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Regional geochemical databases for the northern Midwest USA are being compiled to examine the various geogenic and anthropogenic factors that control the chemistry of groundwater. At the regional scale, variations are seen that are attributable to agricultural and urban effects, or to geologic factors. Examples of the former include enrichments of nitrate in groundwater, while examples of the latter mainly highlight geochemical differences between carbonate rocks and all other rock types in the region. This paper examines a few of these regional effects and the spatial scales at which they can be observed.

The search for superhard materials, driven by their widespread use in industrial applications, highlights one of the most difficult problems in the field of materials science: the accurate characterization of a material’s intrinsic physical properties. This paper reports on the full elastic tensor of two polycrystalline isotropic specimens and one specimen of ReB2 consisting of highly oriented grains. The high-monocrystal bulk modulus value extracted from the grain-oriented specimen, measured by resonant ultrasound spectroscopy, validates the ultra-incompressibility of ReB2. An observed hardness of 40 GPa and a Debye temperature of 731 K were calculated for the ReB2 crystal, confirming its superhard and super-stiff properties. All the measured moduli of the ReB2 grain-oriented crystal exceed the comparable ones for the polycrystal by amounts that cannot be explained by averaging over direction, which may reveal why recent measurements reported on ReB2 containing excess boron yield values that are not as hard or incompressible as the crystal.

Oriented bicrystals of pure C11b MoSi2 have been grown in a tri-arc furnace using the Czochralski technique. Two single crystal seeds were used to initiate the growth. Each seed had the orientation intended for one of the grains of the bicrystals, which resulted in a 60° twist boundary on the (110) plane. Seeds were attached to a water-cooled seed rod, which was pulled at 120 mm/h with the seed rod rotating at 45 rpm. The water- cooled copper hearth was counter-rotated at 160 rpm. Asymmetric growth ridges associated with each seed crystal were observed during growth and confirmed the existence of a bicrystal. It was also found that careful alignment of the seeds was needed to keep the grain boundary from growing out of the boule. The resulting boundary was characterized by imaging and crystallographic techniques in a scanning electron microscope. The boundary was found to be fairly sharp and the misorientation between the grains remained within 2° from the disorientation between the seeds.

High-spin states were studied in ${}^{181,183}\mathrm{Au}$ and resulted in the identification of several new prolate rotational bands based on $\ensuremath{\pi}{i}_{13/2},$ $\ensuremath{\pi}{h}_{9/2},$ $\ensuremath{\pi}{f}_{7/2},$ and $\ensuremath{\pi}{h}_{11/2}$ configurations. The alignment and moment of inertia features of the intruder bands are compared with ground-state bands in Pt nuclei. From these features, it can be concluded that a strongly interacting $(\ensuremath{\pi}{h}_{9/2}{)}^{2}$ alignment is occurring in the $\ensuremath{\pi}{i}_{13/2}$ bands in Au and the ground-state bands in Pt. In addition, bandhead energies and deformation parameters are calculated for deformed configurations in the framework of a microscopic-macroscopic shell-correction model. These calculations are compared with experimental values in Re and Ir, as well as, Au isotopes. Interaction properties between known $\ensuremath{\pi}{h}_{9/2}$ and $\ensuremath{\pi}{f}_{7/2}$ rotational bands are also discussed and compared with results from a cranked-shell model. Experimental $B(M1)/B(E2)$ ratios between these bands are compared with results from a particle-rotor calculation.

We report angular dependent X-ray absorption measurements at the Mo L 3,2 edge and the Si K-edge for a MoSi 2 single crystal. The crystal was oriented so that an azimuthal rotation of the crystal about the surface normal (direction of the incident photons) would align the c-axis of the crystal anywhere between parallel and perpendicular to the polarization of the photons. It was found that while the Mo L 3,2 edge XANES shows little angular dependence, the Si K-edge XANES shows a very strong polarization dependence of which the intensity exhibits a two-fold symmetry. This angular dependence of the Si K-edge XANES is attributed to the high densities of unoccupied states localized perpendicular to the Si-Si bond.

