Journal of sciences An Assessment of Absorbed Dose … Assessment of Absorbed Dose and Radiation...

International Journal of Science and Technology Volume 4 No. 3, March, 2015

IJST © 2015– IJST Publications UK. All rights reserved. 80

An Assessment of Absorbed Dose and Radiation Hazard Index from Natural

Radioactivity in Soils from Akwa Ibom State, Nigeria

1Bede, M. C, 1Essiett, A. A and 2Inam, E. 1Department of Physics, University of Uyo, P.M.B. 1017, Uyo, Nigeria.

2Department of Chemistry, University of Uyo, P.M.B. 1017, Uyo Uyo, Nigeria.

ABSTRACT

An assessment of Absorbed Dose Rate and Radiation hazard Index from Natural Radioactivity in Soils from Eastern Obolo, Eket,

Ibeno, Ikot Abasi and Uyo local government area of Akwa Ibom state was carried out. The levels of naturally occurring radioactivity

in the soil samples were evaluated using NaI (Tl) Model 802 Gamma Ray Spectrometer: The mean concentration of 238U were

respectively 11.93±1.63, 8.91±1.39, 21.78±2.32, 12.42±1.63 and 12.13±1.98 Bq.kg-1. The mean concentration of 232Th were

respectively 14.75±0.70, 18.96±0.62, 21.47±0.76, 12.76±0.75 and 19.09±0.71 Bq.kg-1.The mean concentration of 40K were

respectively 136.86±3.66, 56.82±3.01, 62.34±3.33, 76.16±3.24 and 67.37±3.29 Bq.kg-1. The Absorbed Dose Rate, Eternal Hazard

Index and Internal Hazard Index were calculated using the activity concentrations of 238U, 232Th and 40K and the mean values

obtained were respectively 20.45, 18.26, 25.99, 16.86, 20.27 nGy.h-1; 0.17, 0.10, 0.15, 0.21, 0.10 Bq.kg-1 and 0.26, 0.13, 0.21, 0.13,

0.15 Bq.kg-1. The obtained values were less than the recommended safety limits of 51 nGy.h-1 and 1 Bq.kg-1.

Keywords: Dose, Radiation, Hazard Index.

1. INTRODUCTION

The stellar material, from which the earth was formed, about

4.5 billion years ago, contained many unstable nuclides [1].

Some of the original primordial nuclides, whose half-lives are

about as long as the earth’s age, are still present [2]. The

exposure of human beings to ionizing radiation from natural

sources is a continuing and inescapable feature of life on

earth; for most individuals, this exposure exceeds that from

all man-made sources combined [3]. Over 60 radionuclides

(radioactive element) can be found in nature, and they can be

placed in three general categories i.e. Primordial – formed

before the creation of the earth, Cosmogenic- formed as a

result of cosmic ray interactions and Human produced-

enhanced or formed due to human actions (minor amounts

compared to natural) [4]. The natural terrestrial gamma

radiation dose rate is an important contribution to the average

dose rate received by the world’s population [5, 6].

Estimation of the radiation dose distribution is important in

assessing the health risk to a population and serve as

reference in documenting changes to environmental

radioactivity in soil due to anthropogenic activities [7].

Human beings are exposed outdoors to the natural terrestrial

radiation that originates predominantly from the upper 30cm

of the soil [8]. Radionuclides with half-lives comparable with

the age of the earth or their corresponding decay products

existing in terrestrial material such as 232Th, 238U and 40K are

of great interest. More specifically, natural environmental

radioactivity and the associated external exposure due to

gamma radiation depend primarily on the geological and

geographical conditions, and appear at different levels in the

soils of each region in the world [9, 10]. Naturally occurring

radioactive material (NORM) found in the earth’s crust,

largely in the form of 226Ra and their associated

radionuclides, is brought to the surface during gas and oil

production processes. The NORM represents a potential

internal radiation exposure hazard to both workers and

members of the public through the inhalation and ingestion of

radionuclides [11]. The major potential hazard from the

natural radiation is from external exposure either by direct

exposure to the soil or as they enter in many building material

[12]. The specific levels of terrestrial environmental radiation

are related to the geographical composition of each

lithologically separated area, and to the content of the rock

from which the soils originated in each area in the radioactive

elements of Thorium (Th), Uranium(U) and Potassium (K). It

is well known, for instance, that igneous rocks granite

composition are strongly enriched in Th and U as compared

to rocks of basaltic or ultramafic composition [9, 13, 14].

