Talk:Demon core

Rufus

There are some references on the net, that the "Daemon Core" was nicknamed "Rufus".

Is this true? Some References:

http://www.curtainup.com/louisslotinsonata.html http://www.paulmullin.org/Slotin%20Sonata.htm http://query.nytimes.com/gst/fullpage.html?res=9E06E7DA113FF930A35757C0A9679C8B63&sec=&spon=&pagewanted=2 —Preceding unsigned comment added by 77.49.82.116 (talk) 23:56, 13 March 2009 (UTC)

It appears that the references to "Rufus" being the core's nickname has come into popular culture by a fairly recent play by Paul Mullin called "Louis Slotin Sonata." I have not yet found any information on his source for that name. This may be a good thing to put into the popular culture section.

Rememberlands (talk) 22:41, 28 March 2010 (UTC)

all but three?

Shouldn't the innocent victims get a mention, and not just the man who caused their deaths? One assumes they were lab techs. —Preceding unsigned comment added by 71.185.20.180 (talk) 03:38, 22 January 2009 (UTC)

The number was incorrect. There were 8 men in the lab, and only Slotin died. His quick reaction doubtless kept the other seven from receiving fatal radiation doses. SBHarris 06:50, 22 January 2009 (UTC)

The other man in the room in Daghlian's accident is mentioned. I don't think saying who was present for Slotin's accident is unreasonable, and I'd like to see this sort of information preserved somewhere, so I'm going to add a paragraph similar to Daghlian's. SkoreKeep (talk) 18:08, 4 January 2013 (UTC)

Someone made a table out of the other people in the room. OK, but if a table highlights them, the list should be exhaustive, even if a bit repeticious. SkoreKeep (talk) 16:21, 31 March 2014 (UTC)

Someone made a table out of the other people in the room – Maybe something about that should be added to Human furniture. EEng 06:08, 22 December 2022 (UTC)

Caps

Seems like Demon Core should be capitalized —Preceding unsigned comment added by 129.105.140.83 (talk) 02:15, 22 January 2009 (UTC)

My thoughts exactly. Not capitalizing it implies it was a common item, which is clearly not the case, though other plutonium cores may have been given similarly Bible-reminiscent names. (There are demons in the Bible, aren't there? I haven't read the whole thing.) – 2001:569:72B0:D900:B4EC:195E:C69A:DBBB (talk) 19:58, 28 September 2024 (UTC)

Thanks for finding data!

Hi there Rememberlands,

Thank you for locating the data on the demon core-did it refer to the core as "The Demon Core", as well when it was placed into ABLE?--Read-write-services (talk) 22:31, 29 November 2007 (UTC)

The source made the connection between the two incidents and implied that the same core was used in ABLE. It did not mention when it was put into the ABLE bomb except that Slotin's test was originally intended to be the final demonstration of the core's ability to go critical before ABLE. The core was not referred to as "The Demon Core." (Rememberlands (talk) 23:47, 8 December 2007 (UTC))

Personally, I would recommend that a [citation need] sign be placed after the end of the first paragraph although I do not know understand how to indicate that. Rememberlands (talk) 06:36, 17 December 2007 (UTC)

Done--Read-write-services (talk) 21:31, 17 December 2007 (UTC)

Demon core incidents

Were these two incidents the basis for the scene in Fat Man and Little Boy where Cusack's character is involved in a similar accident? Might be worth adding to the article, if so. 68Kustom (talk) 21:59, 3 May 2008 (UTC)

Yes, these two incidents have been rolled into one for the film. There's some reference to the film in the separate discussion of the incidents (see the Slotin and Daghlian Wikis) but there's nothing here on this one. Feel free to add a short "Cultural reference" tag if you feel it's needed here. SBHarris 06:52, 22 January 2009 (UTC)

Composition?

Should there be a section with more detail about the composition of the Demon Core? Xitit (talk) 22:19, 3 July 2009 (UTC)

Do you really want to get too much more detailed? 68.13.238.221 (talk) 17:56, 2 September 2009 (UTC)

Time of Death

There is a discrepancy as to when the first victim died. This article says 25 days later but the plutonium article that linked me to this article said 28 days later. —Preceding unsigned comment added by 68.174.194.98 (talk) 06:25, 29 November 2010 (UTC)

Joseph Kanon's Los Alamos

I note an addition in the Cultural references section [1]

Joseph Kanon uses the first criticality incident as a key plot piece in his 1998 novel "Los Alamos".

which was reverted [2] as being "probably not notable." but asking for "a reference describing this allusion"

So I went over to Amazon [3] logged in there and used their 'look inside' feature; if you search for the word "dragon" the criticality accident is indeed mentioned. Repeating the search on Google Books confirms this [4] and here is a NY Times book review, which is the kind of ref I think was requested: [5]

-- Limulus (talk) 05:39, 4 May 2011 (UTC)

Inaccurate

The Slotin article has cited reference that he conducted the experiment without the normal safety precautions, this article makes it seem, uncited, like there were no safety precautions and the tests always conducted with a screwdriver. --94.134.214.19 (talk) 21:13, 8 June 2011 (UTC)

In addition, the article seems incoherent in one respect. It states that the point of the "experiment" was "to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors." This does't seem to make sense, for two reasons. (1) As was already known and as the outcome of the "experiment" demonstrated, the fissile material would become critical when the two beryllium domes came into contact. The way the article is worded, it sounds like the experiment was a deliberate act of suicide. (2) If this was really about determining something exactly, one would not do the experiment with one's hands, but with instruments designed for that purpose, which would provide a precise reading of the distance between the two domes, for example. We do not live in Galileo's time, after all.

This "experiment" does not seem to have been so much an experiment as a demonstration. All the people in the room were Slotin's juniors, apparently; he was showing them a procedure that he had done many times before but they had never seen. And the only point of the procedure as far as I can tell was to demonstrate how the Geiger counter starts clicking wildly a you bring the two neutron reflectors closer together. This is probably why Richard Feynman called this procedure "tickling the tail of a sleeping dragon".

Here's an article that gives a description of the procedure which makes sense: Slotkin was demonstrating to the person who was supposed to become his replacement how he does criticality testing. Bitten by the Nuclear Dragon

Your point and the ones I just made clearly indicate that the section on the Slotin accident requires some serious editing. -- Herzen (talk) 06:45, 11 July 2011 (UTC)

Accurate

I have added the direct link to document LA-3611 which describes the accident in detail. http://lib-www.lanl.gov/cgi-bin/getfile?00314607.pdf the differences between the movie "Fat Man and Little Boy" are essentially the date, the fact that in reality one screwdriver was used, and one hand was on the core when it happened, whereas in the movie, two screwdrivers were used, and both hands were on the safe side of the bricks at the time of the accident. Otherwise, the movie is probably an accurate depiction. 167.142.46.244 (talk) 21:39, 25 July 2011 (UTC)

Ummm, except that there was no metal brick barrier in the Slotin accident (see the recreation photos, one of which is on the page). That was borrowed from Daghlian's accident, probably because it looked more sinister, where he was building such a wall when he dropped the fatal brick. SkoreKeep (talk) 03:34, 20 May 2014 (UTC)

Radiation Induced Heart Attack?

