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We report the results of a study of the yrast excitation spectrum for ' Rn via the Pb(' C,n2n) ' Rn reaction. Measurements of y-y coincidences, y-ray angular distributions, and y-x-ray coincidences were made. We propose a level spectrum up to J =(10+) which does not exhibit the alternating parity structure observed in several isotopes of radium and thorium. From an examination of information on ' Rn and the neighboring nuclei, we can tentatively determine that the radon isotopes of masses 216 to 222 and the N =128 isotones " Ra and "Th define a lower mass boundary of a region beyond which static intrinsic reflection asymmetric shapes may exist in the nuclear ground states.

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