The disintegration of a secondary beam of ${}^{11}\mathrm{Be}$ has been studied in the Coulomb plus nuclear field of Au and Be targets. The vector momentum (longitudinal and transverse components) was measured with a magnetic spectrograph with sufficient precision to detect previously reported differences in the velocity of the ${}^{10}\mathrm{Be}$ fragments and the incident beam. Coincident $\gamma$ rays, detected by an array of ${\mathrm{BaF}}_2$ scintillators surrounding the target, were used to identify events in which the target was simultaneously excited. No evidence for the previously suggested velocity difference was observed.

Detailed structure information on ${}^{133}\mathrm{Sb}$ has been obtained in a high-sensitivity study of the ${}^{133}\mathrm{Sn}$ decay. The $d_{3/2}$ single proton state was found at 2439.5 keV. The $\gamma$-ray branching gives $B({M1;d}_{3/2}\to d_{5/2})/B({E2;d}_{3/2}\to g_{7/2})=0.037\mathrm{}\left(3\right)$ in W.u. For the $h_{11/2}$ state, a half-life of 11.4(4.5) ps was measured for the first time, giving $B(M2;h_{11/2}\to g_{7/2})=0.55\mathrm{}\left(22\right)\mathrm{W}.\mathrm{u}.\mathrm{}$ and $B(E3;h_{11/2}\to d_{5/2})=22\mathrm{}\left(13\right)\mathrm{W}.\mathrm{u}.\mathrm{}$ The single proton transition strengths in ${}^{133}\mathrm{Sb}$ and ${}^{209}\mathrm{Bi}$ are found to be remarkably similar. In contrast, the spin-orbit splitting in these nuclei show important differences.

The neutral ${\pi }^0$ and $\eta$ mesons are studied in ${}^{197}\mathrm{Au}{-}^{197}\mathrm{Au}$ collisions at an incident energy of $800A\mathrm{MeV}$, substantially below the threshold for $\eta$ production in $N-N$ collisions. While the gross ${\pi }^0$ multiplicity increases almost linearly with the number of participant nucleons, the multiplicities of $\eta$ and hard ${\pi }^0$ mesons show a stronger than linear dependence. The nonlinearity is governed by the average transverse-mass excess $〈m_t〉-\left(\sqrt{s}{-2m}_N\right)$ of the mesons and is insensitive to their final-state interaction in the nuclear medium.

An earlier measurement of the ${\rho }^0$ mass in the nuclear medium, reported by the TAGX Collaboration, indicated a substantial mass reduction of $\delta m_{{\rho }^0}=160\mathrm{}\mathrm{MeV}{/c}^2$ in the ${}^3\mathrm{He}(\gamma ,{\pi }^{+}{\pi }^{-})$ reaction. In this Letter, we report the reanalysis of previously published data for the same reaction at lower photon energies, $E_{\gamma }=380\mathrm{}–700\mathrm{MeV}$, which lie below the ${\rho }^0\to {\pi }^{+}{\pi }^{-}$ detection threshold unless the ${\rho }^0$ mass is significantly modified by the nuclear medium. We find the resulting mass shift in this region to be even larger, $\delta m_{{\rho }^0}=280\mathrm{}\pm 40\mathrm{MeV}{/c}^2$, consistent with ${\rho }^0$ decay in the field of the nucleon as the dominant effect.

The electric quadrupole interaction frequencies ${\mathrm{eQV}}_{\mathrm{zz}}/h$ of ${}^{77}\mathrm{Br}$ ( $I^{\pi }=3\mathrm{}/2^{-}$; $T_{1/2}=57\mathrm{}$ h) and ${}^{82}\mathrm{Br}$ ( $I^{\pi }{=5\mathrm{}}^{-}$; $T_{1/2}=35\mathrm{}$ h) in hcp Co were measured with modulated adiabatic fast passage on oriented nuclei. The electric quadrupole moment of ${}^{77}\mathrm{Br}$ is deduced to be $Q=+0.530\mathrm{}\left(22\right)\mathrm{b}$, which, on the condition of strong coupling, implies a nuclear deformation of ${\beta }_2=+0.354\mathrm{}\left(15\right)$. This manifests a drastic increase of the nuclear deformation between ${}^{79}\mathrm{Br}$ ( ${\beta }_2\sim +0.22\mathrm{}$) and ${}^{77}\mathrm{Br}$.

