Spin-spin cross sections of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ have been measured for neutrons between 20 and 50 MeV with high precision. Absolute size and energy dependence of the data agree well with existing predictions from folding model calculations. The data can also be reproduced with phenomenological spin-spin potentials, but do not allow to distinguish between spherical and tensor interactions. The deduced spin-spin strengths are close to 1 MeV.

The reaction ${\pi }^{\mathrm{-}}$${+}^3$He→η+t has been observed by detecting η→2γ decays. The observed forward-angle cross sections vary from ∼100 μb/sr at 680 MeV/c to ∼2 μb/sr at 590 MeV/c. Distorted-wave impulse-approximation calculations reproduce the shape but underestimate the magnitude of the observed cross section. These cross sections are approximately 100 times larger than those for the reaction p+d→η${+}^3$He measured at similar η center-of-mass energies.

We present a measurement of subthreshold antiproton, kaon, and energetic pion production at 0° for the reactions ${}_{}{}^{28}{}_{}{}^{}$Si${+}^{28}$Si at 2.0 GeV/nucleon ($E_{\mathrm{available}/\mathrm{A}=0.82\mathrm{}}$ GeV) and 1.65 GeV/nucleon ($E_{\mathrm{available}/\mathrm{A}=0.70\mathrm{}}$ GeV), and for ${}_{}{}^{20}{}_{}{}^{}$Ne+NaF at 2.0 GeV/nucleon. For a given reaction, the particle yields, plotted as a function of the required excitation energy, exhibit a scaling behavior independent of particle species. Implications for collectivity and a common production mechanism are discussed.

Using the Heidelberg-Darmstadt Crystal Ball spectrometer the γ decay of the superdeformed shape isomer in ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ has been investigated employing the ${}_{}{}^{235}{}_{}{}^{}$U(d,p) reaction at 11 MeV. The isomer was isolated by requiring that the prompt and delayed γ sum energy add up to the initial excitation energy of ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ as determined from the energy of the recoiling proton. The shape isomer was found to have an excitation energy of E${(0\mathrm{}}_{\mathrm{II}{}^{+})=2.75\mathrm{}\pm 0.01}$ MeV and to decay by four different γ transitions in competition with its well known fission mode. The corresponding branching ratio of γ decay to fission was determined to be ${\Gamma }_{F\gamma }$/${\Gamma }_{\mathrm{Ff}}$=8±3, thus resolving the long-standing problem of the missing γ decay branch.

Multiple superdeformed rotational bands have been identified in a nucleus for the first time. Cascades of 14, 13, and 11 transitions have been assigned to three bands in ${}_{}{}^{153}{}_{}{}^{}\mathrm{Dy}$. Despite the small intensities, it has been possible to follow the decay of these bands from an angular frequency of 0.7 down to 0.4 MeV/ħ. In all three cases, the dynamic moment of inertia ${\mathrm{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$ is nearly constant. Assignments to high-N intruder orbitals are suggested through comparison of these values of ${\mathrm{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$ with theoretical calculations based on the cranked shell model.

Deformed single-particle levels are derived from a boson-fermion Hamiltonian in which the odd fermion occupies several j orbits. The geometric-oriented approach applied to ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ clarified the role of algebraic interactions and provides an intuitive interpretation and guidance to numerical calculations in deformed nuclei.

We report the first observation of the disappearance of flow in heavy-ion collisions. This is accomplished by measuring the excitation function of the average in-plane transverse momentum for the symmetric system ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, using beam energies of 130, 70, and 50 MeV/nucleon. The observation is indicative of a change from dominantly repulsive to attractive scattering. We also present the results of calculations performed with the Boltzmann-Uehling-Uhlenbeck equation which support the concept of vanishing flow for this system in the energy region between 30 and 50 MeV/nucleon.

Our investigation of the energy dependence of dispersive effects in elastic electron scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been extended to a beam energy of 690 MeV. The cross section observed in the minimum of the form factor is larger than that predicted using a static charge density obtained by fitting lower-energy data with the customary phase-shift analysis. This ‘‘filling-in’’ of the minimum at 690 MeV is even larger than that observed previously at 430 MeV. This indicates an increase in the relative strength of higher-order processes in the minimum with an increase of beam energy; the presence of dispersive effects is the most likely explanation for this effect.

Four-body integral equations are used to calculate dd→dd and dd→${\mathrm{p}}^3$H amplitudes using a single-term separable nucleon-nucleon potential in channels ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{S}_1^{}{}_{}{}^{}$${\mathrm{-}}^3$${\mathrm{D}}_1$. First-order perturbation theory is used to include in the four-body kernel the contribution of d-wave two- and three-nucleon channel components that result from the tensor force. Cross sections and analyzing powers are calculated using all positive- and negative-parity four-body amplitudes with total angular momentum J≤4. Comparison with data is presented.

A canonical-ensemble calculation of the specific heat in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ using the eigenstates of a number of realistic interactions and the energies of the states obtained experimentally exhibits a prominent peak at T≃1.7–2.5 MeV which is associated with the deformed-to-spherical phase transition seen in finite-temperature mean-field calculations. This phase transition arises from a change in the relevant degrees of freedom describing the system and will occur for any nucleus which has a low-lying collective spectrum. Including a continuum in addition to the discrete spectrum does not produce an additional peak in the specific heat at low temperatures.

