<unk>  is the process of concentrating specific<unk> s of a chemical element by removing other<unk> s, for example<unk> g natural uranium into enriched uranium and depleted uranium. This is a crucial process in the creation of a uranium based nuclear weapon, though it is not necessary for construction of a plutonium based weapon.
Isotope separation
Mixture
Scientific consensus
Association 
Quality control
Quantization 
Design of experiments
Resonance