Preparation of facilities for fundamental research with ultracold neutrons at PNPI

TL;DR

This paper discusses the design and potential of a facility at PNPI's reactor to produce ultracold neutrons using high flux, superfluid helium, and advanced shielding, enabling new fundamental research opportunities.

Contribution

It presents a detailed proposal for a UCN source at PNPI's reactor, including technical design and expected performance improvements.

Findings

High neutron flux environment for UCN production

Estimated UCN density of 10^4 n/cm^3 in 40L volume

Feasible heat removal at 1.2 K with 20 W capacity

Abstract

The WWR-M reactor of PNPI offers a unique opportunity to prepare a source for ultracold neutrons (UCN) in an environment of high neutron flux (about 3*10^12 n/cm^2/s) at still acceptable radiation heat release (about 4*10^-3 W/g). It can be realized within the reactor thermal column situated close to the reactor core. With its large diameter of 1 m, this channel allows to install a 15 cm thick bismuth shielding, a graphite premoderator (300 dm^3 at 20 K), and a superfluid helium converter (35 dm^3). At a temperature of 1.2 K it is possible to remove the heat release power of about 20 W. Using the 4pi flux of cold neutrons within the reactor column can bring more than a factor 100 of cold neutron flux incident on the superfluid helium with respect to the present cold neutron beam conditions at the ILL reactor. The storage lifetime for UCN in superfluid He at 1.2 K is about 30 s, which is sufficient when feeding experiments requiring a similar filling time. The calculated density of UCN with energy between 50 neV and 250 neV in an experimental volume of 40 liters is about 10^4 n/cm^3. Technical solutions for realization of the project are discussed.