A superfluid helium converter for accumulation and extraction of ultracold neutrons

TL;DR

This paper demonstrates the first successful extraction of ultracold neutrons from a superfluid helium converter, showcasing a portable, rapid-cool cryostat and measuring UCN storage and extraction efficiencies.

Contribution

It introduces a novel superfluid helium UCN converter with a windowless extraction method and a portable cryostat design, enabling efficient UCN production and extraction.

Findings

UCN extraction from superfluid helium was successful

Measured UCN storage and extraction time constants at various temperatures

UCN production rate aligns with theoretical predictions

Abstract

We report the first successful extraction of accumulated ultracold neutrons (UCN) from a converter of superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. Windowless UCN extraction is performed in vertical direction through a mechanical cold valve. This prototype of a versatile UCN source is comprised of a novel cryostat designed to keep the source portable and to allow for rapid cooldown. We measured time constants for UCN storage and extraction into a detector at room temperature, with the converter held at various temperatures between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of extracted UCN is close to the theoretical expectation.