Searching for evidence of ‘‘cold’’ nuclear fusion in deuterium-loaded Ti and Pd foils with plastic track detectors, we detected the emission of α particles from trace-heavy-element decay, but found no evidence of dd fusion. Cycling ${\mathrm{TiD}}_2$ and ${\mathrm{PdD}}_{>0.4\mathrm{}}$, in high-pressure ${\mathrm{D}}_2$ cells between 1 and 15 bars and 77 and 300 K, gave an upper bound of 0.7 ${\mathrm{cm}}^{\mathrm{-}3}$ ${\mathrm{s}}^{\mathrm{-}1}$ for the mean rate of dd${\to }^3$He+n fusion. For electrolytically deuterated ${\mathrm{PdD}}_{0.8}$ our upper bound is 0.0018 ${\mathrm{cm}}^{\mathrm{-}3}$ ${\mathrm{s}}^{\mathrm{-}1}$ for the mean rate of dd→p+t. This is ∼1.5×${10}^6$ and 180 times lower than ‘‘cold’’-fusion rates reported by Fleischmann, Pons, and Hawkins and Jones et al., respectively.

We present the first measurements of spin effects in ${\pi }^{+}$ elastic and inelastic scattering from complex nuclei, ${}_{}{}^{15}{}_{}{}^{}$N→${\left(\right(1/2\mathrm{}}^{\mathrm{-}}$) and ${}_{}{}^6{}_{}{}^{}$Li→${(1\mathrm{}}^{+}$). For the case of ${}_{}{}^{15}{}_{}{}^{}$N→, the analyzing power $A_y$ was measured at $T_{\pi }$=164 MeV between 60° and 100°. Although large values of $A_y$ are predicted by theory, the data are consistent with zero. For the case of ${}_{}{}^6{}_{}{}^{}$Li→, the analyzing power ${\mathrm{iT}}_{11}$ was measured at $T_{\pi }$=134 and 164 MeV, between 50° and 110°. Large values of ${\mathrm{iT}}_{11}$ were found at some angles, but the measured angular distributions differ considerably from theoretical predictions.

Using the one-boson-exchange model a relativistic covariant analysis is carried out of the elastic electromagnetic form factors of the deuteron including the ρπγ and ωεγ mesonic-exchange-current contributions. The theoretical predictions are compared with the recent experimental data at high momentum transfer.

We have measured analyzing powers in d(p→,${\pi }^{\mathrm{-}}$pp)p at a beam energy of 400 MeV and laboratory pion detector angles of 35° and 43°. The ${\pi }^{\mathrm{-}}$ and two of the outgoing protons were detected in coincidence in a geometry which selected the quasifree two-body reaction pn→${\pi }^{\mathrm{-}}$pp${(}^1$$S_0$). The analyzing-power data combined with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\pi }^{\mathrm{-}}$,pn)n differential cross sections allow determination of the transition amplitudes. The results indicate a significant contribution from a very short-range part of the nucleon-nucleon interaction.

We report the results of an experimental search for neutrinoless double-β decay using isotopically enriched foils of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$ interleaved in a stack of 40 silicon detectors. With an exposure of 69.9 mole days, we place lower half-life limits on the $J^P$${=0\mathrm{}}^{+}$→$0^{+}$ transition of 4×${10}^{21}$ yr (68% C.L.) and on the $0^{+}$→$2^{+}$ transition of 4×${10}^{20}$ yr (68% C.L.).

We have made a good-resolution, high-sensitivity search for a $T=2\mathrm{}$ dibaryon in the missing-mass spectra for the reaction $d({\pi }^{-}, {\pi }^{+}){\pi }^{-}\mathrm{nn}$ at 292 MeV. Our results are consistent with there being no resonance peak due to such a state in the mass region 2001-2070 MeV. 95%-confidence upper limits for the integrated cross sections for such a state are presented. It is found that a quasifree model calculation, without final-state interactions, considerably underpredicts the continuum yield in the vicinity of the threshold.

We have measured the ${(}^3$H+p) and ${(}^3$He+n) breakup of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’c) coincidence experiments at low momentum transfer (q≊0.39 ${\mathrm{fm}}^{\mathrm{-}1}$) in the excitation energy region 22≤$E_x$≤36 MeV. Both channels were studied simultaneously by detecting the charged fragments c=p, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$, and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the same detector system. The measured ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’n${)}^3$He angular correlations as well as the deduced total ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’n${)}^3$He cross sections are reproduced by microscopic model calculations with a charge-symmetric nuclear Hamiltonian.

Collisions of Si(14.5A GeV+Au are investigated in the relativistic-quantum-molecular-dynamics approach. The calculated pseudorapidity distributions for central collisions compare well with recent experimental data, indicating a large degree of nuclear stopping and thermalization. Nevertheless, nonequilibrium effects play an important role in such complex multihadron reactions: They lead to a strong enhancement of the total kaon production cross sections, in good agreement with the experimental data, without requiring the formation of a deconfined quark-gluon plasma.

A gas-filled, liquid-nitrogen-cooled cell on-line with an accelerator permits fluorescence spectroscopy of atoms of heavy-ion reaction products generated at rates less than ${10}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. This low required rate of production allows the optical spectroscopy of radioactive atoms to be extended further from stability. With the cell we have measured isotope shifts of ${}_{}{}^{152,154,156,158,166}{}_{}{}^{}\mathrm{Yb}$, reaching N=82, four nuclides further than previously reached with other techniques. The change in rms charge radius near the shell closure is surprisingly large.

We calculate the M1 spectrum and the distorted-wave Born-approximation (e,e’) form factors of the strong ${\mathrm{K}}^{\mathrm{\pi }}$${=1\mathrm{}}^{+}$ states in ${}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$, using a deformed Woods-Saxon potential and the quasiparticle random-phase approximation with quadrupole, spin, and spin-quadrupole interactions. A residual rotation-vibrational coupling ensures the exclusion of the spurious state. We find strongly orbital M1 states at 3.1 MeV which fit the experimental spectrum very well and exhaust 40% of the collectivity of the $1^{+}$ mode. The form factor of the lowest one of these states is also in a good agreement with the experimental form factor.