Analysis of Neutron Dark Scattering from Plastic Scintillators*

Background:

Plastic scintillators are widely used for detecting energetic particles in nuclear physics applications. The MoNA Collaboration uses these detectors to measure the neutrons emitted from neutron-rich nuclei. Detailed simulations are needed to interpret the data.  Dark scattering - events when the neutron scatters from a plastic scintillator but doesn’t produce enough light to be detected - needs to be studied more as these events make the interpretation of the data more challenging as the neutrons scatter from one site without record to another.

Purpose:

The purpose of the work is to observe neutron dark scattering off of plastic scintillator detectors. The observations are compared to two different simulation packages in Geant4, a simulation toolkit that simulates the interaction of particles through matter.

Methods:

An experiment was performed at the Los Alamos Neutron Science Center with a beam of neutrons ranging from 20 to 400 MeV. The neutrons were scattered off of plastic scintillators. Properties of the incident and scattered neutrons like beam energy, scattering angle, and the kinetic energy of the scattered neutron are calculated from recorded data like x, y, z coordinates, time of flight of the particles, and the light output in the scintillators. A variety of analysis techniques were required to eliminate sources of background such as cosmic muons and neutrons scattered at the collimator.

Results:

The different versions of scaling for background allowed us to analyze dark scattering and compare it to predictions from simulations up to 100 MeV. We observed that scattering angles from dark scatter in lower energies have a very good correlation but the measure angles start to shift higher as the energy gets higher compared to both Geant4 and MenateR simulations.