What Caused The Demon Core Criticality In Each Incident?

There’s something almost mythic about the phrase 'demon core'—not because of supernatural forces, but because of how a few human decisions and a very unforgiving bit of physics combined into tragedies. I dug into the stories years ago while reading 'The Making of the Atomic Bomb' late one sleepless night, and what struck me most was how normal the setting felt: tired scientists, hands-on tinkering, casual confidence. Two incidents stand out: one where a tungsten-carbide reflector brick was dropped onto the core, and another where a pair of beryllium hemispheres were being nudged apart with a screwdriver. Both were trying to push a subcritical plutonium mass closer to criticality to measure behavior, and both crossed a deadly threshold. From a physics perspective, the core was dangerously close to critical mass as-built, because the design intended to be compressed into a supercritical state in a bomb. Neutron reflectors—metallic bricks or hemispheres—reduce leakage of neutrons and thus increase reactivity. In plain terms, adding or closing a reflector can turn a harmless pile into a prompt-critical event almost instantly. The accidents produced an intense burst of neutron and gamma radiation (a prompt critical excursion) that didn’t blow the core apart like a bomb, but was enough to deliver a fatal dose to whoever was nearest. People weren’t vaporized; they received overwhelming radiation that caused acute radiation syndrome over days to weeks. Why did this happen twice? There was a blend of human factors: informal experimental practices, assumptions that dexterity and care were sufficient, single-person demonstrations, and a culture that prized hands-on 'knowing' over remote, engineered safety. The first incident involved dropping a reflector brick by mistake; the second was a public demonstration with the hemisphere only held apart by a screwdriver. Both show how ad hoc methods—bricks, hands, and tools—were being used where remote apparatus or interlocks should have been. There was also secrecy and pressure: schedules, wartime urgency, and the novelty of the devices meant procedures lagged behind what the hazards really demanded. Those deaths changed things. Afterward, strict criticality safety rules, remote handling, and formalized procedures became the norm. The name 'demon core' stuck because it felt like a cursed object, but the real lesson is less mystical: when you’re working with systems that have non-linear thresholds, casual handling and human overconfidence can turn boring measurements into lethal events. I still picture those cramped lab benches and feel a chill at how close those teams walked to disaster before the safety culture finally caught up.

I spent a long afternoon once digging through old lab reports and first-person recollections about those Los Alamos incidents, and the more I read the more I could feel how sharply the culture shifted after the two criticality accidents. At the time, experiments were often improvised, done by hand, and treated almost like puzzle-solving games — which sounds romantic until you see the photographs and realize how dangerously close people got to an assembled core. The immediate practical reaction was brutal and direct: hands-on approach to critical assemblies was effectively outlawed. Simple tools and stunts — the infamous screwdriver trick, for example — were swept away and replaced by engineered barriers, remote rigs, and explicit written procedures. People who had been allowed to ‘‘feel’’ the experiment were replaced by remote manipulators and mechanical shims so no human body could be the last line of defense between subcritical and critical geometry. Beyond those immediate mechanical changes, the institutions themselves rebuilt how they governed work. Formal criticality safety programs were created — complete with specified mass and geometry limits, mandatory peer review for experiments, and the emergence of dedicated safety specialists who signed off on procedures. The ‘‘double contingency’’ mindset became a core design principle: systems had to be safe unless two independent things went wrong at once. That rippled into administrative controls too: stricter access rules, buddy systems or team sign-offs, mandatory dosimetry and area neutron detectors, and fast-acting criticality alarms. Emergency response protocols and medical follow-up were written into the playbook so exposures were tracked and treated systematically rather than ad-hoc. Over the longer term I’ve loved seeing how technology and culture joined forces. Remote tooling, cameras, and robotic manipulators took over the fiddly parts; computer codes allowed far safer pre-calculation of margins; and formal standards and audits meant lessons were taught across labs instead of being internal folklore. But the human lesson always sticks with me: you can invent all the tools you want, but the single most important change was people agreeing not to re-glorify risky behavior. That cultural shift — from ‘‘brave tinkerer’’ to ‘‘procedural scientist’’ — probably saved more lives than any single gadget. I still think about how those policy changes map to other risky hobbies I have, and I try to bring that same stubborn caution to anything I tinker with at home.

