${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{12}{}_{}{}^{}\mathrm{C}, p\gamma ){}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ proton-$\gamma$ angular correlations were measured at $E_B=38.82\mathrm{}$ MeV for the 9.042- and 9.805-MeV states in ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ which decay to levels at 7.270, 6.235, and 5.534 MeV with branching ratios of 20%, 60%, and 20%, respectively, for the 9.042-MeV state, and 30%, 50%, and 20%, respectively, for the 9.805-MeV state. Angular correlations and lifetime data eliminate $\frac{17}{2}$ assignments for either state.

Anomalous $\frac{\epsilon }{{\beta }^{+}}$ branching ratios for hindered allowed transitions in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{143}{}_{}{}^{}\mathrm{Sm}$ decay are explained in terms of second-order corrections to normal allowed theory. These calculations lead to correction factors as large as 1000 in nuclei near $Z=80\mathrm{}$, and explain a smaller anomaly for ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ decay. A simplified equation is presented to estimate skew ratios, $\frac{{\left(\frac{\epsilon }{{\beta }^{+}}\right)}_{\mathrm{expt}}}{{\left(\frac{\epsilon }{{\beta }^{+}}\right)}_{\mathrm{theor}}}$, for moderately hindered transitions.

Elastic-electron-scattering cross sections for ${}_{}{}^{92,94,96,98,100}{}_{}{}^{}\mathrm{Mo}$ in an effective momentum transfer range of 0.6-2.1 ${\mathrm{fm}}^{-1\mathrm{}}$ are analyzed in a practically model-independent way, using a Fourier-Bessel expansion for the charge distribution. The ratios of cross sections of neighboring isotopes yield differences of charge distributions, which exhibit pronounced shell effects.

We measure cross sections for ${{\mathrm{N}}_2}^{+} \left(B{}_{}{}^2{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}\right)$ production in 5-eV ${\mathrm{He}}_2^{+}$-${\mathrm{N}}_2$ and ${\mathrm{He}}^{+}$-${\mathrm{N}}_2$ collisions by observation of emission in the first negative system of ${\mathrm{N}}_2^{+}$. For ${\mathrm{He}}_2^{+}$ the cross section is unusually large (∼10 ${\mathrm{\AA }}^2$) and the vibrational-state distribution shows primarily $v^{\prime }=0\mathrm{} \mathrm{and} 1$, consistent with vertical ionization of ${\mathrm{N}}_2$. ${\mathrm{He}}^{+}$ produces a much wider distribution, as do most other simple ions. Explanations for the large cross section and observed state distributions are proposed.

Photon-scattered-atom coincidence measurements with polarization analysis of the photons have been made for 3.0-keV ${\mathrm{He}}^{+}$ -He collisions leading to He ($3{}_{}{}^3{}_{}{}^{}P$) excitation in a charge-transfer process. The phase difference between the scattering amplitudes for $m_l=0\mathrm{}$ and $m_l=1\mathrm{}$ magnetic sublevel formation is an approximately constant function of scattering angle. We propose a theory which predicts the constancy of this phase difference.

We find a solution of the nonlinear Schrödinger equation which describes a standing electron plasma wave confined in the half-space underdense region with reflected electrons in the other half space. The shock moves with the ion-acoustic speed and the density jump is proportional to the electron-wave amplitude.

Two qualitatively different structural models are currently popular for the stable 2×1 superstructure characteristic of the Si(100) surface. We report the results of realistic self-consistent calculations of the electronic spectrum for both. Comparison with uv photoemission data clearly favors the pairing model over the vacancy model. Our results on surface Fermi-level pinning and bond saturation support this conclusion.

We have made measurements of the critical velocity for vortex formation in right cylinders of circular, elliptical, and rectangular cross section. The procedure used seems to produce the superfluid in its equilibrium state and the results are in good quantitative agreement with theoretical calculations based on equilibrium thermodynamics.

We investigate energy transfer between ${\mathrm{Sm}}^{3+}$ ions in different crystal-field sites in CaW${\mathrm{O}}_4$ crystals by use of laser time-resolved spectroscopy techniques. The dependence of the results on time and temperature show the interaction to be electric quadrupole-quadrupole and the interaction strength to be much less than the inhomogeneous line-width of the transition. This leads to the localization of the energy at low temperatures, confirming the predictions of Anderson.

We report first-principles calculations at $\overline{\Gamma }$ for a (001) iron thin film. Four different potentials have been investigated, and we find for the first time that the existence and symmetry of surface states depends crucially on details of the potential. For the potential which we consider most physical we find a surface state which peaks more than one-half layer outside the last plane of atoms.

We have extended the Gutzwiller variational scheme to investigate the antiferromagnetic ground state in the Hubbard model with one electron per atom. Virtual electron hopping is found to be essential for the antiferromagnetic ordering. A paramagnetic-metallic to antiferromagnetic-insulator state transition is obtained with increasing $\frac{U}{W}$ ratio. The ${\mathrm{V}}_2$${\mathrm{O}}_3$-type phase diagram follows from the present theory.

