fast breeder

pressurised water

boiling water

sodium graphite

ordinary fluid

heavy water

molten lead

hydrogen gas

maximum in center and zero at side

maximum at side and zero in center

uniform throughout

zero throughout

1-99%

1-25%

1-50%

1-75%

high energy (fast) neutrons alone

low energy (slow) neutrons alone

either fast or slow neutrons

medium energy neutrons