Talk:Criticality accident

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Replaced the introduction:

A criticality accident is when nuclear fission is unexpectedly and accidentally triggered. The term refers to the achievement of criticality in fissile material, such as uranium, plutonium, or thorium, which releases an often fatal amount of beta radiation (neutrons).

There are a number of things wrong here. For a start, it's not just any fission reaction. It must be a chain reaction, otherwise it's neither a criticality nor likely to be dangerous. Fission is happening all the time, spontaneous fission of Pu-241 for example is the main problem in trying to make weapons from low grade plutonium. For another, thorium is neither fissile nor capable of criticality. Thirdly, I see there's already been a dispute (but no discussion here) on whether beta radiation is a problem in this context. It's not, the problem is the neutrons. They are not the same thing.

I've flagged the article as disputed because there are a number of equally suspect claims throughout the article and they'll take a while to check. Rather than stubify the whole thing, I've left this material in for the moment, but it means the article now has a good introduction followed by some very shaky stuff! Andrewa 03:48, 25 Oct 2004 (UTC)

• Your point on the chain reaction is well-taken -- I misclarified. I had thought that thorium-232 is fissile but now that I look into a bit more it seems that it is just fertile. And I seem to have gotten mixed-up about beta radiation, for some reason I think was thinking of it being neutrons but again, I see that's not the case. Ugh, I occasionally get slightly turned around on such things, it is embarassing. Nevertheless, the historical aspects ought to be just fine, for whatever that's worth; that's more my area than the physics. --Fastfission 20:32, 25 Oct 2004 (UTC)

Fair enough, on that basis I've removed the dispute notice. Andrewa 00:33, 26 Oct 2004 (UTC)

Contents 1 A probable error. 2 Einstein was wrong? "Charged particles travelling faster than the speed of light 2.1 Some rewording might make things more clear 3 Problems, questions 4 Criticality monitors 5 Light current and removal of images and information 6 Godiva device

[edit] A probable error.

Harry K. Daghlian, Jr. is listed in this article as having died after a mistake in an experiment involving using two hemispheres of plutonium; on his own article, in Lists of Nuclear Accidents. and in Tungsten Carbide, he is listed as having dropped a brick of tungsten carbide onto a subcritical mass of plutonium at Los Alamos while doing research into using neutron reflectors to reduce the mass necessary to attain criticality.

As I do not yet feel myself competent to make the change personally, I simply put this forth for someone more experienced to consider.

You are right. Edit away!--Deglr6328 02:44, 16 August 2005 (UTC)

It is done. Swuboo 05:59, August 16, 2005 (UTC)

Cool. see? 'twas easy! :) --Deglr6328 06:14, 16 August 2005 (UTC)

[edit] Einstein was wrong? "Charged particles travelling faster than the speed of light

I allways heard that the speed of light was an absloute limit, however this article indicates Cherenkov radiation is produced by charged partickles traveling faster than the speed of light.

"However, this is merely a coincidence. Cherenkov radiation is produced by charged particles travelling faster than the speed of light in a medium other than a vacuum. The only charged particle radiation types produced in the process of a criticality accident (fission reactions) are alpha particles, beta particles, positrons (which all come from the radioactive decay of unstable daughter products of the fission reaction) and energetic ions"

http://en.wikipedia.org/wiki/Criticality_accident

• Take a look at the linked article on Cherenkov radiation. You can go faster than the speed of light when the light is slowed down, i.e. is in a medium. Einstein's rule about the speed of light is when it is in a vacuum. --Fastfission 18:03, 2 September 2005 (UTC)

[edit] Some rewording might make things more clear

Maybe it would be better to reword this as:

Cherenkov radiation is produced by charged particles travelling faster than the propagation speed of light in a medium (which is slower than the normal speed of light when the medium is not a vacuum).

By adding the word propagation, you're illustrating that the light isn't so much traveling through the medium, but being absorbed and re-radiated from atom to atom through the medium. And this, as far as I understand it, is what "slows" the light down.

— Ke6jjj 23:02, 11 November 2005 (UTC)

[edit] Problems, questions

The summary of criticality accidents from the Los Alamos report should be placed here. That report details many dozens of accidents; by contrast, this article would lead one to believe that there are relatively few. Its rather morbid, gruesome reading, but compelling.

The Los Alamos report uses a number of terms I don't understand, and would like to have defined: "prompt critical" "delayed critical", "superprompt", etc.

A recurring theme from that report is "favorable geometry" (which I do know how to define); this article should describe this, as it is an important aspect of many/most of the accidents.

Not at all clear to me why this article spends so much time discussing the "blue light"; this seems to be a minor point. linas 07:11, 22 March 2006 (UTC)

It spends so much time on the 'blue light' because people were constantly, CONSTANTLY coming along and mislabelling it as cherenkov radiation. I got tired of reverting it so I put in this exhaustive explanation which I must say seems to have worked as I have only had to revert one cherenkov edit since adding it. If the article needs more information (it does) that can simply be added. Though I do NOT think this page needs a list of crit. accidents as many (all?) can already be found on the subpages of this page and even if we did list all these types of accidents separately the list would not belong here but instead on another page. --Deglr6328 09:24, 22 March 2006 (UTC)

[edit] Criticality monitors

THese should be mentioned, but I have no up to date info.--Light current 23:42, 11 September 2006 (UTC)

[edit] Light current and removal of images and information

Hi, regarding your recent removal of informaion on the article I'd like if you could clarify your reasoning for doing so. Firstly, the statement which you removed regarding the Slotin incident:"Immediately realizing what had happened he quickly disassembled the device, likely saving the lives of seven fellow scientists nearby." is not some random speculation. The other scientists recieved very severe doses of radiation due to this criticality (see the slotin article) and if it had not been stopped they would have unquestionably received lethal doses within mere seconds.