Charge redistribution upon metal silicide formation in a series of early 4d transition metal silicides; Zrsi 2 , Nbsi 2 , and MOSi 2 , together with the corresponding pure elements has been investigated with XANES at both the metal L 3,2 -edge and the Si K-edge. It is found that the metal L 3,2 -edge exhibits very intense whitelines characteristic of localized unoccupied densities of states of d character at the Fermi level and there are substantial differences between the metal and the silicide. The Si K-edge for the silicides also change markedly compared with pure Si. These results will be discussed in terms of densities of state calculations.

The status of the new Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory (ORNL), which is slated to start its scientific program late in 1996 is discussed, as is the new experimental equipment which is being constructed at this facility. Information on the early scientific program is also given.

A statistical analysis of the distribution of level spacings for states with the same angular momentum and parity is described in which the average spacing is calculated for the total ensemble of states of given I π in even-even, odd-even, or even-odd nuclei. Though the resulting distribution of level spacings for states of deformed nuclei with Z = 62−75 and A = 155−185 is the closest to that of a Poisson distribution yet obtained for nuclear levels, significant deviations are observed for small level spacings. Such deviations are observed independent of spin, parity, nuclear type (even-even, even-odd, or odd-even), and intrinsic nuclear excitation. Many, but not all, of the very closely-spaced levels have K -values differing by several units.

Lifetimes of high-spin states in 164 Yb have been measured by the Doppler-broadened line shape (DBLS) method using the reaction 124 Sn( 44 Ca, 4n) 164 Yb at a bombarding energy of 189 MeV. The Q t values from the data decrease sharply over the rotational frequency range 0.3 to 0.5 MeV ( I = 20 to 32 ħ). At the same rotational frequencies the kinematic moment of inertia is nearly constant, increasing slightly at the higher frequencies h ω = 0.40 to 0.55 MeV . These observations can be understood qualitatively as a rotationally-induced deoccupation of strongly shape polarizing anti-aligned high- j , low-Ω orbitals i.e., those in which the nucleons are moving in the opposite direction to the rotation. A summary of the Q t values extracted from the lifetime data for the yrast decay sequences of the even- A nuclei 160–168 Yb are compared with the deformations from self-consistent cranking TRS calculations. The TRS calculations show the expected neutron number dependence, i.e., Δβ 2 β 2 ( h ω = 0) is smaller with increasing N and the corresponding loss of collectivity, Q t vs ħ ω, has a smaller slope at the larger ħ ω with increasing N . For 164,166,168 Yb the loss of collectivity from the DBLS measurements occurs at higher ħ ω than predicted and the slope of Q t vs ħ ω is much larger than predicted. The enhanced E1/E2 branching ratios and the large transition dipole moments for decay of the states in the (−, 1) band to the ground band and the (+, 0) band in 164 Yb suggest an octupole instability for 164 Yb.

Lifetimes of {sup 160}Yb yrast states at high rotational frequencies have been measured by the Doppler broadened line shape technique. Excited states in {sup 160}Yb were populated by the reaction {sup 120}Sn({sup 44}Ca,4{ital n}){sup 160}Yb at a beam energy of 200 MeV and the experimental measurements were carried out in the coincidence mode with an array of Compton-suppressed germanium detectors. The results for the 24{sup +} to 32{sup +} yrast states led to values of the transition quadrupole moments similar to those obtained for the lower members ({h_bar}{omega}{le}0.29 MeV) of the ground band in previous recoil-distance measurements. The trend of reducing {ital Q}{sub {ital t}} values found for the {ital I}=34{sup +} and 36{sup +} states are suggestive of band termination. The results are discussed in the light of current theoretical predictions. {copyright} {ital 1996 The American Physical Society.}

The high-spin states in $^{184}\mathrm{Hg}$ have been investigated via the $^{154}\mathrm{Gd}$ ${(}^{32}$S,4n) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to ${10}^{+}$ and ${26}^{+}$, respectively, and seven new bands are observed. A new band with odd spins, 13 to 25, has a much larger moment of inertia than the other bands in $^{184}\mathrm{Hg}$. Two of the new bands feed the prolate excited band and are interpreted as quadrupole vibrational bands. Also, two new signature partner bands are observed for which the configuration of \ensuremath{\nu}${\mathit{i}}_{13/2}$${\mathit{f}}_{7/2}$ is proposed. The similarity of the band with odd spins to the band with intermediate deformation (${\mathrm{\ensuremath{\beta}}}_{2}$\ensuremath{\sim}0.34) in $^{186}\mathrm{Hg}$, and signature partner bands to the bands observed in 104 isotones $^{180}\mathrm{Os}$ and $^{182}\mathrm{Pt}$, is discussed.

