And they're so insanely positive all the time that they can rip the negativity out of you twice in such a way that it scrambles your DNA.

Never underestimate the toxic positivity of an alpha particle...

And unfit for the pubic to interact with.

Comic book authors

If you're talking about the neutron it's because concrete has a lot of hydrogen. Alpha particles, beta particles, and light (gamma rays in this picture) interact with electrons, with the probability of being stopped increasing with electron density. Lead has a lot of electrons (its lower on the periodic table, called a "high z" element).

Neutrons, however, don't care about electrons and instead interact with the nucleus, with the probability of being stopped depending on the spin state of the nucleus and the neutron. This doesn't follow a specific pattern on the periodic table, but hydrogen has a big chance of interacting with the neutron while lead doesn't. Cadmium, boron, and I think lithium 7 also would stop neutrons easily (there are more of course but those are what I remember offhand).

Narrativium

Gives new meaning to Jimmy Neutron

"Oh, that's-"

The speaker was crushed as OPs sudden extreme gravity ripped the earth asunder

Gotta blast!

I am a gamma male.

This is why you need to drink a lot of water

or 4 morbid humans on each direction

Sure, but just because it's chock full of Hydrogen, which happens to be about the same mass as a neutron and thus takes up a lot of its energy per collision. Plastic, being a hydrocarbon, does the same thing.

That being said, water is pretty cool. You could use 2 inches of lead to stop 90% of gamma radiation, or 2 feet of water for the same effect. On top of that, metal is terrible at slowing neutrons (due to metal not being hydrogen), but that same 2 feet of water will slow down the neutrons by about 99.5%.

They come and just keep going.

The Neutrinos? From Dimension X? They're so cool they're frozen!

Gamma rays are stopped by things with a lot of electrons, so a sufficiently thick block of lead will stop it

EDIT: higher energy light has more penetration power (so gammas are quire penetrating), but it's a finite value

The madder they get, the stronger they get.