physics-subatomic-particles

This conservation law or selection rule is important because it does not allow a verylarge number of reactions, such a sP + K- K°+ p + -reto take place .In 1925 L'hlenbeck and Goudsmit noticed that the bands in atomic spectra, ,thich ha dpreviously been assumed to be continuous, were in fact made up of two or more thinne rbands, the number of bands increasing as a greater magnetic field was applied to thesample (Zeeman ,ufect) . This led them to suggest that, in addition to the angula rmomentum it obtained from orbiting around an atomic nucleus, the electron also possesedits own angular momentum or spin . According to Schrddingerstheory which he postulate din 1976, atoms have at least three basic quantum numbers, as they are called, whic hdescribe the state of the atom's electrons . The first of these was the principalquantum number, n, which described the degree of excitation of the atom, and couldtake the value of any positive integer . The second was the orbital quantum number, 1 ,which described the angular momenta of the electron orbits, and could take any positiv eintegral value less than n ; and the third was the magnetic quantum number, m, whic hdescribed the spatial orientation of the electron orbits, and could take any integra lvalue between -1 and .e 1, where 1 is the orbital quantum number . In 1927 Pauli showedthat if sp in, s or j, was added to the atomic or spectral quantum numbers, then th estate of an atom could be defined uniquely by giving its spectral quantum numbers ,and in 1928, using Relativity Theory, Dirac showed that it was possible to predictthese quantum numbers theoretically . Soon after, Stern and Gerlach, in a verycomplicated experiment, measured the magnetic moment of the electron and found it tobe about 9 .9732 x 10 s.4 JT - ; and verified the idea that a particle of spin s can alig nitself in 2e+ 1 ways with respect to a uniform magnetic field . Since angular momentumis a fora of energy, it must be quantised, and it has been found that the minimu mpossible positive spin is „ and, because of some of the findings of quantu melectrodynamics, this was the spin assigned to the electron . We see that we may'project' this spin in two ways, so that an electron may have a spin of either z o runits .It is often the case that an equation yields some conservation law because som equantity is found to be equal to a constant . So it was with the Lagrangian esuatior sof motion . It was found that both angular and linear momentum must be conserve dquantities . The former has been verified by observing the motion of neutral pion sproduced in stationary proton-antiproton annihilations, and has been found to hol dgood down to one part in ten thousand . The conservation of angular momentum has bee nchecked to a much lower accuracy by observing scatter angles in various elasti ccollisions . The conservation of angular momentum has been proved at great length bymaking use of wave mechanics, notably by Schrgdinger . We may think of the conservationof linear and angular momenta as natural consequences of the fact that the geometrica ltransformations of translation and rotation are isometrics wherever they may be applied .We may therefore say with confidence that in any reaction the sum of the spins of th einitial particles is equal to the sum of the spins of the resultant or final particles .Let us now consider how we sight measure or calculate the spins of various particles .The electron, proton, and photon are thought to have spins of '- and it is on thi sassumption that the spins of most other particles are calculated . We may say whethera particle has integral or half-integral spin by examining its decay, since we knowthat spin is conserved . Hence we may say, from the decay2 ythat the n• has integral spin . ye may evaluate its spin, as did Cartwright et al . in