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Little John



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PostPosted: Sun Jun 16, 2013 7:37 am    Post subject: Reply with quote

kenneal - lagger wrote:
That any radiation is considered dangerous even in very small doses.
Well, you'd better find another planet or, indeed, another universe to live in then... Laughing

This is precisely what I mean by the complete irrationality in a large swathe of the general public when it comes to all thing nuclear as amply and rather depressingly demonstrated by some of the things I am reading on here that have been written by otherwise rational and well educated people.


Last edited by Little John on Sun Jun 16, 2013 10:29 pm; edited 1 time in total
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RenewableCandy



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PostPosted: Sun Jun 16, 2013 9:45 pm    Post subject: Reply with quote

While it is true that we live in surroundings bathed with low levels of ionising radiation of all sorts, and yet we nevertheless live (by, for example, constantly repairing and replacing the damaged bits), it is also true that no-one has yet identified the lowest threshold below which no ill effects are felt. Even Cornish granite, it has been demonstrated statistically, knocks (iirc) about a year off lifespan of those who live upon it.
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biffvernon



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PostPosted: Sun Jun 16, 2013 10:03 pm    Post subject: Reply with quote

Possibly because there is no lowest threshold. See Linear No-threshold Model:
http://en.wikipedia.org/wiki/Linear_no-threshold_model
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Little John



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PostPosted: Sun Jun 16, 2013 10:22 pm    Post subject: Reply with quote

biffvernon wrote:
Possibly because there is no lowest threshold. See Linear No-threshold Model:
http://en.wikipedia.org/wiki/Linear_no-threshold_model


"The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data"

http://radiology.rsna.org/content/251/1/13.full

Quote:
....Summary

Biologic data demonstrate that the defense mechanisms against radiation-induced carcinogenesis are powerful and diverse (Figure) (10,16,78,95,96). This is not surprising, because organisms have been subjected to reactive oxygen species from physiologic processes and environmental insults during evolution. Life is characterized by the ability to build defenses against toxic agents, whether internal or environmental. The defenses are overwhelmed at high doses and are stimulated at low doses, which is incompatible with the LNT model.....


The linear no threshold model, whilst seeming to make intuitive sense as well as being based on the otherwise sensible precautionary principle, has been shown by several studies to simply not stack up with the actual empirical biological data on the ground. Several counter-theories have been proposed for this. It's too early to decide which one, or combination of theories, will turn out to be right, but I am quite attracted to the theory that certain, low doses of radiation actually stimulate innate immune system responses and cause cell repair mechanisms to radically increase their activity, in turn actually reducing the risk of developing cancer.

In other words, very low doses of ionizing radiation may actually be good for you in the same sense that a polio vaccine is good for you. All of which makes elegant evolutionary sense.


Last edited by Little John on Sun Jun 16, 2013 10:58 pm; edited 4 times in total
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RenewableCandy



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PostPosted: Sun Jun 16, 2013 10:22 pm    Post subject: Reply with quote

I have a feeling that there is, but it is indeed very low and for that reason has not yet been accurately identified. I have suffered dozens, possibly hundreds, of injuries both major and minor in my time, and I have recovered from all of them. Obviously, if the rate at which I were sustaining damage were to exceed the rate at which I could renew myself, there would be a problem.

Given that the body is even capable of running-repairs of damaged DNA, then there is no reason to believe that it's any different for any type of injury, including that inflicted by ionising radiation.

NB this is not an argument in favour of nuclear tech of any kind, it's just me marvelling at the wonders of the human body.
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biffvernon



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PostPosted: Mon Jun 17, 2013 8:26 am    Post subject: Reply with quote

stevecook172001 wrote:
It's too early to decide which one, or combination of theories, will turn out to be right,
which is the time that the precautionary principle is applicable.
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Little John



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PostPosted: Mon Jun 17, 2013 9:43 am    Post subject: Reply with quote

biffvernon wrote:
stevecook172001 wrote:
It's too early to decide which one, or combination of theories, will turn out to be right,
which is the time that the precautionary principle is applicable.
No, no. We already know the LNT model is seriously flawed. The time to have used the precautionary principle of the LNT model is when we did not know it was flawed. I repeat, the biological data on the ground seems to be suggesting that very low doses of ionizing radiation has either no effect or, even, a health benefit because it simulates the immune system.

Can you address why, if the LNT model is correct, the above should be the case?

I should also say, there is another area of research that has been carried out that throws serious doubt on the LNT model: If it is the case there is no safe threshold of exposure and even a single radioactive particle has a significant capacity to raise the probability of cancer, it logically follows that the more biological cells are exposed to a given dose of radiation, no matter how small that dose is, will increase the likelihood of cancer forming in those cells because of the higher hit rate.

In fact, though, low doses of ionizing radiation have shown no difference at all in the probability of causing cancer between mammals of wildly varying sizes. The LNT model would clearly predict the larger mammal would be far more likely to contract cancer when exposed to a given dose as compared to the smaller mammal because of the higher cellular hit rate.

Can you address this further discrepancy between the data on the ground and the theory's prediction?
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biffvernon



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PostPosted: Mon Jun 17, 2013 11:58 am    Post subject: Reply with quote

You say:

Quote:
It's too early to decide which (theory) will turn out to be right

We already know the LNT model is seriously flawed


I would say those two statements don't sit happily together. Let's start by acknowledging that no theory in science is ever proved - it's all provisional. The precautionary principle should always be applied in situations where the consequences are serious. A glance through the literature quickly shows that scientists from a biological background tend to support LNT while those from the nuclear industry or government tend in the opposite direction. There is likely to be a case of institutional bias.

