December 1955 L E T T E R S T O T H E E D I T O R 1087

Nuclear Spin of Polonium-209 (Po209) K. L. VANDER SLUIS AND P. M. GRIFFIN

Oak Ridge National Laboratory, Oak Ridge, Tennessee (Received August 15, 1955)

Structure of the polonium-209 isotope. The excitation of the spec­trum was obtained in an electrodeless discharge tube by means of a Raytheon Microtherm unit, Model CMD-4, operating at a frequency of 2450 megacycles per second. The discharge tube was fabricated from standard 9-mm quartz tubing 3 inches in length and contained 70 millicuries of the metal (33 micrograms of Po208, 11 micrograms of Po209) with 5 mm of He as a support gas. As a safety precaution this tube was encased in a 13-mm quartz tube which was sealed off with a half-atmosphere of He between the two tubes.

The spectrum was photographed in the region from 2200 A to 9000 A by using a Fabry-Pérot interferometer in conjunction with a 21-ft Wadsworth mount grating spectrograph. Interfero-grams were obtained for spacings of 3, 5, 8, 10, 13, 15, 25, and 45 mm by using aluminum films for the region below 4000 A and silver films for the region above 4000 A.

One hundred and five polonium lines were observed2 with 33 of them showing hyperfine or isotope structure. Twenty-one of these 33 lines had a two-component hyperfine pattern due to the 209 isotope and a single component from the 208 isotope. Eleven lines consisted of two components, one from Po208 and the other from Po209; however, it is possible that in some cases one component of the 209 hyperfine pattern falls on the 208 line because of an over­lap of orders. Final measurements should remove this ambiguity. One line exhibited a three-component hyperfine pattern plus a single component from the 208 isotope.

All the data are consistent with the conclusion that the two-component structures are due to the 2I + 1 components of the hyperfine pattern and that the nuclear spin I=½. In agreement with qualitative relative intensities the three-component pattern (λб245.5) is very probably due to a level having a ƒ of ½. Con­clusive proof of the structures being due to a nuclear spin of ½ rather than J's of ½ comes from preliminary Zeeman data which show that λ4493.13 (a typical two-component hfs) is a J =2 to ƒ = 1 type transition. Measurements are now being made to deter­mine the hyperfine splitting of the energy levels and will be re­ported at a later date.

The authors are grateful to J. Richmond, J. Birden, and L. Gnagey of Mound Laboratory for their splendid cooperation in the fabrication of the discharge tube. We wish also to acknowledge the interest of Dr. J. R. McNally, Jr., and Dr. G. W. Charles in the pursuance of this problem.

1 This sample was cyclotron produced by the Electronuclear Research Division at The Oak Ridge National Laboratory for Mound Laboratory. 2 The wavelengths of 64 of these lines have been previously reported by Charles, Hunt, Pish, and Timma in Mound Laboratory Report No. MLM-941 (January, 1954); also J, Opt. Soc. Am. (to be published).

T HE availability of a sample of polonium1 composed of 75% Po208 and 25% Po209 has prompted a study of the hyperfine