What Is It?

A croquet ball or cannonball mold.

Damn! I don't really know, but that sounds spot-on from the picture!

It is the plutonium core that killed Louis Slottin... he was working on an experiment and a screwdriver slipped and a critically happened. He died 2-3 days later. This core was later named the "demon core" if my memory serves me correct.

His prompt actions saved others that were in the room, but cost him his life. A scientist to the end... he documented the effects. He was a Canadian from Winnipeg by the way.

The year before Slottin was killed, the demon core was involved in another criticality accident. Harry Daghlian received around 200 rad neutron radiation and died 25 days later.

Robert Hemmerly, who was about 10 feet away from Daghlian and the core at the time of the accident received about 8 rad neutron radiation. He died of leukemia 33 years later.

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I don't think 'demon core' would have stuck as a name if the tragedy had been limited to Slottin alone.

What happened to the guys who machined the Demon Core?

The Demon Core is sub-critical in free space, but is close to criticality. A neutron reflector can shift the core from sub to super-critical, a condition of positive neutron feedback as long as the reflector is present.

It was machined in isolation from criticality calculations and experiments like this were done to find the limits.

more details here

Ah yes the pit as it's called, is not machined but formed in a hot press with powder...

"The pits of the first nuclear weapons were solid, with an urchin neutron initiator in their center. The Gadget and Fat Man used pits made of solid hot pressed material (at 400 °C and 200 MPa in steel dies) half-spheres of 9.2 cm diameter, with a 2.5 cm internal cavity for the initiator. The gadget's pit was electroplated with 0.13 mm of silver; the layer, however, developed blistering and the blisters had to be ground and plated with gold leaf before the test. The Fat Man pit, and those of subsequent models, were all plated with nickel. A hollow pit was considered and known to be more efficient but ultimately rejected due to higher requirements for implosion accuracy.

Later designs used TOM initiators of similar design but with diameters of only about 1 cm. The internal neutron initiators were later phased out and replaced with pulsed neutron sources, and with boosted fission weapons.

The solid-cores were known as the "Christy" design, after Robert Christy who made the solid pit design a reality after it was initially proposed by Edward Teller.^[2][3][4] Along with the pit, the whole physics package was also informally nicknamed "Christy['s] Gadget".^[5]""

https://en.wikipedia.org/wiki/Pit_(nuclear_weapon)

In the 60's my father worked at the Rocky Flats nuclear weapons facility near Boulder CO run by the Dow Chemical Co. under the auspices of the Atomic Energy Commission AEC. He worked in the "hot shop" machining uranium and the plutonium behind leaded walls and gloves. The plutonium parts came into the shop on conveyors of some sort and the parts had to be manually moved from one conveyor to another using gloves thru a protective wall and glass to get them to his machine. He said the coolant used when cutting plutonium had to be kept directed on the part to keep it cool at all times. He had seen chips fly and land on the lathe and slowly turn color, turn red and burn. From what I recall him telling me some parts were hollow hemispheres machined outside and then held in a vacuum pot to turn the inside to get an exact thickness . Another one he said was a full hollow sphere with one hole in it. The inside of the sphere was machined with a boring bar that was inserted into the hole and then an articulated end on the bar slowly fed in a full arc cutting the inside of the sphere. I don't know that I would want to work under the pressure to get those parts exactly right. Apparently the hollow sphere was supposed to be surrounded by explosives to implode it to a critical mass. All these parts were measured to millionths on an inch with special equipment I assume. I'm sure they needed to know the exact mass of the part. I was always fascinated with the processes he told me about.

He wore radiation monitoring tags and I recall as youngster he had to constantly provide them with urine samples. I recall seeing the jars at home even.

My father passed away at a ripe old age of 93 - and not from any disease related to radiation. Fortunate.

This plant is now sealed up I think partly due to a fire. This can be looked up on Wikipedia for interesting details.

My mistake - I think it was the 50's when my Dad had started working there but I don't recall when he quit.

"A scientist to the end... he documented the effects. He was a Canadian from Winnipeg by the way."

Right after the blue flash and his re-opening of the gap to end the criticality, (a mere second or two, most of the people in the room hadn't even realized what had happened yet), he ordered everyone to freeze in position, and document their location and facing in the room. so there was a record of distance, direction, and exposed sides to the event. He saw this as an unexpected and impromptu experiment, and since the 'test' was already done, he wanted good data on the results.

His dedication to Science!⁽¹⁾ was phenominal, since he was the one who kept a detailed journal of his symptoms, and pains, even more detailed than the doctor's notes on his continuing condition. We learned so much from the accident that he turned into his Final Experiment.

Notes:

1. When talking about that level of dedication, the word needs the extra emphasis. We're talking about the level of dedication and passion that rivals that of ordained clergy to their religion. A less dedicated man might have stood there in shock after reopening the core, or would have wandered around before realizing that 'someone should take notes.' He took charge immediately, and got the vital tata on the event itself, and kept up his journal, dictating when he could no longer write, even through the debilitating pain.
   