Magnetic-susceptibility and EPR measurements are reported which provide the first unambiguous evidence for a spin-Peierls transition in a system of linear one-dimensional antiferromagnetic Heisenberg chains. The material studied is TTFCu${\mathrm{S}}_4$${\mathrm{C}}_4$${\left(\mathrm{C}{\mathrm{F}}_3\right)}_4$ (TFF stands for tetrathiafulvalinium). At 12 K, the spin-lattice system undergoes a second-order phase transition to a singlet ground state.

On the assumption that the $\psi$ is an $\Omega \overline{\Omega }$ bound state, we find that the expected widths for $\psi \to \Xi \overline{\Xi }$, though dependent on the wave-function assumptions, are likely to be orders of magnitude bigger than experimentally allowed.

We determine the ratio of the partial decay width for $\psi \mathrm{}\left(3684\right)\mathrm{}\to {\mu }^{+}{\mu }^{-}$ to that for the cascade decay $\psi \mathrm{}\left(3684\right)\mathrm{}\to \psi \mathrm{}\left(3095\right)+X$ to be (1.4 ± 0.3)% and, by direct observation of associated charged particles and $\gamma$ rays, find the ratio of the partial decay width for $\psi \mathrm{}\left(3684\right)\mathrm{}\to \psi \mathrm{}\left(3095\right)+{\pi }^0{\pi }^0$ to that for $\psi \mathrm{}\left(3684\right)\mathrm{}\to \psi \mathrm{}\left(3095\right)+{\pi }^{+}{\pi }^{-}$ to be 0.64 ± 0.15.

Recently reported observations suggest the existence of a new particle without strong interactions. We interpret it as a massive neutral lepton $L^0$ produced by decays of a new charged lepton $L^{\pm }$ which in turn is pair-produced electromagnetically by cosmic rays. The mass of $L^{\pm }$ must be ∼2 GeV; the lifetime of $L^0$ must be ∼ ${10}^{-5\mathrm{}}$ sec. Possible gauge models incorporating the new leptons are discussed, as are other experimental consequences.

Left-right asymmetries from a deuterium target in a polarized-proton beam were observed with the Argonne National Laboratory effective-mass spectrometer. Results were obtained for both $\mathrm{pp}$ and $\mathrm{pn}$ elastic scattering from $-t=0.15\mathrm{} \mathrm{to} 1.0$ Ge${\mathrm{V}}^2$ at 2, 3, 4, and 6 GeV/c. For $-t\lesssim 0.6$ Ge${\mathrm{V}}^2$ the $\mathrm{pn}$ polarization was found to have the same sign as for $\mathrm{pp}$, but with faster energy dependence, the ratio $\frac{P\left(\mathrm{pn}\right)\mathrm{}}{P\left(\mathrm{pp}\right)\mathrm{}}$ at $-t=0.3\mathrm{}$ Ge${\mathrm{V}}^2$ falling from 0.78±0.02 at 2 GeV/c to 0.22±0.03 at 6 GeV/c.

In view of the possible observation at SPEAR of events which could be interpreted as the production of charmed mesons followed by decays into purely leptonic channels, we suggest the possibility that the stable charmed mesons may be vectors rather than pseudoscalars. Estimates of decay rates and branching ratios are given in this case.

We report here the observation of surprisingly simple behaviors in the massive-hadron-pair ($m>\mathrm{}2\mathrm{}$ GeV) production from proton-nucleon collisions. With a 28.6-GeV incident proton beam and a pair spectrometer to detect the hadrons, the measured cross section decreases like $\frac{d^2\sigma }{\mathrm{dxdm}}\propto e^{-5m}$ and can be grouped into three groups: ${\pi }^{-}+p$; ${\pi }^{+}+{\pi }^{-}$, $\overline{p}+p$, $K^{-}+p$; and $K^{-}+{\pi }^{+}$, ${\pi }^{+}+p$. Within a given group the yield is the same to ±20%; different groups are separated by a factor of ∼ 10 from each other.

$\gamma$-ray spectra have been observed following the interaction of 220-MeV ${\pi }^{+}$ and ${\pi }^{-}$ and 200-MeV protons with ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$ and 100-MeV ${\pi }^{+}$ with ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. Product nuclides have been identified from characteristic $\gamma$-ray lines corresponding to total cross sections of ∼500 mb. The systematic trends with projectile and energy are explored; rather substantial differences are found between pions and protons.

Collisions with rare-gas atoms are observed to produce a lengthening of the lifetime of the highly excited ($n=5-10\mathrm{}$) $d$ states of Na. The effect is interpreted as collisional angular momentum mixing of the $d$ state with $l>\mathrm{}2\mathrm{}$ states; thus the average lifetime of all states for which $l>~2$ is observed. The cross section for the process appears to increase as the geometrical cross section of the excited atom.