Multiplicities of intermediate-mass fragments (IMFs), neutrons, and charged particles were measured for ${}^{112}\mathrm{Sn}{+}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}{+}^{124}\mathrm{Sn}$ at $E/A=40\mathrm{}\mathrm{MeV}$. Significantly different scalings of the mean IMF multiplicities with neutron and charged-particle multiplicities are observed for the two reactions. These differences can be qualitatively understood in terms of fragment emission from an expanding evaporating source for which the initial rates of cooling by neutron and light-charged-particle emission depend on the neutron and proton numbers of the source according to statistical expectations.

We report an absolute measurement of the tensor analyzing powers $T_{20}$ and $T_{22}$ in elastic electron-deuteron scattering at a momentum transfer of $1.6{\mathrm{fm}}^{-1\mathrm{}}$. The novel approach of this measurement is the use of a tensor polarized ${}^2\mathrm{H}$ target internal to an electron storage ring, with in situ measurement of the polarization of the target gas. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors. The techniques demonstrated have broad applicability to further measurements of spin-dependent electron scattering.

A new, sensitive method allows one to search for the enhancement of events with nearly equal-sized fragments as predicted by theoretical calculations based on volume or surface instabilities. Simulations have been performed to investigate the sensitivity of the procedure. Experimentally, charge correlations of intermediate mass fragments emitted from heavy ion reactions at intermediate energies have been studied. No evidence for a preferred breakup into equal-sized fragments has been found.

A Comment on the Letter by I. Ahmad, et al. Phys. Rev. LLett. 75, 2658 (1995). The authors of the Letter offer a Reply.

A Reply to the Comment by Thomas E. Cowan and Jack S. Greenberg.

Forward-angle coincident electroproduction cross sections of charged pions from ${}^3\mathrm{He}$ have been measured at electron energies $E_0=855\mathrm{}$, 675, 600, and 555 MeV. The overall features of the data for energy transfers of $\omega =370\mathrm{}$ to 430 MeV with pions detected along the momentum transfer axis are reproduced in terms of a microscopic model, including pole terms, final state rescattering and produced and preformed $\Delta$ resonances. Separation of the cross section into its longitudinal and transverse parts was performed at $Q^2=0.045(\mathrm{GeV}/c{)}^2$. The longitudinal part of the cross section in the ${\pi }^{+}$ channel does not contradict with the assumption of a preformed ${\Delta }^{++}$.

Secondary ions of ${}^{100}$Ag, ${}^{100}$Cd, ${}^{100}$In, and ${}^{100}$Sn were produced via the fusion-evaporation reaction ${}^{50}\mathrm{Cr}{+}^{58}\mathrm{Ni}$ at an energy of 51 MeV/nucleon, and were accelerated simultaneously in the second cyclotron of GANIL. About 10 counts were observed from the production and acceleration of ${}^{100}\mathrm{Sn}{}^{22+}$. The masses of ${}^{100}$Cd, ${}^{100}$In, and ${}^{100}$Sn were measured with respect to ${}^{100}$Ag using the GANIL cyclotron, with precisions of $2\times {10}^{-6\mathrm{}}$, $3\times {10}^{-6\mathrm{}}$, and ${10}^{-5\mathrm{}}$, respectively.

An iterative procedure for simultaneous extraction of fine structure in the level density and the γ-ray strength function from a set of primary γ-ray spectra has been developed. Data from the reactions ${}^{163}$Dy${(}^3$He, αγ${)}^{162}$Dy and ${}^{173}$Yb${(}^3$He, αγ${)}^{172}$Yb reveal steplike enhancements in the level density in the region below 5 MeV and peaks in the γ-ray strength function at low γ energy ( $E_{\gamma }\approx 2–3.5$ MeV). Tentative physical interpretations are presented.

We report the first experimental observation of the pionic fusion of two heavy ions. The ${}^{12}\mathrm{C}{(}^{12}\mathrm{C}{,}^{24}\mathrm{Mg}){\pi }^0$ and ${}^{12}\mathrm{C}{(}^{12}\mathrm{C}{,}^{24}\mathrm{Na}){\pi }^{+}$ cross sections have been measured to be $208\pm 38$ and $182\pm 84\mathrm{pb}$, respectively, at $E_{\mathrm{cm}}=137\mathrm{MeV}$. This cross section for heavy-ion pion production, at an energy just 6 MeV above the absolute energy-conservation limit, constrains possible production mechanisms to incorporate the kinetic energy of the entire projectile-target system as well as the binding energy gained in fusion.

The double beta decays of ${}^{76}\mathrm{Ge}$, ${}^{82}\mathrm{Se}$, and ${}^{136}\mathrm{Xe}$ are studied in very large shell model spaces. The dimensions of the shell model spaces used in these calculations reach $O\left({10}^8\right)$. The two neutrino matrix elements obtained are in good agreement with the available experimental data. Assuming that the mass of the neutrino is smaller than 1 eV, we get the following upper bounds to the half-lives for the neutrinoless decays: $T_{1/2}^{\left(0\nu \right)}\left(\mathrm{Ge}\right)>1.85\mathrm{}\times {10}^{25}\mathrm{yr}$, $T_{1/2}^{\left(0\nu \right)}\left(\mathrm{Se}\right)>2.36\mathrm{}\times {10}^{24}\mathrm{yr}$, and $T_{1/2}^{\left(0\nu \right)}\left(\mathrm{Xe}\right)>1.21\mathrm{}\times 10^{25}\mathrm{yr}$.

