Background radiation and radioactivity in India

                                                                      May 5, 2011

Background radiation and radioactivity in India

We live in a sea of radiation. In any city, an unsuspecting owner of a 0.1 acre backyard garden may not know that the top one metre of soil from his garden contains 11,200 kg of potassium, 1.28 kg which is of potassium- 40 (K-40, a radioactive isotope of potassium), 3.6 kg of thorium and one kg of uranium.

These values may be higher or lower depending on the soil. Uranium and thorium decay through several radio-nuclides to lead, a stable element. The presence of radioactive nuclides does not pose any significant risk.

Total dose

The total annual external dose from sources in soil and cosmic rays in Mumbai, Kolkata, Chennai, Delhi and Bengaluru is 0.484, 0.81, 0.79, 0.70 and 0.825 milligray respectively. Gray is a unit for absorbed dose; when the radiation energy imparted to a kg of material is one joule, it is called a gray. Since gray is very large, milligray (one thousandth of a gray), and microgray (one millionth of a gray), are commonly used.

Cosmic rays come from outer space. Their intensity at a place depends on the altitude. Cosmic rays alone contribute 0.28 milligray at the first three cities as they are at sea level; the column of air helps to reduce their intensity. At high altitudes, the protection from the column of air is less.

The cosmic ray contributions are higher at 0.31 milligray and 0.44 milligray respectively at Delhi and Bengaluru as these cities are at altitudes of 216 metre and 921 metre. Air passengers receive 5 microgray per hour from cosmic rays.

Parts of Kerala and Tamil Nadu are high background radiation areas (HBRA) because of the presence of large quantities of monazite in the soil. Thorium content in monazite ranges from 8-10.5 per cent. Researchers found that the radiation levels in 12 Panchayats in Karunagappally varied between 0.32 to 76 milligrays per year; the levels in 90 per cent of over 71,000 houses were more than one milligray per year.

The average value of population dose in HBRA is 3.8 milligray per year. One milligray is the average value for areas of normal background radiation. The units milligray and millisievert are the same in these instances. Study at the HBRA during 1990-99 by the researchers from the Regional Cancer Centre and Bhabha Atomic Research Centre did not show any health effect attributable to radiation.

Radon, which occurs in uranium series present in soil seeps into homes. In temperate areas radon decay products build up in air due to poor ventilation and deliver high doses to the lungs of millions of people. In tropics ventilation is adequate to disperse radon .In the United Kingdom persons in 5 per cent of the homes are exposed to doses above 23.7 mSv/year. One per cent of the population receives doses above 55.8 mSv/year. The highest estimated dose was 320 mSv/year in Cornwall.

All foodstuffs contain potassium-40 (K-40). We need potassium for sustenance. K-40 is 0.012 per cent of potassium. Once ingested, most of the potassium enters the blood stream directly and gets distributed to all tissues and organs.

Homeostatic control

The potassium content in the human body is strictly under homeostatic control. The body retains only the amounts in the normal range essential for its functioning; it is independent of the variations in the environmental levels.

The body excretes excess amounts with a biological half life of 30 days. K-40 delivers a constant annual radiation dose of 0.18 mSv to soft tissue. This dose is unavoidable as potassium is an essential element. Every time we eat a banana, we are introducing 14 Bq of K-40 in to our body. Trucks containing bananas have triggered radiation alarms at border posts in the U.S.

Brazil nut

Brazil nut is probably the most radioactive food. Scientists have measured 700Bq of radium per kg of Brazil nut.

The roots of the Brazil nut tree pass through acres of land; They have a tendency to concentrate barium; along with barium, the roots collect radium as well. Radium appears in the nuts. Many vegetables like brinjal, carrot etc. also contain the radioactive isotope.

Indian researchers have measured polonium-210 in fish and other marine organisms. Our whole body is hit by particles coming from all sides. Radiation is a part of our life. We cannot avoid eating food just because it contains radioactivity

(Raja Ramanna fellow, Department of Atomic Energy)

ksparth@yahoo.co.uk

Keywords: radio activity, potassium, radiation in food

How safe is Madras Atomic Power Station?

