Terrestrial gamma radionuclides and radon concentration in and around Udupi region

1.    Introduction

1.1 Sources of background radiation

            Human beings constantly and all along are exposed to ionising radiations exiting in nature.  These natural background radiations have both terrestrial and extraterrestrial origin.  The extraterrestrial radiation is largely due to cosmic rays. Earth's atmosphere is continuously bombarded with high energy cosmic rays which originate from our own cosmos.  The primary interaction of high energy cosmic rays with the atmosphere produce numerous secondary radiations in the form of neutrons and protons of various energies which in turn produce a variety of radionuclides through nuclear reactions with nitrogen, oxygen and other nuclei in atmosphere and through other processes.  In addition, sub atomic particles like mesons, muons and electrons are also produced. 

            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.  The radionuclide Rubedium-87 which is another singly occurring radionuclide is of secondary importance.  ⁴⁰K is fairly abundent forming about 0.012% of total K, and is widely distributed in environmental martix.  Moreover, K is an essential element for most life forms.  In addition, ⁴⁰K contributes significantly to gamma radiation in the environment.  No significant fractionation of ⁴⁰K takes place in the environment so that the radioactivity of ⁴⁰K is almost constant  under  all  conditions.  Since the abundance of ⁴⁰K is 0.012%, 1 kg of soil contains about 2.36 mg of radioactive ⁴⁰K.

            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.  About 98% of the external dose from uranium series is delivered by ²²⁶Ra and its daughter products. The ²²⁶Ra is distributed in soil in varying concentration.  Its concentration in soil of normal background region varies from 2.59 Bq kg^-1 to 140.6 Bq kg^-1 covering two orders of magnitude, because of the wide range of soil characteristics.

            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 ²³²Th content of igneous rocks is about four times the uranium content, but since the specific activity of ²³²Th is 2.97 Bq g^-1 compared to 8.92 Bq g^{-1 238}U, the radioactivity due to the two nuclides is nearly 1:1.  The ²³²Th (T_1/2=1.4X10¹⁰ years) decays to ²²⁸Ra (T_1/2 = 5.76 years) by alpha emission.  Radium-228 is a beta emitter and has considerable significance in environmental radioactivity studies.  All the daughters of ²²⁸Ra are short lived.  One of the daughter products ²²⁰Rn, is a radioactive gas.  But it has short half life 55 sec. and therefore the emanation of ²²⁰Rn is significantly less compared to ²²²Rn.

            The radioactive decay of ⁴⁰K and radionuclides of ²³⁸U and ²³²Th series give rise to the terrestrial gamma rays.  The average outdoor terrestrial absorbed dose rate in air from gamma radiation was found to be 44 nGy h^-1 and the relative contribution of ⁴⁰K, ²³⁸U and ²³²Th are about 35%, 25% and 40% respectively (UNSCEAR 1982). There are regions in the world where the out door terrestrial radiation exceed substantially from the normal variability ranges due to the enrichment of certain radioactive minerals leading to the formation of what are known as high background areas. The presence of high background areas have been reported in several countries like China, Iran, Germany, USA, Brazil and India.

1.2 Artificial radionuclides

The open air nuclear weapon tests and operation of nuclear power reactors are the major sources of artificial radionuclides.  Among the several hundred radionuclides produced by nuclear explosions, only ⁹⁰Sr(T_1/2=28.6 years), ¹³⁷Cs(T_1/2=30.2 years) and ¹³¹I((T_1/2=131 days) contribute significantly to human exposure. 

