<P> In analysing the nature of the decay products, it was obvious from the direction of the electromagnetic forces applied to the radiations by external magnetic and electric fields that alpha particles carried a positive charge, beta particles carried a negative charge, and gamma rays were neutral . From the magnitude of deflection, it was clear that alpha particles were much more massive than beta particles . Passing alpha particles through a very thin glass window and trapping them in a discharge tube allowed researchers to study the emission spectrum of the captured particles, and ultimately proved that alpha particles are helium nuclei . Other experiments showed beta radiation, resulting from decay and cathode rays, were high - speed electrons . Likewise, gamma radiation and X-rays were found to be high - energy electromagnetic radiation . </P> <P> The relationship between the types of decays also began to be examined: For example, gamma decay was almost always found to be associated with other types of decay, and occurred at about the same time, or afterwards . Gamma decay as a separate phenomenon, with its own half - life (now termed isomeric transition), was found in natural radioactivity to be a result of the gamma decay of excited metastable nuclear isomers, which were in turn created from other types of decay . </P> <P> Although alpha, beta, and gamma radiations were most commonly found, other types of emission were eventually discovered . Shortly after the discovery of the positron in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons (positron emission), along with neutrinos (classical beta decay produces antineutrinos). In a more common analogous process, called electron capture, some proton - rich nuclides were found to capture their own atomic electrons instead of emitting positrons, and subsequently these nuclides emit only a neutrino and a gamma ray from the excited nucleus (and often also Auger electrons and characteristic X-rays, as a result of the re-ordering of electrons to fill the place of the missing captured electron). These types of decay involve the nuclear capture of electrons or emission of electrons or positrons, and thus acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons . This consequently produces a more stable (lower energy) nucleus . </P> <P> (A theoretical process of positron capture, analogous to electron capture, is possible in antimatter atoms, but has not been observed, as complex antimatter atoms beyond antihelium are not experimentally available . Such a decay would require antimatter atoms at least as complex as beryllium - 7, which is the lightest known isotope of normal matter to undergo decay by electron capture .) </P>

Why do some atoms decay and emit radioactive rays