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The spectrum of the luminescence from ruby excited by 2 MeV electrons has been compared with that excited by ultra-violet light. Two effects have been noted: an additional pair of lines at 7165 and 7218 Å, and an asymmetric broadening on the long-wavelength side of the R 1 R 2 doublet. The first effect is attributed to multiple ionization in the neighbourhood of a chromium atom, and the second to local heating by the electron beam.
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Mitchell et al. (1963) studied this question.
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