There are exceptions, however, as some shale and phosphate

rocks have relatively high content of those radionuclide [9,

10]. Based on these facts, one can certify that the knowledge

of natural occurring radionuclide materials (NORMs), such as 238U, 232Th and 40K, is an important pre-requisite for

evaluation of the rate of exposure absorbed dose by the

population in order to estimate their radiological impacts and

to establish a data base which will be used as reference by a

radiation observer in the studied area [15].

The objectives of this study therefore are to determine the

radioactivity concentrations of 40K, 238U and 232Th in top soil

samples collected from the study areas; to estimate the

radiation absorbed dose, annual effective dose, radium

equivalent activity and radiation hazard index from the

radioactivity measured in the study area. The study ensures

radiological hazard control, since predominant part of the

environmental radiation is found in the upper soil layer.

2. MATERIALS AND METHODS

2.1. Sampling and Sample Preparation

The soil samples for this research were collected within

Akwa Ibom State, an oil producing state in the Niger Delta

International Journal of Science and Technology (IJST) – Volume 4 No. 3, March, 2015


region of Nigeria. The Niger Delta is situated in the Gulf of

Guinea: (3 - 6 ) N, (5 - 8 ) E. It is the largest delta in

Africa, and is very rich in hydrocarbons, covering an area of

about 7500km2 [16]. The first set of samples (6 in number)

were collected from Iko Town, Eastern Obolo (04°30′9′′ −04°31′3′′) N, (007°45′3′′ − 007°45′3′′) E within an

abandoned oil operational area and around estuary where

dredging activities were carried out. The second set of

samples (5 in number) were collected from Ikot Abasi

(04°32′6′′ − 04°33′3′′) N, (007°32′6′′ − 007°34′02.2′′) E

around Uta Ewa beach and Aluminum Smelting Plant,

Ibekwe. The third set of sample (1 in number) was collected

from Eket (04°39′00.8′′𝑁, 007°55′6′′𝐸) around an area of

deep gully erosion, Ikot Ebok.

The fourth set of samples (5 in number) were collected from

Ukpenekang in Ibeno (04°32′23′′ − 04°34′9′′) N,

(008°009′8′′ − 007°59′8′′) E where some oil spill traces

were observed. The last set of soil samples (3 in number)

were collected from the permanent site of University of Uyo,

Use Uffot, Uyo (05°02′3′′ − 05°02′0′′) N, (007°58′29.8′′ −007°58′8′′) E around Advanced Space Technology

Applications Laboratory (ASTAL). Soil sampling and

measurements started 8am – 3pm each day for 5 days in the

month of July, 2013 under sunny weather condition. The

study location is shown on Figure 1.

Figure 1: Study locations on the map of Akwa Ibom State

The samples were collected and prepared according to the

method reported by Agbalagba and Onoja [17]. The top

surfaces of the soils at all the soil sampling sites were scraped

off to remove stones, vegetation and organic debris as

recommended by Senthilkumar [18]. Thereafter, about 5kg

weight of field samples of the soil at each of the sites were

collected at a depth of 5-15 cm, thoroughly mixed and loaded

in labeled black polyethylene bags. Each of the twenty soil

samples collected was a composite of five subsamples. At all

the sample locations, Global Positioning System (GPS) was

used in locating the coordinates of each sample station. The

soil samples collected from the field were quartered and

exposed to ambient air. The soil samples were then oven

dried to a constant weight at 60 − 80°C for about 24 hours in

a monitored KETONG 101 oven. The dried samples were

ground with mortar and pestle and then passed through a 2

mm mesh sieve and weighed. Five hundred grammes (500 g)

of each soil sample was weighed and wrapped in labeled

black polyethylene bags for easy transportation to the

laboratory for analysis.



