# Evaluation of commercial nickel-phosphorus coating for ultracold neutron guides using a pinhole bottling method

## TL;DR

This study evaluates commercial nickel-phosphorus coatings for ultracold neutron transport and storage, measuring their potential and loss rates, and introduces a new guide coupling design to improve experimental accuracy.

## Contribution

It provides the first comprehensive assessment of NiP coatings for UCN guides, including a novel guide coupling design and detailed methodology for pinhole bottling experiments.

## Key findings

- Measured material potential of NiP coatings as 213 neV.
- Determined UCN loss per bounce as 1.3 x 10^-4.
- Developed a new guide coupling to reduce gaps and improve measurements.

## Abstract

We report on the evaluation of commercial electroless nickel phosphorus (NiP) coatings for ultracold neutron (UCN) transport and storage. The material potential of 50~$\mu$m thick NiP coatings on stainless steel and aluminum substrates was measured to be $V_F = 213(5.2)$~neV using the time-of-flight spectrometer ASTERIX at the Lujan Center. The loss per bounce probability was measured in pinhole bottling experiments carried out at ultracold neutron sources at Los Alamos Neutron Science Center and the Institut Laue-Langevin. For these tests a new guide coupling design was used to minimize gaps between the guide sections. The observed UCN loss in the bottle was interpreted in terms of an energy independent effective loss per bounce, which is the appropriate model when gaps in the system and upscattering are the dominate loss mechanisms, yielding a loss per bounce of $1.3(1) \times 10^{-4}$. We also present a detailed discussion of the pinhole bottling methodology and an energy dependent analysis of the experimental results.