P. Geltenbort

Neutron life time value measured by storing ultracold neutrons with detection of inelastically scattered neutrons

Abstract The neutron life time τ n was measured by storage of ultracold neutrons (UCN) in a material bottle covered with Fomblin oil. The inelastically scattered neutrons were detected by surrounding neutron counters monitoring the UCN losses due to upscattering at the bottle walls. Comparing traps with different surface to volume ratios the free neutron life time was deduced. Consistent results for different bottle temperatures yielded τ n sec =885.4±0.9 stat ±0.4 syst .

Neutron lifetime measured by monitored storing of ultra-cold neutrons

Abstract The method of measuring the neutron β -decay lifetime τ β by storage of ultra-cold neutrons (UCN) with simultaneous recording of inelastically scattered neutrons is presented. The result of the measurement is τ β [ s ]=885.4±0.9 stat ±0.4 syst .

Cooling and heating of ultracold neutrons during storage

The rare processes of weak heating and cooling of ultracold neutrons reflected from the surface of fluorosubstituted oil are studied. The probability of these processes is estimated at 10−6 per single reflection at energy transfer commensurate with the primary neutron energy. Weak heating and cooling are shown to be a manifestation of a more general phenomenon—quasielastic neutron reflection whose probability is dependent on temperature.

Cooling of ultracold neutrons during their long storage in a trap

We have observed the cooling of ultracold neutrons during their long storage in a trap, with a probability estimated as 1×10−6/reflection and with an energy transfer of about 3 neV.

Investigation of the radiative capture of UCN at the matter surface

Abstract The method of radiative capture analysis with ultra-cold neutrons (UCN) was used to investigate the UCN interaction with the surface of the materials usually employed in UCN physics. The values and upper limits which were obtained for the capture probabilities for homogeneous media were in accordance with the standard theory. New results for alloys confirmed the existence of a selective enhancement effect.

Cold-neutron storage owing to diffusion reflection

Results are presented that were obtained from experiments devoted to storing very cold neutrons in vessels whose walls are made from structures involving a spatial inhomogeneity of the average Fermi potential. The possibility of storing neutrons owing to diffusion reflection from the walls is shown, and prospects of elaborating the method are discussed.

Flexible polyvinyl chloride neutron guides for transporting ultracold and very cold neutrons

The transmission of ultracold neutrons (UCNs) through flexible polyvinyl chloride (PVC) tubes with lengths of up to 3 m and an internal diameter of 6–8 mm has been studied. High UCN transmission is found even for arbitrarily bent tubes (single bend, double bend, triple bend, figure eight, etc.). The transmission can be improved significantly by coating the inner surface of the tube with a thin layer of liquid fluorine polymer. The prospects of these neutron guides in fundamental and applied research are discussed.

Observation of selective enhancement of the capture of ultracold neutrons by nuclei

The subbarrier reflection of ultracold neutrons (UCNs) from stainless steel (an alloy of iron, nickel, chromium, and titanium) is investigated by means of neutron-radiation analysis. It is found that the increase in the probability of capture of UCNs by nuclei is large compared to the standard theory. The effect is selective, the enhancement factor varying From 3 for iron to 90 for titanium.

Cluster structure of the material surface as the cause of the selective enhancement of ultracold-neutron capture associated with subbarrier reflection

Neutron-radiation analysis is used to investigate the subbarrier reflection of ultracold neutrons from the surface of a titanium-stabilized Fe-Ni-Cr stainless steel. A significant selective increase in the probability of neutron capture by nuclei of the medium in comparison to theory is discovered. An explanation is given for the effect, which is associated with the existence of titanium-containing clusters and structural defects that distort the form of the distribution of the effective interaction potential between ultracold neutrons and the material surface.

Storage of ultracold neutrons in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice

The possibility of attaining the calculated probabilities of the losses of ultracold neutrons (UCN) stored in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice is tested experimentally. It is found that UCN hitting the walls of a graphite vessel undergo additional inelastic scattering not predicted by the theory. It is shown that this scattering may be due to the presence of surface hydrogen that provides a channel of UCN leakage slightly varying with temperature. For vessels whose walls are coated with fluorine polymer oil, additional inelastic UCN scattering is also observed and is found to be efficiently suppressed with decreasing temperature. The experimentally observed and calculated values of the probabilities of UCN losses are shown to be in good agreement for vessels whose walls are made from heavy-water ice.