2.2.Measurement of Activity Concentrations

of Radionuclides in Top Soils

The gamma spectrometric measurement was carried out using

Gamma ray spectrometric system coupled with a NaI(Tl)

model 802 detector at the National Institute of Radiation

Protection and Research (NIRPR) University of Ibadan

Campus, Ibadan. The detector is mounted vertically coupled

with 8K PC based Multi- Channel Analyzer (MCA) and the

detector is enclosed in a massive lead shield to reduce

background from the system. The detector was calibrated

with point sources 60Co, 137Cs, 241Am and 22Na for energy

calibration and the efficiency calibration of the detector was

done with volume source, IAEA-385. The detector which was

well calibrated, used Genie 2000 (template which computes

energy, percentage error, count, uncertainty, Activity

concentration, uncertainty in activity, Gamma probability,

uncertainty in Gamma probability, Efficiency and uncertainty

in Efficiency) as its operating software in the analyses of

various energies of 238U, 232Th and 40K. Each sample was

sealed in an already washed Marinelli beaker for twenty eight

days in order for it to attain secular equilibrium (to allow

buildup of radionuclide in the beaker) before placing it in the

shielded detector. The counting time for the samples was

36,000 seconds. Each sample was counted for 36,000 seconds

to reduce the statistical uncertainty. An already washed empty

Marinelli beaker was also placed in the detector for the same

counting time (36,000 seconds) under identical geometry to

determine the background radiation level of the laboratory

environment. It was later subtracted from the measured γ−ray

spectra of each sample. At the end of the measurement, the

various regions of interest which were deducted from the

background reading were computed with a specialized

template. This template (which covers energy, percentage

error, count, uncertainty, Activity concentration, uncertainty

in activity, Gamma probability, uncertainty in Gamma

probability, Efficiency and uncertainty in Efficiency) was

used to determine the radionuclide concentration in each

sample.The activity concentration A , in unit of Bq.kg-1, for a

radionuclide with a detected photopeak at energy E, can be

obtained from Equation given by Awudu et al. [19] and

Faanu et al. [20]:

Mt

NA

where N is the net peak-area of the radionuclide, is the

detector energy-dependent efficiency, t is the counting live

time in seconds, is the gamma-ray yield per disintegration

of the nuclide, and M is the mass of the sample measured in

kilograms.

3. RESULTS AND DISCUSSION

3.1.Radionuclide Activity Concentrations

Table 1 shows the radionuclide activity concentrations for 238U, 232Th and 40K in Eastern Obolo, Ikot Abasi, Ibeno, Eket

and Uyo Local Government Area of Akwa Ibom State,

Nigeria. Twenty (20) samples were analyzed and the mean

activity concentrations of 238U, 232Th and 40K obtained are

shown.

The Figure 2 is a graphical representation of the mean activity

concentrations for 238U, 232Th and 40K in top soil samples. It

shows that Eastern Obolo L.G.A. has the highest activity

concentration of 40K while Eket has the lowest. It also shows

the accumulation effect of the activity concentrations of 238U

and 232Th in Ibeno. This could be due to industrial activities

in the area.



Table 1: Radionuclide (238U, 232Th and 40K) activity concentrations in top soils.

Sample

code

Location

North East

Activity Concentration (Bq.kg-1)

