will,
I'm 99% sure that that the inverse square law comes from assuming that the radioactive particles are static (and also that radiation doesn't get absorbed). That's certainly the answer for that problem.

I'm curious about this situation, in which most of the radiation seen 20 km is presumably coming from particles that have floated 20 km and a lot of released radiation (particular beta and alpha particles) is absorbed by the air pretty quickly after release. I'm sure that there's no perfect formula, but I wonder if there's a reasonable simplification that results in a rough equation.

Ah, yes 20km is much too far to see any effect of radiation whose source is from the sight. I don't know of any easy formula that will tell you the concentration of radioactive material as you get further from the site.

Wouldn't the inverse square law also apply to other particles radiating from a source? It doesn't matter if it's photons or bowling balls, right? Doing calculations like that to determine the spread of radioactive particles would assume equal wind in every direction, so it'll obviously be wrong, but it could give ballpark figures.

I think it would be 1/r and not 1/r^2 because I'm guessing they like going horizontally a lot more than they like going up... i.e. I'm using 2 dimensions instead of three.

But in addition to that, they obviously are going to have some tendency to stop moving....

In a perfect system it should work, but as you point out there are way too many variables involved

In this situation you are not dealing with radiation "in a vacuum". By that I mean if I have a piece of equipment that is reading Xmr/hr gamma, than under no circumstances will it read >X mr/hr the further from the source you move. However, in a release situation, it would be possible for X amount of radioactivty to be dropped on the ground, move 50 ft away from the plant (the source in this case) and see >Xmr/hr due to the fact that there may be a bigger deposit there, and with contamination, the bigger the "pile", the more dose you are going to see. So for this there really is no perfect formula.

Noah, I can see what you're thinking, but there's another (probably stronger) effect, and that's wind. If (as you surmise) the contamination doesn't really go up or down so it is diffusing in 2D, the 1/r rule would be correct. There's probably a bit of vertical diffusion, so that would make the rule something between 1/r and 1/r^2.

But--I would guess the contamination is more driven by the wind. That would cause much higher contamination than the 1/r rule would suggest in certain directions--obviously where the wind is blowing to, and much less in other directions.

0330: The police manning those water cannons are donning protective gear right now in preparation for their attempt to fill the spent fuel storage pool at Reactor 4. The cannon are thought to be strong enough to allow crews to remain a safe distance from the plant.

This effort could be critical in determining how bad things get.

It seems so cruel that a lack of water is the problem in Japan now. Bleh, how awful.

Yeah.. this is basically my exact thought process, and it sorta leads me to think 1/r is the best estimate. But, meh, we're not gonna come up with an answer. Sorry for the derail.

Hurry up with the offsite power they are evidently "close" to having. Hopefully the government isnt lying about that one.

Legit question, no derailment.

I may have missed it earlier in the thread, but what is your background? You seem quite authoritative about this.

You and Will have been a big help in this thread.

I think rather than the government/TEPCO having concealed information for the purpose of misleading the public, it's a cultural issue. There's an article about it in the NY Times. Money quote:

You can't understand how different Japanese society is from Western unless you've engaged it directly. It's a different world over there.

+1 to this. Sadly, it might be important to know where all the contaminated dust/smoke/ash may be going.

Ive worked in Radiation Protection at a nuclear plant for the last 4 years. The footage you see of the people being "scanned" as they call it in the media with the geiger-counters? That would be the type of things I am trained to do, among several others of course.

Protecting the employees, the public, or both?

ChrisV,

Funny that you mention that. I thought of the same thing in another thread:

There's an old story about the Japanese never saying "no" to a request. The way they say no is more like, "Mmm." Or, "This might be difficult." But if it were 100% about this, then the public should know exactly what the government is trying to tell them without telling them: that this situation is ****ed.

But that doesn't seem to be what's going on. I feel like this is also a bit of cover-up from national embarrassment in the eyes of the international community, which is difficult for me to wrap my head around in light of a 9.0 earthquake, but other cultures are... different.

We are trained to do both. If we were in this situation at the nuclear plant where I work, I (or somebody from my department) would be out driving the countryside taking dose rates, contamination levels, and air samples, and then relaying that information back to the site (where we would also be supporting the event obv).

Or maybe not?

Not to derail the thread, but further to this, there's a chapter in Malcolm Gladwell's "Outliers" that explores the use of language in Korean society, similar to Japanese. In our society language has what's called a "transmitter orientation" where if the listener fails to understand what is said, it's assumed to be the fault of the speaker for not being clear enough. In Korea and Japan there is a "listener orientation" where if there is a miscommunication, it's the fault of the listener for not making enough effort to understand the intentions of the speaker. In the book's example he's talking about a crash on board a Korean Airlines flight where the flight crew are attempting to alert the Captain to the dangers of bad weather at the destination. The first officer tries "Don't you think it rains more, in this area here?". The flight engineer tries "Captain, the weather radar has helped us a lot". Both are attempts to make the Captain understand that weather will hamper their efforts to make an approach to the destination. That's what I think has been going on with TEPCO. The ethic of making clear and unambiguous statements is not one present in the society in which they operate.

The national embarassment thing doesn't ring true for me. I feel like this has been a lot of "Oh ****.. We screwed up, and things could go really bad, so let's not tell anybody and hope things work out" combined with the more altruistic "We don't want people to panic".

skunkworks, heh, I see you dug out an Outliers reference too. I definitely think you have to filter TEPCO and govt statements through that lens.

That's a really good point that I hadn't thought of earlier in this context. One thing that's interesting about that, though, is that it also seems like people are saying the locals are generally pretty chill and that expats are getting freaked out by their embassies. One would think that if the information is still being communicated by subtle channels that there'd be more general agitation . . . but of course that could be the case.

Malcolm Gladwell is really good at mixing statements that are obviously true and boring with things that are obviously untrue in a way that makes people think he's saying things that are both true and fascinating. Please don't draw conclusions based on his crap.