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Re: [Phys-l] XKCD.com

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 Sv/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.