The article says that Graves died 20 years after the accident from a heart attack that was "radiation induced". Surely there is no such thing as a radiation induced heart attack. Rwflammang (talk) 18:44, 2 September 2011 (UTC)

A Google search suggests otherwise:

• Late Effects to the Heart "radiation can damage the heart in one of several ways, including damaging the heart muscle, the valves, or the coronary arteries."
• Radiation-Induced Heart Disease: Vigilance Is Still Required "older radiotherapy (RT) techniques used in the treatment of breast cancer, particularly after mastectomy, resulted in increased rates of both cardiac morbidity and mortality."

Perhaps rewrite to 'and radiation induced cardiac damage led to a significant shortening of his lifespan; he died of a heart attack 20 years later.' -- Limulus (talk) 19:25, 2 September 2011 (UTC)

I would have thought you'd need a "probably" here as there's no way to ever know for certain, if for no other reason than the statistical unreliability of a sample base of one. Britmax (talk) 08:45, 10 April 2012 (UTC)

If a autopsy was performed, one may have a basis for this. http://radionucleide.free.fr/Stresseurs/Radioactive_caesium_and_heart_eng.pdf

"Taking into account lineal dependence between mentioned parameters, prolonged period of 137 Cs half-life and, therefore, its existence as a chemical element, small, in terms of radiation effect, levels of its accumulation in the organism, one could assume not only its radiation but pretty much its toxic influence on cardiac muscle"--Patbahn (talk) 00:00, 26 April 2012 (UTC)

This incident had nothing to do with radioactive Cesium; also it would need to be *ingested* for that effect to be seen, if it even occurs- as I recall, that is not generally accepted science -- Limulus (talk) 00:48, 26 April 2012 (UTC)

are you volunteering for the CS-137 clinical trial? Excellent.--Patbahn (talk) 03:16, 27 April 2012 (UTC)

http://en.wikipedia.org/wiki/Fission_product_yield when U-235 fissions it produces radioactive cesium at 6%, and I imagine if you are close enough, you end up breathing it. --Patbahn (talk) 03:57, 28 April 2012 (UTC)

- I remember somewhere was mentioned the likely number of fissions that occurred, and the number is ridiculously tiney compared to the number of Pu-239 atoms present in the core. Something like 1 fission for every 10^15 atoms or some such. You'd never find them.

- The fissions would happen throughout the core, but most likely in the center. No way out for the tiny number of fission product nuclei.

- The core was plated with nickel. More physically difficult armor.

- Cesium is a metal. It is not a gas, not is it likely to become a breatheable particle from fission production inside a core unless shattered. SkoreKeep (talk) 08:24, 19 January 2014 (UTC)

Cultural Reference : We were there at the opening of the atomic age

Does anyone remember the "We were there" novels?

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

well, as I recall the one "We Were There at the Opening of the Atomic Era" includes the tickling the dragons tail incident in the book.

Now I don't know if anyone can get a page and volume cite, to make it official, but, I thought I would mention it.

http://www.amazon.com/were-there-opening-atomic-books/dp/images/B0007E1AAS the cover art was actually pretty cool....

so at any rate, shouldn't the cultural references section include a reference to this? Patbahn (talk) 05:18, 10 April 2012 (UTC)

Improved performance

From the Intro:

"The core ... proved in practice to have a slightly increased yield over similar cores which had not been subjected to criticality excursions."

This statement seems to imply some unexplained influence that the excursions may have had on the core. My understanding on this is that if anything (and I think any physical influence would have been vanishingly, immeasurably small), the buildup of fission products should have caused it to be ever-so-slightly worse, and slightly more prone to premature fizzle. The reasons I have heard stated for the better performance is that the prolonged experiments (8 months of experiments leading to Daghlian's and Slotin's fatalities) caused the core to be better tuned than the "good-enough" war cores were. The experiment was designed to maximize the mass of the core for higher super-criticality during the implosion, while maintaining safety and stopping premature warming behavior before firing. Does anyone have a reference which might support that conclusion, or even the reverse? Until such is supplied, I'm removing the sentence. SkoreKeep (talk) 18:01, 4 January 2013 (UTC)

I object to your removing a simple verifiable statement of fact over what you think it might imply, when no such intimation is actually made (though I wouldnt object to a caveat statement that none of this proved much except that a thing like this could still work after a couple of excursions). Particularly if the only reason for removing the factual statement is that it might imply something that contradicts your own far more unlikely theory that this core was somehow modified along the way to maximize anything. The core was existent so soon after the end of the war that it was in all likihood the core of bomb #3, already in San Francisco being readied for shipment to Tinian to be assembled with the next bomb when Japan surrendered. These things were made In a very standardized size, to such tolerances that they couldn't even fit the core of the Trinity bomb until the casing warmed up after cooling overnight in the shot tower. They were nickle plated, full of toxic material, and not the sort of thing people would be grinding, shimming or messing with. I wouldn't have expected a few fissions, a tiny part of the total yield, would have any effect, up or down, unless some long lived fission product like Cs-137 or Sr-90 somehow initiated some odd nuclear reaction that led to a spallation neutron, pre-detonation and fizzle. Apparently that didn't happen, and that's about all the test tells us. SBHarris 19:33, 4 January 2013 (UTC)

The implication in the quoted statement is that the excursions were the cause of the improved performance; that does not seem to be a "simple verifiable statement of fact". If you have a reference to back the implication up, then I will yield the point. As a matter of fact there is a statement near the bottom of the article (which I did not put there) which states my claim, that it was their tuning of the core that improved its performance, not the excursions themselves. I agree with what you are saying about the machining; it seems to me that the excursions would have created fission products in the core, including the neutron poisons mentioned in the article by that name, under fission products. (83Kr, 95Mo, 143Nd, 147Pm and so on).

Perhaps I'm missing something. Why exactly were the core subjected to the tickling? Was it merely to confirm the high probability of criticality at implosion? That would make an interesting line at add to the experiment description, if anyone knows or can find the truth.

