physics-subatomic-particles

dwarf, and stopping the star, which would otherwise have gravitationally collapsed ,from collapsing inwards .But the 'reclusion Principle does not only apply to electrons in any condition . I nthe mid-1950's it was found that protons and neutrons also obeyed it, so that no twoprotons in a given atomic nucleus could have the same energy and spin, and similarly ,neither could any two free protons . This extension of the reclusion Principle le dto the discovery of the so-called 'magic numbers', which are simply the numbers o fnucleons which each nuclear shell can hold . These numbers are 2, 8, 14, 20, 28, 50 ,82, 126 and, apart from corresponding to the number of particles which a nuclea rshell can hold, they also correspond to the number of electrons which electron shell scan hold .Now let us consider the Exclusion Principle from the standpoint of wave mechanics .We interpret different energy levels as being different 'vibration modes' . Thus, whe nin classical theory we would say that an electron moved into another orbit of higherenergy, we would now say that it is statistically likely that one vibration mode die sout, and another, at a higher energy, is born . ;row our rtcclusion Principle state sthat, just as one can not strike a key on a piano twice simultaneously, so no tw ovibration modes or waves with the same energy and spin can exist at the same time .it was in terms of wave functions that Pauli initially stated and proved his :occlusio nPrinciple . We find that, if the particles in question are p and q, and the paramete rwe are attempting to measure is A, then, adding a normalisation factor of two, we have :r(Ae Ay) _ (1W.V.)N2 and 1F(n , Ay) ° (Wp 'r)I 3L .The first of these wave functions is said to be symmetric, because when we interchang ethe two particles, this does not result in a change of sign, whereas the second functio nis antisymmetric, because, by swopping around p and q, we change the sign of th eoverall function . But how can two functions be both equal and opposite in sign: Th eonly answer is that both are z ero, and that therfore the probability of two particle sbeing identical in any set of parameters is zero, we see that the reclusion Principl edoes not only apply to energy and spin, but also, for example, to space and time .in this example, we discover the fact that no particles which obey the & elusionrrinciple may be in the same place at the same time, it is this result that stops allmatter from disintegrating immediately, because particles like photons may be hoarde dtogether in as large a quantity as is desired in the same space-time .Rut probably the most important consequence of the Exclusion Principle was Dirac' stheory of positrons . In 1928 P .Dirac developed a wave equation, known as the Dira cequation, in accordance with Relativity and wave mechanics, which described the motio nand properties of the electron in exact agreement with its experimentally observe dcharacteristics . However, one of the most far-reaching results of this equation wa sthat it was found that the electron could have negative energy and mass because of th eexistence of a negative root of the expressionj((m_c a )' )/(1-(v/c)z ) which was foundto represent its relativistic energy. Dirac did not immediately understand th esignificance of this negative root and would have simply assumed it to be an unrealsolution to his problem, had it not been for the discovery of the positron in 1933 .On August the second, 1933, while photographing cosmic ray tracks obtained in a15 000 gauss vertical Wilson cloud chamber, C .Anderson noticed some tracks which coul donly be explained as having been produced by the passage of a particle of similar mas sto an electron, but carrying a positive charge . Inside the cloud chamber there wa sa 6 mm thick lead plate, through which the new particle passed, and in doing so ,changed the curvature of its track . If this positive particle were a proton, then, in