Gamma waves are highly energetic photons and require thick, dense materials to stop them. Lead (Pb) and tungsten (W) are dense elements with high atomic numbers that are effective in blocking gamma rays. The thickness required to block a particular gamma wave depends on the energy of the wave, with higher energy waves requiring thicker materials.

For instance:

- Lead (Pb): A thickness of approximately 10 mm of lead is generally sufficient to reduce gamma radiation to safe levels.

- Tungsten (W): Tungsten is denser and more effective than lead, with a thickness of about 5 mm providing similar blocking capabilities.

- Uranium (U): Depleted uranium is known for its high density and effectiveness in stopping gamma radiation, but its use is typically restricted due to its radioactive properties.

- Concrete: Thick layers of concrete can provide some protection against gamma rays due to their high density. However, they may require a substantial thickness to be effective.

It's important to note that the choice and thickness of the blocking material should be based on the specific requirements of the application and the expected gamma wave intensity. If unsure, it is advisable to consult with experts in radiation safety and shielding.