21 November 2010

Reminder !!


Important follow up to my previous postings about this issue.

Biological effects of low doses of ionizing radiation: A fuller picture

The two latest reports of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) provide a comprehensive overview of current knowledge

effects of low level radiation does not exist and will probably not be obtainable for a long time. Obtaining unequivocal evidence would require ...

Also, from the report:

Radiation Doses
The term radiation means energy propagating in the form of electromagnetic
waves or photons, or in the form of subatomic particles. Ionizing
radiation is radiation of sufficiently high energy to cause — in the medium
through which it passes — the production of pairs of ions, i.e. of atoms or
groups of atoms that have either lost or gained one or more electrons to
become positively or negatively charged, and the corresponding complementary
electrons. For biological effects, the medium in which ion pairs are
produced is biological material, more specifically cellular material.
The term radiation (absorbed) dose generally means the amount of
energy which is absorbed from ionizing radiation by a unit mass of material.
This quantity is expressed in unit energy per unit mass, that is in joules per
kilogram, which takes the special name gray (Gy); [1 Gy = 1000 milligray
(mGy)]. For radiation protection purposes, the absorbed dose is weighted to
take account of the effectiveness of different radiation types and the radiosensitivity
of various organs and tissues. The resulting quantity is termed
effective dose, and its unit sievert (Sv) [ISv = 1000 millisievert (mSv)]; for
photons in the intermediate energy range, 1 mGy is approximately equal to
1 mSv.
The term low radiation dose is used to mean a radiation dose lower than
designated levels; sometimes it is also informally used to mean a low dose
rate, i.e. low dose per unit time. In specialized radiobiological forums, low
radiation dose (and dose rate) refers to exposures for which it is very unlikely
that more than one event of energy absorption from radiation will occur in
the critical parts of a cell (and damage it) within the time during which repair
mechanisms in the cell can operate. Thus, UNSCEAR concluded that low
radiation dose refers to a total dose of less than 200 mSv and dose rates below
, 0.1 mSv per minute (which in fact is a very high dose rate of around 5000
mSv per annum).
For the non-specialized public, low radiation doses are deemed to
correspond to levels similar to those from, for instance, natural background
exposure or some very common radiation exposures such as those arising
during air travel. Natural background exposure varies widely around the
world. Some "normal" [and "elevated"] values of annual dose rates are as
follows: for cosmic rays, 0.38 mSv [2.0 mSv]; for terrestrial radiation 0.43
mSv [4.3 mSv]; and for exposure to radon, 1.2 mSv [10 mSv]; leading to an
average total of around 2.4 mSv per annum. The average annual dose for
very frequent flyers (such as aircrew) is around 2.5 mSv. These dose rate
levels of a few mSv per annum are expected to deliver, during a lifetime,
doses of above around 100 mSv, which are of the order 
of magnitude of the low radiation doses designated by UNSCEAR."

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