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Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70 Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation rays in the highly segmented MINIBALL -ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2 state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2 state in 70 Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes. DOI: 10.1103/PhysRevLett.98.072501 PACS numbers: 21.10.Ky, 25.70.De, 27.50.+e A remarkable property of the nucleus is its ability to assume different configurations giving energy minima corresponding to different shapes of the mean field. It is often claimed that the presence of low-lying excited 0 states in even-even nuclei is strong evidence for such shape coexistence, since it is difficult to account for the presence of such states otherwise [1,2]. Arguably the most striking example of this is the case of 186 Pb [3], where both the first and second excited states have a spin parity of 0 . These states were interpreted as the bandheads of oblate and prolate rotational configurations, in close competition with the spherical ground state expected for this singly magic (Z 82) nuclear system. The region close to the N Z line from 56 Ni to 80 Zr is believed to be one of rapidly changing nuclear shape. At the upper end of this region, strongly prolate deformed shapes are found: 80 Zr is suggested to have 2 0:4 on the basis of the high moment of inertia [4], and a strongly prolate ground state, consistent with 2 0:4, has recently been established from the Gamow-Teller strength distribution in 76 Sr [5]. For the midshell nuclei near N Z 34 and 36, large shell gaps exist for protons and neutrons at both prolate and oblate shape, which would favor shape coexistence near the ground state. In the light krypton isotopes, 72-78 Kr, a low-lying excited 0 state is observed. There is good experimental evidence that this state has an oblate intruder configuration, and it most likely becomes the ground state in 72 Kr [6,7]. An analysis of the mixing of this state with the ground state, through consideration of their perturbed energies and the excited state lifetime, suggests an oblate ground state for 72 Kr [6], while the recently measured BE2; 0 ! 2 value in this nucleus, PRL 98,

The electrical conductivity and Hall coefficient of a variety of single crystals of zinc selenide have been measured. As-grown, undoped crystals have a resistivity ( approximately 1012 Omega cm) which is too large for successful Hall measurements to be made. However, after heat treatment at 850 degrees C in molten zinc, the resistivity of a sample is reduced to about 10-1 Omega cm. The samples are fairly heavily compensated. The Hall mobility of the free electrons is about 530 cm2 V-1 s-1 at room temperature when optical mode scattering is the dominant mobility-limiting mechanism. At lower temperatures, ionized impurity scattering becomes dominant. Crystals containing grown-in impurity donors such as indium, gallium and chlorine have also been investigated, as have crystals containing aluminium. Increasing the concentration of aluminium leads to overlap of the shallow donor wavefunctions with consequent impurity banding and the production of a degenerate semiconductor. Increasing the concentration of indium, gallium or chlorine is accompanied by anomalous behaviour.