> the Navy explained to me that it was balanced out because I was underwater and not receiving radiation exposure from the sun
With the greatest respect to the Navy, I smell more fish than in the seas that submarine travelled through.
My non-scientific understanding is that sun exposure is UV radiation exposure which causes skin melanoma. Meanwhile with nuclear reactors, UV is not the problem and the problem with exposure goes deeper than skin melanoma.
My feeling is you received a standardised "policy explanation" rather than an entirely scientific one. Happy to be proven wrong with links to scientific fact though !
Cosmic background radiation is a thing and water is really good at blocking it, so it's not complete bullshit. Of course, without knowing what dose the GP received, it's impossible to say whether it's a comparable dose to what they would have received on the surface - but it's plausible.
There is some good information about the relative exposure levels to cosmic radiation that one can expect to encounter on this site. They have been doing balloon launches and measuring in-flight levels for quite a while now.
Indeed. But isn't it really only "a thing" for airline pilots, cabin crew and a few unfortunate people at ground level who happen to live/work high-altitude on mountains or somewhere lower down with the wrong kind of rocks ?
Depends how you look at it. Cosmic radiation might not be extremely high level on the sea level, but it is a thing. So the total radiation dosis in a nuclear submarine might equal or even be less than on the surface.
Fun story: as part of my physics education we did an experiment on the cosmic radiation with a "radiation" telescope. That were 2 Geiger counters with a logic that only registered events which basically occured in both counters at the same time. That made the observation reasonably detectable and you could "see" the sun with this. This experiment was conducted indoors, just on the top floor of the building. We had about 1 event/second, our bodies would be getting a similar dosis all the time.
No, it is a gradient, with more exposure happening higher up. Radiation damage is considered “additive” over your lifetime. So if you are somewhere with less background radiation, you can receive more radiation from other sources and still be considered within “safe” limits. This is the basis for the policy mentioned.
I think they just poorly explained that his exposure in the sub was lower than background radiation levels on the sea surface. You get more rads living in Colorado for a year than anyone would get working in a nuclear power plant for a year at sea level.
Humans receive about 3-4 mSv per year of background radiation on average. Some of this is from radioactive decay, and some from cosmic radiation. Being underwater much of the year might shave 1-2 mSv off this.
Civilian radiation workers can receive, by regulation, doses up to 50 mSv per year. Typical reactor workers in the civilian energy sector get a couple mSv per year of dose. It is plausible that he was close to breakeven.
100mSv/year is the lowest dose that has shown a clear link to increased cancer risk.
The dose-dependent risk of cancer is in textbooks as an example of linearity. While it is hard to shown for low values of exposure because any measurements/estimates would drown in noise and errors, there is little doubt that the relation shown for higher values is just as valid at the lower end. That also conforms with the stochastic model of how radiation causes cancers and the mutagenic effects of low-dose radiation seen in vitro.
We're not absolutely confident that there's not some threshold dose. LNT is a decent conservative assumption for calculating the harms from low doses and reasonable to use for regulatory purposes.
Even so, radiation hormesis has been noted in lab models, etc (slight benefits from low doses).
We accept occupational risks all the time. Here, the threshold for radiation workers allows a dose half of what has been ever linked to any amount of cancer.
The overall average, across all industries, fatal work injury risk is something like 35 per 1,000,000 worker-years. Compare to this, where the risk to radiation workers from radiation, if they receive the highest allowed dose (and basically no one does) can be confidently bounded to be well under 1 per 1,000,000 worker-years. (And, if it should ever happen, is likely to be far in the future and cost less life expectancy as a result).
Why? 1 Sv (over a year) equates to a 5.5% increase chance of fatal cancer within a lifetime. Assuming the dosage is linear (it isn't but we use a Linear _no threshold_ model because it over estimates risk) 100mSv is a 0.55% increase in risk. So 50mSv is a 0.055% increase risk (note the parent is slightly wrong. Most countries and workers have a 20mSv maximum).
