Another idiot here who found this answer interesting: https://www.quora.com/Why-is-concrete-the-best-shield-for-neutrons

Neutrons need something that provides them with lots of chances to have interactions. Water is good too. What blocks neutrons may not block gamma and vise versa. To block neutrons and high energy particles like cosmic rays that actually have mass to them you need something like a crash barrier.

Same. Aren't neutrons capable of crossing the entire planet unless they directly colide with another particle?

If you throw a ball at a brick wall it will bounce. If you throw a ball into a ball pit it will be slowed down and stop