Production of quasi-stellar neutron field at explosive stellar temperatures

Neutron-induced reactions on unstable isotopes play a key role in the nucleosynthesis i-, r-, p-, rp- and νp-processes occurring in astrophysical scenarios. While direct cross section measurements are possible for long-lived unstable isotopes using the neutron Time-of-Flight method, the currently available neutron intensities (≈ 10 ⁶ n/s) require large samples which are not feasible for shorter-lived isotopes. For the last three decades, the ⁷Li(p, n) reaction has been used with thick lithium targets to provide a neutron field at a stellar temperature of ≈ 0.3 GK with significantly higher intensity, allowing the successful measurement of many cross sections along the s-process path. In this paper we describe a novel method to use this reaction to produce neutron fields at temperatures of ≈ 1.5–3.5 GK, relevant to scenarios such as convective shell C/Ne burning, explosive Ne/C burning, and core-collapse supernovae. This method will enable the use of high intensity proton beams with thick lithium targets to provide several orders of magnitude increase in the available neutron intensity relative to state-of-the-art neutron Time-of-Flight facilities, hence will allow direct cross section measurements of many important reactions at explosive temperatures, such as ²⁶Al(n, p), ⁷⁵Se(n, p) and ⁵⁶Ni(n, p).