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On Mar 22, 2011, at 12:43 PM, Bernard Cleyet wrote:
On 2011, Mar 21, , at 22:03, Aburr@aol.com wrote:
It is not wheather I agree or not, it is what is the currently
accepted
definition
Alex. F. Burr
Calling an elephant a tiger doesn't make it so, I agree w/ L.K.
bc
Below is a brief summary; feel free to use it in any way you wish.
Suggestions for improving the summary would be appreciated. Thank you
in advance.
Ludwik
==================
How harmful is nuclear radiation? It depends on the dose received. The
dose density, expressed in terms of energy absorbed per unit mass of
tissue, J/kg, is called Sievert. That unit is often used to
characterize the level of radiation at a given location. Suppose an
instrument reading is 3 Sv/hr, which amounts to 50 mSv/min. What is
the dose received by on organ, in 5 hours, if its mase is 2 kg? The
dose density, accumulated in fife hours, would be 3*5=15 J/kg and the
dose would be 15*2=30 Joules. Some dosimeters display rates at which
dose density would be growing in a given location. Radiation workers
carry personal dosimeters displaying the accumulated dose density
(from time zero to the moment of reading).
Tsunami-related Fukushina accident will probably renew debates about
nuclear electricity. Such debates should be based on what is known
about negative effects of nuclear radiation. Numerical data below,
expressed in Sv and mSv, should be useful in that context. The older
unit, rem, is also in use (1Sv=100 rem)
The accumulated dose density 10 Sv will most likely results in death.
5 Sv would kill about 50% of exposed people or animals.
2 Sv can also be fatal, especially without prompt treatment.
0.25 Sv = 250 mSv is the limit for emergency workers in life-saving
operations.
0.10 Sv = 100 mSv dose is clearly linked to later cancer risks.
0.05 Sv = 50 mSv is the yearly limit for radiation workers.
0.004 Sv= 4 mSv typical yearly dose due to natural radiation (cosmic
rays, etc).
0.003 Sv= 3 mSV typical dose from mammogram
The dose density, accumulated per day, due to Fukushima accident, at a
distance of 30 miles from the damaged reactors, was reported (on 3/16
and 3/17) as 0.0036 mSv. I do not have data on dose densities,
probably very large, received by those who worked near or inside
reactors. But I have no doubt that each of them was carrying an
individual dosimeter. No deaths due to radiation have been reported in
Japan, as far as I know. Many lives, however, were lost in Chernobyl,
by those who worked to minimize damage.
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