Optimization of VANDLE for $\beta $-delayed neutron decay studies using Geant4*

The Versatile Array of Neutron Detectors at Low Energy (VANDLE) is a plastic-scintillator array designed for various experimental setups including $\beta $-delayed neutron spectroscopy and (d,n) transfer reactions in inverse kinematics. The neutron energy is determined through the time-of-flight technique. The array has energy resolution of $\sim$ 120 keV @ 1 MeV and energy threshold of $\sim$ 100 keV. We have developed a Geant4 simulation of VANDLE to optimize array geometry for different types of experiments and test neutron scattering models provided by Geant4. A typical $\beta $-delayed neutron decay study involves coupling with $\gamma $ detectors to collect $\beta $-$\gamma $ coincidence information. The experimental assembly including VANDLE bars, $\beta $ plastic scintillators, HPGe detectors, along with the detector support structure was modeled to assist in the fine-tuning of the setup and give a detailed understanding of the array performance. The simulation was validated by comparing to available experimental data and could serve as an important guide for the design of future experiments.