In any case, I'm not sure such an observation is important for inclusion in the introduction no matter which is right, inasmuch as it is addressed later. If you think that as a n00b I'm just being a cowbell about this and decide to revert, you may want to reconcile the two statements. SkoreKeep (talk) 23:20, 4 January 2013 (UTC)

No, on the contrary, my apologies, as you had already removed the most offensive sentence from the lead and I simply missed the second one. Of course, both are wrong, as the second shot of Operation Crossroads had the same 23 kt yield as the first one (which was the demon core). So clearly the excursions in the first core had no effect either way and anyone saying otherwise is wrong. Why both of these cores gave 23 kt vs. the 21 kt of Nagasaki isn't clear to me, or even that the difference is significant. I don't know the reason for it, but it isn't in the cores. The "demon core" WAS a WW II bomb core, as demonstrated by its very existence for the Daghlian accident Aug 21, 1945, at a time when the US only possessed about two cores and perhaps only one (they were using them as fast as they were making them, and Rhodes says this was about one every month at the time of Nagasaki). The two shots at Crossroads were supposed to be essentially duplicates of the Nagasaki bomb, and it's difficult to think of how else they could have improved on that design without changing the design. So I would put your sources as very unlikely.

The "dragon-tickling by hand" experiments were used (as opposed to the Godiva drop experiments) for investigating the nature and time-constants in the "critical but not prompt-critical" region of criticality in the plutonium critical mass, and not really (so far as I can tell) for improving (or degrading) the assembly in any way. As for neutron-absorbing poisons as fission products, they are well-known, but they only show themselves after some hours of full power in a nuclear reactor (which is why the US didn't even discover them until they ran their first water-cooled scale pre-Hanford reactor at full power for some hours), so it seems really unlikely that these would have been produced in so little an amount of fission that the demon core wasn't even melted (though it probably came fairly close to melting at 10^16 fissions = 320 kJ = 347 C temp excursion for a 920 J/K heat-capacity core; twice that energy WOULD melt it). Also, neutron-poison fission products all have short half lives-- measured in hours, not the weeks needed to degrade this core for a test many weeks later. Again, I'm very skeptical that this kind of thing would make any difference in performance, and (if the second Crossroads shot is our control for the first) it did not.

I'm going to add the fact that the Demon Core was used in the first US bomb test after the war, which it was.SBHarris 04:39, 5 January 2013 (UTC)

Contradicting itself?

In the "Second Incident" section, after the burst of radiation, Slotin reportedly knocks the beryllium half-spheres apart, "stopping the chain reaction and likely saving the lives of the other men in the laboratory." But the article then says that "the heating of the core and shells stopped the criticality within milliseconds of its initiation." From the way it's written, it sounds like it's contradicting itself; first it says Slotin stopped it, then it says it stopped itself. I think it could use some improvement. Light Peak (talk) 20:47, 30 April 2013 (UTC)

The second explanation came somewhat after the accident, and is by its nature something of a speculation, as no one ever has tried to experiment with it, as far as I know. Just how tightly did the spheres fit the core? How quickly did the core heat? Was there any trapped air? Lots of questions there are no good answers to. Then there is a natural tendency to not want to take away from Slotin his correct action; had he not knocked the shell off, it likely would have repeatedly settled back onto the core as it cooled and cycled again. See next question below. SkoreKeep (talk) 08:48, 19 January 2014 (UTC)

In response to User718499522 who complains 'The claim that "it is now known that the heating of the core and shells stopped the criticality within milliseconds of its initiation" is scientifically baseless and is not referenced and/proven in any of this articles sources.' The source is an article about Raemer Schreiber: "...it was stopped by the expansion of the core and the beryllium." Dr. Schreiber, a physicist, was one of those in the room with Slotin when the accident occurred, and who probably knew more about the accident than any other person. Schreiber went on to work for the AEC/DoE until his retirement, and for one thing designed the remote system that replaced the hands-on methods used to such sorrow. However, I will continue looking for a more definitive statement about that, presumably one with numbers to back it up. I believe this statement should suffice in the meantime. Watch your "scientific baseless", if you please, and note that the Schreiber article was one of the article's sources from long before today. SkoreKeep (talk) 07:27, 18 May 2014 (UTC)

I started a recent post about this under "The heating of the core and shells" but just saw this post so wanted to respond. Regarding the sentences, "Instantly, there was a flash of blue light and a wave of heat across Slotin's skin; the core had become supercritical, releasing an intense burst of neutron radiation estimated to have lasted about a half second. Slotin quickly twisted his wrist, flipping the top shell to the floor. The heating of the core and shells stopped the criticality within seconds of its initiation." Source 15 an interview by Dr. Schreiber doesn't mention the color blue, that Slotin felt heat on his skin, that it took seconds to stop, or that it was 'heat' that stopped the reaction but instead that, "It was stopped by the expansion of the core and beryllium, but it was enough to put out a lethal shot of radioactivity." You said, "had he not knocked the shell off, it likely would have repeatedly settled back onto the core as it cooled and cycled again" however I don't see a source saying it had opened before Slotin flipped the top reflector. If regarding Schreiber's comment about expansion and assuming the core's size expanded lifting the top reflector ajar but in nuclear reactions thermal expansion usually refers to heating reducing the core density reducing the core to subcritical and this is what it seems Schreiber is referring to. The "half second" line is referring to source 6 the Los Alamos Labs review of criticality incidents, 2000 Revision report, "The results of fission rate calculations in this sphere, as a function of time for several values of excess reactivity, are shown in Figure 43. Figure 44 represents the total number of fissions to be expected as a function of time for the same excess reactivities. These data are applicable to both accidents because the difference in reflector material has only a small effect on the neutron kinetics. In the first excursion, if the excess reactivity did not exceed 15 ¢, the assembly must have been together for several seconds, which is not unreasonable. In the second event, the experimenter was better prepared to disassemble the material, and it is thought that this was done in a fraction of a second, perhaps <1/2 second." I read it to say exposure calculations were based on the estimated half a second it took Slotin to remove the top reflector which 'implies' that is when the reaction stopped. But the reports analysis also says, "The study and understanding of initiating events and shutdown mechanisms associated with criticality accidents offer potential for limiting the frequency and consequences of such untoward events... These programs, which involved solutions of highly enriched uranium, are supplemented by a series of measurements at Los Alamos using the SHEBA assembly. This assembly is fueled with a 5% enriched uranium solution, that provides information on dose rates near excursions in systems of lower enrichment.88 Analysis of data from KEWB and CRAC has led to relatively simple computer codes that follow the early transient behavior well and rely on thermal expansion and the formation of radiolytic gas for the shutdown mechanisms." So this portion seems to say thermal expansion is a factor if not a key cause of such a shutdown. With out more information I think remarks regarding the color blue, that Slotin felt heat on his skin, and that it took seconds to stop, and even what stopped it, and instead use the reports' implied meaning, 'neutron radiation, the exposure of which was calculated based on the estimated half second between when the sphere closed to when Slotin removed the top reflector.' Also should remove the line, "while Slotin's reaction prevented a recurrence and ended the accident" since there is no source provided saying if it was shut down by thermal expansion if cooling would allow it to restart so at most could currently be described as a precaution but also regarding the phrasing "ended the accident" I don't think you can end an accident any more than you can end a murder, the classification wouldn't change and we still don't have a source in any case. Michaelbaribeau (talk) 19:23, 12 December 2023 (UTC)

