He took a dip in a pool with a functioning nuclear pile some time before that just to avoid having to shut the thing down before doing some maintenance, taking a pretty big dose. He was a daredevil and had the kind of bravado of someone on a work site who scoffs at PPE and rolls their eyes when you tell them they need to wear a damn helmet. Those types usually end up having a bad time eventually.

> multiple other manhattan project people had already told him he was going to die if he kept doing it

To me it seems quite reasonable that the people hired

to work on a bomb intended to kill 150,000 people in one go

against the backdrop of a war where 70-85 million died

might not place the greatest value on health and safety, and the sanctity of human life.

Same reason that chemistry professors demonstrate dramatic reactions in front of the class from time to time. It's fun, and keeps things interesting, even if you already know the chemical processes that are happening.

In a demonstration, not an experiment, it’s sufficient to have the Geiger counter go clicky at different rates while the demonstrator plays the sphere like a theremin.

The point was to show it to people, not to collect data.

It was a boy's club with unlimited funding working on things that were never attempted before, a lot of things weren't exactly done by the books, even their original "safe" protocol would seem completely insane by modern standards. As long as it went boom in the end and they kept it secret I doubt they had many rules

Imagine if you'd invented the world's first modern sink, in a world that had never seen a faucet or a plughole before. And you're training some new guys on the details of what you're working on.

Sure, some of that training is going to involve blackboard calculations and careful measurements.

But you're also probably going to demonstrate a sink to them and say "As you can see, when we turn this knob more hot water is added to the mix. Note how, after I put the plug in the plughole, the water level starts rising."

The purpose of the demo isn't to precisely measure the depth of the water or the temperature at the faucet or the angle the tap is turned to. It's just to let them see the thing in practice, so as they study it in theory they know what to imagine and how the model maps onto the real world.

The honest truth is there's just a certain acceptable level of jank in a scientific lab.

Not everything needs to be measured to a high precision to be useful, and it's always a balance of how much effort you want to expend versus how useful that extra accuracy/precision is.

If all you care about is "when you're getting close to a critical mass, your instruments will look like this," you don't care that you have a wide swing in your data. You just want to show a difference from baseline.

Sometimes science doesn’t have to be precise to demonstrate a result.

Consider trying to measure feedback from a microphone and speaker. You don’t have to be an expert to know that there’s a quick change in system behavior when the microphone gets too close to the speaker.

If the goal is to collect precise data and use it after the experiment to draw conclusions, update a model, etc. then sure.

If the goal is to demonstrate to observers how the neutron output (reaction rate) increases as the reflectors are moved closer together over the source, then that isn't really necessary.

This seems more like an incredibly dangerous version of a demonstration you might see at an interactive science museum or a classroom. You don't need precise measurements to demonstrate the relationship between two phenomenon.

I think it was more about being able to understand/read what the measurement devices were showing. The exact distance probably wasn't as important as the criticality could also vary with other variables (e.g. geometry).

As in, you're trying to understand the situation as "shouldn't they have precisely nailed down all the parameters, if the goal is to measure when X starts happening". But it seems Slotin was more demonstrating "this is what you're going to see on the monitors when stuff is close to going boom". It wasn't about "this specific distance is a safe gap" and more "here's how you can tell whether the gap is safe".

He was about to be reassigned out of the lab, and was demonstrating equipment to his designated successors.

This is just proving 'move spheres closer means more neutrons'. It's something you quickly show someone to explain what you are going to do. The people watching will then get most of the same ideas you are suggesting, and figure out how to design a proper experiment around it.

Presumably the experiment to be done later is about characterizing different cores. They had already done it for this core, and wanted to teach the principles to others.