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Merged nuclear power safe?

The thing that I don't know about, is that air itself stops gamma rays, which is why we don't die from the sun. The atmosphere high up absorbs the energy, which is why there are no gamma or x-rays coming down on us from the sun.

So does half a kilometer of air absorb some of the gamma rays? Is that a factor in distance from a gamma ray source?

If, and this is what they reported yesterday, if the gamma radiation is around 2 mSv/hr at 500 meters, then the gamma at the source (big or small) is going to be around 600 Sv/hr at two meters from the source. That is what the math says.

Now if that math is wrong, I want to know why. If that isn't right, what would the gamma be next to the source?

If they reported it wrong, and it really was microSv at 500 meters, that they reported, then why evacuate? It would only be .6 Sv/hr at two meters.

Either I'm doing the calculation wrong, or they are evacuating because there is high radiation near the source.
 
r-j said:
The thing that I don't know about, is that air itself stops gamma rays, which is why we don't die from the sun. The atmosphere high up absorbs the energy, which is why there are no gamma or x-rays coming down on us from the sun.

So does half a kilometer of air absorb some of the gamma rays? Is that a factor in distance from a gamma ray source?

If, and this is what they reported yesterday, if the gamma radiation is around 2 mSv/hr at 500 meters, then the gamma at the source (big or small) is going to be around 600 Sv/hr at two meters from the source. That is what the math says.

Now if that math is wrong, I want to know why. If that isn't right, what would the gamma be next to the source?

If they reported it wrong, and it really was microSv at 500 meters, that they reported, then why evacuate? It would only be .6 Sv/hr at two meters.

Either I'm doing the calculation wrong, or they are evacuating because there is high radiation near the source.
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Rule of thumb for radiation safety:

If you have a stationary source of radiation, walk away from it. I'm reasonable certain that even within the evacuation zone no one gets much radiation that actually radiates from the NPP.

The problem here is that the sources are moving. They're tiny little critters of radioactive dust that get spewed out and can travel with wind and water flow. That's why there's so much concentration on I-131 and Cs-137. They're water soluble (can get transported out of the fuel by water, steam, and venting processes) and have a long enough half-life to be present. Heavier fission products did not leave the fuel (usually not water-soluble, containment more or less intact, no fire or explosion that blew fuel apart), lighter fission products (gasses) have shorter half-life and decay so fast that you don't have to worry about them.

The problem also is that the sources that cause evacuation of the workers ARE NOT THE REACTORS. It's the fallout that covers the ground and all objects within the exposed areas with various concentration. The radiation gets stronger towards the reactor because the density of the radioactive dust is higher, not because you're getting closer to a source of radiation. That's why they have to evacuate, wait until the dust activity is decayed, or the dust has been washed off.
 
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r-j said:
Well, I did ask for somebody to check my math, using an easy light source, with distances and all that.

If you know the amount of gamma radiation at 500 meters from the source, (which isn't clear at all, but it doesn't matter), which they have published several times, then you can use math to figure out what the radiation will be closer to the source, using the laws of physics.

That the source of the gamma rays might be a large source, that doesn't change the point source calculations, which anyone can do.
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Except, and you have been told this, you can't use the inverse square laws to determine this. Firstly the radioactivity at the boundry is not from a point source, it is from multiple sources, mostly the I-131 and Cs-137 scattered about during the incidents. Secondly these are primarily beta sources, and beta particles can travel some distance in the air, however they rarely travel up the high 10's of metres. The activity at the plant boundry is not from a gamma source in the plant, but rather from sources covering the ground near the boundry, as you move further from the plant, the concentration of these contaminants decreases because they spread out, and so the levels of activity decrease as well. It's not possible to work backwards to determine the concentrations of active material inside the plant by taking the value at the gate and doing math on it.
 
Java Man said:
Huh? Iodine 131 is highly carcinogenic. It is a very serious thing to have high concentrations of that in the water because it can be absorbed by fish which later get eaten by humans.
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And how does that rank against the health effects of mercury contamination in fish?
 
r-j said:
The thing that I don't know about, is that air itself stops gamma rays, which is why we don't die from the sun. The atmosphere high up absorbs the energy, which is why there are no gamma or x-rays coming down on us from the sun.

So does half a kilometer of air absorb some of the gamma rays? Is that a factor in distance from a gamma ray source?

If, and this is what they reported yesterday, if the gamma radiation is around 2 mSv/hr at 500 meters, then the gamma at the source (big or small) is going to be around 600 Sv/hr at two meters from the source. That is what the math says.

Now if that math is wrong, I want to know why. If that isn't right, what would the gamma be next to the source?