Clarification needed

It needs to be stated, preferably in the lead section, whether or not there was any possibility of a nuclear explosion in either of these incidents. When I first read "which went briefly critical" I thought it was saying that there was. Later on, when the article talks about "presumably saving the lives of the other men in the laboratory" (i.e. rather than saving the whole of Los Alamos and surrounding area), I began to think probably there wasn't. I think this should be clarified. 86.160.86.232 (talk) 04:20, 4 December 2013 (UTC)

He saved them from further irradiation from the core. It cannot explode in a nuclear sense, that takes careful timing, but it can pre-detonate, that is, get hot enough to melt quite quickly, spatter all over hell and gone, and at that point very likely loose critical geometry, but in the meantime it could irradiate everything within several hundreds of feet, perhaps out to a kilometer very thoroughly, and release limited amounts of fission products. It could neutron-activate a lot of substances, making the whole area radioactive, just as the bomb does, but without the blast effects. What it could do depends on dozens of external factors, and is difficult to predict with certainty. SkoreKeep (talk) 08:38, 19 January 2014 (UTC)

I read in one of Richard Rhodes' books that a physicist one told him that with a pair of hemispheres of bomb-grade uranium which together were supercritical, banging them together by hand and trusting nature for a wandering neutron would be sufficient to cause a blast in the 1-10 ton TNT-equivalent region. What a way to go. SkoreKeep (talk) 17:43, 1 August 2014 (UTC)

Third Core

The article is short on details about the core itself. We know that a third core was produced and that it was due to leave Kirtland Field for Tinian on 15 August 1945, and that a fourth was scheduled for September. It therefore seems certain that this core was the one involved in Harry Daghlian's death. Can we find a source for this anywhere? Hawkeye7 (talk) 09:59, 4 April 2014 (UTC)

OK, I have a fine source for that history, and I'll write it up today. SkoreKeep (talk) 15:39, 4 April 2014 (UTC)

Done. I'm not absolutely sure that the Demon core was the third or the fourth core; I don't know how strict keeping track of the four available hemispheres was at Los Alamos, but there is no indication that it was not. I doubt there were any distinguishing marks on the halves. According to Wellerstein's blog, there is a discrepancy of 1.376 kg in Hanford's and Los Alamos' assays of the shipped amounts (see footnotes on "Third core's revenge" article), and that lead to some investigations, the result unknown. Mistakes were not unknown. SkoreKeep (talk) 22:38, 4 April 2014 (UTC)

Clarification?

The article says that Daghlian was "working alone" when the accident occurred, but then Hemmerly is listed as having also received radiation with no explanation of how/where. The text should perhaps clarify somehow that Daghlian was the sole person working with the core, but Hemmerly was sitting nearby in the room as a security guard. - Ichneumon~enwiki (talk) 01:18, 15 August 2015 (UTC)

 Done Hawkeye7 (talk) 01:37, 15 August 2015 (UTC)

Me too. Simultaneous edits. SkoreKeep (talk) 01:50, 15 August 2015 (UTC)

shoulda been called "lucky"

Surprisingly FORGIVING despite terminal recklessness by so-called "trained professionals"... kinda shocking how they only did so little damage. The people to feel sorry for are the enlisted guards who were under orders to be present and silently watch as the eggheads messed with lethal things without a second thought. — Preceding unsigned comment added by 68.231.213.34 (talk) 08:17, 15 November 2015 (UTC)

Inaccuracy re: use in Operation Crossroads

A recent article by Alex Wellerstein (who as far as I know is a well regarded nuclear historian) claims that the demon core was not used in Operation Crossroads: it had been scheduled to be used, but was still too radioactive by the time of the test and was later melted and used in a new bomb. Since there are cited claims to the contrary already in the article, it would be great if someone with the requisite knowledge in the field could look into this further and make the correction if necessary.

--Doncurzio (talk) 17:58, 22 May 2016 (UTC)

Alex is so regarded, and if he says there are records stating such a fate for the core, then that quite likely the latest word on the core's fate. I will edit the article to comply, using Wellerstein's article as the source. SkoreKeep (talk) 19:58, 22 May 2016 (UTC)

Agreed. I have also updated the articles on Harry Daghlian and Louis Slotin. Hawkeye7 (talk) 22:29, 22 May 2016 (UTC)

Given Wellerstein lists no sources in his article I disagree that it should be used over other sources. Would like it if someone could find what he used as sources for his article.

--Lucinator (talk) 17:42, 14 June 2017 (UTC)

See [6] here for details. Hawkeye7 (talk) 23:44, 15 June 2017 (UTC) Amended URL: SkoreKeep (talk) 01:07, 16 June 2017 (UTC)

Alex cites his source as a conversation with Glen McDuff, a retired scientist at Los Alamos, who is "working on an article about the fate of the first eight cores". Perhaps ultimately we will have something citable. SkoreKeep (talk) 01:16, 16 June 2017 (UTC)

Suggested update to table of exposures

NOTE: I intend to make the changes mentioned below on or after 1 May, 2018 (PST) unless anyone has any objections. DacodaNelson (talk) 21:28, 27 April 2018 (UTC)

I've already moved the larger list of exposures for everyone involved with the "Demon Core" into its own section on the page as it's more appropriate that way. However, I believe it would be appropriate to add another column to that chart to show the times the individuals were exposed to the dosages. Currently the chart only lists the overall estimated dosage which is alright, but in terms of radiation exposure, time is a critical factor. The measurements in the table are cumulative and therefore the time the individuals were exposed to those doses would effect the seriousness of the exposure. I propose updating the chart as follows. Note: I've taken the information from the source listed in the "Dose" column header reference - they are estimated times of exposure listed in the latest report on the topic. Obviously no one took a stop-watch out to measure their time in the vicinity of the source but give or take 5 minutes isn't going to make a huge difference - these are fairly extreme exposures.