Second, the removal of the image of an external beam of high energy charged particles from a cyclotron is a completely plausable model for what an air glow of a criticality accident looks like. It is not likely at all that an actual image of a criticality accident will ever be taken and this is the closest we will probably ever have to knowing what one looks like. The mechanism for the production of ionized air in a criticality accident (mostly via the photoelectric effect and compton scattering due to high energy x-rays and gamma rays is indescernable from the ionization of air in the image produced by irradiation of high energy charged particle radiation. There is no good reason to remove either of these things from the article. --Deglr6328 01:19, 12 September 2006 (UTC)

"Immediately realizing what had happened he quickly disassembled the device, likely saving the lives of seven fellow scientists nearby." is not some random speculation.

THis implies some knowledge by our editors. We do'nt have that knowledge. Im happy for the quote to stay, but not this speculation by some anon editor.

Also the cyclotron pic doesnt actually have anything to do with the page does it (apart from the color being similar to something else.) Again this is speculation about what a criticality might look like and is therefore not fact. It is misleading to include it.--Light current 01:21, 12 September 2006 (UTC)

What if we remove the word "seven"? I think we can say with a fully reasonable degree of certainty that if Slotin received 2100 REM in a criticality of duration of certainly less than ~2s and two other scientists in the room also suffered the effects of severe radiation exposure (Dr. Graves received something like 350-400 REM) then it is obvious and sane to conclude at least a few other men present at the experiment were mere seconds away from getting lethal doses and the quick action of Slotin probably saved them. I'm not trying to deify him or something, the way he did the experiment was reckless and stupid but his quick action did save lives. --Deglr6328 01:31, 12 September 2006 (UTC)

Surely this says it all and presumably is veriable:

Said Robin Connor, a professor of physics at the University of Manitoba, "Slotin's personal sacrifice undoubtedly saved those who were in the room with him. For himself, there was no hope of recovery, something he must have known at once." We need speculate no more 8-)--Light current 01:46, 12 September 2006 (UTC)

ok that's fine with me. now about the cyclotron image.

I am still unclear on what you mean when you say: "Also the cyclotron pic doesnt actually have anything to do with the page does it (apart from the color being similar to something else.)". The image has direct application to the article I would argue. Nothing is being presented by the inclusion of the image which is misleading (I have always taken extreme caution to ensure my edits do not mislead).

Let us consider the effect of ionization of the air. The consituents of air are more or less the same no matter where you are on the planet and were undoubtedly typical at the site of all criticality accidents that I can recall reading about. It is the particular elemental composition of the air of course, which gives rise to the specific and uniqe emission spectrum of an excited mixture of said gasses. In this case, of mostly nitrogen and oxygen, it is blue (sparks, corona discharge, external cyclotron beam). All criticality accident witnesses who see the airglow event report a blue haze or glow. This is air ionization produced by high energy radiation. Here, we have an image of air ionization produced by irradiation from high energy radiation. They are the same phenomenon. Save for the bragg peak effect exhibited with the cyclotron, the diffuse transparent blue glow is what those people who have seen an accident saw. I think it is a very interesting and valuable part of the aricle, it gives insight where no other substitute can. --Deglr6328 01:48, 12 September 2006 (UTC)

I think we need other comments about the applicability of this picture.--Light current 03:37, 12 September 2006 (UTC)

Ok. list at rfc maybe.--Deglr6328 11:38, 12 September 2006 (UTC)

Yes, if you would do the honours! 8-)--Light current 11:41, 12 September 2006 (UTC)

k. done.--Deglr6328 18:48, 13 September 2006 (UTC)

Thx--Light current 19:17, 13 September 2006 (UTC)

hmmm no one seems to care.--Deglr6328 06:17, 16 September 2006 (UTC)

Well I dont really want to get into an argument over it, so well just leave it for now pending any comments. OK? BTW, thanks for being so cooperative and pleasant to deal with. I wish all my edit conflicts were as easy to deal with!--Light current 16:37, 16 September 2006 (UTC)

Ok, I've just seen the RfC. In my view, the photo is fine provided that a source can be found for the statement that: "Due to the very similar mechanism of production, the blue glow is thought to resemble the "blue flash" seen by Harry Daghlian and other witnesses of criticality accidents." If a source can't be found, it's original research. Best wishes, Jakew 18:42, 1 October 2006 (UTC)

[edit] Godiva device

The article features a pic of a 'Godiva device', but it's not mentioned anywhere in the body or the list of accidents at the bottom. I'd love to know what the story about this device was. -- MiG 23:03, 10 December 2006 (UTC)

I've just created an article on the Godiva device. -- MightyWarrior 23:51, 22 February 2007 (UTC)