Excited states in $^{164}\mathrm{Dy}$ were produced using Coulomb excitation. Rotational properties of the ground-state and gamma-vibrational band were studied. Angular distribution and band-mixing parameters were extracted from the data. No evidence was found for a two-phonon gamma vibration with anharmonicity in the range 1.7\ensuremath{\le}E(${4}_{\ensuremath{\gamma}\ensuremath{\gamma}}^{+}$)/E(${2}_{\ensuremath{\gamma}}^{+}$)\ensuremath{\le}2.7.

In-beam [gamma]-ray spectroscopic studies of [sup 182]Hg have revealed five new bands. The 2[sup +] state of the prolate band has been identified at an energy of 548.6 keV and is higher than in [sup 184]Hg. A two parameter band mixing calculation results in an interaction energy of 83 keV between the prolate 2[sup +] and the oblate 2[sup +] states. Several additional new bands are seen including some which are interpreted as quadrupole vibrational bands built on the excited prolate minimum.

Superdeformed (SD) states with a 2:1 axis ratio have been observed in nuclei in the A = 150, 190, and the actinide regions. These states depopulate into normally deformed (ND) states by gamma decay, but so far the linking transitions have not been observed and the depopulation mechanism is not fully understood. Nuclei in different mass regions decay out at states with different spin (I), excitation energy above the ND yrast line (U) and lifetime ({tau}). This variation is due to differences in the nuclear properties such as the barrier penetration probability, the level densities and the gamma transition strength of SD and ND states. One important factor is the competition between the collective E2 decay along the SD band and the statistical decay to the ND states. These transition rates, or the partial lifetimes, can be determined if the lifetime and the intensity of the gamma rays depopulating the SD states are known.

The solid-solution system La{sub 1-x}TiO{sub 3} was investigated over the range 0 {le} x {le} 0.33, i.e., involving end members LaTiO{sub 3} and La{sub 2/3}TiO{sub 3}. X-ray single-crystal and powder neutron diffraction studies have established the structure of La{sub 2/3}TiO{sub 3} for the first time which is described in Pban with a = 5.461(1) {angstrom}, b = 5.482(1) {angstrom}, c = 7.759(3) {angstrom}. La vacancies are ordered largely in the z = 1/2 plane and Ti atoms are displaced from the centers of Ti-O octahedra toward this plane giving rise to c-axis chains consisting of two short Ti-O bonds (1.906 {angstrom}) alternating with two long Ti-O bonds (1.975 {angstrom}). The Pban structure is found for 0.25 < x < 0.33, an Ibmm structure for 0.20 < x {le} 0.25 and the Pbnm (GdFeO{sub 3} type) structure for 0 {le} x < 0.20. The compounds La{sub 2/3}TiO{sub 3} (x = 0.33) and La{sub 0.70}TiO{sub 3} (x = 0.30) are insulators, La{sub 0.75}TiO{sub 3} (x = 0.25) undergoes a metal-insulator transition and La{sub 0.80}TiO{sub 3} (x = 0.20) to La{sub 0.92}TiO{sub 3} (x = 0.08) are metallic. Electrical, magnetic and structural properties are compared with those of the closely related La{sub 1-x}Sr{submore » x}TiO{sub 3} and SrTiO{sub 3-x} systems. It is also argued that oxidized forms of LaTiO{sub 3}, described previously as LaTiO{sub 3+x}, are better understood as La{sub 1-x}TiO{sub 3}. 26 refs., 15 figs., 11 tabs.« less