Also important: this new chart I've created would be best placed in the "Results of subsequent studies" section I've created. It would include both the first and second incidents' charts all in one location, showing a list of people exposed and the relevant information. DacodaNelson (talk) 00:15, 25 April 2018 (UTC)

Name	Origin	Age at accident	Profession	Dose	Estimated time of exposure	Aftermath	Reference
Haroutune "Harry" Krikor Daghlian, Jr.	New London, Connecticut	24	Physicist	200 rad (2.0 Gy) neutron 110 rad (1.1 Gy) gamma	$\geq$ 10 minutes (estimated)	Died 25 days after the accident of acute radiation syndrome, haematopoietic focus
Private Robert J. Hemmerly	Whitehall, Ohio	29	Special Engineering Detachment (SED) guard	8 rad (0.080 Gy) neutron 0.1 rad (0.0010 Gy) gamma	$\geq$ 10 minutes (estimated)	Died in 1978 (33 years after accident) of acute myelogenous leukemia at the age of 62
Louis Alexander Slotin	Winnipeg, Manitoba, Canada	35	physicist	1,000 rad (10 Gy) neutron 114 rad (1.14 Gy) gamma	$\lesssim$ 5 minutes (estimated)	died 9 days after the accident of acute radiation syndrome, gastrointestinal focus
Alvin C. Graves	Austin, Texas	34	physicist	166 rad (1.66 Gy) neutron 26 rad (0.26 Gy) gamma	$\lesssim$ 5 minutes (estimated)	died in 1965 (19 years after the accident) of myocardial infarction, with aggravating "compensated myxedema and cataracts", while skiing
Samuel Allan Kline	Chicago, Illinois		physics student, later patent attorney		$\lesssim$ 5 minutes (estimated)	died in 2001 (55 years after the accident); refused to take part in studies
Marion Edward Cieslicki	Mt. Lebanon, Pennsylvania	23	physicist	12 rad (0.12 Gy) neutron 4 rad (0.040 Gy) gamma	$\lesssim$ 5 minutes (estimated)	died of acute myelocytic leukemia in 1965 (19 years after the accident)
Dwight Smith Young	Chicago, Illinois	54	photographer	51 rad (0.51 Gy) neutron 11 rad (0.11 Gy) gamma	$\lesssim$ 5 minutes (estimated)	died of aplastic anemia and bacterial endocarditis in 1975 (29 years after the accident)
Raemer Edgar Schreiber	McMinnville, Oregon	36	physicist	9 rad (0.090 Gy) neutron 3 rad (0.030 Gy) gamma	$\lesssim$ 5 minutes (estimated)	died of natural causes in 1998 (52 years after the accident), at the age of 88
Theodore Perlman	Louisiana	23	engineer	7 rad (0.070 Gy) neutron 2 rad (0.020 Gy) gamma	$\lesssim$ 5 minutes (estimated)	"alive and in good health and spirits" as of 1978; probably died in June, 1988 (42 years after the accident), in Livermore, California
Private Patrick Joseph Cleary	New York City	21	security guard	33 rad (0.33 Gy) neutron 9 rad (0.090 Gy) gamma	$\lesssim$ 5 minutes (estimated)	Sergeant 1st Class Cleary was KIA on 3 Sep 1950 while fighting with the 8th Cavalry Regiment, US Army in the Korean War.

Don't see the point myself, and I would have considerable concerns that the proposed treatment might mislead the unwary/average reader. According to p7 of Hempelmann et al (and as one might expect from a criticality of thankfully limited duration):

Neutrons, the principal component of the incident radiation, were emitted instantaneously during the fission process. The gamma ray component was composed of prompt and delayed gamma rays. The prompt gammas were emitted during the fission process or were given off within the bodies of the subjects as a result of hydrogen capture of neutrons. The delayed gammas were emitted by the fission products and by radioactive elements induced by the incident neutrons. In these cases, the delayed gammas accounted for only a small fraction of the total dose.

so (total) exposure time is relevant to only 'a small fraction of the total dose', and most of the estimated dose will have been incurred at a much higher doserate than might be inferred by dividing (estimated dose) by (estimated (total) exposure time) Rjccumbria (talk) 00:03, 28 April 2018 (UTC)

Don't agree with the changes. The changes appear to amount to placing the two groups of victims into one table, and to add a column about exposure time. The numbers in that column are all estimates, and I don't think they represent anything significant in any case. All the victims, especially Daghalian and Slotin, received their fatal doses within, at most, seconds of each incident, not minutes. Five to ten minutes after the events there was likely very little radiation being emitted. These estimates add nothing to the events. Yes, time is important but for dosages the radiation curve is much more so. Of what significance, for example, is that the first accident participants all get awarded 10 minutes exposure while all the people in the second only have 5 minutes? SkoreKeep (talk) 17:56, 14 May 2018 (UTC)

I suppose that I agree with both of these arguments in substance, but not in terms of how they relate to the so-called "average reader." Firstly, who is this average reader that we're concerned is going to start making bad life decisions based on this article and why are they in a position to be exposed to a criticality event in the first place without understanding elementary nuclear physics? Secondly, we should note that the individuals who died were immediately adjacent the core at the time of the event while others were elsewhere: we cannot assume those others were exposed to a majority of their dose immediately since, assuming isotropic emission (which is unlikely given the layout of the room and the core itself but a good guesstimate) then exposure would fall as r^2. While the two who died certainly received their fatal dose virtually instantly, the others were likely given an incredibly high blast, but low enough that it would be prudent to immediately evacuate as every second in the vicinity is going to increase their exposure (let's not forget, prompt or otherwise, neutron emission is going to cause secondary emission and radioactivity in everything it touches so background radiation in the area has now gone up markedly). So I suppose I'd say that if this average reader makes the naive conclusion that all doses can simply be divided by time exposed, they'd be more likely to come to the correct conclusion that immediate evacuation is essential. While it may not make a difference for certain people nearby the event, others could be just shy of enough exposure at t=30 seconds (when everyone begins to realize what just happened) and now need to get out or they're going to die. Whether they know this because they realize they're already at most of their final dose at t=45 seconds and need to limit the small accumulations they're currently receiving, or because they erroneously believe they're reducing their final dose by much at all, the correct procedure is always immediate and orderly evacuation to the nearest medical facility for intensive monitoring. I do like the point about putting both of them in the same chart though. Perhaps this: we add a section specifically for the doses and then create two charts: one for those who died and one for those who were simply exposed, but they both contain the estimated times exposed. We can then add some explanation about how the radiation curve, criticality, and radiation exposure work (with plenty of links to relevant articles of course!) with the point of emphasizing both what you've both mentioned, and what I've been rambling about which is primarily that whether or not a fatal dose is reached by t=3 seconds or t=600, exposure needs to be limited and evacuation procedures carried out immediately if for no other reason than the fact that it may be that 10 seconds of higher than usual background radiation that pushes you to your limit, so becoming fatalistic after criticality is not the way forward. DacodaNelson (talk) 18:12, 14 May 2018 (UTC)

Well, since you agree with the above arguments, it is to be hoped you will not proceed with the table. The article is not intended to be a guide to 'what to do when the crit alarm goes off' - anybody who might find themselves in that situation (many of whom will not have an A-level in nuclear physics (and thereby will probably be less of a risk to their colleagues than the boffins in lab coats who 'know what they are doing')) should have had adequate training (including the vital information of what the crit alarm sounds like, and when it is tested). The article should give reliable information about past events in a form suitable for the 'average reader' . As noted above, for that target readership, the proposed table is doubly misleading. It was originally proposed on the basis that dose rate (rather than total dose) was important, but I see that arriving at dose rate by dividing total dose by the reported time spent in the vicinity of the criticality location (the parameters reported) is now rightly dismissed as "naive". That being so (as indeed it is: everybody who got a significant dose (immediate or committed) did so during the actual criticality), it is not clear what the point of including time in vicinity of location would be. Furthermore, the estimates given of that time in the reports cited have all the signs of being purely nominal, and not deserving of being given the prominence you propose.