South Asians Against Nukes (SAAN) , a Non Governmental Organization has claimed that the radiation levels are high in regions around the Madras Atomic Power Station. They measured the levels by using their own gamma monitor. The results indicate either that they were measuring the widely varying background radiation levels because of the presence of thorium in the soil or they wee using a defective instrument. Since they obtained abnormally high values, there instrument must have been defective!

The author had similar experience when another NGO claimed that the background radiation levels in Lucknow was very high. It turned out that the instrument they used was light sensitive!

K.S.Parthasarathy





How safe is Madras Atomic Power Station?







Within threshold: The releases from the Madras Atomic Power Station have not exceeded the limits prescribed by the regulatory agency.


Background radiation level at any place depends mainly on terrestrial radiation from natural radionuclides such as uranium, thorium and their decay products and potassium-40 present in soil and on cosmic rays (radiation from outer space).
The top one metre soil in a land of area 0.1 acre anywhere in the country may contain 1.28 kg of potassium-40, 3.6 kg of thorium and one kg of uranium.
The soil factor
In different soils these values may be higher or lower. The dose due to natural radiation varies from place to place.
The releases from the Madras Atomic Power Station (MAPS) have not exceeded the limits prescribed by the regulatory agency. The data collected from 1982 to date by the Environmental Survey Laboratory (ESL) at MAPS do not indicate high increases in radiation levels. Nuclear Power Corporation Limited should invite students and public to the ESL to reassure them. BARC scientists have measured outdoor natural gamma radiation levels at 214 locations in different parts of India continuously over a year by using special dosimeters and got an average annual value of 775 microgray.
They got the highest value of 26730 microgray at Chavara, Kerala. (Gray is a unit of radiation dose.
Energy absorbed
When the dose is one gray, the energy from ionizing radiation absorbed is one joule per kg; since gray is a big unit, submutiples such as milli-one thousandth or micro -one millionth-of a gray are usually used).
Using the geological data on the types of rocks and the abundance of uranium, thorium and potassium in these rocks, BARC scientists prepared a radiation map of the country in 1986.
The natural background radiation doses at Mumbai, Kolkata, Chennai and Bangalore are 484, 810, 790 and 825 microgray per year respectively.
The annual cosmic ray dose itself varies from 280 microgray in Chennai to 440 microgray in Bangalore which is 921 metres above the sea level.
Variation of a few hundred microgray is not unusual.
What is the extra contribution, if any, to radiation dose made by a nuclear power station at its fence post?
Data from 1982 to 2007 indicate that for the MAPS, the lowest extra dose was 7.2 microsievert per year and the highest 86.3 microsievert per year. (Sievert — Sv — is another unit. For all practical purposes, background radiation expressed in sievert or gray may be considered numerically equal). These are much less than the AERB limit of 1,000 microsievert.
The status is similar in other power stations.
Activity can escape only if several barriers (ceramic fuel, its cladding, coolant, coolant tube etc) are broken. These are of proven quality. Fail safe devices including redundant and diverse safety systems ensure that such uncontrolled releases do not happen.
In April 1994, an “environmentalist” measured high radiation levels at the MLAs’ hostel and other locations in Lucknow. “Radiation levels at some points are higher than those at Chernobyl,” he claimed. Many newspapers published the story.
Recorded normal
A team of scientists sent by the Atomic Energy Regulatory Board (AERB) found that his Geiger-Mueller counter —based instrument was defective. It was light sensitive. When the detector was made light-proof, the radiation levels recorded normal!
In 2005, Padmanabhan and Nakul of the South Asians Against Nukes (SAAN) claimed that while monitoring radiation levels around the Madras Atomic Power Station in places such as Coimbatore, Chenglepet, Mahabalipuram and Kalpakkam they came across several spots with gamma radiation levels as high as a few millisievert to above ten millisieverts per year. The highest level measured was 54.5 millisieverts.
The speculation
They speculated that the wide variations between the readings taken from the same spot indicated that the source of radiation is not on the ground but are “picoparticles” from uranium fission floating and flying in air! There are simpler explanations.
If they were using a defect-free instrument, they were recording radiation from thorium rich soil in the region. This is nothing unusual.
Since over 70 per cent of their readings were above 2mSv, I believe that they were experiencing the problem faced by the “environmentalist” in Lucknow!
K.S.PARTHASARATHY
Former Secretary, AERB
( ksparth@yahoo.co.uk )
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