2. Objectives

The research programme envisaged in this project have following objectives:

• 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

3. Results:  

3.1 Dosage  Rates:

                                                 

Udupi Taluk  Table-1

Sl No	Place	Reading
1	Physics Department	14.
2.	College Ground	12
3	Kallianpur	12
4	Near Swarna River	12
5	Doopada Katte(Brahmavar)	10
6	Brahmavar( Brahmavar Chemicals)	10
7	UppinaKote	11
8	Mabukala ( Near River)	8
9	Saligrama	8
10	Kota	8
11	Bannadi	10
12	Girike Mata	11
13	Saibra Katte	12
14	Barkur	10
15	Yedthady	18
16	Near Mandharthi	24
17	Mandharthi	11
18	Kadoor	10
19	Kokkarne	12
20	Sural	12
21	Amuje(Karje)	9
22	Kannaru(Near Karje)	14
23	Petri	13
24	Cherkadi	11

25	Ammuje (Near Karje)-2	9
26	Chantharu	10
27	Brahmavar(Near West Cost Chemicals)	13
28	Kolalgiri	12
29	Tenkabettu	13
30	SubasNagar	13
31	Pajaka	13
32	Padubelle	13
33	Manasa	13
34	B.C Road	10
35	Manchakkal	11
36	Bantakkal	10
37	Shankarpura	12
38	Katpady	12
39	Nittur	12
40	Puttur	8
41	Kodavur	11
42	Malpe Beach	8
43	Malpe Beach(Water)	7
44	Malpe Beach(Road)	11
45	Tottam	10
46	Badanidiyur	9
47	Gujjar Bettu	8
48	Hoode Beach	8
49	Kemmannu		11
50	Kelarkalabettu		11
51	Kaup Light House		12
52	Kaup Highway		9
53	Uchila		13
54	Padubidri		8
55	Nandikur(Nagarjuna)		12,
56	Hiriyadka		12
57	Athrady		13
58	Parkala		12
59	Manipal(End Point)		12
60	Perampalli		14

Dosage Rate --  Karkala Taluk     Table  2

Sl No	Place	Readings
1.	Santhoor	10
2	Belman	11
3	Kedinge	10
4	Nitte	9
5	Attur Church(Miraculous Pond)	16
6	Attur Hill	13
7	Anekere	10
8	Gomateshwara Hill	14
9	Kukkundoor	10
10	Jarkala	14
11	Bailur	13
12	Guddeyangadi	13
13

Dosage Rate in Kundapur Taluk   Table  3

Sl No	Place	Reading
1	Koteshwar	8
2	Kundapur	8
3	Tallur	9
4	Gangolli	13
5	Maravanthe beach	6
6	Marvanthe Temple	13
7	Navunda	8
8	Kambadakone	9
9	Byndoor Hill(Road)	12
10	Byndoor Hill top	11
11	Byndoor Hill Down	10
12.	Anegudde Temple	10
13	Someshwar beach Water	7
14	Someshwar temple	9

3.2:   Radio Nuclides in Soil Samples.

