Multinucleon transfer reactions have been used, for the first time, to populate high-spin bands of alternating parity states in 218,220,222 Rn and 222,224,226 Ra. The behavior of the angular momentum alignment with rotational frequency for the Rn isotopes is very different when compared with Ra and Th isotopes with N ഠ 134, indicating a transition from octupole vibrational to stable octupole deformation. Throughout the measured spin range the values of jD 0 ͞Q 0 j remain constant for 222 Ra and 226 Ra and have a very small value for 224 Ra, suggesting that the charge and mass distributions are not affected appreciably by rotations. [S0031-9007(97)02928-1] PACS numbers: 21.10. Re, 23.20.Lv, 25.70.Gh, 27.90. + b Of all nuclear species, radium (Z 88) and thorium (Z 90) isotopes with N ഠ 134 show the best evidence for octupole instability in their ground state [1-3]. These nuclei have low-lying negative-parity states and relatively strong B͑E1͒ values for the transitions between the bands of opposite parity; for the single case of 226 Ra large B͑E3͒ values have been measured consistent with its interpretation as a rotating pear shape [4]. The inaccessibility of these nuclei has, however, meant that there are large gaps in our knowledge of octupole effects in heavy nuclei. Comprehensive measurements of the high-spin behavior of the yrast octupole band exist only for the isotopes of thorium. For the radium isotopes such measurements are available for the weakly quadrupole coupled 218,220 Ra and the strongly coupled 226 Ra. There is only a limited amount of data on 224 Ra and virtually no information exists for 222 Ra. The scarce data do, however, suggest cancellation effects for the electric dipole moment for 224 Ra [5] which do not occur in the thorium isotopes. This effect is not properly established as the spin-dependent behavior for 222 Ra has not yet been measured. There are almost no data on the octupole structures for the radon isotopes. Systematic measurement of the variation of angular momentum with rotational frequency of the octupole bands should provide an insight into the nature of the strength of the octupole interactions in these nuclei.In order to populate the nuclei of interest the properties of multinucleon transfer reactions have been exploited. Previously, yields have been mapped out following the bombardment of a thick 232 Th target with various projectiles [6]. As the reaction 136 Xe 1 232 Th offered the largest yield for radon and radium isotopes with N ഠ 134, this reaction was chosen in order to make spectroscopic measurements of the heavy products.High-spin states in 218,220,222 Rn and 222,224,226 Ra were simultaneously populated following multinucleon transfer between 136 Xe and 232 Th. The 136 Xe projectile was accelerated to an energy of 833 MeV by the 88 in. cyclotron at Lawrence Berkeley National Laboratory. This bombarded a 232 Th target of thickness 36 mg͞cm 2 . Deexcitation gamma rays emitted from reaction products were collected for 49 h with the Gammasphere spectrometer which cons...

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Yrast excitations in the Nϭ82 isotone 137 Cs have been identified for the first time in thick-target ␥-ray coincidence measurements for the system 232 Thϩ 136 Xe using the Gammasphere array. The 137 Cs nuclei were produced in deep inelastic one-proton-transfer reactions. By-products of the main investigation were two well-developed rotational bands which were identified in heavy reaction partner products complementary to 137 Cs and are tentatively assigned to the little studied nucleus 231 Ac. There was no difficulty in placing the 11 observed 137 Cs transitions in a yrast level scheme extending to an I ϭ(31/2 Ϫ ) level at 5494 keV. Interpretation was also straightforward, since the experimental level energies are in close agreement with results of shell model calculations performed earlier using empirical single particle energies and interaction matrix elements derived from experimental data for other Nϭ82 isotones. ͓S0556-2813͑99͒00706-2͔

Prompt and delayed gamma-ray cascades in doubly magic 132Sn and its neighbor 131Sn have been studied at Gammasphere using a 248Cm fission source. Isotopic assignments of unknown gamma rays were based on coincidences with known transitions in A = 112-116 Pd fission partners. The yrast level spectra of both tin nuclei are interpreted using empirical nucleon-nucleon interactions from the 132Sn and 208Pb regions. Results include identification of the (nuf(7/2)h(-1)(11/2))9(+) aligned state in 132Sn and of extensive (nuf(7/2)h(-2)(11/2)), (nuf(7/2)d(-1)(3/2)h(-1)(11/2)) and (nuh(-1)(11/2)x3(-)) multiplets in 131Sn. The previously reported beta(-) decay of an unusual 131In high-spin isomer to levels in 131Sn is also elucidated.