Follow TV Tropes

Following

So what do exceptionally high radiation levels actually mean?

Go To

UnabashedFornicator Since: Oct, 2010
#1: Mar 23rd 2011 at 3:40:47 AM

I know there are already topics related to Japan and Nuclear power, but I was curious if anyone knowledgeable knows exactly what high levels of radiation actually entail. I tried to do some research online, but it was pretty confusing to say the least, especially when it comes to pinpointing quantities. I'm also confused as to how radioactive iodine made its way into Tokyo's drinking water.

Ex: From http://www.asianetindia.com/news/japanese-officials-test-food-seawater-determine-health-risks_253224.html

"Earlier seawater radiation monitoring detected levels of iodine-131 that were 126.7 times higher than government-set standards, the electric company said on its website. Its monitors detected cesium-134, which has a half-life of about two years, about 24.8 times higher than the government standards. Cesium-137 was found to be 16.5 times higher than the standard."

If the government set standard for iodine-131 is 0.033 ppm and we've got something 125+ times that will any fish pulled from the vicinity pose massive health risks in the long run, or does the 8 day half-life mean any fish you eat in about a year should be okay? Should we be worried that Cesium-137 has a 30 year half-life?

edited 23rd Mar '11 3:42:24 AM by UnabashedFornicator

AndrewGPaul Since: Oct, 2009
#2: Mar 23rd 2011 at 5:20:21 AM

After seven half-lives, the amount of a radioactive isotope will be 1/(2^7) = 1/128th of its starting amount. In the case of Iodine-131, this means that after 56 days, the levels should be back below the official standard.

it takes 5 half-lives for it to drop to 1/32nd, so the Ce-134 should be back below the limit in 10 years, and about 4 half-lives, or 120 years, for the Ce-131 to decay back down to the allowed limit.

This assumues that the levels of I-131 aren't being replenished (or actively removed, in the case of contaminated land) and doesn't take into account thhe fact that these elements may decay into other radioactive elements with different half-lives. Also, official limits may not be the same as "safe" limits. For example, one news report mentioned that the Japanese government had increased the maximum allowed annual radiation dose for plant workers from 100mSv to 250mSv. Sounds bad for the workers? Could be, but the US official limit is 500mSv, or 1,000mSv if you're engaged in life-saving emergency work.

edited 23rd Mar '11 5:24:11 AM by AndrewGPaul

del_diablo Den harde nordmann from Somewher in mid Norway Since: Sep, 2009
Den harde nordmann
#3: Mar 23rd 2011 at 5:41:45 AM

http://xkcd.com/radiation/
Look no further

A guy called dvorak is tired. Tired of humanity not wanting to change to improve itself. Quite the sad tale.
TibetanFox Feels Good, Man from Death Continent Since: Oct, 2010
Feels Good, Man
#4: Mar 23rd 2011 at 6:03:56 AM

Yeah I was about to link to that.

The main thing is it's not so much about how big a dose, but also for how long you're exposed to it.

Most of the government imposed safety limits are way below medically significant thresholds, so that way if there's an accident, you're still not likely to go over into dangerous levels unless you're a first responder.

Unfortunately, most people don't know that government guidelines on radiation err heavily in favour of caution and thus assume that anything over the normal safety limits means they're in serious danger of contracting radiation poisoning.

And since the Placebo Effect works both ways the upshot of this is a lot of people developing psychosomatic illnesses as a result of being afraid they've been exposed to dangerous levels of radiation when actually, they haven't.

Considering how miserable it is to be in the affected parts of Japan at present, I am saddened to see people's ignorance of radiation safety levels making their lives even more unnecessarily miserable.

NativeJovian Jupiterian Local from Orlando, FL Since: Mar, 2014 Relationship Status: Maxing my social links
Jupiterian Local
#5: Mar 23rd 2011 at 10:44:14 AM

Part of the reason that radiation is confusing is because it's so damn complicated. Effects depend on how much you're exposed to, what type you're exposed to, how long you're exposed to it, how quickly you're exposed to it, how you're exposed to it (eg, standing next to a reactor vs. being exposed to fallout), etc etc etc.

The (very, very) short version is that "acute" dosages (large amounts over small times) causes direct damage to cell tissue, which causes everything from headaches and nausea ("radiation sickness/poisoning") to literally frying your brain at high enough doses. Acute affects come in two stages; the immediate effects upon being dosed, and latent effects that only surface days or weeks later. This is because the body reacts differently to the deaths of different kinds of cells. In the worst case scenario, the radiation kills the bone marrow that produces red blood cells — which has no immediate effect, but once the current crop of blood cells begin to die off, symptoms reassert themselves. This is called the "walking ghost" stage, where a person has recieved an unavoidably fatal dose, but still has several days of apparently perfect health left. Not fun.

"Chronic" dosages (low amounts over long periods) tend to have no immediately obvious affects, but lead to an increased rate of things like cancer. This is because the radiation mucks up cell DNA, which is the most sensative to that sort of thing. It can also cause birth defects and the like for the same reason.

