Radioactive isotopes and their decay

An element is defined by its atomic number, which is the number of protons in the nucleus. The number of neutrons can vary, however, which leads to the existence of isotopic forms of an element. So, for example, for hydrogen (atomic number 1), the normal isotope is ( H) and the other isotopic forms are deuterium ( H) and tritium (iH). Whereas deuterium is a stable isotope, tritium is unstable upon emission of an electron (p particle) and a neutrino (v) it is converted into helium  

This process of radioactive decay is characterised by the product, the maximum energy of the emitted electron (3H 0.018 MeV) and the half-life of the isotope (3H 12.3 a). Other p emitters commonly used in biochemistry are  

These differ significantly in their half lives and in the energy of emitted /3 particles (Table 2-4). Whereas 3H and 14C are relatively long-lived isotopes, 32P, 33P, and 35S have comparatively short half-lives. 3H, 14C, 33P and 35S are weak fi emitters (maximum energy of the / rays 0.2 MeV), and 32P is a strong emitter (maximum energy of the rays 1 MeV). 

Some radioactive isotopes decay with emissions of [i particles and y rays (Rontgen emission) as for example 131I  

Others decay by taking up an electron from the inner electron shell and emitting y rays 

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