Very low dose radiation: The Petkau effect. (not good)

[trof]

I've been reading about this all day.
Google it.

From wiki:
"The Petkau effect is an early counterexample to linear-effect assumptions usually made about radiation exposure. It was found by Dr. Abram Petkau at the Atomic Energy of Canada Whiteshell Nuclear Research Establishment, Manitoba and published in Health Physics March 1972.

Petkau had been measuring, in the usual way, the dose that would rupture a particular cell membrane. He found that 3500 rads delivered in 2¼ hours (26 rad/min) would do it. Then, almost by chance, he tried again with much weaker radiation and found that 0.7 rads delivered in 11½ hours (1 millirad/min) would also destroy the membrane. This was counter to the prevailing assumption of a linear relationship between total dose or dose rate and the consequences.<1>

The radiation was of ionising nature, and produced negative oxygen ions. Those ions were more damaging to the membrane in lower concentrations than higher (a somewhat counterintuitive result in itself) because in the latter, they more readily recombine with each other instead of interfering with the membrane. The ion concentration directly correlated with the radiation dose rate and the composition had nonmonotonic consequences."

:-(

[aquart]

1. So we're all going to die?

[Mojeoux]

2. Will any one tell us? nt

[madrchsod]

3. i`d say yes we are..

[trof]

4. Yes. Guaranteed. Absolutely.

:-)

[KT2000]

5. Another example of

the inadequacy of "the dose makes the poison" tenet.

[Yo_Mama]

6. I think you need to look at units

1 rad = 10 millisieverts. 3,500 rads = 35,000 millisieverts or 35 sieverts. The LD50 on sievert dosage (whole body ionizing radiation) is generally quoted to be about 4.5 sieverts. At 8 sieverts survival is not expected; most people will be dead in a week or two.

So, the first dose is a hugely massive dose. Of course it was lethal to the cell. A dose ten times less would be lethal as well.

The second dose - 1 millirad/min = total dosage of 690 millirads. 1 millirad = 10 microsieverts, so total dosage = 6,900 microsieverts or 6.9 millisieverts.

Now, many human beings get that much each year. And many get much more either from natural exposure or from medical exposure or from occupational exposure. There's a lot of radiation in certain foods.

There are places in northern Europe where just about everyone gets considerably more than that in a year. In fact, some human populations get 15-120 millisieverts from natural exposure in a few known "hotspots" such as Kerala and Ransur.
http://www.angelfire.com/mo/radioadaptive/ramsar.html
And many cabin crew and pilots get considerably more than 15 millisieverts annually, because they spend a decent portion of time up in the sky where the atmosphere is thinner and cosmic radiation is stronger.

So obviously there IS a declining relationship between dosages over time and damage to the organism. Of course, if your whole body is exposed to levels such as those tested, most of your cells wouldn't get dosed, would they? So the total damage to all your cells is far, far less than when you expose isolated tissue to a similar dose of direct radiation. This is the reason that you can go out and get sunburned, kill a ton of your skin cells and not get leukemia from the experience. You may get skin cancer later, but you won't get leukemia, because your bone marrow was protected.

But in case you still feel like panicking, you might want to realize that when safety levels for human radiation exposure are set, they calculate the total expected dose over a year. In other words, the level is set using a calculation which assumes that you will be exposed to the same level of radiation every hour every day for an entire year (and in some US cases, that the exposure will continue every year for lifetime).

Or it is set using a total accumulated value.

For example, in the US radiation workers are limited to 50 millisieverts a year and 100 in 5 years (or 20 millisieverts a year). Very few get close to the 20. Studies have shown that US nuclear worker lifespans appear to be longer than those of non-nuclear workers, so it doesn't appear that those dosage levels in our society are correlated with death.

So far, this incident has not changed natural US background radiation. It seems less and less likely every day that it ever possibly could.

And if you still think this is a vast conspiracy, you might want to rethink. Because of the US workers that have a higher exposure to radiation, medical professionals figure largely. So they have a very substantial interest in ensuring that they are not killing themselves, and they do indeed have our minimum exposure levels set at very conservative levels.

When the doctors and nurses who work in radiology and nuclear medicine start worrying, you can start worrying. Until then, it's just going to be a waste of time and the relatively short human life span.