1.
Introduction
The terrestrial sources of radiation
can be divided into those that occur singly and those that are components of
the three chains of radioactive series namely the uranium series, the thorium
series and the actinium series. Among the singly occurring radionuclides
Potassium-40 with half life of 1.3X109 years is the most prominent
one and it is widely distributed in rocks and soil.
Uranium-238
and Thorium-232 and their daughters generate the bulk of natural ionising
radiation in our environment.
Uranium-238 is the head of a series of 15 principal radionuclides . It is the most abundant (99.28%) isotope of
natural uranium and is found in all rocks and soil with varied concentration.
The 238U decays through 234U and 230Th to 226Ra,
which has a relatively long half life of 1628 years. 226Ra and its daughter products
constitute an important part of natural radiation exposure.
The
other major source of terrestrial radiation is 232Th and its decay
products. Thorium-232 is the only long lived radionuclide in its chain and is
widely distributed in rocks and soil in varied concentration.
The
radioactive decay of 40K and radionuclides of 238U and 232Th
series give rise to the terrestrial gamma rays.
In addition to the natural source of radiation
some of the present day technological activities enhance the natural radiation
exposure to human population. The production of electric power through oil and
coal power stations release radio nuclides like Uranium, Thorium and K-40
mailnly due to escape of fly ash.
The coastal Karnataka is witnessing rapid
industrialization and power generation activities by Nuclear as well as Thermal
Power stations which are coming up in the region. There fore it is important to
ensure that the impact of these scientific and industrial endeavors on the
environment are kept minimum and systematic studies are under taken to safe
guard the environment.
This is
the first systematic and comprehensive study in the Udupi District which is the
Coastal District of Karnataka which consists of a number of beautiful
beaches and where a controversial
Thermal Power plant is coming up.
2. Objectives
The main
objective of the present investigations are
- To evaluate the gamma radiation
dose to the population of Udupi district
- To measure the concentrations of 226Ra,
232Th and 40K in soil/sand and
- To calculate the contribution of
cosmic radiation to the radiation dose received by the population
The data on
above aspects would help in establishing a reliable data base on baseline level
of radiation and distribution of different primordial radio nuclides for Udupi
District and would help to understand the dynamics of natural radiation
background of the region. This baseline data would also help in assessing, in
future, the impact of our scientific and technological endeavors on the
environment.
3.Area covered:
Selection of Soil Samples:
·
Udupi District consists of
three taluks namely Coondapur, Udupi and Karkala. Coondapur, Udupi are coastal
taluks while Karkala is hilly contains
granite rocks.
·
Radiation is measured in 60
places in Udupi Taluk, 12 places in Karkala Taluk and Places in Coondalpr taluk.
·
25 soil samples from Udupi
Taluk, 6
soil samples from Karkala Taluk qand 6 soil samples from Coondapur
Tauk were selected . The total extend is about 150 Km. The area
covers sea shores some of them are very famous tourists spots, pilgrimage
centres and hilly regions. The are also
covers the places where major Industries are coming up like Nandikoor near Padubidri
and Brahmavar.
4 Experimental
method:
4.1 Dosi
meter
The gamma exposure rate in
air were measured using a portable gamma level survey meter procured from Nucleonix
Systems (Hyderabad
The
instrument was factory calibrated. The gamma radiation levels were measured at
a height of 1m from the ground level. Several measurements were made in a
single region so as to get a representative reading of gamma radiation level
prevailing in the region. The radiation exposure levels were converted into
absorbed dose in air using appropriate conversion factor (Nambi et al., 1986).