The highest spin states in a T(z)=1/2 nucleus have been observed in 77Sr: I(pi)=(49/2+) and (29/2-). In addition, states up to I(pi)=(22+) have been seen in 78Sr. The alpha=1/2, g9/2 band and both signature partners of the negative parity band in 77Sr were found to be identical to the yrast band in 78Sr with relative alignments of 1.22(7)HBAR, 0.52(5)HBAR (alpha=1/2), and 0.42(4)HBAR (alpha=-1/2), respectively. In one of the negative parity bands, the identicality persists through the first proton band crossing. The odd spin decay sequence of the 4- band in 78Rb is identical to the ground band of 78Sr [3.02(3)HBAR] at low spin and to the alpha=1/2, g9/2 band in 77Rb [1.11(3)HBAR] at higher spins. These are the only known examples of identical bands in the neutron deficient A=80 region. The analysis indicates that the [301]3/2 Nilsson orbital is a very good spectator orbital. (Less)

High spin states in the [sup 191]Tl nucleus have been populated via the [sup 159]Tb ([sup 36]S,4[ital n]) reaction at 165 MeV. Two weakly populated rotational bands have been observed with properties (energy spacings and dynamic moments of inertia) very similar to those of other superdeformed bands in the [ital A][similar to]190 region. The two bands can be interpreted as signature partners which exhibit some signature splitting for rotational frequencies [h bar][omega][ge]0.2 MeV. They are interpreted within the framework of cranked Woods-Saxon calculations as being based on the proton [ital i][sub 13/2]([Omega]=5/2) intruder orbital, in agreement with pairs of superdeformed bands seen in neighboring odd Tl nuclei.

A decay sequence above the I= 47 2 , 5.4 MeV level in 193Hg has been established through discrete γ-ray spectroscopy. The new energy levels exhibit single-particle character implying the dominant role of individual particle angular momentum alignment at moderate spins in the neutron-deficient Hg isotopes.

Lifetime measurements on the 5/2[sup +][402] band in [sup 173]Re have been carried out by the recoil-distance technique. Lifetimes of the stretched E2 transitions in both signatures of this band were measured up to a spin of 35/2[sup +] as were the lifetimes of most of the M1 transitions between the two signatures. Large deformation increases were found in both signatures at low rotational frequencies ([Dirac h][omega] [approx] 160 keV) as predicted by TRS calculations and, thus, offer new insight into the behavior of the 5/2[sup +][402] band in [sup 173]Re and perhaps into other light nuclei in this region. The B(M1) values also show an increase at about the same rotational frequency. Particle-rotor calculations can account qualitatively for the M1 and E2 transition rates at low spins, but the enhanced MI rates remain a puzzle.

High-spin data are presented for levels in 163Er and in particular the structure of three high-K rotational bands are discussed and interpreted within the tilted rotation scheme. Large observed B(E1) values are interpreted in terms of coupling to octupole degrees of freedom.

A comprehensive study of odd-A rotational bands in normally deformed rare-earth nuclei indicates that a large number of seniority-one configurations (21% for odd-Z nuclei) at low spin have moments of inertia nearly identical to that of the seniority-zero configuration of the neighboring even-even nucleus with one less nucleon. It is difficult to reconcile these results with conventional models of nuclear pair correlation, which predict variations of about 15% in the moments of inertia of configurations differing by one unit in seniority.

The Oak Ridge RIB Facility has been approved and is under construction. The general layout and capabilities of this facility are described, as is the possibility of studying nuclei near the 100 Sn double closed shell, new regions of exotic nuclear shapes, proton halo nuclei, and rp-process nucleosynthesis.

The level structure of 169 Ta has been studied using the reactions 155 Gd( 19 F,5n), E = 85.5–100 MeV and 122 Sn ( 51 V ,4 n ), E = 223 MeV . Four rotational bands of 169 Ta have been identified with assignments 1 2 − [541] , 9 2 − [514] , 5 2 + [402] , 1 2 + [411] and a decoupled band was identified but not assigned to any configuration. Different configurations are observed to have different band-crossing frequencies and these differences are consistent with configuration-dependent deformation driving effects. The crossing frequency of the band based on the 1 2 − [541] configuration is deduced to be 0.305MeV/ħ which is delayed by about 55 keV in comparison with the yrast bands of its even neighbours. The first band crossings of 169 Ta are attributed to the alignment of a pair of i 13 2 quasineutrons, while the second band crossings may correspond to h 11 2 two-quasiproton alignment. The deformation driving effects of quasiparticle orbitais, B ( M 1)/ B ( E 2) values of the 9 2 − [514] and 5 2 + [402] bands and the band crossings in 169 Ta are discussed.

