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 Post subject: Re: Is LNT model dead?Posted: Oct 27, 2015 12:36 am

Joined: Jun 05, 2011 6:59 pm
Posts: 1332
Location: NoOPWA
Cyril R wrote:
KitemanSA wrote:
I think the actual values are 100mSv acute and ~25µSv/h.
This leads me to support the LED model wherein the effective dose is the integration of any dose in excess of 12.5µSv/h and that effective dose that exceeds 50mSv is put into the LNT equation for ERR.
Very interesting figures, thanks Kite.

What is the basis for these numbers? 25µSv/h is 0.6 mSv/day, much lower than the experiments I've seen. The lowest radiation beagle dogs were 3 mSv/day, no increase in cancer but a 5% reduction in life expectancy. Below 3 mSv/day there is little experimental data.

Where does the 12.5 µSv/h come from? Is it just a safety factor of 2 thing?

Also is there really proof that 50 mSv or 100 mSv prompt dose has no real bad health effects? I mean, if a million people each received a medical scan of 100 mSv worth, surely there would be some detectable health effect?

I'd be fine with a population risk model that ignores the first 25 µSv/h and treats everything over cumulatively a la LNT. That would solve the biggest concern I have with LNT, the overexaggeration of health effects of tiny doses at low dose rates, over large populations.
Well, if you can convince folks of 25µSv/h, I won't argue. 25µSv/h is about the maximum natual background radiation found in an inhabited area, Ramsar. However, assuming that the hormesis function in the beneficial range is about symmetric, then the maximum benefit would be at about 1/2 that and anything beyond that would start to loose benefit. So I like ~12.5µSv/hr.

There is no data I am aware of that shows damage below 100mSv acute. So again, as a degree of conservatism, I support 50mSv acute (i.e., cummulative above the 12.5µSv/h).

The main point though is that it become "unreasonable" to expende resources to reduce the groundshine below 12.5µSv/h. That limits ALARA.

_________________
DRJ : Engineer - NAVSEA : (Retired)

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 Post subject: Re: Is LNT model dead?Posted: Oct 27, 2015 7:49 am

Joined: Jul 14, 2008 3:12 pm
Posts: 5058
Quote:
25µSv/h is about the maximum natual background radiation found in an inhabited area, Ramsar. However, assuming that the hormesis function in the beneficial range is about symmetric, then the maximum benefit would be at about 1/2 that and anything beyond that would start to loose benefit. So I like ~12.5µSv/hr.

From what I've read, going by animal experiments, the hormesis peak is actually higher than that, more like 50 µSv/hr or greater even. Hourly limits may be too high a resolution anyway.

I think a 1 mSv/day is a reasonable regulatory limit below which no action is needed, then something like >10 mSv/day is immediate evacuation or other serious measures, in between 1 and 10 mSv/day there would be a grey area where no evacuation is needed but some kind of economic compensation (\$/mSv) would be in order. I'm not a big fan of ALARA. It is unreasonable to devise unclear and ambiguous regulations, therefore ALARA is unreasonable and an oxymoron.

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 Post subject: Re: Is LNT model dead?Posted: Oct 28, 2015 2:22 am

Joined: Jun 05, 2011 6:59 pm
Posts: 1332
Location: NoOPWA
Cyril R wrote:
From what I've read, going by animal experiments, the hormesis peak is actually higher than that, more like 50 µSv/hr or greater even. Hourly limits may be too high a resolution anyway.

I think a 1 mSv/day is a reasonable regulatory limit below which no action is needed, then something like >10 mSv/day is immediate evacuation or other serious measures, in between 1 and 10 mSv/day there would be a grey area where no evacuation is needed but some kind of economic compensation (\$/mSv) would be in order. I'm not a big fan of ALARA. It is unreasonable to devise unclear and ambiguous regulations, therefore ALARA is unreasonable and an oxymoron.
Well, the IAEA uses 25µSv/h as the level at which it is about equally hazardous to evacuate or stay. And that level seems to require very little evacuation. Also, stopping clean-up at 12.5µSv/h seems reasonable.

By the way, did you mean hormesis PEAK or crossover? That value seems a bit high for the peak.

_________________
DRJ : Engineer - NAVSEA : (Retired)

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 Post subject: Re: Is LNT model dead?Posted: Oct 28, 2015 9:13 am

Joined: Jul 14, 2008 3:12 pm
Posts: 5058
Quote:
Well, the IAEA uses 25µSv/h as the level at which it is about equally hazardous to evacuate or stay.

Surely a major organization such as the IAEA is obliged to use the "consensus" LNT for such risk assessments?

Also evacuation is a lot more damaging than most people think, especially when you consider the long term mental trauma and second order effects (economic, health care etc.) from that.

Quote:
By the way, did you mean hormesis PEAK or crossover? That value seems a bit high for the peak.

Crossover to average global background levels or radiation as reference point. There is actually not that much data to suggest a hard peak, there seems more data for the crossover. The 125 microsieverts/hour that the lowest irradiated beagle dogs got was slightly too much, no increase in cancer but a slight reduction in life expectancy. So 125 is very probably beyond the crossover point, but not too much.

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 Post subject: Re: Is LNT model dead?Posted: Oct 30, 2015 5:50 am

Joined: Sep 02, 2009 10:24 am
Posts: 509
Here's a story of some people who "don't believe the LNT model".
http://www.theguardian.com/world/2015/o ... usion-zone

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