Page 18 - Radiochemistry and nuclear chemistry

Origin of Nuclear Science 7

Our understanding of the nucleus has grown rapidly since Rutherford's scattering
experiments. Some of the important steps in the history of nuclear science are listed in
Table 1.1. Many of these discoveries and their practical consequences are discussed in the
subsequent text.

TABLE 1.1. Historical survey of nuclear science
Essential steps in the development of modern science
- 490-430 B.C. Empedocles suggests that everything is made up of four elements: air, earth, water and fire.
Every matter can be formed by transmutation between these. (This is principally correct if
the four elements are interpreted as being the gaseous, solid and liquid states of matter, and
fire interpreted as being energy.)
- 460-370 B.C. Democritos proposes that all matter consists of eternal, moving and indestructible atoms,
qualitatively alike but differing in size, shape and mass.
1661 Boyle writes that the nature is made up of a limited number of substances (elements) which
cannot be broken down into simpler ones.
1808 Dalton: All chemical compounds (molecules) are combinations of atoms in fixed
proportions.

1896 Becquerel discovers radiation from uranium (radioactivity). The intensity of the radiation
is measured either through its ionization of air or through the scintillations observed when
the radiation hits a fluorescent screen.
1896 - 1905 Crookes, Becquerel, Rutherford, Soddy, Dorn, Boltwood et al. Radioactive decay is
found to be transformation of atoms leading to different radioelements which are genetically
connected in radioactive decay series.
1898 P. and M. Curie discover polonium and radium; the first radiochemical methods.
1898 - 1902 P. Curie, Debierne, Becquerel, Danilos et al. discover that radiation affects chemical
substances and causes biological damage.
1900 Villard and Becquerel propose that -/-radiation is of electromagnetic nature; finally proven
in 1914 by Rutherford and Andrade.
1900 Becquerel:/~-rays are identified as electrons.
1902 First macroscopic amounts of a radioactive element (radium) isolated by M. and P. Curie
and Debierne.
1903 Rutherford: c~-radiation is shown to be ionized helium atoms.
1905 Einstein formulates the law of equivalence between mass and energy.
1907 Stenbeck makes the first therapeutic treatment with radium and heals skin cancer.
1911 Rutherford, Geiger, and Marsden conclude from measurement of the scattering of c~-
radiation against thin foils that atoms contain a very small positive nucleus.
1912 Heresy and Paneth, in the first application of radioactive trace elements, determine the
solubility of PbCrO 4 using RaD.
1912 Wilson develops the cloud chamber, which makes tracks from nuclear particles visible.
1913 Hess discovers cosmic radiation.
1913 Fajans and Soddy explain the radioactive decay series by assuming the existence of
isotopes. This is proven by J. J. Thomson through deflection of neon ions in
electromagnetic fields. Aston separates the isotopes of neon by gas diffusion.
1913 N. Bohr shows that the atomic nucleus is surrounded by electrons in fixed orbitals.
1919 Rutherford: first nuclear transformation in the laboratory, 4He + 14N --* 170 + IH.
1919 Aston constructs the first practical mass spectrometer and discovers that isotopic weights are
not exactly integers, v
1921 Hahn discovers nuclear isomers: 234mpa(UX2) ...... > 234pa(UZ).
1.2 rain
1924 de Broglie advances the hypothesis that all moving particles have wave properties.
1924 Lacassagne and LaRes use radioactive trace elements (Po) in biological research.