The total cross section for the ${\pi }^{-}p\to {\pi }^{-}{\pi }^{+}n$ reaction has been measured at incident pion kinetic energies of 200, 190, 184, and 180 MeV. In addition, the ${\pi }^{+}p\to {\pi }^{+}{\pi }^{+}n$ reaction was measured at 200 and 184 MeV. A fit of the cross sections by heavy baryon chiral perturbation theory yields values of $8.5\pm 0.6\left(m_{\pi }^{-3\mathrm{}}\right)$ and $2.5\pm 0.1\left(m_{\pi }^{-3\mathrm{}}\right)$ for the reaction matrix elements $A_{10}$ and $A_{32}$, which correspond to values for the $s$-wave isospin-0 and isospin-2 $\pi -\pi$ scattering lengths of $a_0=0.23\mathrm{}\pm 0.08\left(m_{\pi }^{-1\mathrm{}}\right)$ and $a_2=-0.031\mathrm{}\pm 0.008\left(m_{\pi }^{-1\mathrm{}}\right)$, respectively.

A spectroscopic study of the proton-rich, particle unstable nucleus ${}^{11}\mathrm{N}$ has been performed using the multinucleon transfer reaction ${}^{12}\mathrm{C}{(}^{14}\mathrm{N}{,}^{15}\mathrm{C}{)}^{11}\mathrm{N}$ at $30A\mathrm{MeV}$ incident energy at GANIL. Levels of ${}^{11}\mathrm{N}$ are observed as well defined resonances in the spectrum of the ${}^{15}\mathrm{C}$ ejectiles. They are localized at 2.18(5), 3.63(5), 4.39(5), 5.12(8), and 5.87(15) MeV above the ${}^{10}\mathrm{C}+p$ threshold. The comparison of the measured widths with $R$-matrix calculations allows the estimation of spins and parities for these resonances.

We have observed a clear peak below the ${\Sigma }^{+}$-production threshold in the ${}^4\mathrm{He}(K^{-},{\pi }^{-})$ reaction at $600\mathrm{MeV}/c$ and ${\theta }_{K\pi }{=4\mathrm{}}^{\circ }$. This is confirmation of the existence of the bound state of ${}_{\Sigma }^4\mathrm{He}$, which was reported in the ${}^4\mathrm{He}(\mathrm{stopped}{K}^{-},{\pi }^{-})$ reaction. As in the case of stopped kaons, no such peak was found in the ${}^4\mathrm{He}(K^{-},{\pi }^{+})$ spectrum. Quantitatively reliable parameters for this level have been established. The binding energy and the width of the bound state are $4.4\pm 0.3\left(\mathrm{stat}\right)\pm 1\left(\mathrm{syst}\right)$ MeV and $7.0\pm 0.7\left(\mathrm{stat}{)}_{-0.0\mathrm{}}^{+1.2\mathrm{}}\right(\mathrm{syst})$ MeV, respectively.

Precision measurements of the $\beta$-decay spectrum of ${}^{63}\mathrm{Ni}$ with a hermetic, calorimetric low-temperature detector have yielded quantitative evidence for the atomic exchange effect in $\beta$ decay. The exchange effect is due to the probability that the $\beta$ electron is created into a bound state orbital of the daughter atom and is predicted to lead to a small relative enhancement in the spectrum at low energies. In the experiment reported here the energy release in each of $6\times {10}^7$ $\beta$-decay events was measured by detecting the nonequilibrium phonons produced in two InSb crystals which enclose the ${}^{63}\mathrm{Ni}$ source. The best-fit value of the exchange factor is $0.98\pm 0.06$ (statistical) times the theoretical value, with an experimental systematic error of $\pm 0.06$.

Charged pion photoproduction is proposed as a new method to study halo nuclei. In particular, it is demonstrated that the reaction ${}^{17}\mathrm{O}(\gamma ,{\pi }^{-}{)}^{17}\mathrm{F}({\frac{1}{2}}^{+},0.495\mathrm{}\mathrm{MeV})$ is well suited to investigate the well-known proton halo in ${}^{17}\mathrm{F}$ which is not amenable to radioactive beam experiments. The cross sections are shown to be very sensitive to the halo structure of the loosely bound proton.

We show that a hadron gas model with continuous particle emission instead of freeze-out may solve some of the problems (high values of the freeze-out density and specific net charge) that one encounters in the latter case when studying strange particle ratios such as those from the experiment WA85. This underlines the necessity to understand better particle emission in hydrodynamics to be able to analyze data. It also reopens the possibility of a quark-hadron transition occurring with phase equilibrium instead of explosively.

Lifetimes of states in two rotational bands in ${}^{108}\mathrm{Sn}$ and one in ${}^{109}\mathrm{Sb}$ have been determined using the Doppler shift attenuation method. The deduced quadrupole moments for the states are in excellent agreement with cranked Nilsson model predictions, which imply a gradual change in the nuclear shape from collective near-prolate at medium spin to noncollective oblate at high spin. This change results from the gradual alignment of the spin vectors of the valence particles and holes in a specific configuration. These data provide crucial evidence in support of the phenomenon of smooth band termination.