Table    4. Udupi Taluk

Place	K-40	Cs-137	Th-232	Ra-226	Pb-210
1. Kodavoor	21.894±1.22	15.726±0.10	7.759±0.291	10.484±0.272	14.303±1.889
2. Cherkady	65.754±1.98	BD	13.460±0.355	7.837±0.255	5.004±1.89
3.Kakkunje	33.495±1.55	BD	11.334±0.33	12.119±0.28	14.098±2.004
4.Karje	152.97±3.144	1.302±0.11	4.594±0.255	1.882±0.203	17.01±1.83
5.Kukke Halli	35.3±1.50	0.1798±0.108	8.069±0.287	6.39±0.24	6.04±1.707
6.Dupadakatte	37.348±1.62	B.D	15.497±0.38	13.255±0.30	9.477±2.09
7.Kemmannu	109.95±2.54	1.223±0.116	5.668±0.262	3.849±0.211	16.179±1.819
8. Barhmavar Sugar Factory	31.011±1.489	5.437±0.074	8.722±0.300	10.130±0.277	20.590±2.080
9.Kallianpur	57.139±1.920	BD	14.360±0.368	16.450±0.328	14.573±2.16
10.Pamboor	59.840±1.930	BD	12.939±0.354	10.420±0.270	8.620±2.060
11.Shivally	55.147±1.840	0.724±0.131	11.673±0.341	16.54±0.319	20.682±2.17
12.Nejar	58.430±1.960	BD	15.430±0.380	19.060±0.34	22.53±2.44
13. Tenkanidiyur	73.467±2.70	BD	8.879±0.306	5.908±0.248	5.839±1.850
14. Hebri (Near Karje)	61.677±2.540	BD	24.177±0.520	14.830±0.369	13.437±2.870
15. Yedthady	41.780±1.598	BD	6.504±0.270	6.521±0.234	7.201±1.950
16.  Kukkehalli North	43.130±1.697	0.453±0.119	10.115±0.309	8.286±0.260	9.920±0.260
17. Kokkarne	28.050±1.426	2.177±0.127	11.264±0.323	5.819±0.237	30.360±2.060
18.Hebri Nisargadama	80.040±2.190	BD	14.865±0.368	96.850±0.283	10.110±1.970
19. Perampalli	27.833±1.480	3.870±0.167	12.200±0.349	14.666±0.3110	15.090±2.100
20. Herror	39.940±1.590	3.322±0.149	10.250±0.319	16.540±0.319	20.680±2.170
21.Cherkady	82.120±2.510	1.150±0.160	17.100±0.449	8.389±0.311	13.490±2.46
22.Malpe Sand	95.003±2.580	BD	0.950±0.220	1.05±0.180	BD
23. Hoode sand	35.830±1.990	BD	37.730±0.670	17.460±0.420	11.37±3.540
24. Nandikoor	51.330±2.014	BD	2.058±0.479	6.540±0.296	14.530±2.370

Radio Nuclides in Soil Samples of  Karkala Taluk

Table--5

Place	K-40	Cs-137	Th-232	Ra-226	Pb-210
1Nakre	66.30±2.06	BD	36.83±0.548	12.07±0.32	6.18±1.889
2. Ajekar	92.09±2.45	BD	47.36±0.629	22.23±0.39	17.39±3.00
3.Karkala	66.88±2.06	BD	17.67±0.39	15.62±0.39	12.99±2.41
4.Bailur	138.36±2.978	0.534±0.126	13.62±0.36	9.81±0.278	19.10±2.32
5.Nitte	68.13±2.01	1.07±0.121	11.311±0.335	8.657±0.268	9.32±1.86

Radio Nuclides in Soil Samples of  Kundapura Taluk

Table 6

Place	K-40	Cs-137	Th-232	Ra-226	Pb-210	Th-234
1Maravanthe Beach	22.38±1.49	BD	0.622 ±0.218	13.52±2.25	BD
2. Byndoor  Beach	55.07±1.99	BD	1.378±0.218	1.047±2.07	4.88±1.51
3.Kambadakone	41.945±1.61	BD	0.280±0.105	9.519±0.308	7.54±0.25	8.58±1.83
4.Tallur	62.78±1.97	BD	16.89±0.394	16.43±0.329	BD	17.58±2.41
5.Gangolli	41.76±1.59	BD	6.503±0.27	6.521±0.234	7.20±1.95	6.44±1.78
6Byndoor Hill	3.85±1.00	B.D	5.069±0.259	4.678±0.211	7.017±1.51	5.508±1.36

5. Analysis and conclusions:

We can see from Table1, Table 2 and Table 3 that average dosage rate people receive is quite normal. Only at Yedthady , Mandarthi and miraculous pond of Attur church the activity slightly high but at normal rate. The higher activity could be due to the presence of thorium  in the granite. Dosage rate at the beaches of Udupi district is quite low compared to hilly reagion. So there is no posibility of thorium content like Kerala or Ullal beach. ( Siddappa et all )

Table 4, Table 5 and Table 6 show that Radio Nuclide K-40 is present in all the soil samples in good amount and this radio nuclede is the main source which contributes for the sose rate that the people of udupi district receive. The value is quite high in Kemmannu and Karje area.

  The isotope cs-137 is present in very small quantity and almost BD in all the soils. Hence the contribution of this nuclide is negligible in the Udupi district.

The Radio isotopes Th-232, Ra-226, and Pb-210 are present in all the soil samples in a small quantity.