neutrons

On the surface of the earth, the effect is mostly abated by the atmosphere - except for neutrons.

Instead, reactors are designed to be subcritical considering only prompt neutrons and then be made critical via the remaining delayed neutrons.

Environmental sources of neutrons are actually pretty rare normally and most neutrons you do see will be pretty low energy and won't have a huge amount of penetrative power.

They started out with the apparatus surrounded with radiation alarms in case it generated dangerous amounts of neutrons.

Then they moved the equipment to the inside of a cube of lead bricks, to eliminate external neutrons.

Nuclei with an odd number of nucleons (protons and neutrons) would have to have an even number of quarks.

First, why make your neutrons via fusion when that's essentially the most difficult way to do it?

A mm coating of the stuff will keep out pretty much any common source of neutrons.

It's also important to highlight that the UPower design can consume the entire actinide vector because it uses fast neutrons.

The underlying mechanics are highly theoretical, but it has something to do with the quarks that compose protons and neutrons.

I think you mean neutrons - neutrino deflectors would be quite interesting...

If you really want to protect something from neutrons you just coat it with boron.

In the reactor normally there's two classes of neutrons present - "prompt", which are emitted directly from fission, and "delayed", which are secondary neutron emissions from decay of fission byproducts.

However, if there isn't enough control material in the core that the proportion of prompt neutrons is enough to make the reactor critical by itself then it goes "prompt critical" and exactly what happens in the article occurs.

As a "code word" for Uranium-235 they took the last digit from 92 and the last digit from 235 and referred to it as 2+5 = 25 Same with plutonium-239 which has 94 protons and 239 protons + neutrons.