95 research outputs found
Polarization of superfluid turbulence
We show that normal fluid eddies in turbulent helium II polarize the tangle
of quantized vortex lines present in the flow, thus inducing superfluid
vorticity patterns similar to the driving normal fluid eddies. We also show
that the polarization is effective over the entire inertial range. The results
help explain the surprising analogies between classical and superfluid
turbulence which have been observed recently.Comment: 3 figure
Measurement of the neutron lifetime using an asymmetric magneto- gravitational trap and in situ detection
The precise value of the mean neutron lifetime, , plays an important
role in nuclear and particle physics and cosmology. It is a key input for
predicting the ratio of protons to helium atoms in the primordial universe and
is used to search for new physics beyond the Standard Model of particle
physics. There is a 3.9 standard deviation discrepancy between
measured by counting the decay rate of free neutrons in a beam (887.7 2.2
s) and by counting surviving ultracold neutrons stored for different storage
times in a material trap (878.50.8 s). The experiment described here
eliminates loss mechanisms present in previous trap experiments by levitating
polarized ultracold neutrons above the surface of an asymmetric storage trap
using a repulsive magnetic field gradient so that the stored neutrons do not
interact with material trap walls and neutrons in quasi-stable orbits rapidly
exit the trap. As a result of this approach and the use of a new in situ
neutron detector, the lifetime reported here (877.7 0.7 (stat) +0.4/-0.2
(sys) s) is the first modern measurement of that does not require
corrections larger than the quoted uncertainties.Comment: 9 pages, 3 figures, 2 table
A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)
A new boron-coated CCD camera is described for direct detection of ultracold
neutrons (UCN) through the capture reactions B
(n,0)Li (6%) and B(n,1)Li (94%).
The experiments, which extend earlier works using a boron-coated ZnS:Ag
scintillator, are based on direct detections of the neutron-capture byproducts
in silicon. The high position resolution, energy resolution and particle ID
performance of a scientific CCD allows for observation and identification of
all the byproducts , Li and (electron recoils). A
signal-to-noise improvement on the order of 10 over the indirect method has
been achieved. Sub-pixel position resolution of a few microns is demonstrated.
The technology can also be used to build UCN detectors with an area on the
order of 1 m. The combination of micrometer scale spatial resolution, few
electrons ionization thresholds and large area paves the way to new research
avenues including quantum physics of UCN and high-resolution neutron imaging
and spectroscopy.Comment: 10 pages, 8 figure
Recommended from our members
Conceptual design of large-bore superconducting quadrupoles with active magnetic shielding for the AHF
The Advanced Hydrotest Facility, under study by LANL, utilizes large-bore superconducting quadrupole magnets. In the paper we discuss the conceptual design of such quadrupoles using active shielding. The magnets are specified to achieve gradients of up to 24T/m with a 28-cm warm bore and to have 0.01% field quality. Concepts for the magnet cryosystems and quench protection are also briefly discussed to confirm the reliability of the proposed design
Status of the UCNÏ„ experiment
The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τ_n = 877.7s (0.7s)_(stat) (+0.4/−0.2s)_(sys). We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ
Recommended from our members
Magnetic design of large-bore superconducting quadrupoles for the AHF.
The Advanced Hydrotest Facility (ANF), under study by LANL, utilizes large-bore superconducting quadrupole magnets to image protons for radiography of fast events. In this concept, 50-GeV proton bunches pass through a thick object and are imaged by a lens system that analyzes the scattered beam to determine object details. Twelve simultaneous views of the object are obtained using multiple beam lines. The lens system uses two types of quadrupoles: a large bore (48-cm beam aperture) for wide field of view imaging and a smaller bore (23 cm aperture) for higher resolution images. The gradients of the magnets are 10.14 T/m and 18.58 T/m with magnetic lengths of 4.3 m and 3.0 m, respectively. The magnets are sufficiently novel to present a design challenge. Evaluation and comparisons were made for various types of magnet design: shell and racetrack coils, cold and warm iron, as well as an active superconducting screen. Nb{sub 3}Sn cable was also considered as an alternative to avoid quenching under high beam-scattering conditions. The superconducting shield concept eliminates the iron core and greatly lessens the cryogenic energy needed for cool down. Several options are discussed and comparisons are made
Recommended from our members
A compact layout for a 50 GeV proton radiography facility
We describe a new compact layout for a 50 GeV proton radiography facility. The more compact design utilizes two-point extraction from the main ring to drive an optimal 8 view imaging system. The lattice design of both the main ring, and of the corresponding 8.5 GeV booster ring is described. The rings have very good longitudinal stability, which is of interest for other applications of high current proton machines in this energy range
Monte Carlo of Trapped Ultracold Neutrons in the UCNÏ„ Trap
In the UCNτ experiment, ultracold neutrons (UCN) are confined by magnetic fields and the Earth’s gravitational field. Field-trapping mitigates the problem of UCN loss on material surfaces, which caused the largest correction in prior neutron experiments using material bottles. However, the neutron dynamics in field traps differ qualitatively from those in material bottles. In the latter case, neutrons bounce off material surfaces with significant diffusivity and the population quickly reaches a static spatial distribution with a density gradient induced by the gravitational potential. In contrast, the field-confined UCN—whose dynamics can be described by Hamiltonian mechanics—do not exhibit the stochastic behaviors typical of an ideal gas model as observed in material bottles. In this report, we will describe our efforts to simulate UCN trapping in the UCNτ magneto-gravitational trap. We compare the simulation output to the experimental results to determine the parameters of the neutron detector and the input neutron distribution. The tuned model is then used to understand the phase space evolution of neutrons observed in the UCNτ experiment. We will discuss the implications of chaotic dynamics on controlling the systematic effects, such as spectral cleaning and microphonic heating, for a successful UCN lifetime experiment to reach a 0.01% level of precision
- …