Radioactive substances are:
The atomic nuclei of certain substances can undergo decay and emit rays that cannot be seen or felt by the naked eye, and which can only be detected by specialized instruments; this property of a substance is called radioactivity.
Radioactive substances are those that naturally radiate energy and emit rays. They are usually metals with high atomic mass, like plutonium, uranium, and so on. The main types of rays emitted by radioactive substances are alpha rays, beta rays, gamma rays, positrons, protons, neutrons, neutrinos, and other particles.
Harms of Radioactive Substances:
Radioactive substances not only act locally where they are located, but also have an effect on the whole organism. Radioactive substances can cause damage to the central nervous system, the neuro-endocrine system and the blood system. It can cause changes in the permeability of blood vessels, leading to bleeding, as well as complications of infection. The above phenomenon seriously destroys the living functions of the organism and stops the vital activities.
High doses of radioactive substances can cause rapid pathological changes; however, at small doses, these changes are slow and are accompanied by a latent period of varying length. For example, at 400 rad irradiation, 5% of the irradiated people died.
If exposed to 650 rad, 100% of people die. At doses of 150 rad or less, the mortality rate is zero, but it is not harmless, and it often takes 20 years for some symptoms to show up. Radioactivity can also damage genetic material, mainly in causing gene mutation and chromosome aberrations, so that one generation or even several generations of victims.
The above reference? Baidu Encyclopedia-Radioactive material