40K 238U 232Th

Eastern Obolo

EO1 04030`40.9`` 007⁰45`11.3`` 147.17±3.69 14.61±1.92 19.99±0.77

EO2 04⁰30`41.9`` 007⁰45`11.4`` 136.80±3.42 12.47±1.75 14.65±0.60

EO3 04⁰30`43.9`` 007⁰45`11.7`` 122.01±3.23 9.50±1.39 12.87±0.67

EO4 04⁰30`44.8`` 007⁰45`07.8`` 137.30±3.71 10.80±1.45 12.92±0.74

EO5 04⁰30`48.7`` 007⁰45`02.6`` 214.12±4.34 7.84±1.32 14.71±0.66

EO6 04⁰31`19.3`` 007⁰45`17.3`` 63.75±3.55 16.36±1.78 13.36±0.78

Range 63.75 - 214.12 7.84 – 16.36 12.87 – 19.99

Mean 136.86±3.66 11.93±1.60 14.75±0.70

Eket

EK1 04⁰39`00.8`` 007⁰55`07.6``

56.82±3.012 8.91±1.39 18.96±0.62

Ibeno

IB1 04⁰32`23`` 008⁰009`8.8``

62.69±4.00 38.50±2.38 30.59±0.82

IB2 04⁰34`12.2`` 007⁰59`16.2``

65.33±2.95 13.74±1.98 16.43±0.70

IB3 04⁰34`14.0`` 007⁰59`16.6``

75.15±2.64 11.42±1.75 12.19±0.58

IB3 04⁰34.306` 007⁰59.218`

60.70±3.75 28.12±2.94 29.64±0.94

IB5 04⁰34`21.9`` 007⁰59`12.8``

47.81±3.29 17.10±2.57 18.49±0.74

Range 47.81 – 75.15 11.42 – 38.50 12.19 – 30.59

Mean 62.34±3.33 21.78±2.32 21.47±0.76

Ikot Abasi

IK1 04⁰32`32.6`` 007⁰32`51.6`` 101.91±3.24 13.90±1.98 14.96±0.65

IK2 04⁰32`55.7`` 007⁰32`55.3`` 80.31±3.49 13.65±1.76 17.15±0.70

IK3 04⁰32.843` 007⁰32.825` 34.65±2.56 5.12±0.38 4.31±1.15

IK4 04⁰33.692` 007⁰32.568` 77.86±2.93 11.89±1.89 14.97±0.62

IK5 04⁰33`58.3`` 007⁰34`02.2`` 86.06±3.96 17.56±2.12 12.42±0.64

Range 34.65 – 101.91 5.12 – 0.38 4.31 – 17.15

Mean 76.16±3.24 12.42±1.63 12.76±0.75

Uyo

UY1 05⁰02`20.0`` 007⁰58`37.5`` 65.71±3.36 11.24±1.65 17.06±0.72

UY1B 05⁰02`31.0`` 007⁰58`34.8`` 65.24±3.14 10.80±1.96 19.98±o.70

UY3 05⁰02`15.3`` 007⁰58`29.8`` 71.17±3.37 14.36±2.32 20.22±0.72

Range 65.24 – 71.17 10.80 – 14.36 17.06 – 20.22

Mean 67.37±3.29 12.13±1.98 19.09±0.71



Figure 2: Mean activity concentrations for 238U, 232Th and 40K in top soil samples.

CORRELATION STUDIES

In order to find the extent of the existence of these radioactive

nuclides together at a particular place, correlation studies

were performed between the combination of radionuclides

(238U, 232Th), (238U, 40K) and (232Th, 40K) using Microsoft

Office Excel 2007. The Excel was also used to compute the

coefficient of variability, R2 which is a measure of the

proportion of variability in a data set that is accounted for by

a statistical model. Figure 3 A. clearly shows a strong

correlation between the activities of (238U, 232Th) with N = 20

(number of samples in the study areas) and R2 = 0.6076. The

strong correlation between the activities indicates that the

individual result for any one of the radionuclide concentration

in the pair is a good predictor of the concentration of the other

and that the two elements accompanied each other, but in

Figure 3B and C., there is weak correlation between (238U, 40K) and (232Th, 40K) with N = 20 and R2 = 0.0181 and -0.163

respectively.

A.

0

20

40

60

80

100

120

140

160

Eastern Obolo Eket Ibeno Ikot Abasi Uyo

Me

an A

ctiv

ity

Co

nce

ntr

atio

ns

(Bq

kg-1

)

Local Government Areas

K-40

U-238

Th-232

ATh = 0.5047AU + 10R² = 0.6076

0

5

10

15

20

25

30

35

0 10 20 30 40 50

ATh

(Bq

kg-1

)

AU (Bqkg-1)



B.

C.

Figure 3 (A, B, C): Correlation between Activity Concentrations (238U, 232Th), (238U, 40K)

and (232Th,40K) for soil samples from the study areas. Figure 4, shows a strong correlation between the annual

effective dose rate (AEDR Outdoor) and annual effective

dose rate (AEDR Indoor) with N= 20 and R2 = 0.876. This

suggests that in areas of high annual effective dose rate

outdoors, there is also a corresponding high annual effective

dose rate indoors.

Figure 5, shows a weak correlation between external and

internal hazard index with N = 20 and R2 = 0.0017. It

appears in most figures that the number of points is less than

twenty because points having the same activity

concentration/annual effective dose rate/hazard index in

more than one sample (with little difference) coincidence

with each other.

AK = -1.2268AU + 109.64R² = 0.0181

0

50

100

150

200

250

0 5 10 15 20 25 30 35

AK

(Bq

kg-1

)

AU (Bqkg-1)

AK = 1.9579ATh + 50R² = -0.163

0

50

100

150

200

250

0 5 10 15 20 25 30 35

AK

(Bq

kg-1

)

ATh (Bqkg-1)

AEDR Outdoor = 0.1934AEDR Indoor + 0.003R² = 0.876

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 0.05 0.1 0.15 0.2

AED

R O

utd

oo

r (m

Sv)

AEDR Indoor (mSv)



Figure 4: Correlation between annual effective dose rate (outdoor) and

annual effective dose rate (indoor).