What I don't get is how, according to the Wikipedia article, Slottin's body shielded the rest of the people in the room from the high energy neutron beam that killed him. Wouldn't that have passed through him like a hot knife through butter and affected anyone else in its path?

It was not focussed.

A) It was a 'fan' of particles, not a 'beam.'

B) Plutonium produces Alpha particles (blocked by a sheet of paper, of the layer of dead skin surrounding your body (even after exfoliation) and beta-negative particles (absorbed by the human body, but not high enough energy to penetrate completely and exit the other side)⁽¹⁾. The alphas were harmless, and Slottin's body 'ate' most of the beta that escaped the reflector shell.

Notes:

1. Also produces heat, and in the right conditions, Cherenekov radiation⁽²⁾, but the first is no different from any other heat source, and the second is a harmless byproduct, and pretty to look at⁽³⁾.
2. A blue flash of caused by an electron exceeding the local speed of light, generally is only noticeable in water, although it may be visible in air if the electron passes through a water droplet.
3. As long as you realize that seeing it in person generally means you have just taken a lethal dose of radiation. If the light had a straight line to your eyes, the beta and gamma particles had a straight-line path to you as well.
   

Neutron radiation was the real problem in the demon core criticality accidents. The alpha, gamma, and beta radiation was survivable even at Slottin's proximity.

High energy neutrons take a lot of material to be slowed down (lacking charge) and even when thermalized do tremendous damage.

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This may be nit picky, but 'gamma particles' sounds strange....kind of like saying 'x-ray particles'. Not that it is really wrong, wave particle duality and all that, just awkward.

I'm not a Nuclear Engineer⁽¹⁾, so my understanding may not be complete, but I learned there were four 'types' of 'nuclear radiation':

• Alpha particles, which are two neutrons and two protons. Stopped by a sheet of paper, or your own dead skin layer. Alpha radiation is only dangerous if you ingest the radiation source.
• Beta particles are high energy electrons, they can penetrate farther and so need better protection,such as metal foil.
• Gama radiation is the stuff you need heavy lead shielding, that will go right through your body and into the person behind you.
• Ionizing Radiation is the 'odd man out' as it's not the product of nuclear decay, it's extreme high energy photons, with sufficient energy to ionize common materials and cause them to become 'secondary emitters' of radiation. If memory serves, a suitable laser with the proper strength and tuning can cause this⁽²⁾.

It's been a while since I've done research, and I don't have time this morning to check Wikipedia, but I think Gamma are photons, which means they're particles only part of the time, when nobody's looking, or not looking, or something like that. Trying to describe photons just becomes a big quantum mess.

Notes:

1. Although I DO enjoy Timbuk3's song about a recent Nuclear Engineering graduate, The Future's so Bright, I Gotta Wear Shades.
2. Some MIT or Asian postgrad came up with a method of using these high-powered lasers to cause radioactive material to decay faster than normal.
   

Much of that is correct, but there are a couple problems.

Neutron radiation is another important form of radiation.

Ionizing radiation isn't a distinct form as much as a threshold important for safety. Neutrons, gamma, betas (+ or -) and alphas can all be ionizing. Also many nuclear decays are sufficiently energetic to be ionizing. As an example, most alpha decays are several MeV which is strongly ionizing.

As I said, my information may not be complete, but it is more complete now. Thank you.

Guess this guy's job is safe from me replacing him:

Funny post, really great!!

It seems to be accurate as far as I remember as well! Though its over 50 years since I last checked!!!

So its also a good post!! GA!!

I also like being the first one to give a good post a GA!!

Indeed this is the demon core... This was during the development of the atomic bomb and experiments to determine the exact point at which the plutonium mass would go supercritical were a little sketchy using the plutonium gallium alloy...the Demon core would take several lives before finally being deployed in a 23 kiloton bomb on the Bikini Atoll in July 1946....The ball was just 3.5 inches in diameter and weighed 14 lbs....

https://en.wikipedia.org/wiki/Demon_core

I guess that's what is meant by playing hard ball!

Most definitely a Plutonium core.

Wanna toss around the glow-in-the-dark Shot in the next Olympics?

Looks like a water feature, water pumped up makes the ball float and turn, the water then falls over the edge into a pond.

Thanks for posting this, very interesting.....

The Olympic 'standard' for balls used in shot-putting.

Out of curiosity - the blocks its nested in, are they lead?

No.

The sphere of plutonium is surrounded by neutron-reflecting tungsten carbide blocks....since the mass is below critical, there is a trick that is used by reflecting the neutrons back into the mass to achieve supercritical activity level...the critical mass of plutonium 238 is 16 - 20 lbs...

Don't need to encase it in lead, it's 'subcritical,' it's just sitting there, decaying away. It's not something you want to spend all day with in your lap, but it's safe enough for a short exposure, as in: (enters room) "What is tha- holy carp! I'm outa here!" *doorslam*

Cure all you play with the ball and it cures you of what ails you in a few days.

As long as you define "what ails you" as "having a bad habit, it's called 'breathing'".