4.2
Sample
processing
All
samples were processed following the standard procedure (EML Procedure Manual,
1983). Soils were well mixed after removing extraneous materials such as roots,
mat portions, pieces of stones and gravel. Samples were weighed and then dried
in an oven at 105°C for 24 h and re-weighed to find the water content. After
mixing thoroughly, the samples were shaken in a sieve shaker and particle sizes
of <250 250="" 30d="" a="" allow="" and="" containers="" factions="" for="" in="" microns="" minimum="" ml="" obtained.="" of="" period="" plastic="" samples="" sealed="" sieved="" stored="" sup="" to="" were="">226
4.3 226Ra, 232Th
and 40K determination
The activities of 226Ra, 232Th
and 40K were determined by gamma spectrometry employing a 41%
relative efficiency n-type low background HPGe detector having a composite
carbon window (Canberra , USA Canberra ,
USA Compton
3. Results and Discussion:
Table 1
Terrestrial
Radio Nuclides Concentration (Bq\Kg) in
the soil of Udupi District and Gamma Dose rate
Place
|
K-40
|
Th-232
|
Ra-226
|
Gamma Dose rate nGy\h
measured directly using gamma dose survy
meter nGy\h
|
Gamma Dose rate calculated from radio
nuclide activities nGy\h
|
1.Kodavoor
|
73.0
|
26±1.0
|
34.9±0.0
|
79
|
35
|
2.Cherkady
|
219.2
|
44.9±1.2
|
26.1±0.9
|
79
|
48
|
3.Kakkunje
|
128.8
|
43.6±1.3
|
42.9±1.1
|
105
|
52
|
4.Karje
|
493.5
|
14.8±0.8
|
6.1±0.7
|
105
|
32
|
5.Kukke Halli
|
108.6
|
24.8±0.9
|
19.7±0.7
|
105
|
29
|
6.Dupadakatte
|
124.5
|
51.7±1.3
|
44.2±1.0
|
88
|
57
|
7.Kemmannu
|
366.5
|
18.9±0.9
|
12.83±0.7
|
96
|
33
|
8.Barhmavar 9.Sugar Factory
|
89.9
|
25.28±0.9
|
29.4±0.8
|
88
|
33
|
10.Kallianpur
|
190.5
|
49.9±1.2
|
54.8±1.1
|
105
|
63
|
11.Pamboor
|
199.5
|
41.3±1.2
|
34.7±0.9
|
114
|
49
|
12.Shivally
|
183.8
|
38.9±1.1
|
55.1±1.1
|
123
|
57
|
13.Nejar
|
194.8
|
51.4±1.3
|
63.5±1.1
|
96
|
69
|
14.Tenkanidiyur
|
222.6
|
26.9±0.9
|
17.9±0.8
|
79
|
34
|
15.Hebri (Near Karje)
|
202.3
|
79.3±1.7
|
48.6±1.2
|
70
|
79
|
16.Yedthady
|
137.0
|
21.3±0.9
|
21.4±0.8
|
114
|
28
|
17.Kukkehalli North
|
119.7
|
28.1±0.9
|
23.0±0.7
|
123
|
33
|
18.Kokkarne
|
72.9
|
29.3±0.8
|
15.1±0.6
|
105
|
28
|
19.Hebri Nisargadama
|
254.1
|
47.2±1.2
|
30.8±0.9
|
105
|
53
|
20.Perampalli
|
92.8
|
40.7±1.2
|
48.9±1.0
|
123
|
51
|
21.Herror
|
105.1
|
27.0±0.8
|
43.5±0.8
|
88
|
41
|
22.Cherkady
|
256.6
|
53.4±1.4
|
26.2±1.0
|
79
|
55
|
23.Malpe Sand
|
231.7
|
2.31±0.5
|
2.6±0.4
|
70
|
12
|
24.Hoode sand
|
84.3
|
88.8±1.6
|
41.1±1.0
|
70
|
76
|
25.Nandikoor
|
171.1
|
6.9±1.6
|
21.8±1.0
|
88
|
21
|
26.Nakre
|
213.9
|
118.9±1.8
|
38.9±1.0
|
114
|
99
|
27.Ajekar
|
323.1
|
166.2±2.2
|
78.0±1.4
|
112
|
150
|
28.Karkala
|
230.6
|
60.9±1.3
|
53.9±1.3
|
114
|
71
|
29.Bailur
|
477.1
|
47.0±1.2
|
33.8±1.0
|
114
|
64
|
30.Nitte
|
190.6
|
37.1±1.1
|
28.4±0.9
|
70
|
43
|
31.
|
57.4
|
1.6±0.6
|
1.2±0.5
|
53
|
40
|
32.