And yes, you should always evacuate promptly if the crit alarm goes off, but hopes should not be raised that this gives significant dose mitigation, although in some circumstances it might mean avoiding dose from a subsequent repeat criticality. Quite simply, there needs to be a roll-call and a debrief away from the scene of the event before anybody makes a re-entry to tackle the aftermath. Rjccumbria (talk) 00:51, 15 May 2018 (UTC)

References

Atlantic Article change

Comes DonFB adding information to the Demon Core article based on an Atlantic magazine article. He wants to add "Early in the manufacturing process the core existed as rods of stable uranium-238.", a fact quoted from the Atlantic article. Another addition is "similar to the second core used in the bombing of Nagasaki)". That last is true enough, though also somewhat off the path.

The first sentence refers to the fact that the fuel used at Hanford reactors was rods of somewhat enriched uranium from the calutrons at Oak Ridge; it is not pure U-238, which would be essentially inert. The fact that they originated that way is not germane to the Wikipedia article; it doesn't add any understanding. That's OK in an Atlantic article, but here it is not appropriate. The Atlantic is trying to make a point about the core itself:

"The demon core, destined for use in a weapon of mass destruction, was designed to have a hair trigger. It was meant to be in a “-5 cents” configuration, meaning that it would take only 5 percent more plutonium for the core to go supercritical and result in a radiation accident. In other words, the core was always right on the edge of going off. A few errant neutrons would be enough to trigger a deadly chain reaction. The scientists knew that the core was unstable, though now they had the opportunity to measure just how close it was to going critical and how, with different techniques, it might be brought even closer."

The paragraph is misleading about how "unstable" the core was; it also is somewhat facetious about what the purposes of the test and the testers were. As it was, it was incredibly stable. The only things that could push it over the edge were specially shaped beryllium castings, tungsten bricks, a uniquely designed explosive lens, or more specially shaped plutonium pieces, which did not exist in the solar system at the time. It was perfectly safe to handle, it could have been dropped, smashed with hammers, melted down, all without a possibility of criticality. Pictures of it or its cousins being carried around in a plywood box further attest to that, or at least the belief that it was safe. It is safer than the cast ring pictured in Plutonium. The article misleads to make a point, that in my opinion is weak and doesn't need to be made.

Off with its head. SkoreKeep (talk) 17:34, 14 May 2018 (UTC)

• Agreed.

Although in terms of stability, don't confuse criticality and prompt criticality. A weapons-grade criticality, with a full power explosion, might need compression by explosives and a neutron initiator, but a fizzle (a low power detonation) would be less fussy and a criticality incident, sufficient to raise the neutron flux to a human-fatal level was, with hindsight, all too easy. Andy Dingley (talk) 17:40, 14 May 2018 (UTC)

Certainly I am aware of that, and everything written was written from the understanding of plain old criticality. The only way to achieve prompt criticality, afaik, is with the use of the explosive lenses, which drive the core from it's normal $-0.05 to well over $1.00. Had it been possible to drive it that high with any simpler measure, all the development work of the Manhattan Project would have been useless overkill. I have to disagree with the "easy" part. In one case it took machined tungsten carbide blocks; in the other a pair of specially cast and machined beryllium parts. While they may be found on street corners in Los Alamos, I've never seen either in my lifetime, and I know of no other possibilities. SkoreKeep (talk) 18:14, 14 May 2018 (UTC)

@SkoreKeep: Is your primary objection to my edit because you believe--unjustifiably in my opinion--that the added information "is not germane to the Wikipedia article; it doesn't add any understanding", or because you would prefer that Wikipedia not introduce its readers to the Atlantic article, which you assert is "misleading"? You misstated that I made "another addition", namely, the text "similar to the second core used in the bombing of Nagasaki", when in fact virtually identical text already existed, with the only change being from "like" in the original text to "similar" in my edit. Regarding the section of the WP Demon core article titled "Manufacturing and early history": the information I added to that section about the manufacturing process is no less germane than, for example, telling readers the plutonium "was shipped from the Hanford Site in Washington state to the Los Alamos Laboratory", nor less germane or helpful to readers' "understanding" (your term) than showing them a quotation of arcane terminology that Los Alamos had "expended HS-1, 2, 3, 4; R-1" (and two additional such quoted terms). Regarding your assertion that part of the Atlantic article is misleading: is this your personal opinion based on your academic expertise, or is it based on reference(s) that you can adduce? Existing text in the lede of the Wikipedia article–"It was designed with a small safety margin to ensure a successful explosion of the bomb"–appears to contradict your comments about the Atlantic article. DonFB (talk) 21:49, 14 May 2018 (UTC)

Hanford produced Pu starting with natural U, so the one piece of information added from the Atlantic article would seem to be slightly wrong, which would suggest it shouldn't be added. End of story.

That would also seem to rule out the Atlantic article as a reliable source, but @SkoreKeep: is probably 'selling beyond the close' by pointing out that there seems to be quite a bit of axe-grinding going on in the Atlantic article. However, he is right: a safety margin of 5% would justify a claim that the scientists knew it needed to be handled with care, it does not justify a claim that it was unstable : there was a safety margin, and it was adequate against normal perturbations. "Annual income twenty pounds, annual expenditure nineteen nineteen six, result happiness. Annual income twenty pounds, annual expenditure twenty pounds nought and six, result misery." Rjccumbria (talk) 01:34, 15 May 2018 (UTC)

I used the phrase "Early in the manufacturing process", not "Before manufacturing began....", so, no, it's not "end of story", and it is flatly wrong to say the rather uncontroversial information I added is "slightly wrong." However, I will acknowledge that the Atlantic's use of "unstable" is not the best descriptive choice, but my edit did not allude to that portion of the Atlantic article. DonFB (talk) 04:44, 15 May 2018 (UTC)

error in definition of reactivity

-5 cents of reactivity is an amount of reactivity equal to 5% of the delayed neutron fraction. This is pretty small, about 0.03% reactivity. The article mistakenly equates that to 5% reactivity. 5% reactivity is pretty huge ... for example, the NRC requires that the spent fuel pits are kept less reactive than -5%. If the demon core was -5% reactivity it could never have accidentally gone critical just like a spent fuel pit cannot accidentally go critical.