Short primer on radiation notation! The most useful unit for measuring the effect of radiation on people is the sievert (Sv), which measures the effect of radiation on biological tissue. The sievert is derived from the gray, which measures absorbsion of radiation in general. A gray is 1 Joule of radiation per kilogram of the absorbing mass. To get sieverts, you take the amount of radiation in grays and multiply it by a number depending on the type of radiation; more harmful types of radiation multiply by a higher number. For things like gamma and x-ray radiation, 1 gray = 1 sievert. For things like alpha particle radiation, it can be as high as 1 gray = 20 sieverts.

To make things even more confusing, you might also hear things given in rems or rads instead. These are just different units for the same thing; 1 sievert = 100 rems, and 1 gray = 100 rads. To give some perspective on this, some people are also fond of using the Banana Equivalent Dose, which is (as you might suspect), the amount of radiation you can expect to absorb from eating a banana (which naturally contain a small amount of radioactive potassium). 1 BED = 0.1 μSv = one ten-millionth of a sievert. It takes around 1 Sv for acute radiation sickness to start showing up reliably. A long-distance flight will net you about 1 μSv per hour over background levels.

For the iodine you were asking about, it's one of the byproducts from the reactor core; it's particularly notable because the thyroid gland tends to absorb a lot of iodine, and having it absorb radioactive iodine is bad for obvious reasons. It's fairly easy to counter, however; simply taking idoine pills will fill it up with non-radioactive iodine, so it won't bother absorbing any of the nasty stuff. But as has been mentioned, it's got a fairly short half-life, so it's a short-term concern rather than a long-term one.

edited 23rd Mar '11 10:45:24 AM by NativeJovian

Really from Jupiter, but not an alien.
tnu1138 Dracula Since: Apr, 2009
Dracula
#6: Mar 23rd 2011 at 10:46:37 AM

It means you'll turn in to a Ghoul.

We must survive, all of us. The blood of a human for me, a cooked bird for you. Where is the difference?
TheStupidExclamationMark Orbs from In ur cupboard Since: Dec, 2009
Orbs
#7: Mar 23rd 2011 at 10:51:30 AM

That you Glow In The Dark!

"That said, as I've mentioned before, apart from the helmet, he's not exactly bad looking, if a bit...blood-drenched." - juancarlos
TibetanFox Feels Good, Man from Death Continent Since: Oct, 2010
Feels Good, Man
#8: Mar 23rd 2011 at 5:04:23 PM

To be honest, my rule of thumb with regards to measurements is "If they're not talking in Sieverts, they are probably full of shit".

Sieverts are the SI unit for medically significant radiation exposure, they are what industry professionals are supposed to use. Someone who is talking in outdated units like Rads probably has outdated knowledge.

edited 23rd Mar '11 5:04:49 PM by TibetanFox

EricDVH Since: Jan, 2001
#9: Mar 24th 2011 at 5:06:36 AM

The reason government standards for atomic radiation are set so low is because doses are forever. Very much like UV light exposure, the radiation you receive over your entire lifespan is cumulative, so people exposed to radiation are somewhat like timebombs in that every dose you receive takes a certain number of grains from your metaphorical hourglass. As your TOTAL lifetime dosage accumulates, more and more Bad Thingsā„¢ are likely to happen, until it hits a certain level, at which point you're basically a dead man walking.

This is why professionals involved in major incidents are often banned from the industry, because they simply can't withstand any more exposure. Similar things happen with stuff like fiberglass epoxy sensitivities too.

Eric,

UnabashedFornicator Since: Oct, 2010
#10: Mar 24th 2011 at 4:47:45 PM

Thanks for the responses. I feel that I have a slightly better understanding now. I never bought the idea that people in the US should be overly worried, but was wondering if my family in Tokyo have reason to be concerned (in which case I need to be more forceful in my offers to house them here for a while).

Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#11: Mar 24th 2011 at 5:04:05 PM

[up][up] Er...sorta. More like every bit of ionizing radiation is a (very small) chance to knock a hole in something crucial. It's cumulative in that you're rolling the dice more than necessary over the course of your life, and getting a high dose is a shitload of dice rolls all at once that are going to poke a lot of holes all at once. But they're still essentially memoryless occurrences and have a very limited amount of dependence on previous doses.

It's more like rolling the dice bajillions of times than filling a glass, is what I'm trying to say. Some parts of the body retain radioactive matter or damage from it more stubbornly than others, but it's not quite as simple as "you were exposed to something 20 years ago, you can't take any more radiation."

The reason government-set doses are so low in many cases is because that's what's considered safe for continual dosage, and is erring on the side of major caution for that too. Going 10-100 times over it for a few days with a short-lived isotope is undesirable but not exactly a doomsday scenario.

Consider that a good portion of Nebraska has higher than the recommended dosage of uranium in its groundwater. It's nothing new, it's been there the whole time and the total lifetime risk added from it is really low compared to other kinds of cancer and stuff — we just have really low accepted doses as a buffer.

edited 24th Mar '11 5:25:20 PM by Pykrete

Add Post

Total posts: 11
Top