PJLindsey said:

What always got me chuckling was the dental asst placing a lead shot apron over me before a dental xray. Exactly how much shielding does that apron really provide? The only reason I can see is that it makes the patient feel protected.

You’re thinking of gamma rays which are usually, but not always, far more energetic and penetrating than dental x-rays.

The half-value layer for a 100 kV x-ray tube(which generates a spectrum of x-rays, with no x-rays above 100 keV) is ~0.3 mm in lead.

        Carl Willis said:

The model may be inaccurate at low doses, but has not been found to be so. The LNT model may be accurate at low doses because it has been found to be accurate at higher doses, and human epidemiological data continues to support it well (par. 539)

-Carl

That simply is not so. There is a large amount odata from Chernobyl where the 250,000 deaths predicted by LNT failed to happen, to the Cohen study showing a negative correlation with radon to the Taiwan apartments which saw a 97% reduction in cancers to the undisputable fact that natural background radiation is & always has been far higher in some parts of the world (eg Kerala, India where it is 17 times the safe limit) with no observed ill effects. See http://a-place-to-stand.blogspot.com/2010/03/low-level-radiation-evidence-that-it-is.html for these & others.

By comparison can you produce any evidence for LNT at low levels, produced before or indeed after it was accepted as “science”?

LNT extrapolators: How do you think vaccines work?

It doesn’t appear that you understand what is being objected to in the criticisms being leveled against how LNT is used, or even to recognize that there is is a problem and that it extends beyond the rightness or wrongness of the LNT hypothesis or my personal opinions of it. Nor have you attempted to address them except with restatements of the positions that the regulators have taken on the matter.

As for who to trust and not to trust, in this and every other topic it is best to recognize that we’re dealing with a spectrum of trust, among other things – trusting anyone to trusting no one. Credulity to cynicism. But not to indulge in reflexive centrism, but to find the healthiest point in this spectrum which is somewhere between the two ends. This being the case, it is pertinent to question even professional scientists to some extent and examine the rationale behind their positions, but never to accept or reject purely on the bases of presumed authority, what now you seem to be suggesting we do.

Given this, it is impossible to have a productive discussion with you, and now it seems you were never interested in having one.

The rest of the discussion is going in circles now.

To clarify my background: When I write something here, I speak for myself and don’t presume to speak for anyone else. I am a nuclear engineer for a particle accelerator company in New Mexico. A small ancillary duty is to manage the radiation safety program for that company, but that is neither a duty I aspired to nor was originally hired to carry out. I don’t find that occasional work to involve ideological indoctrination, subversion, or conspiracy to sap and impurify my precious bodily fluids. I am completing my doctorate in nuclear engineering at Ohio State. Relating to radiobiology, I have authored a couple little publications on mixed-field dosimetry for clonogenic assays and some of my academic research focus has been on boron-neutron capture therapy, but I don’t consider that background to be “expertise” in the context of the LNT controversy as compared to, say, the expertise at UNSCEAR or the NCRP or the French Academy of Sciences or Eric J. Hall. I advocate a high level of trust for professional scientists, especially from those whose expertise does not compare. Attempting to pawn off expert findings as being politically motivated, without direct and compelling evidence, is symptomatic of a broad constellation of anti-science superstition (anti-evolution, anti-climate-change, anti-vaccination, and so on). I see suspect language in that direction, and lots of misinterpretations, in this thread. I have done what I can to add the appropriate degree of balance, and I appreciate the opportunity.

That’s it from me.

-Carl

        Carl Willis said:

On the contrary it is the analysis that we do dispute.

We? I read this to mean that you, “DV82XL” (whom I presume is a single individual), dispute the analysis (of UNSCEAR, NCRP, etc.) That’s your right. However, there’s ample evidence that you misunderstand that analysis, or simply and inexplicably discount it in favor of less-comprehensive and / or outlying sources. For instance, what is the source of this comment?

the human epidemiological data [...] shows evidence of some sort of radiobiological hormesis.

The comprehensive expert analysis (e.g. UNSCEAR) do not ignore evidence of hormesis or threshold responses. Such evidence is weighed and considered on its merits, along with much other data.

Carl, I made a point of linking to a list of papers supporting the hormesis hypothesis, and specifically to a report by France’s Académie des Sciences — Académie nationale de Médecine up thread, that would be considered source in any academic context that I can think of.

I did not write the lead article in this section, nor are the other people commenting here with me in agreement with him sockpuppets of mine, so your attempt to try and isolate me as a lone voice against LNT fails on that alone, and there are many others out there that also feel this has gone too far.

Objectors to LNT know what the party-line is Carl, the point is that there is a great suspicion that is is overly conservative due to political considerations, that is at the core of this debate. If you, or anyone else think,s this UN committee is any different from any other in that organization in that it is not motivated by the politics of its members more than by fact, I have some penny stock in a company that can make cars run on tap water you might be interested in.

Well I don’t know what you call support in this context, but it seems to me like your ’scientific literacy crusade’ looks very much like support of the status quo, and the fact that you are a RSO is at the very least a potential conflict of interest in this debate, which you might have cleared up earlier on.

At any rate the debate here should not be on the LNT as a hypothesis, I have tried to make this clear in several comments I have made up thread, only how it is used in the making of policy, and by the antinuclear movement. It is only in those contexts that LNT is misapplied

On the contrary it is the analysis that we do dispute.