When I fixed the error, my fix was reverted.

Beprepn (talk) 15:55, 27 February 2019 (UTC)

References

• Yeah, that didn't sound right to me either. Fixed. ST47 (talk) 02:06, 2 July 2019 (UTC)

One historian's opinion

Djkinney desires to add a parenthetical comment in the text to let the reader know that the facts of the case are only one historian's opinion. I object to this on the grounds that while it is one historian's researched opinion on what happened, Wellerstein, very well regarded in this field, has backup from Glen McDuff, another scientist/historian working in the testing history. Further, there is no alternative theory about where the core went. The parenthetical comment is true enough, but has no place in this article; in this kind of esoteric field, it's often true that we are working on a single person's memories or logical conclusions. It represents Djkinney's opinion about the paragraph contents (I presume), and that opinion is uncalled for in the actual article. The references are there for the reader to draw his own conclusions.

I removed the comment. SkoreKeep (talk) 17:14, 31 August 2019 (UTC)

Solid core hemisphere?

Quote: The demon core was a solid sphere ... It consisted of three parts: two plutonium-gallium hemispheres and a ring

That's a direct contradiction. Was it a solid sphere or two hemispheres? And what's a "ring"? Thanks, Maikel (talk) 10:06, 18 July 2020 (UTC)

The core was a solid sphere, as opposed to a hollow one. The grapefruit-sized core consisted of two hemisphere-shaped sections. If you put two hemispheres together, they can slip sideways, so in the middle was a ring with a triangular cross-section which prevented this. Putting the three together created a sphere. There was a small hole in the centre for the polonium-beryllium neutron initiator. The short half-life of polonium-210 (about 138 days) was why the core needed to be capable of being pulled apart. Hawkeye7 (discuss) 19:14, 18 July 2020 (UTC)

Graves' health

The article claims that "Graves was hospitalized for several weeks with severe radiation poisoning and developed chronic neurological and vision problems as a result of the exposure" but I can't find any sources on this. The source provided for this claim does not say this, at all. The source says "After recovery from a six month episode of weakness following exposure, Case 4 resumed his scientific duties. Except for mild hypertension, which predated the accident, he appeared to have recovered completely from the effects of the exposure." Also, he appeared to have some heart and thyroid problems (unclear if related to the incident) but neither of those are "chronic neurological and vision problems" — Preceding unsigned comment added by 84.217.48.2 (talk) 15:15, 19 October 2021 (UTC)

confused by the introduction

The introduction currently states:

It was involved in two criticality accidents, on August 21, 1945, and May 21, 1946, each of which resulted in a fatality. [... cut unrelated sentence regarding the origin ...] As a result of two separate criticality experiments performed at the Los Alamos Laboratory attempting to show that the core was close to criticality, the device was accidentally placed into a supercritical configuration. As a result, scientists Harry Daghlian and Louis Slotin suffered acute radiation poisoning and died soon after.

So, is that two criticality accidents and another two criticality accidents after the previous ones (total four criticality accidents, four deaths)? That's how the introduction reads to me currently.

Maybe you should move the unrelated sentence a bit up and adjust the wording to fix it? --91.150.22.107 (talk) 12:24, 2 July 2022 (UTC)

Possible "Popular Culture" Section in wake of current events

I would like to raise the question of perhaps adding a "Popular Culture" section to discuss the internet popularity of the incidents. In particular, the recent video by Kyle Hill about his previous video regarding the incident. Would it be feasible to discuss this element while still respecting the integrity of the accident's victims? If so, I would like someone more knowledgeable on the subject to make the edits, as I myself only possess a surface level understanding of the subject.

ZachT1234 (talk) 20:06, 2 August 2022 (UTC)

Prompt critical or supercritical

Article currently reads in each case, the core was accidentally placed into a supercritical configuration.

That's not what happened at all. Criticality or even supercriticality was not enough. Supercriticality would produce a growing chain reaction, but not necessarily a rapidly growing one. There is every chance that prompt criticality was briefly achieved. And that is a different thing altogether. Andrewa (talk) 07:58, 1 December 2022 (UTC)

LANL report (footnote 11 currently) describes Daghlian accident: "...the brick slipped and fell onto the center of the assembly, adding sufficient reflection to make the system superprompt critical..." (page 30) Report does not specifically assign a term to the Slotin accident; simply says, "a burst occurred". (page 31) Discussing both incidents, the report says, "...the fact that the nickel coating did not rupture indicates that the excess reactivity over prompt critical was not more than 10 or 12 cents." (page 32) So the report in one case explicitly mentions "superprompt critical" and for both, it apparently indicates prompt critical was exceeded.

https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-03611

DonFB (talk) 11:24, 1 December 2022 (UTC)

Exactly. Thank you for the source.

Supercriticality was not enough to cause the accident. The accident was that excessive supercriticality was produced. I am happy to accept that even prompt criticality was briefly achieved, as your source indicates. The rig was supposed to go briefly and slightly supercritical. That was the whole idea.

But many people seem to believe that supercriticality means prompt criticality. In fact every nuclear reactor is designed to go supercritical, and would not work otherwise. Blogs and political websites commonly make this mistake. Perhaps it's not always even a mistake. Supercritical sounds much scarier than prompt critical, when really it is the other way around.

Do you think your source is sufficient to correct the article to read in each case, the core was briefly and accidentally placed into a prompt critical configuration? IMO that would be the normal and accurate way of expressing what occurred according to your source. The current text is just repeating the common confusion. Andrewa (talk) 13:33, 2 December 2022 (UTC)

I think your wording--"placed into a prompt critical configuration"--is probably more accurate than the existing text. I would like to advocate, however, for a less jargony expression. Here is my proposal for the Introduction:

------------

The demon core was a spherical 6.2-kilogram (14 lb) subcritical mass of plutonium 89 millimeters (3.5 in) in diameter manufactured during World War II by the U.S. Manhattan Project as a fissile core for an early atomic bomb. The core acquired its nickname after causing the deaths of two physicists, Harry Daghlian and Louis Slotin, who were experimenting with it at the Los Alamos Laboratory. In each case, on August 21, 1945, and May 21, 1946, they were doing tests to demonstrate how close the core was to criticality, but they unintentionally made the material become highly radioactive, subjecting them to brief but intense radiation that caused their deaths within days.

