However, whereas walking is a low-impact activity because one foot is always in contact with the ground, in jogging and in running, impact is introduced. This is a high-impact exercise that places strain on the body, notably the joints of the knee.
Most background radiation comes from natural sources, while most artificial radiation comes from medical examinations, such as x-ray photographs. Radiation can damage cells and make them cancerous.
Alpha, beta and gamma. There are three main types of radiation that can be emitted by radioactive particles. They are called alpha, beta, and gamma. All three types of radiation come from the nucleus of the atom. All three types of radiation will cause ionisation, but they behave slightly differently, because of the way they are made up. The diagram below shows the penetration of alpha, beta and gamma rays.