We? I read this to mean that you, “DV82XL” (whom I presume is a single individual), dispute the analysis (of UNSCEAR, NCRP, etc.) That’s your right. However, there’s ample evidence that you misunderstand that analysis, or simply and inexplicably discount it in favor of less-comprehensive and / or outlying sources. For instance, what is the source of this comment?

the human epidemiological data [...] shows evidence of some sort of radiobiological hormesis.

The comprehensive expert analyses (e.g. UNSCEAR) do not ignore evidence of hormesis or threshold responses. Such evidence is weighed and considered on its merits, along with much other data. For some narrow situations threshold models are more accepted (e.g. risk of bone cancers from internal exposure to radium). My intention is to make sure that other readers understand that the comprehensive, mainstream, expert scientific analyses do look at the range of evidence, and on the basis of all of it, do not endorse hormesis or any threshold model of radiation risk as pertains to the general issue of external whole-body radiation exposure. Data and its analysis can be found in may places, but the logical places to start looking at these things are the broad, general, overviews of the field. I mentioned the major radiobiology textbook previously; also, Appendix G (“Biological Effects at Low Radiation Doses”) of UNSCEAR 2000 may be downloaded here:

http://www.unscear.org/docs/reports/annexg.pdf

Well there is the other shoe down, isn’t it Carl? That’s fine, you have to apply the regulations as they are written, but that does not make them right.

Huh? I personally have not made any comment endorsing or opposing the regulations, or opining in any way on whether or not they are “right.” I could offer opinion and join the endless windbaggery, but I try not to. I’m on a little scientific literacy crusade, because on the basis of just a few comments above, I perceive some shortcomings in that department. That’s all.

-Carl

        drbuzz0 said:

Of course this is not for radiation protection. They were showing the system at its extreme and the purpose is to avoid radar and make most surface to air weapons useless.

Most SAM’s are not designed or programmed to go after a target that low and won’t be able to track it from ground clutter.

Of course, if there was a low level threat to be avoided, the final shot showed the aircraft swing the wings all the way back, light the afterburners and take off at a steep angle up.

Thing is, the ground-effect cargo plane (can’t remember its name at the moment) wouldn’t have that advantage. Slow, loud, clumsy, and about six *feet* off the ground. And totally unable to use things like canyons and forests for protection; if it tried that, the enemy would be the least of its worries.

I seem to recall reading of an experimental light sport aircraft in the ground effect category. Well, I say light sport aircraft, but I think it actually got registered as a *boat* instead, because although it did technically lift off, it physically could not fly outside of ground effect. The upshot of such a vehicle was that if you had a bunch of money to spend but didn’t want to go to the effort of getting a pilot’s license, this technically-a-boat airplane would give you a chance to fly. I don’t think it caught on.

        Carl Willis said:

If you don’t dispute the data and the analysis (and realistically you shouldn’t, unless you are confident in your expertise in epidemiology, statistics, and so on), then the point just seems to come down to semantics and matters of taste. De gustibus non disputandum est.

-Carl

On the contrary it is the analysis that we do dispute. Even if data for higher exposures is not questioned, even though there should be more of it, the extrapolation down to zero is only justified statistically.

However data from the low exposure region has been gathered, and it shows that the linear extrapolation breaks down, below a certain threshold so LNT is not applicable, no matter how justified the mathematics might be.

The problem is that radiation protection regulators and other authorities will not recognize, and that is a political issue more than anything else.

The whole point of this debate is that the human epidemiological data does not. It fact it shows evidence of some sort of radiobiological hormesis. Compounding this is that the LNT has been stated in such a way it cannot be disproved except by experiments needing impractically huge sample spaces

Well there is the other shoe down, isn’t it Carl? That’s fine, you have to apply the regulations as they are written, but that does not make them right. Nor do those regulations make it right for radiophobes to tell people not to get x-rays, radiotherapy, eat irradiated food, or claim that spent fuel remains dangerous for tens of millions of years. Yet this is exactly how LNT is being misinterpreted out on the street.

Worse this creates a problem for any regulator, who’s political masters are not going to permit the rules to be relaxed because of a feared backlash of public opinion and the lobbying of the radiation protection industry. And this is causing issues with the development and deployment of useful nuclear technologies.

The model may be inaccurate at low doses, but has not been found to be so. The LNT model may be accurate at low doses because it has been found to be accurate at higher doses, and human epidemiological data continues to support it well at lower and lower doses (in utero exposure carries a significant risk of cancer induction at doses above 20 mGy, etc). Other empirical models may be fit to the data and be found to be accurate over some range of that data. More than one model may simultaneously be accurate for the same data. Some models may be higher order than linear, they may have thresholds, etc. The data has imprecision, and it is not possible yet to know which if any of these models best reflect the underlying reality. Some models are known to be inaccurate right now, for instance a model that predicts a threshold at greater than 10 rad:

For most tumour types in experimental animals and in man a significant increase in risk is only detectable at doses above about 100 mGy. (UNSCEAR 2000, Annex G, par. 537)

If there is a threshold, it is below about 10 rad. For workers in a facility like the one for which I function as RSO (among other duties), it is appropriate to say that the 2 rem we’re permitted to receive in a year doesn’t carry a statistically significant risk of cancer (reflecting imprecision in data); and it is also appropriate and entirely compatible to say that any exposure to radiation is thought to carry an increased risk of cancer (our simplest, most widely-accepted model for the data that is known to be accurate for the range in which we have data) and we should follow ALARA. In other words, as UNSCEAR 2000 puts it,

there are no circumstances where it is scientifically valid to equate the absence of an observable biological effect with the absence of risk. (par. 539)

-Carl