The [ital K][sub [alpha]]-x-ray yields associated with the superdeformed and normal-deformed bands in [sup 193]Hg have been measured. The results indicate an excess yield of [ital K][sub [alpha]]-x rays in coincidence with the superdeformed cascade relative to that in coincidence with the normal-deformed cascade. The internal conversion of known transitions along the superdeformed cascade cannot account for the observed [ital K][sub [alpha]]-x-ray yield. It is likely that this excess x-ray yield is associated with low-energy interband-[ital M]1 transitions competing with the low-spin superdeformed-[ital E]2 transitions.

Lifetimes of states associated with the ridges in the Eγ-Eγ correlation spectrum of 164Yb and 170Hf were measured by the Doppler-shift attenuation method. The results indicate a reduction of the quadrupole collectivity associated with γ-rays with energy from 0.7 to 0.9 MeV and an enhancement of collectivity for those above 0.9 MeV. The reduced and the enhanced collectivity can be understood as rotationally-induced modifications of the occupation of high-j orbitals originating from below and above the Fermi surface, respectively. The effect of rotational damping on the lifetimes of continuum states is also discussed.

The two-quasiproton structure of 164Dy has been investigated in a study of the 165Ho(t, α) 164Dy reaction. The experiment was performed using a 37.3 MeV triton beam delivered by the Daresbury tandem Van de Graaff accelerator. Magnetic analysis of ejectile ions was achieved using a QMG/2 magnetic spectrometer, and ion identification and detection employed a hybrid gas-filled, multielement, focal-plane detector. The two-quasiproton strengths accessed in this reaction are discussed with reference to the detailed spectroscopy of 164Dy. In particular, a rotational band built on a Kπ = 1+ state, previously interpreted as a collective structure, was observed and assigned as a two-quasiproton excitation which at zero deformation is based on the spherical (h112)2 shell-model state. The structure of the octupole-vibrational band and that of other states in the final nucleus have been elucidated.

High-spin states in 171Re have been studied using the reaction 123Sb(52Cr, 4n)171Re. A back-bend in the i132 band of a Re nucleus has been fully delineated for the first time. A new back-bend has also been observed in the 52+[402] band and other bands have been extended to higher spin and added to the level scheme. Band crossings are interpreted using the CSM and three-band mixing calculations. These appear to show evidence for shape coexistence and configuration-dependent neutron pairing.

Excited states in 167 W and 168 W, populated in the 142 Nd ( 30 Si , x n ) reaction, were investigated at high spins using the ESSA30 array with 29 Compton-suppressed Ge detectors. The level schemes are extended to higher spins and several new rotational bands are identified. The results are discussed in comparison with existing data on the neighbouring N = 93 and 94 isotones and on the Z = 74W isotopes. A theoretical analysis is presented within the framework of a pairing-self-consistent cranked shell model using shape parameters obtained from total-routhian-surface calculations.

A comprehensive study of odd-{ital A} rotational bands in normally deformed rare-earth nuclei indicates that a large number of seniority-one configurations (30% for odd-{ital Z} nuclei) at low spin have moments of inertia nearly identical to that of the seniority-zero configuration of the neighboring even-even nucleus with one less nucleon. It is difficult to reconcile these results with conventional models of nuclear pair correlation, which predict variations of about 15% in the moments of inertia of configurations differing by one unit in seniority.

An analysis of high-spin moments of inertia for the yrast sequences of deformed nuclei from A =72–184 indicates that within each deformed mass region, the moment of inertia is surprisingly constant. In contrast, between the different deformed mass regions the A 5 3 dependence of the moment of inertia, expected for a macroscopic rotor, is approximately restored.

High-spin states in 175Re were studied using the 156Gd(23Na, 4n) reaction. Five rotational decay sequences have been identified and assigned to proton configurations. Eight strong interband transitions are observed connecting the members of the [ 303 ] 5 2 , 7 2 pseudo-spin doublet. Both the interband and intraband M1 and E2 transition rates can be understood in the pseudo SU(3) formalism with Coriolis mixing.