You're getting caught up in _detectable_ but not thinking enough about the actual level of risk. The danger/risk from 100mSv is far less of a risk than very common activities we do. Remember that that fatal cancer risk is over a lifetime (so let's say 40 years, or 0.01%/year if you receive that dose once). Smoking a cigarette a day (singular, not a pack) is a 30+% chance increase in stroke and heart disease. I'd argue that this is far more dangerous but something we don't worry about as much.
"The NRC requires its licensees to limit occupational exposure to 5,000 mrem (50 mSv) per year. Occupational dose does not include the dose received from natural background sources, doses received as a medical patient or participant in medical research programs, or "second-hand doses" received through exposure to individuals treated with radioactive materials."
I'm not sure what you're trying to say here. NRC is a US government. I said _most countries_ which in fact includes countries other than America. The EU standard is 20mSv. You'll also notice that this NRC listing specifies which workers. For DOE 50 mSv is regulatory limit and 20mSv is administrative control level. Of course, all this also changes based on occupation. I mean astronauts are allowed higher levels and pilots lower. But most countries and (radiation) workers have a 20mSv limit.
> I'm not sure what you're trying to say here. NRC is a US government.
I thought it was perhaps appropriate, if we're quantifying US Navy occupational exposure to a US citizen, to compare to US civilian reactor exposure limits. It doesn't seem appropriate to call me "wrong" in this context.
> For DOE 50 mSv is regulatory limit and 20mSv is administrative control level.
Sure: one needs controls well short of the regulatory limit to keep pretty much everyone short of the limit. Most nuclear medicine workers and reactor workers are well under 2mSv/year in the US. A few outliers end up with lifetime doses of a few hundred mSv.
P.S. Something went wrong here:
> 100mSv is a 0.55% increase in risk. So 50mSv is a 0.055% increase risk
In that you halved the dosage but divided the risk by 10, when saying you were evaluating it under LNT.
There are any number of substances where there’s little doubt that they can cause cancer even at minuscule doses, just at similarly low rates. Get enough data and you will find that a single whiff of tobacco smoke (or any other smoke) can cause cancer. The “lowest dose linked to cancer” is the result of our ability to measure such effects, not anything intrinsic to the harm these substances do.
That’s specific for cancer. For other forms of toxicity, the concept of “maximum safe dosage” does make sense when the dose/effect relationship is not linear. Pharmaceuticals, for example, can be entirely benign at small dosages yet lethal if you overdose.
But we can still set a significance threshold. Your point applies equally to radiation exposure flying on an airplane but we don't worry about the cancer odds from a single flight since it's lower than the (already miniscule) odds of crashing.
Would you say more? What that suggests to me is the authority responsible for setting the max allowed said “Well let’s keep it below the threshold linked to cancer, reduce it by half for safety factor, and call it a day”. IE they chose one of the simplest possible approaches- doesn’t seem surprising, but I am probably missing your point.
You're probably right. I thought the same thing, but since I didn't care I didn't pursue it. I would have cared if the scuttlebutt was that people were getting sick and dying, but that was not the case. Sub sailors were not dying in an detectable numbers.
A large chunk of that average dose, 4 mSv, is from radon, where the dose varies a lot depending on where you live, and if you live in such a radon-prone location, whether you have sufficient ventilation in your house.
Yes, you're correct. The page I linked to has this to say:
"For example, the health risk caused by radon is estimated on the basis of epidemiologic examinations, not the effective dose. Every year, an average of 280 Finns die from lung cancer caused by radon. Of these cases, 240 deaths are induced by smoking in addition to radon."
So they're not actually measuring an average 4 mSv/y dose from radon, but rather going the other way, that is that 280 yearly deaths from radon would be consistent with an average dose of 4 mSv/y (assuming LNT, presumably).
With the greatest respect to the Navy, I smell more fish than in the seas that submarine travelled through.
My non-scientific understanding is that sun exposure is UV radiation exposure which causes skin melanoma. Meanwhile with nuclear reactors, UV is not the problem and the problem with exposure goes deeper than skin melanoma.
My feeling is you received a standardised "policy explanation" rather than an entirely scientific one. Happy to be proven wrong with links to scientific fact though !