Basic Concepts 1.1 History
Although this book will not follow a strictly historical development, to 'set the scene' this first chapter will start with a brief review of the most important discoveries that led to the separation of nuclear physics from atomic physics as a subject in its own right and later work that in its turn led to the emergence of particle physics from nuclear physics. 1
1.1.1 The origins of nuclear physics
Nuclear physics as a subject distinct from atomic physics could be said to date from 1896, the year that Henri Becquerel observed that photographic plates were being fogged by an unknown radiation emanating from uranium ores. He had accidentally discovered radioactivity: the fact that some nuclei are unstable and spontaneously decay. In the years that followed, the phenomenon was extensively investigated, notably by the husband and wife team of Pierre and Marie Curie and by Ernest Rutherford and his collaborators, 2 and it was established that there were three distinct types of radiation involved: these were named (by Rutherford) -,and -rays. We know now that -rays are bound states of two protons and two neutrons (we will see later that they are the nuclei of helium atoms), -rays are electrons and -rays are photons, the quanta of electromagnetic radiation, but the historical names are still commonly used.
1 An interesting account of the early period, with descriptions of the personalities involved, is given in Se80. An overview of the later period is given in Chapter 1 of Gr87. 2 The 1903 Nobel Prize in Physics was awarded jointly to Becquerel for his discovery and to Pierre and Marie Curie for their subsequent research into radioactivity. Rutherford had to wait until 1908, when he was awarded the Nobel Prize in Chemistry for his 'investigations into the disintegration of the elements and the chemistry of radioactive substances'.