In the region 6709–2302A the wavelengths of sixty lines in the first spectra of the even isotopes of mercury, 80Hg198 and 80Hg202, have been measured relative to 5460.7532A. Electrodeless tubes (see reference 3) containing 0.5 mg of mercury were excited by radio waves of 90- to 300-mc frequency. Comparison with the data of Meggers and Kessler (see reference 5) shows the median difference AOW–MK to be 0.0001A. A comparison of the wavelength and level systems of the two isotopes confirms our opinion that the spectrum of natural mercury may be useful as a source of secondary standards, since the isotope shift of the odd level 6p 1P1° is nearly the same as that of several even levels.
We are indebted to Director Condon and Dr. Meggers of the National Bureau of Standards for a sample of 80Hg198 which was derived from radioactive gold in cooperation with the United States Atomic Energy Commission. The sample of 80Hg202 was produced by Carbide and Carbon Chemical Division, Oak Ridge National Laboratory, Y-12 Area and obtained on allocation from the Isotopes Division of the AEC.
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