Radioactivity of elements

Where the number of both protons and neutrons in an atom is known we are able to identify a specific isotope of a specific element and this is termed a nuclide. Some naturally occurring elements are radioactive and specific isotopes of these elements are called radionuclides. This term implies that their nuclei are unstable and spontaneously decay, transforming the nucleus into that of a different element. Radioactive decay is written in equations that look a little like those for chemical reactions, but they need to express the atomic mass of the elements involved and the type of rotation emitted. A number of modes of radioactive decay are possible, and here we outline some of the common ones. The decay of potassium (40K) can be written  

In this transformation an electron of the potassium is captured by the nucleus, a proton within it is converted to a neutron and excess energy is lost as a y 

Unstable heavy elements with an excess of protons in the nucleus decay to produce radiation as an a particle (alpha decay), which is in fact a helium (He) nucleus, for example  

As the a particle loses energy, it picks up electrons and eventually becomes 4He in the atmosphere. As the helium nucleus contains two protons and two neutrons the nucleus Z number changes from that of U (Z = 92) to Th (Z = 90), while the mass number decreases by 4. Another source of helium is the alpha decay of radium (Ra)  

Other heavy elements with an excess of neutrons in the nucleus decay by transforming the neutron into a proton by ejecting an energized electron known as a negative beta particle (P ). An example of beta decay is  

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After the work by Marie Curie and her daughter Irene established a new field of research in the radioactivity of elements, others carried out similar experiments to begin to understand the internal stmcture of the nucleus and a period of increased research occurred in the 1930s. At the Kaiser Wilhelm Institute in Berlin and the Niels Bohr Institute in Stockholm, a drama unfolded in 1938 that ushered in the atomic age. Lise Meitner was a petite, shy Austrian girl who made friends with a... 

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