SPECTRUM AND SPECTROSCOPE (Part 3 of 3)

Moseley, Henry Gwyn-Jeffreys (1887-1915), British physicist, born in Weymouth, England; gave his name to the Moseley number.

In 1913 and 1914 the English physicist H.G.J. Moseley (1887-1915) announced the discovery of far-reaching relations among X rays produced from the surfaces of different metals by the impact of electrons. He found that each metal gives certain groups of X-ray lines, corresponding to certain frequencies. As he passed from a lighter to a heavier metal, each successive element showed lines of higher frequencies. Moseley reasoned that this was not due to increasing atomic weight, since several substances of different atomic weights showed the same spectra. It must have been due to a regular increase in the number of orbiting electrons, corresponding to the atomic number, of the atoms of the metals. Moseley's work provided the basis for the modern periodic classification of elements.

Modern Applications

Spectroscopes are used in almost every technical field, especially for identifying constituents and processes in any source that emits light. In some industries many similar samples must be analysed quickly and simultaneously for their light-absorbing characteristics. A physician may have several hundred samples of blood serum to analyse in a short period of time. Fortunately, fully automated analytical spectroscopes are available. New techniques of analysing samples based on how they absorb radiation to differing extents have given scientists new ways to determine a substance's properties.

Infra-red spectroscopy, ultraviolet spectroscopy, and nuclear magnetic resonance spectroscopy are the most commonly used of such techniques.

In the 20th century, scientists discovered that all atomic particles behave as if they had wavelengths much like those of light waves. Spectroscopes were used to study these particles. The study of the various elementary particles themselves is divided into baryon and meson spectroscopy, and elementary-particle spectrometers are used for such studies.

One of the accomplishments of neutron spectroscopy, another field, was the plotting of the structure of large complex molecules like those of DNA and RNA, the basic materials of heredity. Furthermore, spectroscopes are used to measure temperatures in controlled thermonuclear fusion.