reply to post by Zaphod58
Except is it the dose, or the dose RATE? There is a very important difference. You can be exposed to 36 mRems in one dose, but if your dose
rate every other day stays the same as background, or even a little higher, than your dose rate for the year is going to be about the same as previous
years, and is going to be low. It's only when you get into the really high exposure levels that the dose and dose rate become synonymous.
That is the million dollar question and it is not easy to answer when you consider that such terms as "normal background" and "safe levels" are
The difference being between external radiation sources and internal (to the body) radiation sources. You sit in the sun long enough and you will
shrink because of "radiation". Get too close to a fire and you will get burned by radiation. Heat is radiation. Remove yourself from the source and
the radiation levels decrease. Those two examples are of "non ionizing" radiation. They would not set off a geiger counter.
An (ionizing) source of external radiation would be a "cosmic ray" (from space), an "x-ray" (from the doctor) or a "gamma ray" from the reactors.
These are still from sources outside your body that pass thru it and likely don't hit anything. The latter sources of ionizing radiation are all added
up to indicate what is called "normal background" radiation. But really the term is a misnomer. What is the "normal temperature" on any given day?
Normal rainfall? If you get caught in a flash flood and drown you don't die of "normal rainfall".
So now lets consider dose. All things totaled up and averaged, the external sources of ionizing radiation will subject the "normal" person to an
average back ground of say 30 Counts per minute (CPM). A single "count" or "click" is one "decay event" detected in an "ionization chamber" inside a
detector or geiger "counter".
That is the "dose rate" we all receive every minute of every day of our lives. If you take an airline flight or get a chest x-ray, your dose rate
goes up for that period of time but ends when you get off the flight. People that work at the Fukushima site cleaning up the mess also have to deal
with a dose rate that accumulates and has a "safe limit" for exposure not to exceed. That is accumulative. A person can only take a higher than
background dose for a certain amount of time depending on the exposure dose rate. Once the allowable maximum dose (from any rate) has been reached the
worker leaves the area and the dose rate diminishes to "normal". This is still however from sources of radiation external to the body. The
accumulation of exposure to external radiation sources is the "dose". Again the safe limits are determined by people who average such things based on
experience and documented records of this.
All that crap I just wrote is irrelevant when it comes to "ingested" sources of radioactivity. This material aka., radionuclides, isotopes,
radioactive elements, hot particles, radioactive contamination, fission by products, the stuff that is the source for the clicks and counts that are
detected, takes on a whole new meaning when ingested thru breathing or eating.
You see, all their external "normal back ground" and "allowable safe dose" or "dose rate" is thrown out the window when you actually eat a bit of it.
Now your body is "radioactively contaminated". The source for those emissions (decay events. clicks or counts) is now inside you. There is no way to
walk way from that continuos source. There is no way to decrease the levels that bit of active contamination is emitting. As long as it is in you it
is irradiating nearby cells and that is what gives rise to cancer. Instead of a single (any) ray passing through you and being gone, now the little
x-ray machine is inside you and it can't be turned off. You overall body dose may be low, but right where the cells are being irradiated the dose is
potentially fatal. Once you get cell mutations that might develop into cancer and that is not treated in time.
To sum up. Accumulated dose, dose rate and normal background are not as important to us as ingesting the sources of "ionizing" radiation from
contamination which is a different thing entirely. Detectors don't detect "sources" of radiation, they detect decay events which indicate nearby
sources of radiation. An ingested bit of radioactive contamination might be a "low dose" over all but does considerable damage to cells local to its
Accumulated dose or dose rate mean nothing when comparing it to internal sources of radioactive contamination.
The continuous bombardment of "rays" can deform the cells genetic structure and cause mutations that give rise to cancer, even from one single decay
event or "click".
There is no "safe level" or "low dose" in this regard.
edit on 16-1-2013 by intrptr because: (no reason given)