Steps to take in the event of a nuclear reactor accident
α-, β-, and γ-radiation can be completely blocked or attenuated with the appropriate materials. Whereas α-radiation can be stopped by cardboard, and β-radiation cannot penetrate brick or a metal sheet, the blockage of γ-radiation presents a serious problem. In research with nuclear materials, all radiation can be stopped completely by 5-centimeter lead plates. However thick brickwork, iron and steel plates, rock layers and water can diminish the radiation through scattering, and the hard γ-radiation energy is partially absorbed by the materials. Complete blockage of γ-radiation, e.g. such as in a nuclear power plant, is only achieved with a layer of special concrete 2 meters thick.
The first measure to take is to keep a distance. The farther one is from the site of a nuclear accident, the weaker will be the radiation. This becomes difficult if the radioactive isotopes have spread into the atmosphere or have already taken the form of fallout. In that case, one should stay indoors and keep the windows and doors closed. A locally substantial amount of fallout can occur when rain washes the radioactive elements out of the air. If this should take place, the use of plants, mushrooms, and wild game for food must be avoided for years. The radiation load can exhibit significant regional variation.
For immediate protection of the thyroid gland from incorporating radioactive iodine, iodide tablets can be taken by (and only by!) order of the authorities. Avoid ingesting fresh milk products from the local region, since the cows grazing in the pasture are precisely the ones that first take in the radioactive iodine.
Use a respirator that can protect you from inhaling the larger, radiation-producing particles.
If you have been out in the open air, or if you have come into contact with dust, particles on the skin can be removed with a thorough washing.