Sebanyak 24 sampel diperolehi dari 5 stesen persampelan. Ukuran

aktiviti 210

Pb telah dibuat dengan menggunakan alat pengesan Germanium Hiper Tulen

(HPGe). Jumlah keaktifan 210

Pb ditentukan dengan mengukur aras tenaga gamma 46.5

keV dan keaktifan 210

Pb lebihan yang turun dari udara boleh diukur pada aras tenaga

295, 351 dan 609 keV. Perbezaan jumlah keaktifan antara 210

Pb keseluruhan dan 210

Pb

lebihan yang turun dari udara akan memberikan nilai sebenar keaktifan 210

Pb yang

terhasil dalam tanah. Terdapat dua model yang telah digunakan dalam kajian ini, iaitu

Constant Initial Concentration (CIC), dan Advection-Diffusion Equation (ADE). Hasil

kajian menunjukkan bahawa terdapat perbezaan dalam kadar pemendapan di setiap

stesen bagi setiap jenis model. Nilai yang diperolehi bagi CIC berubah dari 0.08 ke 0.37

cm / thn dan ADE berbeza dari 0.43 kepada 0.93 cm / thn.

viii

TABLE OF CONTENTS

CHAPTER ITEMS PAGE

DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENTS v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENT viii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

LIST OF ABBREVATIONS xv

LIST OF APPENDIXS xvi

I INTRODUCTION

1.1 Background of Study 1

1.2 Research Problem 2

1.3 Objectives 3

1.4 Research Scope 3

1.5 Significant 3

ix

II LITERATURE REVIEW

2.1 Introduction to Sedimentation 4

2.2 Method on Sedimentation Rate Study 5

2.2.1 Artificial Horizon Marker 5

2.2.2 Natural Occurring Radiotracer 6

2.3 210

Pb Radiotracer in Sedimentation Rate Study 8

2.4 Previous Study 9

2.5 Sampling Area 12

2.6 Mathematical Models 13

2.6.1 Constant Initial Concentration (CIC) 13

2.6.2 Advection-Diffusion Equation (ADE) 15

III RESEARCH METHODOLOGY

3.1 Introduction 17

3.2 Sample Collection 17

3.3 Sample Preparation 22

3.4 Detecting System 23

3.4.1 Spectrometer Calibration 26

3.4.1.1 Detector Calibration 26

3.4.1.2 Detector Efficiency Calibration 28

3.4.1.3 Minimum Detection Limit (MDL) 28

3.5 Data Calculation 29

3.5.1 210

Pb Activity 29

IV RESULTS AND DISCUSSION

4.1 Background Radiation 30

4.2 Detector Efficiency 32

4.3 Minimum Detection Limit (MDL) 33

4.4 210

Pbex Vertical Profile 34

x

4.5 Mathematical Models 40

4.5.1 Constant Initial Concentration (CIC) 40

4.5.2 Advection-Diffusion Equation (ADE) 44

4.6 Result and Discussion 48

V CONCLUSION

5.1 Conclusion 51

5.2 Recommendations 52

REFERENCES 53

APPENDIXS 58

xi

LIST OF TABLES

NO TITLE PAGE

2.1 Uranium Decay Scheme 7

3.1 Coordinate of the Five Setiu Station 18

3.2 Energy for Each Isotope 27

4.1 Background Counts 31

4.2 Efficiency Data 32

4.3 Minimum Detection Limit 34

4.4 Activity of 210

Pb for Setiu 1 35

4.5 Activity of 210

Pb for Setiu 2 36

4.6 Activity of 210

Pb for Setiu 3 37

4.7 Activity of 210

Pb for Setiu 4 38

4.8 Activity of 210

Pb for Setiu 5 39

4.9 ln (210

Pbex) Activity for CIC Model 41

4.10 Sedimentation Rate Using CIC Model 44

4.11 Sedimentation Rate for Setiu 1 Station 45

4.12 Sedimentation Rate for Setiu 2 Station 45

4.13 Sedimentation Rate for Setiu 3 Station 46

4.14 Sedimentation Rate for Setiu 4 Station 46

4.15 Sedimentation Rate for Setiu 5 Station 47

4.16 Overall Sedimentation Rate by Using ADE Model 47

4.17 Sedimentation Rate for CIC and ADE Model 48

xii

LIST OF FIGURES

NO TITLE PAGE

2.1 210

Pb Decay Chain 8

2.2 Maps of Terengganu and Setiu 12

3.1 Map of Setiu 17

3.2 Transparent Corer Box and Cylindrical Container 19

3.3 PVC “holder” 19

3.4 Setting Up Transparent Corer Box 20

3.5 Inserting Corer Box 20

3.6 Sediment is Placed in Cylindrical Container 21

3.7 Sediment Sample 21

3.8 250 micron Sieve 22

3.9 Marinelli Beaker 23

3.10 Hyper Purity Germanium (HPGe) Detector 24

3.11 Dewar Tank 24

3.12 Generalized MCA Block Diagram 25

3.13 Sample Reference Material IAEA-314-Ra226,Th and U in

Stream

26

3.14 Energy Calibration Spectrum 27

4.1 Net Peak Area and Continuum in Gamma Spectrum 31

4.2 Efficiency Calibration Curve 33

4.3 Vertical Distribution of 210

Pbex in Setiu 1 35

4.4 Vertical Distribution of 210

Pbex in Setiu 2 36

4.5 Vertical Distribution of 210

Pbex in Setiu 3 37

xiii

NO TITTLE PAGE

4.6 Vertical Distribution of 210

Pbex in Setiu 4 38

4.7 Vertical Distribution of 210

Pbex in Setiu 5 39

4.8 ln 210

Pbex (bq/kg) versus Depth (cm) for Setiu 1 41

4.9 ln 210

Pbex (bq/kg) versus Depth (cm) for Setiu 2 42

4.10 ln 210

Pbex (bq/kg) versus Depth (cm) for Setiu 3 42

4.11 ln 210

Pbex (bq/kg) versus Depth (cm) for Setiu 4 43

4.12 ln 210

Pbex (bq/kg) versus Depth (cm) for Setiu 5 43

xiv

LIST OF SYMBOLS

SYMBOL TITLE PAGE

α Slope of the line ln Ax versus x (depth) 14

λ 210

Pb Decay Constant 15

x Depth of Sediment 14

t Time (year) 14

xv

LIST OF ABBREVATIONS

