90 research outputs found
Calculation of the ultracold neutron upscattering loss probability in fluid walled storage bottles using experimental measurements of the thermomechanical properties of Fomblin
We present experimental measurements of the properties of a liquid "Fomblin"
surface obtained by the quasielastic scattering of laser light. The properties
include the surface tension and viscosity as a function of temperature. The
results are compared to the measurements of the bulk fluid properties.
We then calculate the upscattering rate of ultracold neutrons (UCN) from
thermally excited surface capillary waves on the liquid surface and compare the
results to experimental measurements of the UCN lifetime in Fomblin
fluid-walled UCN storage bottles, and show that the excess loss rate for UCN
energies near the Fomblin potential can be explained. The rapid temperature
dependence of the Fomblin storage lifetime is explained by our analysis.Comment: 25 pages, 13 figures; 2nd version corrects several error
Neutron Lifetime Measured with Stored Ultracold Neutrons
The neutron lifetime has been measured by counting the neutrons remaining in a fluid-walled bottle as a function of the duration of storage. Losses of neutrons caused by the wall reflections are eliminated by varying the bottle volume-to-surface ratio. The result obtained is τβ=887.6±3 s
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
Neutron lifetime measurements using gravitationally trapped ultracold neutrons
Our experiment using gravitationally trapped ultracold neutrons (UCN) to
measure the neutron lifetime is reviewed. Ultracold neutrons were trapped in a
material bottle covered with perfluoropolyether. The neutron lifetime was
deduced from comparison of UCN losses in the traps with different
surface-to-volume ratios. The precise value of the neutron lifetime is of
fundamental importance to particle physics and cosmology. In this experiment,
the UCN storage time is brought closer to the neutron lifetime than in any
experiments before:the probability of UCN losses from the trap was only 1% of
that for neutron beta decay. The neutron lifetime
obtained,878.5+/-0.7stat+/-0.3sys s, is the most accurate experimental
measurement to date.Comment: 38 pages, 19 figures,changed conten
Testing the Unitarity of the CKM Matrix with a Space-Based Neutron Decay Experiment
If the Standard Model is correct, and fundamental fermions exist only in the
three generations, then the CKM matrix should be unitary. However, there
remains a question over a deviation from unitarity from the value of the
neutron lifetime. We discuss a simple space-based experiment that, at an orbit
height of 500 km above Earth, would measure the kinetic-energy, solid-angle,
flux spectrum of gravitationally bound neutrons (kinetic energy K<0.606 eV at
this altitude). The difference between the energy spectrum of neutrons that
come up from the Earth's atmosphere and that of the undecayed neutrons that
return back down to the Earth would yield a measurement of the neutron
lifetime. This measurement would be free of the systematics of laboratory
experiments. A package of mass kg could provide a 10^{-3} precision in
two years.Comment: 10 pages, 4 figures. Revised and updated for publicatio
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
The Evaluation of V_{ud}, Experiment and Theory
The value of the V_{ud} matrix element of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix can be derived from nuclear superallowed beta decays, neutron decay, and
pion beta decay. We survey current world data for all three. Today, the most
precise value of V_{ud} comes from the nuclear decays; however, the precision
is limited not by experimental error but by the estimated uncertainty in
theoretical corrections. Experimental uncertainty does limit the neutron-decay
result, which, though statistically consistent with the nuclear result, is
approximately a factor of three poorer in precision. The value obtained for
leads to a result that differs at the 98% confidence level from the
unitarity condition for the CKM matrix. We examine the reliability of the small
calculated corrections that have been applied to the data, and assess the
likelihood of even higher quality nuclear data becoming available to confirm or
deny the discrepancy. Some of the required experiments depend upon the
availability of intense radioactive beams. Others are possible today.Comment: 21 pages, 1 figure, LaTe
Measurement of the Neutron Lifetime by Counting Trapped Protons in a Cold Neutron Beam
A measurement of the neutron lifetime performed by the absolute
counting of in-beam neutrons and their decay protons has been completed.
Protons confined in a quasi-Penning trap were accelerated onto a silicon
detector held at a high potential and counted with nearly unit efficiency. The
neutrons were counted by a device with an efficiency inversely proportional to
neutron velocity, which cancels the dwell time of the neutron beam in the trap.
The result is s, which
is the most precise measurement of the lifetime using an in-beam method. The
systematic uncertainty is dominated by neutron counting, in particular the mass
of the deposit and the Li({\it{n,t}}) cross section. The measurement
technique and apparatus, data analysis, and investigation of systematic
uncertainties are discussed in detail.Comment: 71 pages, 20 figures, 9 tables; submitted to PR
Right Handed Weak Currents in Sum Rules for Axialvector Constant Renormalization
The recent experimental results on deep inelastic polarized lepton scattering
off proton, deuteron and He together with polari% zed neutron
-decay data are analyzed. It is shown that the problem of Ellis-Jaffe
and Bjorken sum rules deficiency and the neutron paradox could be solved
simultaneously by assuming the small right handed current (RHC) admixture in
the weak interaction Lagrangian. The possible RHC impact on pion-nucleon
-term and Gamow-Teller sum rule for nuclear reactions is
pointed out.Comment: to be published in Phys. Rev. Lett. LaTeX, 8 pages, 21 k
Mineral-PET: Kimberlite sorting by nuclear-medical technology
A revolutionary new technology for diamond bearing rock sorting which has its roots in medical-nuclear physics has been taken through a substantial part of the R&D phase. This has led to the construction of the technology demonstrator. Experiments using the technology demonstrator and experiments at a hospital have established the scientific and technological viability of the project
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