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We present estimations of systematic corrections and results of their experimental studies for our neutron lifetime experiment carried out in 2008-2010 at ILL. Taking into account these systematic corrections, we reduce the data of three independent sets of measurements (obtained during period 2008-2010) performed with different energy spectra of ultracold neutrons (UCNs) at different trap temperatures to the mean neutron lifetime value equal to 880.2(1.2) s.

224New results of neutron lifetime measurements have recently appeared [1][2][3], which noticeably (by 5-6 s) differ from a world average value of 885.7(0.8) s [4]. Since a noticeable contribution to the world average value came from the value τ β = 885.4 ± 0.9 stat ± 0.4 syst s presented in our work [5], we additionally analyzed this result. Moreover, this result was critically analyzed in [6,7].The method of measurement of τ β in [5] was based on the storage of ultracold neutrons in two vessels with liquid fluoropolymer coating and different frequencies of collisions of ultracold neutrons with the walls (Fig. 1). In geometries 1 and 2, neutrons were stored inside vessel 7 and in the slit space between vessels 7 and 8, respectively. The vacuum housing of the vessel was surrounded by 24 thermal neutron counters 10, which detected ultracold neutrons that inelastically scattered from the vessel walls.In the process of storage of ultracold neutrons, the total probabilities of their leakage from the vessels were determined:Here, , , , and are the numbers of ultracold neutrons detected when leaking from the vessels, T (1) and T (2) are the durations of the storage intervals (superscripts 1 and 2 mark geometries and subscripts i and f refer to the initial and final times of storage, respectively), λ β = 1/τ β , and the probabilitiesof loss of ultracold neutrons interacting with the vessel walls are given by the expressions Here, ε (1) and ε (2) are the efficiencies of the detection of ultracold neutrons, J (1) and J (2) are the numbers of neutrons detected by external detector 10 in the stor age interval, and are the efficiencies of the detection of inelastically scattered ultracold neutrons, and σ ie and σ c are the probabilities of the inelastic scat tering and capture of ultracold neutrons interacting with the walls of the vessel. If ε (1) = ε (2) and = , the ratio of the loss probabilities is ξ = = ; therefore, λ β = .A more accurate relation for ξ associated with the use of a wide spectrum of ultracold neutrons was given in [5,8].The statistical error of the result λ β was determined in terms of the statistical errors of the measurement of six quantities , , , , J (1) , and J (2) tak ing into account the data on the time dependence of the count rate of detectors of thermal neutrons j (1) (t) and j (2) (t) in the storage intervals. The systematic errorCorrections have been introduced into the result τ β = 885.4 ± 0.9 stat ± 0.4 syst s of our measurements of the neu tron lifetime. The corrected value is τ β = 881.6 ± 0.8 stat ± 1.9 syst s.

No abstract

For more than a decade, detonation nanodiamond (DND) powders have been actively studied as a material for efficient reflectors of very cold neutrons (VCNs) and cold neutrons. In this work, we experimentally demonstrate, for the first time, the possibility of enhanced directional extraction of a VCN beam using a reflector made of fluorinated DND powder. With respect to the theoretical flux calculated from an isotropic source at the bottom of the reflector cavity, the gain in the VCN flux density along the beam axis is ∼10 for the neutron velocities of ∼57 and ∼75 m/s. The use of such reflectors for enhanced directional extraction of VCN from neutron sources will make it possible to noticeably increase the neutron fluxes delivered to experiments and expand the scope of VCN applications.