The NA50 Collaboration has recently observed a strong suppression of $\frac{J}{\psi }$ production in Pb-Pb collisions at 158 GeV/nucleon. We show that this recent observation finds a quantitative explanation in a model which relates the suppression mechanism to the local energy density, whose value is higher in Pb-Pb collisions than in any other system studied previously. The sensitivity of the phenomenon to small changes in the energy density could be suggestive of quark-gluon plasma formation.

The decay-out spectrum of the superdeformed yrast band in ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ comprises a quasicontinuum, from which about 50 weak discrete transitions of energy between 1 and 3.2 MeV are resolved. The fluctuations of the one-dimensional quasicontinuum spectrum are studied with the fluctuation analysis method, which shows that of the order of a few thousand different transitions are available in the first step of the decay-out cascades. The experimental effective number of transitions is compared to schematic theoretical calculations.

The Eurogam-2 array has been used to study $\gamma$ rays emitted following the spontaneous fission of a ${}_{}{}^{248}{}_{}{}^{}\mathrm{Cm}$ source. Analysis of Doppler-broadened line shapes corresponding to decays from excited rotational states in neutron-rich Sr, Zr, and Mo fission fragments has enabled the first measurements of state lifetimes in these nuclei at around $I=10\mathrm{}$. The results are consistent with a predicted rotation-induced change in the triaxiality of the yrast states of the Mo isotopes that contrasts with the more stable behavior observed in the Zr and Sr nuclei.

A reformulation of the external potential Bethe-Salpeter formalism is developed for two-electron atoms. QED and relativistic corrections to energy levels of order ${\alpha }^{7}m{c}^2\ln \alpha$ are derived and expressed in terms of expectation values of nonrelativistic operators. Corrections of order ${\alpha }^{7}m{c}^2$ from exchange diagrams are also found. The total contributions of order ${\alpha }^{7}m{c}^2\ln \alpha$ to the $1s2p{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}$ fine structure intervals of helium are $\Delta {\nu }_{01}=82.6\mathrm{}$ kHz and $\Delta {\nu }_{12}=-10.0\mathrm{}$ kHz. Results are given for He-like ions up to $Z=12\mathrm{}$ and compared with experiment.

Experimental evidence for the existence of non-nuclear maxima in charge densities is questioned. It is shown that the non-nuclear maxima reported for silicon are artifacts of the maximum entropy method that was used to analyze the x-ray diffraction data. This method can be improved by the use of appropriate prior information. We report systematic tests of the improved method leading to the absence of non-nuclear maxima in Si. Likewise, the non-nuclear maxima reported earlier in beryllium are not substantiated.

Double ionization of helium differential in energy transfer, $\epsilon$, is studied for both high-energy Compton photons and charged particles. The ratios of double to single ionization, $R_C\left(\epsilon \right)$ for Compton scattering, and $R_Z\left(\epsilon \right)$ for charged particles, are found to display an unexpected behavior: For large $\epsilon$ up to the two-body binary encounter (BE) limit, ${\epsilon }_{\mathrm{BE}}$, we find $R_C\left(\epsilon \right)=R_Z\left(\epsilon \right)\simeq 0.86\%$ in good agreement with recent experimental data. For even larger $\epsilon >{\epsilon }_{\mathrm{BE}}, R_C\left(\epsilon \right) \mathrm{and} R_Z\left(\epsilon \right)$ are modified by an "exchange shakeoff" mechanism. At $\epsilon \gg {\epsilon }_{\mathrm{BE}}\gg 1$, both differential (unlike integrated) ratios are predicted to approach the photoionization limit.

We present an experimental investigation of the local dynamics and spatial diffusion of atoms in a rubidium optical lattice using polarization-selective intensity correlation spectroscopy in both the time and frequency domains. Autocorrelations of the circularly polarized components of the fluorescence light are shown to give access to the atomic dynamics in a single optical potential well. By contrast, cross correlations between opposite circular components of the scattered light provide information about atomic transport in the lattice through escape and recapture between neighbor potential wells.

We demonstrate that the spatial mode of high-order harmonics can be continuously controlled. The control is achieved by spatially modulating the degree of elliptical polarization of the fundamental field using birefringent optics. A highly sensitive relationship between the efficiency of harmonic generation and the degree of laser elliptical polarization leads to atoms emitting harmonics mainly in regions of linear polarization. The harmonics are emitted as annular beams whose angles of divergence can be continuously varied.

Charge-exchange cross sections for collisions between ${\mathrm{H}}_2$ and ions with unusually low center-of-mass energies (≈6 eV) and high-charge states (${\mathrm{Xe}}^{q+}:35, 43\le q\le 46$, ${\mathrm{Th}}^{q+}:73\mathrm{}\le q\le 80$) have been measured using a Penning ion trap. A nondestructive measurement technique permitted both primary and product ion analysis. The data, averaged over the charge states indicated above, are consistent with a total cross section that scales linearly with ion charge $q$. The true double-capture cross section is found to be about 25% of the total cross section at high $q$. The results are compared to predictions of the absorbing-sphere model.

We introduce a simple quantum theory of the lossy beam splitter. When applied to describe a Fabry-Pérot cavity this leads to apparently anomalous commutation relations for the intracavity operators. We show that these unfamiliar properties are nevertheless consistent with the fundamental canonical commutator for the vector potential and electric field operators. This result is derived as a consequence of causality as applied to the properties of mirror reflection coefficients.