Figure 5: Correlation between external hazard index (Hex) and

internal hazard index (Hin).

CONTOUR MAP Global Positioning System receiver Garmin (GPS 12 XL) was

used to record the latitude and longitude of each sample

point. The coordinates of each were converted to degree

decimal unit using CASIO (fx – 991MS) calculator. The

World Geodetic System of 1984 was used for definition of

the coordinate system and it was used to generate the contour

lines. The contour mas of the activity distribution of 238U, 232Th and 40K in the study area are shown in Figures 6 – 8

while the contour map of Radium Equivalent is shown in

Figure 9. In Figures 6 – 8, the numbers on the contour lines

represent the Activity Concentrations of the radionuclide

involved and the intervening spaces are marked with colours

to further highlight the concentrations of these radionuclides.

The higher the number on the contour line, the higher the

concentration of the radionuclide involved. Figure 9 shows

the contour map of Radium Equivalent. From the contour

maps, it is observed that the closer the contour lines the

higher the Activity Concentration/Radium Equivalent. This

could be used in the prediction of Activity

Concentration/Radium Equivalent in the areas outside the

study areas.

Figure 6: Contour diagram for the activity concentration of 238U (Bq.kg-1)

for the collected samples.

Hex = 0.0274Hin + 0.161R² = 0.0017

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.2 0.4 0.6 0.8 1

Hex

(Bq

kg-1

)

Hin (Bqkg-1)



Figure 7: Contour diagram for the activity concentration of 232Th (Bq.kg-1)


Figure 8: Contour diagram for the activity concentration of 40K (Bq.kg-1)




Figure 9: Contour diagram for radium equivalent (Bq.kg-1) for the collected samples.

RISK ASSESSMENT OF 40K, 238U AND 232TH

IN TOP SOIL SAMPLES.

Table 2 shows the absorbed dose rate (D), hazard index

(external, Hex and internal, Hin) (Bq.kg-1), annual effective

dose rate (AEDR) (indoor and outdoor) and radioactivity

level index (Iγ) with their mean values. These mean values are

all below the recommended safety limits. Table 3 lists the

ratio of 238U/232Th activity concentration, the absorbed dose

rate in air surrounded by infinite thickness of soils (D4π), and

radium equivalent, Raeq for top soil samples. The ratio 238U/232Th concentration is less than one in some samples

indicating that uranium is less than thorium, while in some

samples the ratio is greater than one showing that the uranium

concentration is greater than that of thorium. While defining

Raeq activity, it has been assumed that 370 Bq.kg-1, 238U or

259 Bq.kg-1 232Th or 4810 Bq.kg-1 40K produce the same

gamma rate to compare the specific activity of materials

containing different amount of 238U, 232Th and 40K. The mean

radium equivalent, Raeq are 43.51, 40.40, 57.18, 36.54 and

44.61 Bq.kg-1 for Eastern Obolo, Eket, Ibeno, Ikot Abasi and

Uyo L.G.A. respectively. The Ibeno L.G.A. shows an

enrichment of activity due to gas flaring and occasional oil

spillage in the area. Therefore, the radionuclides tend to

accumulate in Ibeno giving rise to highest radium equivalent

activity. Figure 10 shows the radium equivalent activity in

Bq.kg-1 and absorbed dose rate (nGy.h-1) for various L.G.A.

in the study area. Figure 11 shows the surface dose rate, the

annual effective dose, external hazard index and internal

hazard index. The activity concentrations of 238U, 232Th, 40K

and their associated health risk vary in different L.G.A. of the

study area; this is due to industrial activities in these areas.



Table 2: The absorbed dose Rate (D), hazard index

(external, Hex and internal, Hin) (Bq.kg-1), annual effective dose

rate (AEDR) (indoor and outdoor) and radioactivity level index (Iγ),

for various L.G.A. in the study area.