If they reported it wrong, and it really was microSv at 500 meters, that they reported, then why evacuate? It would only be .6 Sv/hr at two meters.

Either I'm doing the calculation wrong, or they are evacuating because there is high radiation near the source.
Click to expand...

Wow, this just gets wronger. The sun is not a huge producer of Gamma Ray radiation. The Moon gives off more Gamma Rays than the sun.

Solar Radiation is mainly particle, consisting of Protons and Electrons. While the Corona does emit X-rays, the surface of the sun is no where near hot enough to do so, so the amount of X-ray radiation from the sun is low as well compared to its size and are really only an issue even above the atmosphere when there is a substantial flare.
 
I was wrong about the sun making gamma rays, they come from all directions, and the sun doesn't produce much at all. And the moon is a gamma ray source because of cosmic rays hitting it!

http://apod.nasa.gov/apod/ap060527.html

I feel like I just entered a science fiction story! The moon is full of gamma rays!

But I was right, the atmosphere absorbs gamma rays. But it's the moon that is the danger!
 
OK so if they are measuring radiation it is the sum total of all the gamma rays, not any one source. So, the entire plant at times is a deadly radioactive source, from all directions.

Well that certainly sounds much better!
 
r-j said:
The thing that I don't know about, is that air itself stops gamma rays, which is why we don't die from the sun. The atmosphere high up absorbs the energy, which is why there are no gamma or x-rays coming down on us from the sun.
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According to NASA the moon is a brighter gamma ray source than the sun.
I feel like I just entered a science fiction story! The moon is full of gamma rays!

But I was right, the atmosphere absorbs gamma rays. But it's the moon that is the danger!
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Technically, the atmosphere doesn't protect from all gamma ray sources. Otherwise we wouldn't know that lightning is somehow correlated with matter/antimatter annihilation.
 
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Corsair 115 said:
And how does that rank against the health effects of mercury contamination in fish?
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in a year, all 131-I is basically gone. Hg sticks around for a while.

Almost every state in the Union has health advisories against excessive consumption of fresh water game fish because of mercury.
 
r-j said:
But I was right, the atmosphere absorbs gamma rays. But it's the moon that is the danger!
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While yes the atmosphere does absorb Gamma, you're still not on the right track, the moon might produce more than the sun, but even it produces a very tiny amount, a fraction of the amount of Cosmic Radiation that creates the Moon's gamma. Most of the Gamma we get hit by from space is from extra-solar sources such as pulsars and super novas so it has already travelled huge distances to get here.
 
BenBurch said:
For the most part, actually, gas. Noble gas radionuclides. Very short half-life.
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Well, yes. I want to keep the text simple.

Gasses are not much concern, except for high concentrations after venting events. They don't stick to surfaces and have a short half-life, as you say. Outside of the NPP, forget about them. No danger.

Inside, a lot more. Hence, evacuation until they're decayed.
 
r-j said:
OK so if they are measuring radiation it is the sum total of all the gamma rays, not any one source. So, the entire plant at times is a deadly radioactive source, from all directions.

Well that certainly sounds much better!
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No, no, no, no, no, no, and no. There are different types of radiation. Alpha, Beta, and Gamma. The radionuclides that are contaminating the areas are mostly particle emitters, so Beta and Alpha. This means that very little of the detected radiation is Gamma.
 
r-j said:
Beta and Alpha are dangerous at 500 meters?
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Again you are assuming point sources. The radionuclides that are creating the radioactivity are the likes of Xenon-137, Krypton-90, Iodine-131, and Cs-137, and Strongtium-90. These are generally gases, daughter products of gases, or small enough particles to be carried about the plant and its surroundings by the steam venting and subsequent explosions. They don't have to be 500m from the plant boundry, they can move.
 
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r-j said:
That makes no sense at all.
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It would if you had an inkling about what was going on.

Some of the products of Uranium based Fission are gases, such as Xenon-137 and Krypton-90. These can escape the fuel rods and be in the atmosphere of the reactor. When the pressure gets to much and they vent it, these gases get out with the steam and cause spikes that force evacuations. They also have very short halflifes, so decay quickly via Beta emmision, Xenon into Caesium-137 and the Krypton into Strongtium-90. Both of these are Beta emitters as well. Further you have the likes of these gases and Iodine-131 from the spend fuel pool rods as they have reacted due to the lower water levels, this further adds to the contamination about the area.

The levels of radioactivity measured at the boundry of the plant are from the contaminants in the area where the reading is being taken, in other words, most of what is measured there tells us approximately how much combined Xe-137, Kr-90, Cs-137, Sr-90, and I-131 is in the air and on the ground within a dozen or so metres of that area. It's not messuring gamma radiation being fired out of the plant 500m away.
 
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