We propose a resonance damping mechanism to explain the disappearance of the peaks around the position of the resonances higher than the $\Delta$ resonance in the nuclear photoabsorption. This phenomenon is understood by taking into account the cooperative effect of the collision broadening of $\Delta$ and $N^{*}$, the pion distortion and the interference in the two-pion photoproduction processes in the nuclear medium.

The ( ${e,e}^{\prime }p$) reaction was studied on targets of C, Fe, and Au at momentum transfers squared $Q^2$ of 0.6, 1.3, 1.8, and $3.3{\mathrm{GeV}}^2$ in a region of kinematics dominated by quasifree electron-proton scattering. Missing energy and missing momentum distributions are reasonably well described by plane wave impulse approximation calculations with $Q^2$ and $A$ dependent corrections that measure the attenuation of the final state protons.

The double differential cross section of low momentum kaons ( $\le 0.3\mathrm{GeV}/c$) from $p+\mathrm{C}$ collisions at subthreshold bombarding energies has been for the first time measured by the use of the CLAMSUD magnetic spectrometer installed at the CELSIUS storage ring. Invariant cross sections extracted from the data show a source rapidity shifted below the nucleon-nucleon rapidity, in agreement with the existence of multistep processes in the $K^{+}$ production cross section. The total cross section of the inclusive reaction ${}^{12}\mathrm{C}\left({p,K}^{+}\right)$ at 1.2 GeV was extracted and compared with recent data systematics as a function of the proton bombarding energy.

Leading-order electromagnetic loop corrections to the one-pion-exchange potential are computed within the framework of chiral perturbation theory. These corrections generate an effective nucleon-nucleon potential, $V_{\pi \gamma }$, which supplements the sum of one-pion-exchange potential and the nucleon-nucleon Coulomb potential. This potential is charge dependent and its construction is demonstrated to be gauge invariant. The potential $V_{\pi \gamma }$ has been included in the Nijmegen partial-wave analysis of $\mathrm{np}$ data. A particular renormalization scheme is chosen that leads to a negligible change in the ${\pi }^{\pm }\mathrm{NN}$ coupling constant and in the $\mathrm{np}$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ scattering length and effective range.

The double differential cross section for $\mathrm{pn}\to \mathrm{pp}{(}^1{S}_0){\pi }^{-}$ at three beam energies has been extracted from the quasifree process $\mathrm{pd}\to \mathrm{ppp}{\pi }^{-}$. A comparison is carried out with single differential cross section measurements for ${}^3\mathrm{He}({\pi }^{-},pn)n$, where the pion is thought to be absorbed onto a $\mathrm{pp}{(}^1{S}_0)$ “diproton” state. A significant difference is observed in the shape of the angular distribution between the production and absorption data. This difference is ascribed to the effects of the ${}^3\mathrm{He}$ nuclear environment characterizing the absorption process; however, an adequate theoretical explanation is not available.

We consider a many-fermion model which exhibits a transition from a superconducting to a rotational phase with variation of a parameter in its Hamiltonian. The model has analytical solutions in its two limits due to the presence of dynamical symmetries. However, the symmetries are basically incompatible with one another; no simple solution exists in intermediate situations. Exact (numerical) solutions are possible and enable one to study the behavior of competing but incompatible symmetries and the phase transitions that result in a semirealistic situation. The results are remarkably simple and shed light on the nature of phase transitions.

The reflection asymmetric phase transition in nuclei at high angular momentum is analyzed in the framework of the cranked Hartree-Fock-Bogoliubov approximation, with the Gogny interaction, using approximate parity projection before variation. The $N=88\mathrm{}$ isotones are studied and our results compared with experimental data. Good agreement is found for the energy splitting of the even and odd parity states and $B\left(E1\mathrm{}\right)$ transition probabilities. Differences on intrinsic deformations, dipole moments, and pairing energies between odd and even parity states found at low spin disappear with increasing angular momentum.

