Nuclear power's danger to health, safety, and even to life itself can be summed up in one word: radiation. Nuclear radiation has a certain mystery about it, partly because it cannot be detected by human senses. It cannot be seen or heard, or touched or tasted, even though it is all around us. There are other things like that. Radio waves are all around us but we cannot detect them, sense them, without a radio receiver. Similarly, we cannot sense radioactivity without a radio detector. But unlike common radio waves, nuclear radiation is not harmless to human beings and other things. At very high levels, radiation can kill an animal or human being outfight by killing masses of cells in vital organs. But even the lowest levels can do serious damage. There is no level of radiation that is completely safe. If the radiation does not hurt anything important, the damage may not be significant. This is the case when only a few are hit, and if they are killed outright, your body will replace the dead cells with healthy ones. But if the few cells are only damaged, and if they reproduce themselves, you may be in trouble. They reproduce themselves in a deformed way. They can grow into cancer. Sometimes this does not show up for many years. This is another reason for some of the mystery about nuclear radiation. Serious damage can be done without the victim being aware at the time that damage has occurred. A person can be radiated and feel fine, then die of cancer five, ten or twenty years later as a result. Radiation can hurt us. We must know the troth. The second paragraph tells us that ______.