|
155.5
|
62.1±0.3
|
19.7±0.9
|
61
|
53
|
33.Kambadakone
|
127.1±4.9
|
28.8±0.9
|
22.7±0.8
|
79
|
33
|
34.Tallur
|
179.3±5.6
|
48.3±1.1
|
46.9±0.9
|
79
|
38
|
35.Gangolli
|
119.3±4.5
|
18.6±0.8
|
18.6±0.7
|
114
|
25
|
36.Byndoor Hill
|
11.8±2.9
|
14.9±0.8
|
13.8±0.6
|
96
|
16
|
4.4
Natural radionuclides distribution in soil
The natural radionuclides activity in surface soils (0-5cm
depth) of Udupi and Karkala and Kundapur
region are presented in Table 1. Results are presented region wise and range
and mean value for each region as well as the overall range and mean values for
the entire study region are also presented in the table. The activity of 226Ra
is in the range 2.6. to 63.5. Bq kg-1 with a mean value of 30.91Bq
kg-1, 232Th in the range 6.9. to 126 Bq kg-1
with a mean value of 30.19 Bq kg-1 and that of 40K in the
range73 to 493 Bq kg-1 with a
mean value of 180.8. Bq kg-1 in the surface (0-5cm) soils. The results of radioactivity measurement in
sand samples collected from sea shore also showed similar variation as that observed
in soil samples of the region. A comparison of the activities of different
radionuclides observed in the present study with those reported for other
environs showed that the activities of 226Ra, 232Th and 40K
are comparable with those reported for other parts of India
Gamma
absorbed dose rates
The
gamma absorbed dose rates in air measured using the plastic scintillometer,
which includes both terrestrial and cosmic ray components, are presented in
Table 1, column 5. It can be seen that
absorbed dose rates vary from 60… nGy h-1 to 158 nGy h-1,
with a mean value of 91.31. nGy h-1. The dose rates were found to be
more or less uniform in the entire study region with results of individual
locations flucatuating around the mean value of the entire region. The mean
value of dose rates prevailing in south west coast of India is comparable with
the mean values of 80.7 nGy h-1 (Mishra and Sadasivan, 1971) and
88.7 nGy h-1 (Nambi et al.,
1987) reported for different regions of India and also with the mean value 74 nGy
h-1 (Siddappa et al., 1994) reported
for environment of Coastal Karnataka region. The dose rates are also comparable
with the world range (28-120 nGy h-1) and the average value (56 nGy
h-1) reported for normal background areas (UNSCEAR, 1993).
From the results of 226Ra,
232Th and 40K activities in soil (Tables 1) the gamma
dose rates in air were calculated using the dose coefficients (nGy h-1
per Bq kg-1) 0.461, 0.623 and 0.0414 given in UNSCEAR (1993) for 226Ra
sub-series, 232Th series and 40K, respectively and by
assuming secular equilibrium between 238U and 226Ra. It
may be noted that about 98% of the external dose from 238U series is
delivered by 226Ra sub-series. Therefore, the disequilibrium between
226Ra and 238U, if any, does not affect the dose estimation from the concentration of
226Ra. Therefore the dose rates derived from 226Ra are
presented as that of 238U. Further, for a typical radiation field,
the layer of soil which makes the predominant contribution to external gamma
dose above the ground is about 30 cm thick (UNSCEAR, 1977). The results of
these calculations are summarized in Table
(column 5).
{The absorbed dose from 238U
sereis varies in ….. to …. nGy h-1 with a mean value of …… nGy h-1.
The dose rate due to 232Th series varies from ….. to …. nGy h-1
with a mean value of …… nGy h-1. Similarly, the minimum and maximum
values of dose rates due to 40K are, respectively ….. nGy h-1
and …… nGy h-1, the mean value being …… nGy h-1. The dose
delivered by these radionuclides, in total, range from ….. to ….. nGy h-1
with a mean value of 44.4 nGy h-1 (column 2). This mean value of
total absorbed dose rate matches well with the world average value of 44.4 nGy
h-1 reported in UNSCEAR (1988).
The percentage contributions of 238U,
232Th and 40K to the external dose rates in air are given
in column 6-8 of Table 5. The mean values are …… and ……% for 238U, 232Th
and 40K, respectively. Mishra and Sadasivan (1971) have reported
these percentage contribution in the order of 17.7, 33.6 and 48.7 due to 238U,
232Th and 40K, respectively for Indian environs. UNSCEAR
(1982) has reported the world wide average values for the relative
contributions from 238U, 232Th and 40K gamma
dose rates in air to be about 25%, 40% and 35%, respectively. It is interesting
to note that the contribution of 40K to the dose is significantly
less in the region under present investigation.
