Temperature dependent ultracold neutron transmission in D$_2$ gas $-$ a test of the Young-Koppel model

TL;DR

This study experimentally tests the Young-Koppel model for ultracold neutron interactions with D$_2$ gas across various temperatures, confirming the model's validity and highlighting differences from low-energy approximations.

Contribution

First experimental validation of the Young-Koppel model for ultracold neutrons in D$_2$ gas over a wide temperature range, and comparison with low-energy low-temperature approximation.

Findings

Young-Koppel model accurately describes UCN scattering in D$_2$ gas.

Temperature dependence differs from low-energy low-temperature approximation.

Confirmed the model's applicability to noble gases and measured UCN cross sections in H$_2$.

Abstract

The Young-Koppel model (YK) describes comprehensively the interaction of slow neutrons with diatomic gases such as H$_2$ and D$_2$. This paper reports on the first experimental results of ultracold neutron (UCN) scattering over a wide temperature range vindicating the YK model for gaseous D$_2$ and showing an important difference in the temperature dependence to a low-energy low-temperature approximation (LETA). LETA is confirmed, however, to be valid for monoatomic gases such as Ne. Calculated cross sections for other noble gases were also confirmed for ultracold neutrons. Finally, the total cross section of UCNs in H$_2$ gas was measured and analyzed applying the Young-Koppel model, however, in a more limited temperature range, confirming the theoretical prediction.