<P> Cosmic ray radiations striking the Earth from outer space were finally definitively recognized and proven to exist in 1912, as the scientist Victor Hess carried an electrometer to various altitudes in a free balloon flight . The nature of these radiations was only gradually understood in later years . </P> <P> Neutron radiation was discovered with the neutron by Chadwick, in 1932 . A number of other high energy particulate radiations such as positrons, muons, and pions were discovered by cloud chamber examination of cosmic ray reactions shortly thereafter, and others types of particle radiation were produced artificially in particle accelerators, through the last half of the twentieth century . </P> <P> Radiation and radioactive substances are used for diagnosis, treatment, and research . X-rays, for example, pass through muscles and other soft tissue but are stopped by dense materials . This property of X-rays enables doctors to find broken bones and to locate cancers that might be growing in the body . Doctors also find certain diseases by injecting a radioactive substance and monitoring the radiation given off as the substance moves through the body . Radiation used for cancer treatment is called ionizing radiation because it forms ions in the cells of the tissues it passes through as it dislodges electrons from atoms . This can kill cells or change genes so the cells cannot grow . Other forms of radiation such as radio waves, microwaves, and light waves are called non-ionizing . They don't have as much energy and are not able to ionize cells . </P> <P> All modern communication systems use forms of electromagnetic radiation . Variations in the intensity of the radiation represent changes in the sound, pictures, or other information being transmitted . For example, a human voice can be sent as a radio wave or microwave by making the wave vary to correspond variations in the voice . Musicians have also experimented with gamma sonification, or using nuclear radiation, to produce sound and music . </P>

Which type of radiation does not produce a particle