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Tuesday, August 19, 2014

WE LIVE IN NATURALLY RADIOACTIVE WORLD

We are exposed to radiation from the sun and outer space, also from the naturally occurring radioactive materials present in the earth, the house we live in, the buildings where we work, the food and drink we consume.

Where we live in
The houses are made up of materials which contain radioactivity. Gamma radiation from walls, floor & ceiling, and Radon and Thoron progeny are major sources of radiation exposure. Especially in closed rooms, Radon is the significant dose contributing factor.

Natural Radioactivity (Bq.Kg-1) in Building Materials used in India
Material
Type of Radioactive isotope
K-40
Ra-226
Th-232
Cement
5-385
16-377
8-78
Brick
130-1390
21-48
26-126
Stone
48-1479
6-155
5-412
Sand
5-1074
1-5047
4-2971
Granite
76-1380
4-98
103-240
Clay
6-477
7-1621
4-311
Fly Ash
6-522
7-670
30-159
Lime stone
6-518
1-26
1-33
Gypsum
70-807
7-807
1-152

We are always in natural background radiation*
Cosmic-from the sun and outer space – 0.4mSv.Yr-1
Terrestrial – from the earth’s crust – 0.5mSv.yr-1
Radon – from decay of Uranium/radium – 1.2mSv.yr-1
Internal sources in the body(eg:  40K)  --- 0.3mSv.yr-1

Total Dose from Natural Sources: ----2.4 mSv.Yr-1

What we drink
Radioactivity in milk  is over 200 times more than in drinking water and 3 times that in beer. 

From a cup of milk , 180 beta particles of Ptassium-40 are emitted per minute

From a cup of tea, 91 beta particles of Potassium-40 are emittd per minute from tea leaves(excluding milk and water)

What we eat

Food stuff
K-40 (Bq.Kg-1)
Rice
40-90
Leafy vegetables
80-220
Brinjal
90-140
Carrot
60-120
Beetroot
90-120


Radiation Doses from Cosmic Rays

Distance above Ground
Dose Rate in ┬ÁSv. h-1
~ 15 Km above ground
10
~ 10 Km above ground
5
~ 8 Km above ground
2
~ 2 Km above ground
0.1
Sea Level
0.03

Courtesy: Radiation Safety, IAEA (1996), NRPB, UK