Radiation exposure question

Factual Questions
1

I just found the website of a woman who drives through the abandoned places near Chernobyl taking photographs. Some of the photographs even include a Geiger counter showing the level of radiation.

So my question is, how idiotic is this? I was under the impression that radiation lingers, and that it’s extremely dangerous to visit these places (that’s why they’re still abandoned). So what will happen to this woman? Cancer, infertility, or mutant offspring?

I’d think I’d have to be terminally ill already to do something like this- if you’re going to die anyway, why not explore these places? It is fascinating seeing these photographs.

2

They’re abandoned because it’s dangerous to stay there. Merely passing through is much less risky; the danger from radiation exposure is a function of both the intensity level and the time of exposure.

3

There’s a lot of speculation that her website is mostly bunk…

4

In what way, specifically? Links to said speculation would be helpful. For reference, [url=http://www.kiddofspeed.com/]here[/ur] is the site in question.

5

Well here’s a start:
http://msgboard.snopes.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=109;t=000628;p=1

http://www.brama.com/travel/messages/41972.html
http://www.stargeek.com/item/141401.html

6

Radiation exposure limits are a function of time, as noted before - Maximum dosages per year and max single or short term exposure. I haven’t worked in the field for a long time, so I don’t have the numbers handy but seems to me that 5 rem/year was the limit, probably much higher for single-dose exposure since workers have a lifetime cumulation to worry about while journalists don’t rack up those kind of numbers each and every year.

7

Bobtheoptimist, you’re right that 10CFR20, the US code governing radiation exposure, limits rad workers to 5 REM per year, and no more than 3 REM per quarter. But the limits for non-rad workers are lower, not higher, 500 mREM per year, no more than 300 mREM per quarter. Basically, the reasoning I recall was that rad workers know what they’re getting into, and have been screened for exposure.

As for passing through an area with active counts on a Geiger counter - that’s a lot harder to quantify the risk. First question is what was the counter reading, and how far away from the sources did it read that? I’ve used some very sensitive radiation dectection meters, that would give screaming counts off of bananas or porcelain, like what’s in a household toilet. But the radiation exposure from those sources were such that I’m not going to worry about using the toilet, or about eating bananas.

The problem with passing through the Chernobyl area these days, as Q.E.D. says, isn’t AIUI, the direct exposure that a person would get from passing through the area. What the problem is that the whole area is heavily contaminated.

There was a lot of particulate radioactive material released from the Chernobyl disaster. This dust, essentially, coated all the surfaces around the world - the closer one gets to the reactor the heavier the coating. Radioactive contamination is a source of radiation, but the real hazard is that since it’s usually a dust, it will be stirred up by walking on it, and so the person going through the area will become coated in the dust, and often breathe it in. Both of those things lead to internal exposure from radioisotopes, which is a far more dangerous thing than the same exposure outside of your skin.

There are essentially four kinds of radiation that are emitted from radioactive isotopes: [ul][li]alpha rays[/li][li]beta rays[/li][li]gamma rays[/li][li]neutrons[/ul][/li]
Going through in order:

Alpha rays are essentially helium nuclei moving at a fraction of the speed of light: They’re relatively heavy, and highly charged. They don’t travel far - because of their charge they interact with lots of things around them, and they can’t avoid transferring energy to the materiel around them. When this happens in a living biological system, it causes a lot of free radicals to be generated, which can really screw up metabolic processes.

When an alpha emitter is being held in your hand, you’re safe from it - the alpha particles can’t penetrate through the dead layers of skin cells to the living ones. But if you’ve got the same alpha emitter in your lungs, or gut, things get a lot different. Mucos deposits can be thick enough to protect, but they aren’t always. It’s hard to judge.

For most part radiation workers will go to great lengths to make sure that alpha emitters stay outside the body.

Beta rays are electrons (or positrons) moving at a signifigant fraction of the speed of light. Again, because they’re highly charged, they don’t travel all that far on their own. The training I got was that they’d be stopped by a normal thickness of clothing and one’s own dead skin layer again. Again, this goes right out the window if the beta (or beta positive) emitter is inside your body, and the damage will be concentrated nearest the source.