ABBREVATIONS TITLE PAGE

Pb Plumbum 1

Th Thorium 2

Be Beryllium 2

Cs Cesium 2

Si Silicon 2

Fe Iron 2

Po Polonium 2

Bi Bismuth 3

Pa Protactinium 7

U Uranium 7

Ra Radium 7

Rn Radon 7

HPGe Hyper Purity Germanium 3

keV Kiloelectron Volt 3

PVC Polyvinyl Chloride 18

MCA Multi Channel Analyzer 25

xvi

LIST OF APPENDIXS

APPENDIX TITLE PAGE

A Peak Locate Report 57

1

CHAPTER 1

INTRODUCTION

1.1 Background Study

In tracing the history of the effect of mankind on the environment, it is evident

that in many places, the period of the greatest impact has been within the last 150 years.

Lake, ocean and lagoon can provide a basis for reconstructing the many aspects of this

impact such as, for estimating rate of change, and for establishing a baseline in

environmental monitoring program (Walling and He, 1993).

The establishment of accurate chronologies of sedimentation rates based on

palynological or stratigraphy methods often provides only historical averages involving

many meters of sediment. Furthermore, such measurements not only lack the necessary

accuracy and details but may not adequately reflects the rates within the upper 20 cm or

so of the sediment where significant sediment-water exchanges are occurring at the

present time (Robbin and Edgington, 1975).

Nowadays, natural radionuclides have become powerful tracer that can provide

basic insights into a variety of marine processes, such as processes in the water column

and in biological and sedimentary system. Radioisotope 210

Pb (half-life 22.2 years) for

instance has become the important tool for determining accumulation rates in sediments

2

on about 100-year time scale. Shorter-lived natural radioisotopes such as 234

Th and 7Be

(half-life of 24 and 53 days) have proved useful in determining deposition and mixing

rates on time scales of a few month (Dibb and Rice, 1989). Similarly the basis of using

137Cs to derive chronologies for sediments during the past 30-40 years is based on the

fact that weapon released atmospheric radio-cesium is washed away by precipitation and

is rapidly and strongly bound to fine particulates of the land surface. Through run-off it

gets washed away from land surface and settles on the lake or ocean bottom.

Since then, application of radiometric methods to sedimentary geochronology

has enjoyed considerable success (Durham and Joshi, 1980). Krishnawami (1971)

evaluated the use of 210

Pb as well as three other radionuclides (32

Si, 55

Fe, 137

Cs) for

dating recent freshwater lake sediments and concluded that 210

Pb is ideal for dating lake

sediments as old as a century. Subsequently, Koide (1972) further validated the utility of

the method and determined sedimentation rates in a series of lakes. Edgington (1991)

used the anthropogenic 137

Cs and natural radionuclide 210

Pb to estimate the recent

sedimentation rates in Lake Baikal. Their results were used for the development of

mass-balance models for sediments and contaminants.

1.2 Research Problem

Most studies on sedimentation rate such as Maria (2009) used 210

Po, an alpha

emitter as proxy to 210

Pb radiotracer. This is due to the gamma decay energy that was

released by 210

Pb (46.5 keV) lies in the low energy region. With high background, the

detection of 210

Pb will be difficult. This study is to prove that 210

Pb can be use in

studying sedimentation rate process without using 210

Po as proxy.

3

1.3 Objectives

The objectives of this research are;

1.3.1 To determine the efficiency of Hyper Purity Germanium (HPGe) for low

energy gamma of less than 100 keV.

1.3.2 To determine the total activity of 210

Pb in sediment samples based on the

46.5 keV gamma energy.

1.3.3 To determine the supported 210

Pb activity based on the average of 295.2

keV (214

Pb), 351.6 keV (214

Pb) and 609.3 keV (214

Bi) gamma energies.

1.3.4 To estimate sedimentation rate at Setiu Lagoon, Terengganu by using

two different mathematical models; Constant Initial Concentration (CIC)

and Advection-Diffusion Equation (ADE) model.

1.4 Research Scope

This study will cover 22 km long of Setiu Lagoon, Terengganu (Setiu Mangroves

forest) which is located on the East Coast of Peninsular Malaysia.

This study is based on the use of natural 210

Pb radioisotope gamma ray of 46.5

keV. Two mathematical models, Constant Initial Concentration (CIC) Advection-

Diffusion Equation (ADE) will be used in this study.

1.5 Significance

This study will help in profiling the sedimentation process within the last 20

years. Apart from that, it can trace back the history of humankind. This method is more

accurate, easy and time saving.

53

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