When I dug into those grim little episodes from Los Alamos history, the hair on my neck stood up — not because the physics was mystical, but because it was brutally simple. A plutonium sphere doesn't need to be part of a bomb to produce a dangerous burst of neutrons and gamma rays; it just needs the right combination of mass, shape, density, and nearby materials that reflect or slow neutrons. In practice that means a near-critical chunk like the so-called demon core could still be pushed into a prompt supercritical state if someone surrounded it with a good reflector (think beryllium or tungsten carbide), closed gaps that let neutrons escape, or accidentally soaked it in something that moderated neutrons like water. I like to picture the old experiments: heavy hands moving reflective bricks, a gap closing millimeter by millimeter. That tactile closeness is what made the original incidents lethal. Modern nuclear materials are kept in geometries and containers designed to be subcritical under all credible disturbances — lots of boronated materials, fixed spacing, and administrative rules to prevent ad hoc tinkering. So yes, in theory, a demon-core-like object could go prompt supercritical if mishandled in the very specific ways that increase reactivity (adding reflectors, shaping into a compact sphere, compressing it). In reality, the combination of safeguards today makes accidental criticality from casual mishandling very unlikely, but the physics hasn’t changed, and that old, cold fact always gives me a chill when I read those accounts.

My curiosity about odd historical mishaps always pulls me toward the strange story of the so-called demon core. Two people died directly from handling that plutonium core during criticality experiments: Harry K. Daghlian Jr. and Louis Slotin. Daghlian’s accident happened on August 21, 1945. He was doing a late-night experiment stacking tungsten carbide bricks as a neutron reflector around the core when one slipped and fell onto it, causing a prompt critical reaction. Witnesses later described a bluish flash; Daghlian was exposed to a massive dose of radiation and developed acute radiation sickness, dying a few weeks later on September 15, 1945. That sequence of events — the nervous fumbling with the reflected core, the sudden flash, the tragic decline — has stuck with me every time I read about the era. The second fatality was Louis Slotin, on May 21, 1946. Slotin was performing the infamous ‘tickling the dragon’s tail’ demonstration, manually separating two beryllium hemispheres that acted as a reflector with a screwdriver. The screwdriver slipped, the hemispheres closed, and a critical excursion occurred. Slotin saw the flash, absorbed a lethal dose, and died on May 30, 1946. Several others in the room received significant exposures but survived. These incidents reshaped how hands-on criticality work was handled and are chilling reminders of how improvised procedures in high-risk labs can have fatal consequences. If you want a deeper dive, I’d recommend reading 'The Making of the Atomic Bomb' — it paints the human side of these technical disasters really well.

I still get a chill thinking about those cramped lab rooms at Los Alamos, the hum of equipment and the quiet confidence everyone had back then. The two technicians who actually handled the infamous 'demon core' during the fatal incidents were Harry Daghlian and Louis Slotin. Harry Daghlian, a young physicist in his twenties, was working alone in late August 1945 stacking tungsten-carbide bricks as a neutron reflector around the core when one brick slipped and fell onto the assembly. That single mistake produced a prompt increase in reactivity — he received a lethal dose of radiation and died a few weeks later. The accident was heartbreaking because it came down to one moment of bad luck and the brutal physics of a supercritical assembly. The second incident, less than a year later in May 1946, involved Louis Slotin. He was famous for performing delicate criticality experiments — the so-called 'tickling the dragon's tail' technique — where a beryllium shell was used as a reflector around the plutonium core and separated by a small gap. Slotin used a screwdriver to keep the halves apart during a demonstration; when the screwdriver slipped the shells closed, the core went prompt critical. Slotin took the brunt of the radiation and passed away about a week and a half later. Several colleagues and supervisors were present in the room during that test, and the event led to a major tightening of safety procedures and a rethinking of how these experiments should be performed. Reading about these incidents always reminds me how dangerous hands-on work with fissile material was before remote tooling and strict protocols became standard—human curiosity and skill were mixed with dreadful risk, and the losses left a deep mark on the laboratory community.