A Comment on the Letter by G. Hackman et al. Phys. Rev. Lett. 79, 4100 (1997). The authors of the Letter offer a Reply.

A Reply to the Comment by R. R. Chasman.

The angular distributions of $\beta$ rays from spin aligned ${}_{}{}^{12}{}_{}{}^{}B$ and ${}_{}{}^{12}{}_{}{}^{}N$ were precisely remeasured using a further refined spin-manipulation technique. Our old data have also been recorrected for precisely determined systematic corrections. A nonzero $G$-parity violating induced tensor form factor $f_T$ has been concluded as ${2Mf}_T{/f}_A=+0.22\mathrm{}\pm 0.05\left(\mathrm{stat}\right)\pm 0.15\left(\mathrm{syst}\right)\pm 0.05(\mathrm{theor}.\mathrm{})$. In this result the asymmetry in the axial charges due to the binding-energy difference of the transforming nucleons is taken into account.

The directed and elliptic flow of protons and charged pions has been observed from the semicentral collisions of a 158 GeV/nucleon Pb beam with a Pb target. The rapidity and transverse momentum dependence of the flow has been measured. The directed flow of the pions is opposite to that of the protons but both exhibit negative flow at low $p_t$. The elliptic flow of both is fairly independent of rapidity but rises with $p_t$.

We present the first fully quantum mechanical calculation of photon radiation accompanying charged particle decay from a barrier resonance. The soft-photon limit agrees with the classical results, but differences appear at next-to-leading order. Under the conditions of $\alpha$ decay of heavy nuclei, the main contribution to the photon emission stems from Coulomb acceleration and may be computed analytically. We find only a small contribution from the tunneling wave function under the barrier.

The damping of the giant dipole resonance (GDR) is studied in ${}^{90}\mathrm{Zr}$, ${}^{120}\mathrm{Sn}$, and ${}^{208}\mathrm{Pb}$ as a function of temperature $T$. The results show that the coupling of GDR to the $\mathrm{pp}$ and $\mathrm{hh}$ states is responsible for the increase of the GDR width with increasing $T$ up to 3 MeV and its saturation at higher $T$. The quantal width, caused by the coupling to $\mathrm{ph}$ excitations, decreases slowly with increasing $T$. An overall agreement is found between the theoretical evaluations and the recent experimental data in heavy-ion fusion reactions and inelastic $\alpha$ scattering. At very high $T$ a behavior similar to the transition from zero to ordinary sounds is observed.

The dynamic properties of the atomic nucleus depend strongly on correlations between the nucleons. We present a combined analysis of inelastic electron-scattering data and electron-induced proton knockout measurements in an effort to obtain phenomenological information on nucleon-nucleon correlations. Our results indicate that the ratio of radial wave functions extracted from precise ${}^{10}\mathrm{B}\left({e,e}^{\prime }\right)$ and ${}^{10}\mathrm{B}\left({e,e}^{\prime }p\right)$ measurements evolve from an interior depression for small $E_m$, characteristic of short-range correlations, to a surface-peaked enhancement for larger $E_m$, characteristic of long-range correlations. This observation can be interpreted in terms of the nucleon effective mass.

Breakup temperatures in central collisions of ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ at bombarding energies $E/A=50\mathrm{}$ to 200 MeV were determined with two methods. Isotope temperatures, deduced from double ratios of hydrogen, helium, and lithium isotopic yields, increase monotonically with bombarding energy from 5 to 12 MeV, in qualitative agreement with a scenario of chemical freeze-out after adiabatic expansion. Excited-state temperatures, derived from yield ratios of states in ${}^4\mathrm{He}$, ${}^{5,6}\mathrm{Li}$, and ${}^8\mathrm{Be}$, are about 5 MeV, independent of the projectile energy, and seem to reflect the internal temperature of fragments at their final separation from the system.