162 research outputs found
UCN anomalous losses and the UCN capture cross-section on material defects
Experimental data shows anomalously large Ultra Cold Neutrons (UCN)
reflection losses and that the process of UCN reflection is not completely
coherent. UCN anomalous losses under reflection cannot be explained in the
context of neutron optics calculations. UCN losses by means of incoherent
scattering on material defects are considered and cross-section values
calculated. The UCN capture cross-section on material defects is enhanced by a
factor of 10^4 due to localization of UCN around defects. This phenomenon can
explain anomalous losses of UCN.Comment: 13 pages, 4 figure
Measurement of the neutron lifetime using a gravitational trap and a low-temperature Fomblin coating
We present a new value for the neutron lifetime of 878.5 +- 0.7 stat. +- 0.3
syst. This result differs from the world average value (885.7 +- 0.8 s) by 6.5
standard deviations and by 5.6 standard deviations from the previous most
precise result. However, this new value for the neutron lifetime together with
a beta-asymmetry in neutron decay, Ao, of -0.1189(7) is in a good agreement
with the Standard Model.Comment: 11 pages, 9 figures; extended content with some correction
A New World Average Value for the Neutron Lifetime
The analysis of the data on measurements of the neutron lifetime is
presented. A new most accurate result of the measurement of neutron lifetime
[Phys. Lett. B 605 (2005) 72] 878.5 +/- 0.8 s differs from the world average
value [Phys. Lett. B 667 (2008) 1] 885.7 +/- 0.8 s by 6.5 standard deviations.
In this connection the analysis and Monte Carlo simulation of experiments
[Phys. Lett. B 483 (2000) 15] and [Phys. Rev. Lett. 63 (1989) 593] is carried
out. Systematic errors of about -6 s are found in each of the experiments. The
summary table for the neutron lifetime measurements after corrections and
additions is given. A new world average value for the neutron lifetime 879.9
+/- 0.9 s is presented.Comment: 27 pages, 13 figures; Fig.13 update
Nanoparticles as a possible moderator for an ultracold neutron source
Ultracold and very cold neutrons (UCN and VCN) interact strongly with
nanoparticles due to the similarity of their wavelengths and nanoparticles
sizes. We analyze the hypothesis that this interaction can provide efficient
cooling of neutrons by ultracold nanoparticles at certain experimental
conditions, thus increasing the density of UCN by many orders of magnitude. The
present analytical and numerical description of the problem is limited to the
model of independent nanoparticles at zero temperature. Constraints of
application of this model are discussed
New Understanding of Ultra-Cold Neutron Production in Solid Deuterium
Our recent neutron scattering measurements of phonons and other
quasi-particle excitations in solid deuterium (sD) and the extraction of
the density of states for phonons and rotational transitions in sD2 have led us
to a new understanding of the production of ultra-cold neutrons (UCN) in sD2.
This new picture is somehow different to earlier published results for sD2. The
cross section for UCN production in sD2 has been determined by using the
density of states G1(E) in combination with the incoherent approximation and by
a direct calibration of our measured neutron cross sections with the known
cross section of the J=1 -> 0 rotational transition in deuterium. Both methods
deliver new data on this cross section and agree quite well with direct
measurements of this energy averaged UCN production cross section.Comment: 4 pages, 6 figure
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