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The complete spectrum of [gamma] rays following the decay of superdeformed (SD) states in [sup 192]Hg has been extracted. The spectrum, which comprises a quasicontinuous component and sharp lines, reveals the decay mechanism and defines the excitation energies of the SD band. The decay of SD states results from the coupling between a cold, ordered SD system with a hot, chaotic one with normal deformation.

Four new superdeformed bands have been observed in {sup 194}Tl, in addition to the two already reported. These six bands consist of three signature-partner pairs, whose energies and spacings closely resemble those in the two superdeformed bands recently reported in {sup 193}Tl. The transition-energy similarities and angular momentum alignments of these bands are discussed.

We have observed Doppler-shifted x rays characteristic of Sb and Sn atoms in coincidence with {sup 108}Xn evaporation residues resulting from the emission of four protons by the compound nucleus (CN) formed in the reaction {sup 58}Ni+{sup 54}Fe. We have attributed the Sb x rays to atomic inner-shell vacancies which are created on the way into the nuclear reaction and filled before the emission of the last proton in the deexcitation cascade. The mean proton partial width of the nuclear states, formed at a mean excitation energy of 25{plus minus}4 MeV by the evaporation of three protons by the CN, has been deduced.

The energies of the excited states in very neutron-rich Si-42 and P-41,P-43 have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of S-42,S-44 at 39A MeV. The low 2(+) energy of Si-42, 770(19) keV, together with the level schemes of P-41,P-43, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that Si-42 is best described as a well-deformed oblate rotor.

The reduced transition probabilities B(E2;0{sup +}{yields}2{sub 1}{sup +}) of the neutron-rich {sup 74}Zn and {sup 70}Ni nuclei have been measured by Coulomb excitation in a {sup 208}Pb target at intermediate energy. These nuclei have been produced at Grand Accelerateur National d'Ions Lourds via interactions of a 60A MeV {sup 76}Ge beam with a Be target. The B(E2) value for {sup 70}Ni{sub 42} is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core. In the Zn isotopic chain, the steep rise of B(E2) values beyond N=40 continues up to {sup 74}Zn{sub 44}. The enhanced proton core polarization in {sup 70}Ni is attributed to the monopole interaction between the neutron in the g{sub 9/2} and protons in the f{sub 7/2} and f{sub 5/2} spin-orbit partner orbitals. This interaction could result in a weakening of magicity in {sup 78}Ni{sub 50}.

The excitation energy of the lowest-energy superdeformed band in Pb-196 is established using the techniques of time-correlated gamma-ray spectroscopy. Together with previous measurements on Pb-192 and Pb-194, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a "superdeformed shell gap."

The neutron-rich ${}^{66,68}\mathrm{Ni}$ have been produced at GANIL via interactions of a $65.9A\mathrm{MeV}$ ${}^{70}\mathrm{Zn}$ beam with a ${}^{58}\mathrm{Ni}$ target. Their reduced transition probability $B({E2;0}_{1}^{+}\ensuremath{\rightarrow}{2}^{+})$ has been measured for the first time by Coulomb excitation in a ${}^{208}\mathrm{Pb}$ target at intermediate energy. The $B(E2)$ value for ${}^{68}{\mathrm{Ni}}_{40}$ is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the $B(E2)$ values and indicates the erosion of the $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40$ harmonic-oscillator subshell by neutron-pair scattering.

Excited states in (216)Th were investigated via prompt and delayed gamma decays and the recoil-decay tagging method. The decay schemes of the I(pi) = (8+), t(1/2) = 128(8) micros, the I(pi) = (11-), t(1/2) = 615(55) ns, and the I(pi) = (14+), t(1/2) > or = 130 ns isomers were established. The configuration pi h(9/2)f(7/2) is assigned to the I(pi) = (8+) isomer, which implies that the h(9/2) and f(7/2) states are nearly degenerate. This is ascribed to increased binding of the f(7/2) orbital by its coupling to a low-lying I(pi) = (3-) state at E(x) = 1687 keV. The role of octupole and pairing correlations for a Z = 92 shell closure prediction is discussed on the basis of shell model calculations.

A new superdeformed rotational band has been observed in Er-154 using the Euroball Ge detector array. The new band and the one previously observed can be understood as based on coexisting superdeformed structures at prolate and triaxial shapes, respectively. The observation resolves long-standing difficulties in the theoretical interpretation of superdeformed states in Er-154.

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)--2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.

One of the superdeformed rotational bands in {sup 194}Hg has transition energies (rotational frequencies) that are equal within about 0.1% to those of the (only known) band in {sup 192}Hg. This excited (two-quasiparticle) band in {sup 194}Hg has an aligned spin of (1.00{plus minus}0.04){h bar} relative to the very similar band in {sup 192}Hg, suggesting an interpretation in terms of aligned pseudo (intrinsic) spin. The implied pseudospin symmetry may be a clue as to why the rotational frequencies are so similar.

F. S. Stephens et al. answer the comments made by C. L. Wu et al. on the quantized spin alignment of superdeformed Hg(mercury) nuclei. (AIP)