Arrhenius-type plots for a multifragmentation process, defined as the transverse energy dependence of the single-fragment emission probability $\left[\ln \right({1/p}_b)\mathrm{vs}1/\sqrt{E_t}]$, have been studied by examining the relationship of the parameters $p_b$ and $E_t$ to the intermediate-mass fragment multiplicity $〈n〉$. The linearity of these plots reflects the correlation of the fragment multiplicity with the transverse energy. These plots contain equivalent information as $N_c$ vs $〈n〉$ plots and do not provide thermal scaling information about fragment production contained in true Arrhenius plots.

We model the disassembly of an excited nuclear system formed as a result of a heavy ion collision. We find that, as the beam energy in central collisions in varied, the dissociating system crosses a liquid-gas coexistence curve, resulting in a first-order phase transition. Accessible experimental signatures are identified: a peak in the specific heat, a power-law yield for composites, and a maximum in the second moment of the yield distribution.

Brooding over bosons, wave packets, and Bose-Einstein correlations, we find that a generalization of the pion-laser model for the case of overlapping wave packets is analytically solvable with complete n-particle symmetrization. Explicit multiplicity and momentum dependence of exclusive correlations and spectra is found. The effective source radii are reduced for low values and enlarged for high values of the mean momentum in the rare gas limiting case.

Optical isotope shift measurements have been performed for the ${}^{240,242}{\mathrm{Am}}^f$ fission isomers with low target production rates of $10{\mathrm{s}}^{-1\mathrm{}}$ employing resonance ionization spectroscopy in a buffer gas cell. Isotope shift ratios ${\mathrm{IS}}^{240f,241}/{\mathrm{IS}}^{243,241}=39.2\mathrm{}\left(8\right)$ and ${\mathrm{IS}}^{242f,241}/{\mathrm{IS}}^{243,241}=41.4\mathrm{}\left(8\right)$ have been measured at the 500.02 nm transition. A difference in the nuclear mean charge radii $\delta 〈r^2{〉}_{\mathrm{opt}}^{242f,241}=5.34\mathrm{}\left(28\right){\mathrm{fm}}^2$ and an intrinsic quadrupole moment $Q_{20}^{242f}=(35.5\pm {1.0}_{\mathrm{st}}\pm {1.2}_{\mathrm{mod}})e\mathrm{b}$ have been deduced, neglecting the nuclear polarization correction. The small difference $\delta Q_{20}^{242f,240f}=0.63\mathrm{}\left(8\right)e\mathrm{b}$ demonstrates the stability of the deformation if two neutrons are removed.

We report a new method for the measurement of quadrupole moments of radioactive nuclei which were not accessible with other techniques until now: modulated adiabatic fast passage on oriented nuclei (MAPON) after recoil implantation into hcp Co. Quadrupole moments of Zr and Nb isotopes were determined which are interesting in the context of the proton and the neutron effective charge at $A\sim 90$.

Cross sections for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction have been measured for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=0.35\mathrm{}–1.4\mathrm{MeV}$ using radioactive ${}^7\mathrm{Be}$ targets. Two independent measurements carried out with different beam conditions, different targets, and detectors are in excellent agreement. A statistical comparison of these measurements with previous results leads to a restricted set of consistent data. The deduced zero-energy $S$ factor $S\left(0\right)$ is found to be 15%–20% smaller than the previously recommended value. This implies a ${}^8\mathrm{B}$ solar neutrino flux lower than previously predicted in various standard solar models.

Starting from a deformed potential we construct separate bases of collective neutron and proton rotational states by exact angular momentum projection. These rotational states are then coupled by diagonalizing a residual pairing plus quadrupole interaction. Many new bands emerge that are not found in the rotation of the usual BCS condensate, and may correspond to the geometrical scissors mode and its generalizations. These excitation modes can be understood as rotational bands built on spin- $1ħ$ phonon excitations; they exhibit a nearly perfect dynamical $\mathrm{SU}\left(3\right)$ fermion spectrum, even though there is no explicit dynamical symmetry in our model.

The single-particle character of states outside the doubly magic (radioactive) nucleus ${}^{56}\mathrm{Ni}$ has been determined through a measurement of the $(d,p)$ neutron transfer reaction using inverse kinematics. From the spectroscopic factors of the low-lying states in ${}^{57}\mathrm{Ni}$, the astrophysically interesting yield for the ${}^{56}\mathrm{Ni}(p,\gamma )$ reaction to the mirror nucleus ${}^{57}\mathrm{Cu}$ has been calculated, utilizing charge symmetry. The rate for this reaction in the temperature range typical of novae, supernovae, and x-ray bursts is found to be more than 10 times higher than previously assumed.

A Comment on the Letter by Nicolas J. Cerf, Phys. Rev. Lett. 76, 2420 (1996). The authors of the Letter offer a Reply.

A Reply to the Comment by S. Rombouts and K. Heyde

Meson-baryon couplings between positive and negative parity baryons are investigated using two-point correlation functions in the soft meson limit. We find that the $\pi {\mathrm{NN}}^{*}$ coupling vanishes due to chiral symmetry, while the $\eta {\mathrm{NN}}^{*}$ coupling remains finite. We perform an analysis based on the algebraic method for SU (2) and SU (3) chiral symmetry, and find that baryon axial charges play an essential role for vanishing coupling constants.