Gamma rats are photons of light, very high energy, but also less liable to concentrate damage to a body. The general rule of thumb I was taught for gamma rays is that 12 inches of water will reduce the amount of gamma radiation passing through it by about 90%. This is known as a tenth thickness - what comes through is about a tenth of what came into it.

But because the damage is so spread out, on a cellular level, from the gamma rays, it’s not as likely to concentrate damage above what a cell’s self-repair mechanisms can deal with. There are some practical reasons for why eating a gamma emitter is bad, but the short answer is that it really doesn’t matter what you do with one.

Finally neutron exposure - the problem with this is that neutrons can cause other things to go radioactive, if they’re absorbed into the nucleus of an atom. But because neutrons are chargeless they also have a much, much smaller chance of actually interacting with any specific pile of matter than any other kind of radiation. (Well, ignoring neutrinos)

But, again, there’s really not much difference between internal and external exposure with neutron emitters.

However, keeping alpha and beta emitters out of the body is a good idea. When talking about things like SR-90, which acts chemically like Calcium, and gets deposited into the bones, the damage that it can do to the active marrow can be devastatating.

Other things I’m not going to touch upon, now, are the effects of physical half lifes and biological half lifes.

To re-iterate, going through Chernobyl area without the proper anti-contamination gear isn’t likely to be quickly fatal, but it’s not a smart idea, either.

Which says nothing about the way that Ukrainian military may react to unauthorized persons on what’s now a militarily enforced exclusion area. Lead particulate contamination is even more of a problem than internal alpha and beta emitter contamination, if you want my opinion.

8

Ah. One of the other Navy Nukes got to it first.

I just felt like mentioning that the accident at Chernobyl happened exactly one week before I started Navy Nuclear Power School :eek:. What an interesting event to hear about just as you are about to get hip deep in the industry.

Nothing useful to add to OtakuLoki’s information, though.

9

:smack: Told you its been a while - 16 years, and I was drinking back then. Rather amazing that I remembered “5”.
Thanks for the post, almost makes me want to dig out my texts.

10

And don’t forget that those limits are based on the body’s ability to heal the minor damage caused by the radiation at those levels. If this woman (or anyone) has received only up to the 5 REM in a one-year period, and not added as much within a year, then any damage will have been (most likely) healed.

And Otaku refreshe my memory: X-rays fall into the gamma radiation spectrum, right?

11

They’re similar. Per wikipedia, gamma waves are “similar to those of X-rays and are very short, in the range of 10^−11 m to 10^−14 m”, while X-rays are “10 to 0.01 nanometers”, or 10^-8 to 10^-11.

12

To address your points in reverse order: yes, x-rays are included in the gamma radiation spectrum, when dealing with radiation health physics. An astronomer may have a different definition, though. Rad health physicists tend to use simpler definitions: If it’s a photon being emitted by the radioactive decay of an atom, it’s going to be called a gamma ray, no matter the exact energy level of the photon. Most of us know we’re playing fast and loose with the terminology, from the point of view of a real physicist or astronomer, but it’s a useful way to group one common emission from radioactive decay.

AIUI, however, you’re mistaken about the rationale for the 5 REM/year limit. Since the days of the Manhattan Project, and before, there has been a debate going on within the rad health physics community about what is the proper model for looking at radiation exposure and damage. There are basically two schools of thought: the cumulative and the threshold schools.

Both schools agree on what the immediate effects of radiation exposure are upon biological tissues. They also agree that cells have self-correcting mechanisms that may be able to deal with the damages done by the free radicals created within a cell by radiation exposure.

Where they differ is how they wish to model the long-term effects of a radiation exposure.

The cumulative school believes, and has some studies to support, that any radiation dose causes permanent damage to an organism, increasing the risk of radiation-related diseases as the organism ages. It doesn’t matter whether we’re talking about someone who’s gotten 1 mREM a day for ten years, or 35 REM all at once in one event - the long-term damage done to the organism is equal. Based on this thinking minimizing any radiation exposure is the path of wisdom.