Let's do a thought experiment. Take a very small particle of plutonium. When a single atom decays it releases an alpha particle. This we know has the capacity to dislodge an atom from a DNA molecule. We also know that such DNA damage can be repaired and that the repair is made most easily if the corresponding opposite part of the DNA is not damaged. In the unlikely but possible event of our plutonium particle suffering two near simultaneous decays that damage both parts of the DNA molecule and that these just happen to be one of the small minority of critical parts then a life-threatening cancer may develop. Low probability - severe consequence.

Thus a single, or at least pair of, plutonium atoms could kill. Of course if our particle were a little larger and were to emit a million alpha particles in a short period of time in one locality....well, we really should ensure that plutonium and the biosphere never mix.

Ho for the windfarms.
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kenneal - lagger
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PostPosted: Mon Jun 17, 2013 3:47 pm    Post subject: Reply with quote

The safe radiation doses set in the 50s at the start of our nuclear program were subsequently found to be unsafe as more people than should have been were dying. The safe level was much reduced but is above background.

Background levels of radiation in some areas can result in harm, as Biff has said, when that radiation is concentrated, for instance by radon gas being caught within the structure of a house. As a result in area where radon gas is found buildings have to be sealed from the ground so that radon gas can't build up.

This shows that the margin between the safe dose and an unsafe dose is small, or at least not large and that the utmost caution should be taken when dealing with matters nuclear.
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biffvernon



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PostPosted: Mon Jun 17, 2013 8:04 pm    Post subject: Reply with quote

kenneal - lagger wrote:

This shows that the margin between the safe dose and an unsafe dose is small, or at least not large and that the utmost caution should be taken when dealing with matters nuclear.


Or it could be that there is no safe dose. (LNT)

It's then the matter of not being able to distinguish the source you're concerned about from the background so you just shrug and say "whatever".

But that doesn't mean it's safe.
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Little John



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PostPosted: Tue Jun 18, 2013 1:25 am    Post subject: Reply with quote

biffvernon wrote:
You say:

Quote:
It's too early to decide which (theory) will turn out to be right

We already know the LNT model is seriously flawed


I would say those two statements don't sit happily together.


I didn't explain my point there clearly enough. When I said that it's too early to decide which theory or combination of them will turn out to be right, what I meant was which of the alternative theories to LNT. That is to say, we already know LNT is not right.
Quote:

Let's start by acknowledging that no theory in science is ever proved - it's all provisional. The precautionary principle should always be applied in situations where the consequences are serious. A glance through the literature quickly shows that scientists from a biological background tend to support LNT while those from the nuclear industry or government tend in the opposite direction. There is likely to be a case of institutional bias.


I would suggest that's not a correct characterisation of the scientific community's attitude to the LNT model.

The National Academy of Medicine (Académie nationale de Médecine) published a report in 2005 (at the same time as BEIR VII report in the United States) that rejected the Linear no-threshold model in favor of a threshold dose response and a significantly reduced risk at low radiation exposure (http://www.radscihealth.org/rsh/Papers/FrenchAcadsFinal07_04_05.pdf)

The Health Physics Society's position statement first adopted in January 1996, as revised in July 2010, states:

"......In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem (50 mSv) in one year or a lifetime dose of 10 rem (100 mSv) above that received from natural sources. Doses from natural background radiation in the United States average about 0.3 rem (3 mSv) per year. A dose of 5 rem (50 mSv) will be accumulated in the first 17 years of life and about 25 rem (250 mSv) in a lifetime of 80 years. Estimation of health risk associated with radiation doses that are of similar magnitude as those received from natural sources should be strictly qualitative and encompass a range of hypothetical health outcomes, including the possibility of no adverse health effects at such low levels....."
(http://hps.org/documents/risk_ps010-2.pdf)

Historical documents suggest that an early study invalidating the LNT model was intentionally ignored by Hermann Joseph Muller when he gave his 1946 Nobel Prize address (http://junksciencecom.files.wordpress.com/2011/09/calabrese-muller-1.pdf)

Recent fundamental research of the cellular repair mechanisms support the evidence against the linear no-threshold model (http://dx.doi.org/10.1073%2Fpnas.1117849108)

None of the above research papers have any overt links to the nuclear industry.

Quote:
Let's do a thought experiment. Take a very small particle of plutonium. When a single atom decays it releases an alpha particle. This we know has the capacity to dislodge an atom from a DNA molecule. We also know that such DNA damage can be repaired and that the repair is made most easily if the corresponding opposite part of the DNA is not damaged. In the unlikely but possible event of our plutonium particle suffering two near simultaneous decays that damage both parts of the DNA molecule and that these just happen to be one of the small minority of critical parts then a life-threatening cancer may develop. Low probability - severe consequence.

Thus a single, or at least pair of, plutonium atoms could kill. Of course if our particle were a little larger and were to emit a million alpha particles in a short period of time in one locality....well, we really should ensure that plutonium and the biosphere never mix.


No, lets look at the empirical facts on the ground. They do not support the LNT model. Also, please address my point about there being no difference between the cancer rates of mammals of different sizes in the presence of a fixed low level radiation dose. The LNT model would clearly predict that the larger the animal, the greater the risk of cancer due to the higher cellular hit rate.
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biffvernon



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PostPosted: Tue Jun 18, 2013 7:57 am    Post subject: Reply with quote

For sure there are plenty of papers and reports that oppose LNT. But then there are plenty of papers and reports that say that Roundup (substitute just about any product you like) is safe, while others disagree. As I said, the sponsoring body, such as nuclear industry of government, tends to introduce bias.

I don't know about big/small animals. Not all cells are equal. A goodly layer of fat that may not be vulnerable to turning cancerous might shield delicate DNA?
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