Which metal cannot be penetrated by the gamma rays ?

Answer 1

Any metal can be penetrated by gamma rays. Even lead.

Uranium, lead and tungsten are among the best shielding materials for gamma rays.

The degree of penetration depends on the wavelength (or energy level) of the gamma rays and the density and thickness of the material the gamma rays are passing through.

There are different wavelengths of gamma rays and they do not all have the same penetrating power.

Their energy is typically expressed in MeV (millions of electron volts)

For example, for gamma rays at 0.5 MeV, it would take about 1.4 centimetres of lead shielding to reduce its intensity to 1/10 of its original intensity.

At 0.8 MeV, it would take about 2.6 centimetres of lead shielding to reduce the intensity of the radiation to 1/10 of its original intensity.

Etc...

See here:
http://www.triumf.ca/EHS/rpt/rpt_7/node17.html
 

Answer 2

The heavier the metal the better it shields off gamma rays, so lead is a good choice. X-ray tubes have a window of beryllium to allow the X-rays to escape from the vacuum tube; beryllium is the lightest metal that doesn't oxidise in air, so it's almost transparent to X-rays and gamma rays.

Answer 3

gamma rays can go through any given metal layer. The biggest factor is the thickness of the metal. Gamma rays can be shielded with a lot of concrete (15 cm per tenth), but lead is usually used because it is the cheapest material with the best shielding (1.4 cm per tenth).

Answer 4

Gamma rays is Waves of pure energy, similar to x-rays. Gamma rays travel at the speed of light through air or open spaces.

Concrete, lead, or steel will block gamma rays.

Hope that helped !!