A unified description is proposed of the following classes of nuclear collective states in terms of an interacting $\mathrm{sp}$-boson model: (i) low-lying collective states and "clustering" in the light nuclei, both odd-odd and even-even; (ii) giant multipole resonances; and (iii) pairing collective motions.

The nuclear radius determined from the minima in the measured charge form factors can be identified with the droplet-model radius. A combined analysis of these radii and binding energies allows a determination of the compressibility of nuclei.

The hyperfine structure of the excited $B^2\Sigma$ state of Ca${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ has been investigated with use of a novel technique that makes possible resolution of optically unresolved hfs components. The desired resolution is achieved through radio-frequency state labeling in a laser-rf double-resonance scheme. This procedure has completely resolved the four hfs components of $B^2\Sigma \leftrightarrow X^2\Sigma$ lines and placed an upper limit of 0.8 MHz on the $B^2\Sigma$ hyperfine structure.

With use of coincidence techniques, oscillations in energy spectra of electrons produced in impact-parameter—controlled 450-keV ${\mathrm{Kr}}^{+4\mathrm{}}$ + Kr collissions have been observed. The decay of an autoionizing state of the Kr—Kr quasimolecule is found to be the dominant electron emission mechanism. The superposition of the emission amplitudes for the incoming and the outgoing parts of the nuclear trajectory explains very well the oscillatory pattern.

Laser absorption on short-wavelength ion turbulence driven by electron-ion streaming instabilities is considered. Contrary to linear theory, which predicts that the turbulent spectra $\varphi \mathrm{}\left(k\right)\mathrm{}$ peaks at $k{\lambda }_{\mathrm{D}}\sim 0.5$, basic plasma experiments find $\varphi \mathrm{}\left(k\right)\mathrm{}$ peaks at $k{\lambda }_{\mathrm{D}}\sim 0.04-0.2$ which, this Letter shows by theory and simulation, heats most strongly at densities $\mathrm{}(0.7-1.2)\mathrm{}{n}_c$ and produces hot electrons $\sim \mathrm{}(5-70)\mathrm{}{T}_e$ (depending on the density) which are another source of preheat that may reduce the compression and yield of laser fusion targets.

A model for random aggregates is studied by computer simulation. The model is applicable to a metal-particle aggregation process whose correlations have been measured previously. Density correlations within the model aggregates fall off with distance with a fractional power law, like those of the metal aggregates. The radius of gyration of the model aggregates has power-law behavior. The model is a limit of a model of dendritic growth.

The decay of high-frequency acoustic phonons in Ca${\mathrm{F}}_2$ at low crystal temperature is studied with use of an optical technique of tunable phonon detection. A strongly frequency-dependent lifetime is found for phonons at frequencies $\nu >{10}^{12}$ Hz. The lifetime decreases proportionally to ${\nu }^{-5\mathrm{}}$, indicating spontaneous phonon decay by anharmonic three-phonon processes. These results suggest that nonlinear elasticity theory is applicable to describe anharmonic interactions of high-frequency acoustic phonons.

New x-ray diffuse scattering results are presented that show that the layer structure in stage-2 alkali-metal graphite intercalation compounds is almost commensurate with a $(\sqrt{7}\times \sqrt{7})R19.11\mathrm{}°$ superlattice. Through model calculations, features of the in-plane diffraction patterns are associated with a hexagonal array of discommensurations oriented parallel to the real-space graphite [110] directions. The array appears to be disordered down to at least $T=10\mathrm{}$ K. Several previously unexplained results are understood through our model.

Optical-field-induced birefringence in nematic 4-cyano-4′-pentylbiphenyl was measured with cw pump and probe beams, and the optical-field-induced Freedericksz transition was observed for the first time. The results are in quantitative agreement with the theoretical prediction.

A discussion is given of the contribution to the Mössbauer linewidth in quasi-one-dimensional antiferromagnets with Ising anisotropy due to thermal excitation of moving domain walls ("kinks" or "solitons"). Experimental data on ${\mathrm{Fe}}^{2+}$ chain compounds are presented that confirm the predicted exponential temperature dependence of the linewidth.

The zero-temperature limit of quantum statistical mechanics is analyzed from the point of view of Nelson's stochastic quantization. An application is given to the quantum effects in critical phenomena by introducing a description of the static properties based on the dynamics of the equilibrium fluctuations.

In a crossed laser-atomic beam experiment the wavelengths of the $2s-3p$ transitions are measured in H and D to a precision of one part in ${10}^9$. Our value for the Rydberg constant is $R_{\infty }=109\mathrm{}737.31521\left(11\right)\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The fine-structure splittings of the $3p$ states in H and D are 3249.8(8) and 3251.7(7) MHz, respectively; the isotope shifts for the $2s-3p_{\frac{1}{2}}$ and $2s-3p_{\frac{3}{2}}$ transitions are 124 260.7(7) and 124 262.6(7) MHz, respectively. Our results largely agree with previous, less precise experiments and with theory.

