First near-threshold measurements of the 13C(α, n1)16O reaction for low-background-environment characterization

The modeling of background sources in large volume detection systems requires accurate nuclear cross sections for a variety of reactions. Among the most important are (alpha, n) on light nuclei, where alpha particles, up to approximate to 9 MeV, are produced from the decay of actinides present in trace amounts in detection and structural material. In order to model the neutron energy spectra and production of other secondary particles, the partial cross sections are needed. Yet very little experimental data exists for these partial cross sections because past measurements, hampered by the experimental challenges of neutron detection, have focused mostly on total reaction cross section measurements. Here the partial cross section of the 13C(alpha, n1)16O reaction is reported for the first time. The measurements were made near the reaction threshold using a high energy resolution helium spectrometer. The measurements show a rapidly increasing cross section, which quickly becomes a significant fraction of the total reaction cross section. Measurements are compared with previous theory estimates and differences of more than an order of magnitude are found. A comparison is made with new total cross section measurements and the current level of consistency is demonstrated.

Automated summary

This article reports the experimental measurements of the partial cross section for the 13C(alpha, n1)16O reaction. The measurements show a rapidly increasing cross section, which quickly becomes a significant fraction of the total reaction cross section. Comparisons with previous theory estimates and new total cross section measurements reveal significant differences and demonstrate the current level of consistency.