W. F. Rogers

A single-crystal chemical-vapor-deposited diamond detector was used at the Los Alamos Neutron Science Center to measure neutron-induced reactions on carbon. Neutrons with a broad energy spectrum were produced via spallation. Relative cross sections are reported from above threshold up to 26 MeV incident neutron energy for $^{12}\mathrm{C}(n,{p}_{2})^{12}\mathrm{B}$, up to 23 MeV for $^{12}\mathrm{C}(n,{p}_{3+4})^{12}\mathrm{B}$, and up to 35 MeV for $^{12}\mathrm{C}(n,{d}_{1})^{11}\mathrm{B}$ and $^{12}\mathrm{C}(n,{d}_{2})^{11}\mathrm{B}$, all of which represent the highest-energy measurements for these reactions to date and the first measurement for $(n,{d}_{2})$. Cross sections for $^{12}\mathrm{C}(n,p){^{12}\mathrm{B}}_{\text{total}}$ and $^{12}\mathrm{C}(n,d){^{11}\mathrm{B}}_{\text{total}}$ are also reported from sums of the partial cross sections. These measurements are compared with recent data from EXFOR as well as talys calculations. These data are useful for future nuclear data evaluations and can be used as cross-section inputs for data-based simulation packages.

Background: The recent discovery and spectroscopic measurements of ${}^{27}\mathrm{O}$ and ${}^{28}\mathrm{O}$ suggests the disappearance of the $N=20$ shell structure in these neutron-rich oxygen isotopes.

Background: The island of inversion near the $N=20$ shell gap is home to nuclei with reordered single-particle energy levels compared with the spherical shell model. Studies of ${}^{31}\mathrm{Ne}$ have revealed that its ground state has a halo component characterized by a valence neutron orbiting a deformed ${}^{30}\mathrm{Ne}$ core. This lightly bound nucleus with a separation energy of only $S_n=170$ keV is expected to have excited states that are neutron unbound.

Neutron-unbound resonant states of ${}^{11}\mathrm{Be}$ were populated in neutron knockout reactions from ${}^{12}\mathrm{Be}$ and identified by ${}^{10}\mathrm{Be}$–$n$ coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in ${}^{11}\mathrm{Be}$ at 3.949(2) MeV decaying to the $2^{+}$ excited state in ${}^{10}\mathrm{Be}$. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state, suggesting a spectroscopic factor near unity for this $0p3/2^{-}$ level, consistent with the detailed shell model calculations.