Organic liquid scintillators are used in a wide variety of applications in experimental
nuclear and particle physics. Boron-loaded scintillators are particularly useful for detecting neutron
captures, due to the high thermal neutron capture cross section of 10B. These scintillators are
commonly used in neutron detectors, including the DarkSide-50 neutron veto, where the neutron
may produce a signal when it scatters off protons in the scintillator or when it captures on 10B.
Reconstructing the energy of these recoils is complicated by scintillation quenching. Understanding
how nuclear recoils are quenched in these scintillators is an important and difficult problem. In this
article, we present a set of measurements of neutron-induced proton recoils in a boron-loaded organic
liquid scintillator at recoil energies ranging from 57–467 keV, and we compare these measurements
to predictions from different quenching models. We find that a modified Birks’ model whose
denominator is quadratic in dE/dx best describes the measurements, with χ
2
/NDF= 1.6. This
result will help model nuclear recoil scintillation in similar detectors and can be used to improve
their neutron tagging efficiency.