Excited states in 167 Ta and 168 Ta, populated in the 142 Nd( 30 Si, p x n) reaction, were investigated using the ESSA30 array with 29 Compton-suppressed Ge detectors. Several rotational decay sequences are identified and for the first time a high-spin level scheme is established for these nuclei. The results for 167 Ta are discussed in comparison with existing data in the neighbouring nuclei and with cranked shell model calculations. The possible intrinsic structure and its consequences for the yrast band in 168 Ta are also briefly discussed.

Thermodynamic data near the superconducting {ital T}{sub {ital c}} on several different single-crystal specimens of the heavy-fermion system URu{sub 2}Si{sub 2} are presented. Multiple-peak structure and narrow transition widths ({Delta}{ital T}{sub {ital c}}/{ital T}{sub {ital c}}=0.05) are observed in the specific heat of the highest-quality samples. By carefully sectioning one of the crystals, it is shown that these peaks occur in macroscopically different parts of the crystal, and not as a result of vector superconductivity. Implications for the multiple-peak structure in UPt{sub 3} are discussed.

The rhenium-rich phase Re2Si crystallizes in a monoclinic unit cell, a = 6.4444(2) A , b = 5.3898(2) A , c = 9.6019(4) A , γ = 94.215(5)° (unique axis c, Pearson symbol mP24, Z = 8 and space group P2 1 b . The structure is based on a hexagonal close packing of rhenium and silicon atoms ordered on distinct sites and represents a new structure type. Re2Si becomes superconducting below 3.8 K.

A statistical analysis of the distribution of level spacings for states with the same angular momentum and parity is described in which the average spacing is calculated for the total ensemble. Though the resulting distribution of level spacings for states of deformed nuclei with Z = 62–75 and A = 155–185 is the closest to that of a Poisson distribution yet obtained for nuclear levels, significant deviations are observed for small level spacings. Many, but not all, of the very closely-spaced levels have K-values differing by several units.

The use of constant-N contours in the (ω,λ) plane is demonstrated both for establishing diabolical points and for studying regularities and fluctuations in the spectrum of single-particle states. Likewise the average properties and fluctuations of empirical proton-neutron interactions, obtained from double differentials of the total energy with respect to N and Z, are discussed for the ground states of all even-even nuclei with N>40 and as a function of the rotational frequency for the lowest even spin, positive-parity decay sequence of deformed rare earth nuclei.

Transition rates for high spin discrete line states in 168 Yb have been extracted using a Doppler Shift Attenuation Method and a loss of collectivity has been found at the highest spins. Similar results for other Yb nuclei are reviewed and an explanation, involving a reduction of deformation due to changes of intrinsic structure, is given. It is shown that this loss of collectivity for the yrast and near-yrast bands is in sharp contrast to the recent finding that the transitions contributing to the ridge structure in a γ-γ coincidence matrix retain full collectivity up to the highest spins. Possible reasons for this difference are discussed

The U.S. Nuclear Science Community in its 1996 Long Range Plan identified an advanced radioactive ion beam (RIB) facility based on the ISOL technique as the next major facility to be constructed for U.S. nuclear physics. The proposed Spallation Neutron Source (SNS) for Oak Ridge National Laboratory, whose construction design funds have recently been appropriated, offers a unique opportunity for the construction of this new facility. Plans for extracting a proton beam from the SNS, transporting it to the RIB facility, and constructing the new RIB facility at the SNS site are discussed, as are the ISOL targets, radiation handling, isobaric separation, acceleration of beams of radioactive ions, and the layout of the experimental areas.

XAFS measurements at the metal and Si K-edge have been made for a series of Tisi 2 and CoSi 2 blanket salicide films as well as bulk CoSsi 2 and TiSi 2 . It was found that the films have essentially the same structure as the bulk TiSi 2 and CoSi 2 and that the Si XANES exhibit very rich structures. Both the materials characterization and spectroscopy aspects of the XAFS are discussed.