It is shown that the percolation problem with blocked, one-way, or two-way bonds is self-dual on a square lattice. The usual directed percolation (blocked or one-way bonds) is dual to a simpler process with one- or two-way bonds. The results of a Monte Carlo simulation of the latter are reported and an improved bound on the critical probability is derived. The corresponding resistance problem in which circuit elements have different forward and backward resistances is also shown to be self-dual.

A composite model for quarks and leptons is proposed. An SU(3)-generation symmetry, which is badly broken not only by the generator $F_8$ but also by the generator $F_3$, is introduced. The model leads to a new formula for the Cabibbo angle ${\theta }_{\mathrm{C}}$ represented in terms of lepton masses, which predicts ${tan\theta }_{\mathrm{C}}=0.225\mathrm{}$.

The corrections to the gluonic width of $\Upsilon$-like mesons in quantum chromodynamics (QCD) through first order in ${\alpha }_s$ are calculated, with the result ${\Gamma }_g={{\Gamma }_g}^0[1+(3.8\mathrm{}\pm 0.5)\times {\alpha }_s\frac{\left(M_{\Upsilon }\right)}{\pi }]$, using the $\overline{\mathrm{MS}}$ scheme definition of ${\alpha }_s$, renormalized at $M_{\Upsilon }$. With this correction, the measured value of the leptonic branching ratio of the $\Upsilon$ can be used to determine ${\alpha }_s$, or, equivalently, the QCD scale parameter ${\Lambda }_{\overline{\mathrm{MS}}}$. The result is ${\Lambda }_{\overline{\mathrm{MS}}}=100\mathrm{}$ MeV, with experimental errors of ${}_{-25\mathrm{}}{}^{+34\mathrm{}}{}_{}{}^{}\mathrm{MeV}$ and comparable theoretical uncertainties. Analysis of the $\psi$ and ${\psi }^{\prime }$ data is consistent with this value.

Fusion reactions are initiated by capture of two incident nuclei to form a quasistable dinuclear complex. Excitation functions for such capture reactions have been measured in bombardments with ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ on targets of ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$, and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Fe}$. Compared with standard fusion models, based on the interaction of rigid spheres, the experiments show major deviations. These are explained by a dynamical model that takes deformations induced upon contact into account.

Measurements of the multiplicity of $K$ x rays accompanying (Li,$\mathrm{xn}$) reactions to residual nuclei with $Z\sim 80$ exhibit plateaus of high and constant multiplicity for neutron numbers between 110 and 120, with rapid falloff for both smaller and larger $N$. A proposed explanation for this systematic behavior assumes that strongly coupled, high-$K$ rotational bands are a much more general feature of this transitional mass region than existing data indicate.

Spectra of neutrons emitted in coincidence with evaporation residues and fission fragments have been measured in the (192 MeV) ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$ and (176 and 239 MeV) ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$+${}_{}{}^{150}{}_{}{}^{}\mathrm{Nd}$ reactions. At the two lower energies, several neutrons are evaporated prior to fission. At the highest bombarding energy essentially all the neutrons are evaporated by the fragments indicating that at high angular momentum, the fission process is rapid compared to the time scale for neutron evaporation.

From a (${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, $3n$) in-beam study of the one-particle nucleus ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ the 1.6-h isomer is assigned at ½+ which is attributed to the $\pi s_{\frac{1}{2}}$ shell-model state. The $\pi d_{\frac{3}{2}}$ level lies at 253 keV, and the $\pi {d_{\frac{5}{2}}}^{-1\mathrm{}}{j_0}^2$ and $\pi {g_{\frac{7}{2}}}^{-1\mathrm{}}{j_0}^2$ states are found at 354 and 719 keV, respectively. These observations provide a clear and consistent picture of the single-proton states in this region. The discontinuity of the observed quasiparticle energies between ${}_{63}{}^{145}{}_{}{}^{}\mathrm{Eu}_{82}^{}{}_{}{}^{}$ and ${}_{65}{}^{147}{}_{}{}^{}\mathrm{Tb}_{82}^{}{}_{}{}^{}$ provides support for a large single-particle energy gap at $Z=64\mathrm{}$, estimated to be ∼ 2.3 MeV.

Nuclear ${\beta }^{\mp }$ decay in the presence of a very intense laser field is considered. If the energy which is available for the decay in the absence of the field is small, the impact of the laser field is very significant, resulting in a large enhancement of the decay and a large upshift of the ${\beta }^{\mp }$ energies.