The World of Atom (Part XVI)



Chapter 94: Parity and Its Ill Fortune – C. N. Yang (b. 1922) and T. D. Lee (b. 1926)

Law of Parity Conservation. In 1953 it was found that theta and tau mesons had identical masses and lifetimes, but they decay in different schemes with different parities. This led to the assumption that they were two different K-mesons, even though they were alike in all other aspects. Lee and Yang, on examining this situation, discovered that the principle of conservation of parity has never been experimentally verified for weak interactions. Lee and Yang proposed that the conservation of parity be discarded in any reaction involving neutrinos and in weak interactions in general. This was then verified experimentally. They won the 1957 Nobel Prize.

Chapter 95: Nuclei and Nucleons – R. Hofstadter (1915 – 1990) 

Structure of Nuclei and Nucleons. Hofstadter received Nobel Prize in 1961 for detailed investigation into the structure of matter. He extended the technique of previous electron-scattering studies to higher energies and discovered that nucleons consist of charged mesonic clouds. In the proton, these clouds appeared to add to the effect of their charges; in the neutron the clouds seem to cancel one another. Thus, nucleons are complex bodies of constituent mesons.

Chapter 96: Elementary Particles – H. A. Boorse (1904 – 2003) and L. Motz (1909 – 2004)


  1. Symmetry is a property of a physical system that is unaffected by certain mathematical transformations.
  2. A particular type of symmetry in nature implies the existence of a conservation law.
  3. In nature, symmetries are everywhere forming an important part of the laws.
  4. The concept of invariance introduced by Einstein is the most important example of symmetry.
  5. Invariance is the property of remaining unchanged regardless of changes in the conditions of measurement. 
  6. Invariance is related to conservation laws; for example, conservation of energy is related to invariance over time.
  7. The existence of quantum numbers is, in a sense, a consequence of the symmetries in nature.
  8. Parity is a property of a wave function or state vector.
  9. Conservation of parity is the rule that odd wave functions must remain odd and even must remain even.
  10. It was found experimentally that the parity was not conserved in the β-decay of cobalt-60.
  11. Protons and the neutron have finite size or a structure.
  12. Both have their magnetic moment distributed over a finite radius.
  13. Proton also has its electric charge similarly distributed.
  14. Both the proton and the neutron consist of cores surrounded by clouds of mesons.
  15. In the neutron the clouds seem to cancel one another.
  16. In the proton these clouds appeared to add to the effect of their charges.
  17. Every nucleus has a core of electric charge surrounded by a thin skin in which the charge falls off to zero quite quickly. 
  18. In this nuclear core the charge density is constant.

The atom is a vortex of condensing substance.


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