How do neon lights work?

Neon is an inert gas atom – it has 10 electrons, 2 in the K – shell and 8 in the L – shell. It is inert to all chemical reactions. But when a small amount of neon gas is placed in a discharge tube and high voltage is applied, electrons from cathode can get enough energy to knock off electrons from Neon's. The voltage must be large enough so that this energy is more than that required to “ionize” the atom.

When the removed electron falls back down to its original orbital, a photon is released or emitted – and the discharge tube glows! A photon's energy (its wavelength or color) depends on the energy difference between orbitals.

This series of photon energies – the emission lines is unique to a particular atom. Neon light photons are orange in color.

If any other colored light is required, then the glass is coated with other compounds of elements like Cu, Zn, Mg, etc. Mercury discharge tubes are used which contain mercury but not neon. Mercury atoms have some high energy ultraviolet photons. When these photons strike these elements, they give off light typical to their atomic energy levels – which will have different visible wavelengths.

Why is lead used as radiation shielding?

Lead is a very good material for radiation protection. Lead has a very high atomic mass of more than 200. It is also a very dense material. It is relatively less hard and non – toxic. It is also more readily available.

Radiations come in various forms such as a, b, g rays and particles such as neutrons. Penetrative properties of these radiations are very high – and they are harmful to humans, causing mutations, and cancers, etc.

a – particles can be stopped by a piece of paper or the surface of your skin. b – particles can be stopped with a sheet of aluminum foil. g rays are hard to stop. Here is where lead comes in handy. A lead shield of appropriate thickness can stop high – energy g – rays.

Neutrons are very difficult to stop as they are neutral electrically and interact with matter very poorly. They are generally stopped with blocks of paraffin wax.

Certain types of radiation also give off neutrons, and since neutrons are neutral in charge, they aren't attracted to anything in the material. Again, the density of the lead helps increase the probability of matter collisions that reduce the energy of the particle.

Astronauts in space are exposed to energetic particles called cosmic rays. These are highly penetrating particles. When astronomers sleep, they see bright flashes of light in their eyes due to such particles hitting their retina. To prevent these bright flashes, astronauts sleep in cabins that have radiation protections.