Before the accidents, the core had been prepared for shipment as part of the third nuclear weapon to be used against Japan, but when that country surrendered, the core was retained at Los Alamos for testing and potential later use.

------------

I have often come across semi-technical articles whose Introductions are loaded with or dependent on jargon that an average reader will not know (like "tamper" in a nuclear context). Such practice goes against multiple site policies/guidelines that urge ledes be written to be readily understandable to the widest possible audience, an idea I heartily support. Many overly technical ledes include linked words to other articles to explain the jargon, which I feel is a disservice to readers who should be able to easily peruse a smooth-reading clear overview, rather than being forced to click multiple links that may take them far afield and waste their time. </rant> Anyway, let me know what you think. DonFB (talk) 04:33, 3 December 2022 (UTC)

but they unintentionally made the material become highly radioactive doesn't mention criticality. That avoids the current (and common) misuse of the term supercritical, true.

But the essence of the incident is not just that the core was briefly intensely radioactive (with neutron radiation). That was a consequence of the fission chain reaction. It was the chain reaction that was the problem. So I think that it needs a mention, whether by (correct) use of a technical term or by explanation or by both. Andrewa (talk) 23:36, 5 December 2022 (UTC)

Here is another possible version of wording for the Introduction, taking into account your focus on fission:

"...but they unintentionally caused excessive fission in the material, subjecting themselves to brief but intense radiation that caused their deaths within days."

In the section "First incident", first paragraph, can be found a reasonably clear explanation, with further details, appropriate for the body of the article, of what happened. DonFB (talk) 10:28, 7 December 2022 (UTC)

The heating of the core and shells

In the Second incident content section, 3rd paragraph is the sentence, "The heating of the core and shells stopped the criticality within seconds of its initiation[15] while Slotin's reaction prevented a recurrence and ended the accident." Saying it was heating is too broad an explanation. In keeping with the actual quote from reference source 15 as well as this additional source, National Academies of Sciences, Engineering, and Medicine. 1995. Management and Disposition of Excess Weapons Plutonium: Reactor-Related Options. Washington, DC: The National Academies Press. https://doi.org/10.17226/4754. https://nap.nationalacademies.org/read/4754/chapter/4#30 and source, Study of the thermal expansion effects of a space nuclear reactor with an integrated honeycomb core design using OpenMC and ANSYS https://www.sciencedirect.com/science/article/abs/pii/S0306454923002207 I recommend updating that part of the sentence to read, 'Thermal expansion reduced the core's density to subcritical stopping the reaction while Slotin's removal of the top shell prevented a possible feedback restarting the reaction.' As for the part about Slotin ending the accident, I don't think one can end an accident, it's like saying one ended a murder, the classification doesn't end. I would just drop that part of the sentence. Michaelbaribeau (talk) 04:46, 8 December 2023 (UTC)

My recommended sentence shouldn't use feedback as that term describes a slightly different process but also additional review of the sources already cited show other issues. Source 15 mentions a flash but neither source 15 or 6 says it was blue. Source 6 'implies' removing the shell stopped the radiation calculating exposure by how long the shell was closed but also says in criticality accidents thermal expansion is a shutdown factor. Neither source 15 or 6 mention thermal expansion shutdown would take a few seconds. I recommend the following change, 'Radiation exposure was calculated on the estimated half second the sphere was closed and removal of the top shell prevented the risk of the core going supercritical again.' Michaelbaribeau (talk) 23:05, 11 December 2023 (UTC)

I found a related talk post "Contradicting itself?" and made this comment... I started a recent post about this under "The heating of the core and shells" but just saw this post so wanted to respond. Regarding the sentences, "Instantly, there was a flash of blue light and a wave of heat across Slotin's skin; the core had become supercritical, releasing an intense burst of neutron radiation estimated to have lasted about a half second. Slotin quickly twisted his wrist, flipping the top shell to the floor. The heating of the core and shells stopped the criticality within seconds of its initiation." Source 15 an interview by Dr. Schreiber doesn't mention the color blue, that Slotin felt heat on his skin, that it took seconds to stop, or that it was 'heat' that stopped the reaction but instead that, "It was stopped by the expansion of the core and beryllium, but it was enough to put out a lethal shot of radioactivity." You said, "had he not knocked the shell off, it likely would have repeatedly settled back onto the core as it cooled and cycled again" however I don't see a source saying it had opened before Slotin flipped the top reflector. If regarding Schreiber's comment about expansion and assuming the core's size expanded lifting the top reflector ajar but in nuclear reactions thermal expansion usually refers to heating reducing the core density reducing the core to subcritical and this is what it seems Schreiber is referring to. The "half second" line is referring to source 6 the Los Alamos Labs review of criticality incidents, 2000 Revision report, "The results of fission rate calculations in this sphere, as a function of time for several values of excess reactivity, are shown in Figure 43. Figure 44 represents the total number of fissions to be expected as a function of time for the same excess reactivities. These data are applicable to both accidents because the difference in reflector material has only a small effect on the neutron kinetics. In the first excursion, if the excess reactivity did not exceed 15 ¢, the assembly must have been together for several seconds, which is not unreasonable. In the second event, the experimenter was better prepared to disassemble the material, and it is thought that this was done in a fraction of a second, perhaps <1/2 second." I read it to say exposure calculations were based on the estimated half a second it took Slotin to remove the top reflector which 'implies' that is when the reaction stopped. But the reports analysis also says, "The study and understanding of initiating events and shutdown mechanisms associated with criticality accidents offer potential for limiting the frequency and consequences of such untoward events... These programs, which involved solutions of highly enriched uranium, are supplemented by a series of measurements at Los Alamos using the SHEBA assembly. This assembly is fueled with a 5% enriched uranium solution, that provides information on dose rates near excursions in systems of lower enrichment.88 Analysis of data from KEWB and CRAC has led to relatively simple computer codes that follow the early transient behavior well and rely on thermal expansion and the formation of radiolytic gas for the shutdown mechanisms." So this portion seems to say thermal expansion is a factor if not a key cause of such a shutdown. With out more information I think remarks regarding the color blue, that Slotin felt heat on his skin, and that it took seconds to stop, and even what stopped it, and instead use the reports' implied meaning, 'neutron radiation, the exposure of which was calculated based on the estimated half second between when the sphere closed to when Slotin removed the top reflector.' Also should remove the line, "while Slotin's reaction prevented a recurrence and ended the accident" since there is no source provided saying if it was shut down by thermal expansion if cooling would allow it to restart so at most could currently be described as a precaution but also regarding the phrasing "ended the accident" I don't think you can end an accident any more than you can end a murder, the classification wouldn't change and we still don't have a source in any case. Michaelbaribeau (talk) 19:24, 12 December 2023 (UTC)