Production of UCN by Downscattering in superfluid He4

TL;DR

This paper investigates the multiphonon process for ultra-cold neutron production in superfluid helium, analyzing how different neutron spectra influence the efficiency of UCN generation.

Contribution

It provides a detailed examination of multiphonon UCN production and its dependence on incident neutron spectra, expanding understanding beyond single phonon processes.

Findings

Multiphonon processes can significantly contribute to UCN production.

The importance of multiphonon production varies with incident neutron spectra.

Different spectra alter the relative efficiency of multiphonon versus single phonon UCN production.

Abstract

Ultra-cold neutrons (UCN) are neutrons with energies so low they can be stored in material bottles and magnetic traps. They have been used to provide the currently most accurate experiments on the neutron life time and electric dipole moment. UCN can be produced in superfluid Helium at significantly higher densities than by other methods. The predominant production process is usually by one phonon emission which can only occur at a single incident neutron energy because of momentum and energy conservation. However UCN can also be produced by multiphonon processes. It is the purpose of this work to examine this multiphonon production of UCN. We look at several different incident neutron spectra, including cases where the multiphonon production is significant, and see how the relative importance of multiphonon production is influenced by the incident spectrum.