(This calculation I shall add later)
The correlation between the absorbed
dose rates in air computed from the measured concentrations of 226Ra,
232Th and 40K and that measured directly using the scintillometer
is shown in Table in the column 5. It should be noted that measured dose
rates includes both terrestrial and
cosmic ray components whereas the calculated dose rates shown is purely due to the activities of 226Ra,
232Th and 40K in soil. The correlation indicates that the overall mean cosmic ray
dose rate, shown by the intercept on scintillometer axis, is ……nGy h-1.
This is higher/lower/comparable with the value of 32 nGy h-1
reported in UNSCEAR (1993) as also with the value 31.96 nGy h-1
reported for India at sea level (Nambi et
al., 1986). }
7.0
Conclusions
Gamma
Absorbed Dose rates in Udupi Taluk
Sl No
|
Place
|
Exposure Rate
nGy/h
|
|
1
|
Physics Department
|
123
|
|
2.
|
College Ground
|
105
|
|
3
|
Kallianpur
|
105
|
|
4
|
Near
|
105
|
|
5
|
Doopada Katte(Brahmavar)
|
88
|
|
6
|
Brahmavar( Brahmavar Chemicals)
|
88
|
|
7
|
UppinaKote
|
96
|
|
8
|
Mabukala ( Near River)
|
61
|
|
9
|
Saligrama
|
70
|
|
10
|
79
|
||
11
|
Bannadi
|
79
|
|
12
|
Girike Mata
|
88
|
|
13
|
Saibra Katte
|
96
|
|
14
|
Barkur
|
96
|
|
15
|
Yedthady
|
114
|
|
16
|
Near Mandharthi
|
105
|
|
17
|
Mandharthi
|
96
|
|
18
|
Kadoor
|
88
|
|
19
|
Kokkarne
|
105
|
|
20
|
Sural
|
96
|
|
21
|
Amuje(Karje)
|
70
|
|
22
|
Kannaru(Near Karje)
|
105
|
|
23
|
Petri
|
114
|
|
24
|
Cherkadi
|
79
|
|
25
|
Ammuje (Near Karje)-2
|
70
|
|
26
|
Chantharu
|
88
|
|
27
|
Brahmavar
(Near West Cost Chemicals)
|
105
|
|
28
|
Kolalgiri
|
105
|
|
29
|
Tenkabettu
|
105
|
|
30
|
SubasNagar
|
114
|
|
31
|
Pajaka
|
114
|
|
32
|
Padubelle
|
114
|
|
33
|
Manasa
|
114
|
|
34
|
B.C Road
|
88
|
|
35
|
Manchakkal
|
96
|
|
36
|
Bantakkal
|
88
|
|
37
|
Shankarpura
|
105
|
|
38
|
Katpady
|
105
|
|
39
|
Nittur
|
105
|
|
40
|
Puttur
|
79
|
|
41
|
Kodavur
|
96
|
|
42
|
70
|
||
43
|
61
|
||
44
|
96
|
||
45
|
Tottam
|
88
|
|
46
|
Badanidiyur
|
79
|
|
47
|
Gujjar Bettu
|
70
|
|
48
|
70
|
||
49
|
Kemmannu
|
96
|
|
50
|
Kelarkalabettu
|
96
|
|
51
|
Kaup Light House
|
105
|
|
52
|
79
|
||
53
|
Uchila
|
114
|
|
54
|
Padubidri
|
70
|
|
55
|
Nandikur(Nagarjuna)
|
88
|
|
56
|
Hiriyadka
|
105
|
|
57
|
Athrady
|
114
|
|
58
|
Parkala
|
105
|
|
59
|
Manipal(End Point)
|
105
|
|
60
|
Perampalli
|
123
|
|
Absorbed Dose in Karkala Taluk
Sl No
|
Place
|
Exposure Rate
nGy/h
|
1.
|
Santhoor
|
88
|
2
|
Belman
|
96
|
3
|
Kedinge
|
88
|
4
|
Nitte
|
70
|
5
|
(Miraculous Pond)
|
158
|
6
|
Attur Hill
|
114
|
7
|
Anekere
|
88
|
8
|
Gomateshwara Hill
|
123
|
9
|
Kukkundoor
|
96
|
10
|
Jarkala
|
123
|
11
|
Bailur
|
114
|
12
|
Guddeyangadi
|
114
|