Funny enough, the story of the demon core keeps popping up whenever people ask for the human side of the Manhattan Project. I got pulled into it the first time I read Richard Rhodes' 'The Making of the Atomic Bomb' — he treats the Daghlian and Slotin accidents with a kind of careful, almost literary attention that made me picture the labs and late-night experiments in a way a dry report never would. That book is probably the single best place to start if you want a well-researched narrative that places the demon core in the broader sweep of World War II and early nuclear history. From there I chased down interviews and archival material; Los Alamos' oral histories and accident reports are publicly available and make the events feel immediate and real, not just a cautionary footnote. Documentary makers have definitely been interested in the drama. If you want film, check out 'The Day After Trinity' — it’s more about Oppenheimer and the Trinity test, but it’s emblematic of how documentaries stitch personal stories into the technical history and it touches the culture at Los Alamos. The 1989 film 'Fat Man and Little Boy' dramatizes the project and includes incidents inspired by those accidents, though it takes cinematic liberties. For more focused, modern takes, historians and writers like Alex Wellerstein have detailed posts on his 'Restricted Data' blog and in journal articles that read like long-format detective work: timelines, people, and the scientific context that made those mishaps possible. Beyond books and big documentaries, the demon core shows up in lots of niche media — magazine longreads, science-channel YouTube pieces, and history podcasts that love telling one-off morality tales about technology. I’ve listened to several podcast episodes that reconstruct the moments surrounding Louis Slotin’s final hands-on test and Charles Daghlian’s earlier accident; they’re good for a compact, human-focused retelling. If you’re curious, mix Rhodes for depth, Wellerstein for technical-historical analysis, and a documentary or two to feel the period. It’s weirdly compelling and sad in equal measure — a reminder that brilliant people can still make tragic mistakes, and that history preserves those moments so we can learn from them.

I dug into this because the story of those criticality accidents always felt like a grim little chapter of Cold War science — and the way physicians reacted at the time tells you a lot about how medicine meets the unknown. When Harry Daghlian and Louis Slotin were exposed, the immediate response was basic emergency care layered over painstaking radiation monitoring. Teams first moved the men away from the source, removed clothing that might be contaminated, and washed skin thoroughly while using Geiger counters and film badges to check for external contamination. Doctors and health physicists worked together: the physicists tried to quantify dose with badges, film, and blood tests, while the physicians focused on symptom control and preventing infection once the bone marrow began to fail. Treatments were largely supportive and reactive. Both men developed acute radiation syndrome — nausea, vomiting, severe burns in irradiated tissues, and progressive loss of white blood cells. Physicians gave fluids, pain control (morphine and other analgesics), antibiotics to chase opportunistic infections, and transfusions when blood counts dropped. Wound care was carried out for irradiated or burned skin; isolation and strict hygiene were emphasized because an irradiated patient’s immune defenses were collapsing. There weren’t targeted anti-radiation drugs then for internal contamination, and hematopoietic growth factors didn’t exist, so doctors were limited to transfusions and palliative measures when the marrow stopped producing cells. What always gets me is the human side — the medical teams were trying their best with incomplete knowledge. Slotin’s agony and Daghlian’s decline were documented with clinical notes that show careful monitoring of temperature, blood counts, and wound infections as they progressed to multi-system failure. Contemporary physicians tried novel things when possible, but many modern interventions (cytokine support, bone marrow/stem cell transplants, specific chelators for transuranics) weren’t available yet. Reading the reports over a coffee in the archives, I felt both respect for those clinicians and a chill at how much they were improvising. It’s a reminder that medicine evolves, and that those early tragedies shaped protocols that protect people today.

