Preparation of facilities for fundamental research with ultracold neutrons at PNPI

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.Comment: 10 pages, more detail

Measurement of the neutron lifetime with ultra-cold neutrons stored in a magneto-gravitational trap

International audienceWe report a measurement of the neutron lifetime using ultracold neutrons stored in a magneto-gravitational trap made of permanent magnets. Neutrons surviving in the trap after fixed storage times have been counted and the trap losses have continuously been monitored during storage by detecting neutrons leaking from the trap. The value of the neutron lifetime resulting from this measurement is τ$_{n}$ = (878.3 ± 1.6$_{stat}$ ± 1.0$_{syst}$) A unique feature of this experiment is the monitoring of leaking neutrons providing a robust control of the main systematic loss

Magnetic storage of UCN for a measurement of the neutron lifetime

International audienceWe present the status of an experimental setup designed and built for the measurement of the neutron lifetime and we describe also details about the measuring sequence. The central element of the setup is a magnetic trap made of permanent magnets. Neutrons surviving in the trap after fixed storage times are counted after their extraction and the trap losses are continuously monitored during the storage periods. The technique has achieved a statistical sensitivity of about 2 s on the storage time what constitutes the most sensitive magnetic trapping technique for ultra-cold neutrons developed so far