Sunday, March 13, 2011

Japan - Danger to the Public

According to Japanese authorities the radiation level near the exploded
reactor 1 could be described by an equivalent dose of 50 µSv (micro-
which is generally regarded as rather harmless. In comparison
with a value of 50 mSv per year which is the German standard limit for
occupational exposure to ionizing radiation, that measured value can be
interpreted as follows:
50 mSv or 50.000 µSv per year is equal to 50.000 : 200 = 250 µSv per
day (on 200 days of work!) or 250 : 24 = 10,4 µSv per hour.

Therefore, one might hold the measured 50 µSv to be an acceptable
dose under the present circumstances of an exploded reactor.

Yet, it should be stressed that the equivalent dose H is by definition
including a factor q intended to weigh the influence of the kind of
X-rays, alpha-, beta- or gamma radiation with different wavelength
or energy ( short wavelength means high energy ).

equivalent dose: H = q x D with D = energy dose [J/kg] and q = "1"
(usual setting for the weighting factor)

Now, the relative biological effectiveness (RBE) of radiation is known
to differ in a range of about one order of magnitude depending of
her energy. That leads to the necessity of determination what kind
of radiation is present and refixing of the weighting factor q. A study
made at the German university of Marburg has come to the conclusion
that the standard weighting factor of one has to be reduced at least
by a factor of 50-60. Same goes for the standard equivalent dose
which must be reduced equally from 50 mSv per year to 1 mSv for
occupational exposure. For public exposure a reduction from 1 mSv
per year to 0,02 mSv per year has to be considered.

The proposed limit of 0,02 mSv per year for public exposure is equivalent
to 20 µSv per year. Now compare these " 20 µSv per year " to the 50 µSv
measured at the Japanese power plant at "time zero" after the explosion !

As we can assume that a broad variety of isotopes is leaving a broken
reactor, and that such isotopes are falling apart by emitting different
kinds of radiation, the real long-term danger to the public cannot be
predicted. The measured isotopes of 137-Caesium for example are
decaying by emission of some kind of beta-radiation that is usually
regarded as especially harmful to human tissue.

By the way, many years ago I had been in charge of radiation security
for my working group which includes a special preparation course to be
finished with an examination. Such are the requirements in my country.
Therefore, you can believe that I still know what I am talking about.

Next are the evening news of NHK World, Tokyo,
recorded on March 13, 2011, 18:00 GMT:

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