Sample

Code

D

(nGy.h-1)

Hazard Index

Hex Hin

AED (mSv.y-1)

Indoor Outdoor

Iγ

(Bq.kg-1)

EO1 25.30 0.14 0.89 0.12 0.03 1.11

EO2 20.56 0.42 0.15 0.10 0.02 1.02

EO3 17.47 0.10 0.12 0.08 0.02 0.89

EO4 18.74 0.10 0.13 0.09 0.02 1.00

EO5 21.69 0.12 0.14 0.10 0.02 1.47

EO6 18.92 0.11 0.11 0.09 0.02 0.29

Range 18.74-25.30 0.10-0.42 0.11-

0.89

0.09-0.12 0.02-0.03 0.29-1.47

mean 20.45 0.17 0.26 0.10 0.02 0.96

EK1 18.26 0.10 0.13 0.08 0.02 0.47

IB1 39.40 0.23 0.33 0.19 0.04 0.81

IB2 19.28 0.11 0.15 0.09 0.02 0.57

IB3 15.98 0.09 0.12 0.07 0.01 0.61

IB4 33.93 0.20 0.27 0.16 0.04 0.69

IB5 21.38 0.12 0.17 0.10 0.02 0.49

Range 15.98-39.40 0.09-0.23 0.12-

0.33

0.07-0.19 0.01-0.04 0.49-0.81

Mean 25.99 0.15 0.21 0.12 0.03 0.63

IK1 19.96 0.44 0.15 0.09 0.02 0.80

IK2 20.42 0.11 0.15 0.10 0.02 0.67

IK3 6.49 0.03 0.05 0.03 0.01 0.28

IK4 18.04 0.39 0.13 0.08 0.02 0.63

IK5 19.41 0.06 0.16 0.09 0.02 0.74

Range 6.49-20.42 0.03-0.44 0.05-

0.17

0.03-0.10 0.01-0.02 0.28-0.80

Mean 16.86 0.21 0.13 0.08 0.02 0.62

UY1 18.53 0.06 0.14 0.09 0.02 0.55

UY1B 20.12 0.11 0.14 0.09 0.02 0.54

UY3 22.16 0.13 0.17 0.10 0.02 0.62

Range 18.53-22.16 0.06-0.13 0.14-

0.17

0.09-0.10 0.02-0.02 0.54-0.62

Mean 20.27 0.10 0.15 0.09 0.02 0.57



Table 3: The ratio 238U/232Th, total absorbed dose rate (D4π) and

radium equivalent activity in the study area.

Sample code 238U/232Th D4π(10-8Gy.h-1) Raeq(Bq.kg-1)

Eastern Obolo

EO1 0.73 17.36 54.23

EO2 0.85 15.51 43.95

EO3 0.74 13.64 37.30

EO4 0.84 15.16 39.85

EO5 0.53 21.10 45.36

EO6 1.22 9.18 40.37

Range 0.53 – 1.22 9.18 – 21.10 37.30 – 54.23

Mean 0.82 15.33 43.51

Eket

EK1 0.47 8.51 40.40

Ibeno

IB1 1.26 13.62 87.07

IB2 0.84 9.44 41.81

IB3 0.94 9.56 34.64

IB4 0.95 12.24 75.18

IB5 0.93 8.49 47.22

Range 0.84 – 1.26 8.49 – 13.62 34.64 – 87.07

Mean 0.98 10.67 57.18

Ikot Abasi

IK1 0.93 12.56 43.14

IK2 0.80 10.88 44.36

IK3 1.19 4.21 13.95

IK4 0.79 10.19 39.29

IK5 1.41 11.19 41.95

Range 0.79 – 1.49 4.21 – 12.56 13.95 - 44.36

Mean 1.02 9.81 36.54

Uyo

UY1 0.66 9.30 40.70

UY1B 0.54 9.59 44.39

UY3 0.71 10.53 48.75

Range 0.54 – 0.71 9.30 – 10.53 40.70 – 48.75

Mean 0.64 9.81 44.61

Figure 10: Radium equivalent activity (Bq.kg-1) and absorbed dose rate ( nGy.h-1) for various L.G.A. in the study area.

0

10

20

30

40

50

60

70

EasternObolo

Eket Ibeno Ikot Abasi Uyo

Ave

rage

Val

ue

s [R

aeq

(B

qkg

-1);

D (

nG

yh-1

)]


Radium Equivalent

Absorbed Dose Rate



Figure 11: Surface dose rate (mR.h-1), annual effective dose, external

hazard Index and internal hazard index for various L.G.A. in the

study area.

4. CONCLUSION The radioactivity concentrations of 40K, 238U and 232Th in top

soil samples collected from the study areas have been

determined. From this study, the obtained values of gamma

dose rate, radium equivalent activity, radiation hazard index

and annual effective dose equivalent were found to be below

the recommended safety limits. These are indications that the

study area is safe for human activity.

REFERENCES

[1] Scholten, L. C., Timmermans. C. W., 1996. Natural

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