Whenever the demon core topic comes up at a museum talk or online forum, I get that little shiver of morbid curiosity — it’s one of those stories that sits at the crossroads of human error, science, and tragedy. The straightforward truth is that you won't find a neat glass case labeled 'The Demon Core' in any public museum. After the two fatal criticality accidents in 1945–46, the 6.2-kilogram plutonium core was deemed far too hazardous and politically sensitive to display. In the years that followed, the material was melted down and recycled into other plutonium components for tests and production, so there’s no intact, original core preserved for public viewing today. That said, museums and archives do hold a lot of the story: replicas, photographs, lab notebooks, safety reports, and the critical assembly apparatus that help tell what happened. If you want to get a tangible sense of the events, the Bradbury Science Museum at Los Alamos and the National Museum of Nuclear Science & History near Albuquerque often have exhibits about the Manhattan Project and criticality experiments (they show models, diagrams, and sometimes period tools). The Department of Energy and Los Alamos National Laboratory retain classified and radioactive materials in secure facilities, and any actual plutonium remnants would be under strict DOE control — not on public display. Museums instead balance public education with safety by using models, declassified documents, and oral histories. There’s also a lot of mythos around the incidents — the famous screwdriver story from Slotin’s experiment is part of that lore — and museums try to be careful about separating dramatized retellings from the documented facts. If you’re hunting for the closest thing to a relic, archival photos, the original procedural reports, and curator-led interpretations are your best bet. I always walk away from these exhibits feeling a mix of awe and somber respect; the physical pieces might be gone or locked away, but the lessons and the human stories are very much on display.

That wardrobe moment with Jennie in 2024 blew up across feeds, and I couldn’t help but follow every clip and thread — it felt like watching someone handle a tricky live moment with total calm. From what was reported and what you can actually see in the clips that circulated, the immediate cause seemed to be a malfunction in the outfit’s fastening: a snap or clasp that came undone at the worst possible second. Add in fast movement, bright camera flashes, and possibly a gust of wind (these things love to conspire), and you’ve got the classic recipe for a brief, embarrassing exposure. What stood out to me was how quickly her styling team and security reacted to shield her, and how Jennie herself stayed composed and professional, which is honestly the most impressive part to me. Practically speaking, these kinds of incidents usually happen because of a few predictable technical factors. First, clothing construction: if a garment relies on a single clip, thin strap, or weak hem in a high-stress area, repeated motion or a snag will expose that weak point. Second, the environment matters — outdoor arrivals, windy sidewalks, or crowded red carpets increase the risk. Third, performance demands and quick outfit changes create tension between the need for dramatic silhouettes and the need for secure fittings. Stylists often push design boundaries for visuals, and sometimes the fastenings or tailoring don’t get the stress-testing they need until they’re worn in real conditions. Seeing those elements line up in Jennie’s case made the malfunction almost inevitable, even if everyone involved had done their best. The aftermath felt very on-brand for the modern idol world: fans rallied with protective memes and praise, praising Jennie’s poise and calling out how invasive some photographers were. I also noticed a practical shift — stylist teams and brands often learn quickly from public incidents like this, tightening protocols, double-securing fastenings, and planning better shields during arrivals. Brands and label reps sometimes release short statements to clarify that it was an accident, and fans usually appreciate an acknowledgement that celebrities are people who can have wardrobe mishaps too. Honestly, watching Jennie handle the situation made me respect her even more. There’s something endearing about someone who can stay graceful under seconds-long chaos — it’s a reminder that behind all the curated red-carpet moments are real people and real teams trying to keep everything flawless. I walked away from that whole episode feeling glad she was okay and impressed by how smoothly her team handled the recovery, and that’s the lasting image I keep returning to.

Sometimes I find those moments oddly surreal: a man explains something to me that I already know, as if my presence erased my expertise. It usually comes from a mix of factors — social conditioning that trains some men to assert control in conversations, quick assumptions about competence based on gender, and the pressure to be seen as helpful or knowledgeable. Add in meeting dynamics like who sits where, who talks first, and who’s introduced as 'from finance' versus 'from product', and the stage is set. Other times it’s less malicious and more about habit: people default to explaining because they’re nervous, excited, or trying to fill silence. But habit still lands as a microaggression when it repeatedly happens to the same person. Organizational culture matters too — if leaders don’t call it out or if interruptions are normalized, those patterns persist. I try to handle it with low drama: a short correction, redirecting the conversation to the person who actually owns the topic, or preempting by documenting my points in the agenda. It’s satisfying to reclaim space quietly, and I feel better when colleagues learn to pause and listen more carefully.