The threshold school points out that, since there are self-repairing mechanisms in all organisms, it’s silly to claim that all radiation exposure will cause an increase in long-term health risks. Rather it’s more sensible to treat radiation exposure as several other environmental hazards are treated - below a certain ‘normal’ exposure the self-correcting mechanisms in the organism will effectively ‘erase’ the damage, with no long-term effects. But above that threshold dose, the cumulative damage mentioned above takes over.

There are also a few studies that support this interpretation, AIUI. One of the problems with measuring health physics risks, at the moment, is that there’s not all that much data for large dose exposures since WWII. (There’s some, and some of those studies are horrifying.) Which is one reason why Chernobyl survivors are being tracked so closely - it’s the large, random population with a variety of histories, that can be accurately tracked, even if exposure numbers are a little ‘iffy.’

However, the reason I bring this up is to point out that even those of us who subscribe to the threshold model of radiation damage agree that the more limiting model is the cumulative model. Since we can’t prove either model, at this time, it’s only the path of wisdom to base our limits on the cumulative model, so we don’t create health problems in the future. For that reason, the 10CFR20 limits are chosen with the following reasoning: first, and most importantly, the limit should be comfortably below the level at which a healthy person exposed to that limit dose would show any physioligical effects of the dose. The number I recall was that until one got hit with an acute whole body dose of 25 REM, there really wasn’t any test that would show any biological effects. Above 25 REM, there would be some measurable changes in blood composition (I can’t recall what the exact changes were, I’d guess white blood cell counts figure prominently, just because they’re one of the most active sets of cells in the body, but I have no cite.) that could be measured. So the 5 REM limit was based on comfortably avoiding that circumstance.

10CFR20 also makes it clear that minimizing the exposure below the maximum is highly encouraged. So, many local operations will have lower administrative limits. The US Navy’s nuclear power program, for example, limits nucs to 500 mREM/year, with no more than 300 mREM/quarter, and for normal operations my ship never got close to those limits.

13

Another aspect of exposure is whether or not the dose is a whole body dose. Though most discussions around exposure implicitly assume a whole body dose, it is important to understand that the human body can tolerate far greater levels to limited areas.

In other words, a dose that would be lethal if the entire body were exposed to it might be quite survivable if limited to the hand that was closest to the substance, for example.
My favorite example of this (which I have brought up here before) was the fellow who carried a radiography source (highly radioactive) in his pocket, and survived. The writeup of the incident included a diagram of his body with the estimated exposures to each body part, using lines like a contour map. IIRC, the head of his johnson was labeled “3000 Rem” Poor fellow.

Just for completeness: there are three things that one can use to their advantage around radiation: time, distance, and shielding. Any trained radiation worker would use all three to his or her benefit to minimize exposure.

14

The only non-arbitrary definition of X-rays vs. gamma rays is to say that gamma rays result from nuclear processes, while x-rays result from atomic processes (i.e., in the electron shell). But this isn’t a complete definition, since there are other ways to produce high-energy photons (synchotron radiation, Bremßtrahlung radiation, positron annihilation, etc.), and some atomic processes produce higher-energy radiation than some nuclear processes. Plus, in some applications (especially in astronomy), it may not be clear what the source of a particular photon is. In practice, “X-ray” and “gamma ray” are mostly just used colloquially, and if one needs to be precise, one specifies a range of wavelengths, energies, or frequencies without caring what the name is for that range.

15

And thus Cockzilla was created…

16

That’s called a dose-volume histogram, they also produce them when they plan radiotherapy or radiosurgery to make sure that the tumour and tumour margin (an area of normal tissue surrounding the tumour) gets the maximum dose whilst sparing as much of the normal tissue as possible. They’re quite important when planning RT around sensitive structures like the optic nerve or reproductive organs (they can make sure that either the beams avoid those areas, or that the fewest possible pass through them).