Abstract
THE chief difficulty in analysing an element with a high melting-point by means of positive rays lies in the construction of a suitable furnace for evaporating the metal. I have recently succeeded in obtaining rays of copper by using a molybdenum furnace, heated with a coil of molybdenum wire embedded in alundum cement. Three isotopes were observed separated by two units in atomic weight. The relative intensities were about 1.4:1:1, the lightest being the strongest. Rays of rubidium were also obtained, probably from the cement, and showed two isotopes, as found by Aston with his method of analysis. The relative intensities gave a mean atomic weight of 85.51, in good agreement with the chemical atomic weight 85.45. To obtain agreement with the chemical atomic weight of copper 63.57, it is necessary to suppose the isotopes to be 62, 64, and 66, since this gives a mean atomic weight of 63.76, which is as close as would be expected. A direct comparison with rubidium is desirable, but further experiments will be necessary before the comparison can be regarded as conclusive, since the rubidium rays probably start at the surface of the cement and may fall through a different potential from the copper rays. A few comparisons suggested the even atomic weights, so that we may provisionally take the isotopes of copper as of atomic weights 62, 64, and 66. This seems to mark the first exception to the rule observed by Dr. Aston to hold for chlorine, potassium, bromine, rubidium, and antimony, that elements with odd atomic numbers have isotopes with odd atomic weights, and may be connected with the fact that copper occupies a place in the series of elements where the atomic weights begin to increase rapidly with atomic number.
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DEMPSTER, A. Positive Ray Analysis of Copper. Nature 112, 7 (1923). https://doi.org/10.1038/112007a0
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DOI: https://doi.org/10.1038/112007a0
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