High-spin states in $^{186}\mathrm{Hg}$ with a quadrupole deformation of ${\mathrm{\ensuremath{\beta}}}_{2}$=0.34(4) have been established from measured gamma-ray coincidences and lifetimes. These data, which provide the first evidence for a deformation midway between normal and super deformed, can be interpreted in terms of the [651] 1/2 and [770] 1/2 neutron configurations.

A statistical analysis of the distribution of level spacings for states with the same spin and parity is described in which the average spacing is calculated for the total ensemble. The resulting distribution of level spacings for states of deformed nuclei with A=155–185 and Z=62–77 is the closest to that of a Poisson distribution yet obtained for nuclear levels. However, when only the even‐spin, positive‐parity data for even‐even nuclei are considered, the level‐spacing distribution becomes double peaked. The anomalously‐large separations are shown to be the result of the low energy of the strongly‐correlated, completely‐paired yrast configuration of even‐even nuclei. Average values of the level spacings also are discussed as a function of spin, parity, and nuclear type (even‐even, even‐Z–odd‐N, etc.). Likewise, deviations from a Poisson distribution for several spacings (s) less than about 60 keV are compared with similar values for 116Sn on an absolute scale. Such discrepancies are attributed to intera...

The structure of recently discovered identical superdeformed bands in $^{151}\mathrm{Tb}$ and $^{152}\mathrm{Dy}$, and in $^{150}\mathrm{Gd}$ and $^{151}\mathrm{Tb}$ are discussed in terms of the strong-coupling approach. Based on the experimental evidence that the superdeformed core of $^{152}\mathrm{Dy}$ is extremely insensitive to the polarization effects induced by the odd particle, the bands are shown to exhibit the presence of the pseudo SU(3) symmetry at extreme conditions of large elongations and high spins.

Neutron scattering and magnetization measurements have been performed on a single crystal of U2NiSi3. Development of long-range ordered ferromagnetic domains, instead of spin glass freezing, was observed below 30 K. The ordered moment is (0.6 ±0.1)μB per uranium atom and lies perpendicular to the hexagonal axis.

Neutron scattering from a high quality single crystal of the heavy fermion superconductor URu 2 Si 2 shows an abrupt onset of antiferromagnetic order at T N = 17 K, unlike the gradual onset previously seen in lower quality samples. The magnetic peak intensity increases linearly down to 5 K, indicating mean-field behaviour and long range RKKY interactions. The intensity remains constant to within 7% between 3 and 0.2 K with no change at the superconducting transition temperature of 1.3 K. The resolution limited Bragg peak shows the order is long-range. The coexistence of antiferromagnetism and superconductivity seen in a lower quality crystal is confirmed and thus is intrinsic.

Data are presented on the crossing frequencies of odd-parity rotational bands in 161 Er. The crossing frequencies are shown to be correlated with the sign and magnitude of the quadrupole moments of the valence neutron orbits in odd- N rare earth nuclei. This can be understood in terms of configuration-dependent “blocking” of pairing-energy contributions requiring the inclusion of quadrupole terms in the pairing-correlation energy.

High-spin states in 163Yb have been studied by the 149Sm(18O, 4n)163Yb reaction with 84 MeV 18O ions from the NBI tandem accelerator. Gamma-gamma coincidence data were accumulated with an array of five Compton-suppressed Ge(Li) detectors resulting in an extension of our knowledge of high spin members of familiar rotational bands as well as of weakly populated side bands. A γγ time coincidence experiment, conversion electrons and angular distribution measurements were performed. Four side bands are observed besides the yrast cascade, which is followed up to its 49 2 + member. The yrast band of the 163Yb nucleus has been interpreted, following the systematics in this region of neutron deficient rare-earth nuclei, as the favoured member of a decoupled i 3 2 neutron band. The negative-parity band ( −, +)1 based on the 3 2 − [521] state was reestablished. The other signature of this band is the newly introduced band ( −, − )1. The signature splitting in the negative-parity band is observed to be small; however, for large zω, band ( −, − )1 lies lower in energy than band ( −, +)1; which is a unique observation in this mass region. The quasiparticle routhians and alignments obtained from these data are compared with results of cranked shell-model calculations and similar data for the heavier and lighter Yb nuclei. The rotational effects on M1 transitions connecting unfavoured members of the band, based on the i 13 2 orbital, with the favoured members are demonstrated.