The extremely neutron-rich nucleus ${}^{19}\mathrm{C}$ has been studied by Coulomb dissociation into ${}^{18}\mathrm{C}+n$ at $67A\mathrm{MeV}$. A large $E1\mathrm{}$ strength of $0.71\pm 0.07e^2\mathrm{fm}{}^2$ has been observed at low excitation energies. An analysis of the angular distribution of ${}^{18}\mathrm{C}+n$ center of mass has led to a determination of the neutron separation energy of ${}^{19}\mathrm{C}$ to be $530\pm 130\mathrm{keV}$. The $E1\mathrm{}$ strength distribution can be well reproduced for a ${}^{19}\mathrm{C}$ ground state structure with a dominant $s$-wave valence neutron, providing a consistent picture of the neutron halo structure of ${}^{19}\mathrm{C}$.

The neutron time-of-flight facility n_TOF features a white neutron source produced by spallation through 20GeV/ cprotons impinging on a lead target. The facility, aiming primarily at the measurement...

Breakup reactions of the one-neutron halo nucleus ${}^{11}\mathrm{Be}$ on lead and carbon targets at about $70\mathrm{MeV}∕\text{nucleon}$ have been investigated at RIKEN by measuring the momentum vectors of the incident ${}^{11}\mathrm{Be}$, outgoing ${}^{10}\mathrm{Be}$, and neutron in coincidence. The relative energy spectra as well as the angular distributions of the ${}^{10}\mathrm{Be}+n$ center of mass system (inelastic angular distributions) have been extracted both for Pb and C targets. For the breakup of ${}^{11}\mathrm{Be}$ on Pb, the selection of forward-scattering angles, corresponding to large impact parameters, is found to be effective to extract almost purely the first-order $E1$ Coulomb breakup component and to exclude the nuclear contribution and higher-order Coulomb breakup components. This angle-selected energy spectrum is thus used to deduce the spectroscopic factor for the ${}^{10}\mathrm{Be}\left(0^{+}\right)\otimes \nu 2s_{1∕2}$ configuration in ${}^{11}\mathrm{Be}$ which is found to be $0.72\pm \mathrm{0.04}$ with a $B\left(E1\right)$ strength up to $E_{\mathrm{x}}=4\mathrm{MeV}$ of $1.05\pm 0.06e^2{\mathrm{fm}}^2$. The energy weighted $E1$ strength up to $E_{\mathrm{x}}=4\mathrm{MeV}$ explains $70\%\pm 10\%$ of the cluster sum rule, consistent with the obtained spectroscopic factor. The non-energy-weighted sum rule within the same energy range is used to extract the root-mean-square distance of the halo neutron to be $5.77\left(16\right)\mathrm{fm}$, consistent with previously known values. In the breakup with the carbon target, we have observed the excitations to the known unbound states in ${}^{11}\mathrm{Be}$ at $E_{\mathrm{x}}=1.78\mathrm{MeV}$ and $E_{\mathrm{x}}=3.41\mathrm{MeV}$. Angular distributions for these states show the diffraction pattern characteristic of $L=2$ transitions, resulting in a $J^{\pi }={(3∕2,5∕2)}^{+}$ assignment for these states. We finally find that even for the C target the $E1$ Coulomb direct breakup mechanism becomes dominant at very forward angles.

The cross sections for single-neutron removal from the very neutron-rich nucleus ${}^{31}\mathrm{Ne}$ on Pb and C targets have been measured at $230\mathrm{MeV}/\mathrm{\text{nucleon}}$ using the RIBF facility at RIKEN. The deduced large Coulomb breakup cross section of 540(70) mb is indicative of a soft $E1$ excitation. Comparison with direct-breakup model calculations suggests that the valence neutron of ${}^{31}\mathrm{Ne}$ occupies a low-$\ell$ orbital (most probably $2p_{3/2}$) with a small separation energy ($S_n\lesssim 0.8\mathrm{MeV}$), instead of being predominantly in the $1f_{7/2}$ orbital as expected from the conventional shell ordering. These findings suggest that ${}^{31}\mathrm{Ne}$ is the heaviest halo system known.

The energy-dependent cross section of the ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of ${}^7\mathrm{Be}$ and by the low reaction cross section have been overcome at n_TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n_TOF facility at CERN, the availability of a sufficient amount of chemically pure ${}^7\mathrm{Be}$, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two $\mathrm{Si}\text{−}{}^7\mathrm{Be}\text{−}\mathrm{Si}$ arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n_TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.