Question

The critical mass of $U^{235}$ can be reduced by

• A. putting a neutron reflector around it
• B. heating it
• C. mixing impurity in it
• D. putting neutron absorber around it

Answer 1

The correct option is A putting a neutron reflector around it

Surrounding a spherical critical mass with a neutron reflector further reduces the mass needed for criticality. A common material for a neutron reflector is beryllium metal. This reduces the number of neutrons which escape the fissile material, resulting in increased reactivity.