2,246 research outputs found
Nuclear pumped laser II
The first direct nuclear pumped laser using the He-2-(n,p) H-3 reaction is reported. Lasing took place on the 1.79 microns Ar I transition in a mixture of He-3-Ar at approximately 600 Torr total pressure. It was found that the electrically pulsed afterglow He-Ar laser had the same concentration profile as the nuclear pumped laser. As a result, nuclear lasing was also achieved in He-3-Xe (2.027 micron) and He-3-Kr (2.52 micron). Scaling of laser output with both thermal flux and total pressure as well as minority concentration has been completed. A peak output (He-3-Ar) of 3.7 watts has been achieved at a total pressure of 4 atm. Direct nuclear pumping of He-3-Ne has also been achieved. Nuclear pumping of a He-3-NF3 mixture was attempted, lasing in FI at approximately 7000 A, without success, although the potential lasing transitions appeared in spontaneous emission. Both NF3 and 238UF6 appear to quench spontaneous emission when they constitute more than 1% of the gas mixture
Recent s from IceCube
IceCube is a 1 km neutrino detector now being built at the South Pole.
Its 4800 optical modules will detect Cherenkov radiation from charged particles
produced in neutrino interactions. IceCube will search for neutrinos of
astrophysical origin, with energies from 100 GeV up to eV. It will be
able to separate , and . In addition to detecting
astrophysical neutrinos, IceCube will also search for neutrinos from WIMP
annihilation in the Sun and the Earth, look for low-energy (10 MeV) neutrinos
from supernovae, and search for a host of exotic signatures. With the
associated IceTop surface air shower array, it will study cosmic-ray air
showers.
IceCube construction is now 50% complete. After presenting preliminary
results from the partial detector, I will discuss IceCube's future plans.Comment: Invited talk presented at Neutrino 2008; 7 page
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy
The Modular Neutron Array (MoNA) and 4 Tm Sweeper magnet were used to measure
the free neutrons and heavy charged particles from the radioactive ion beam
induced 32Mg + 9Be reaction. The fragmentation reaction was simulated with the
Constrained Molecular Dynamics model(CoMD), which demonstrated that the
of the heavy fragments and free neutron multiplicities were observables
sensitive to the density dependence of the symmetry energy at sub-saturation
densities. Through comparison of these simulations with the experimental data
constraints on the density dependence of the symmetry energy were extracted.
The advantage of radioactive ion beams as a probe of the symmetry energy is
demonstrated through examination of CoMD calculations for stable and
radioactive beam induced reactions
Angular Alignment Testing of Laser Mirror Mounts Under Temperature Cycling
A number of commercial and custom-built laser mirror mounts were tested for angular alignment sensitivity during temperature cycling from room temperature (20 C) to 40 C. A Nd:YAG laser beam was reflected off a mirror that was held by the mount under test and was directed to a position-sensitive detector. Horizontal and vertical movement of the reflected beam was recorded, and the angular movement, as a function of temperature (coefficient of thermal tilt (CTT)) was calculated from these data. In addition, the amount of hysteresis in the movement after cycling from room temperature to 40 C and back was determined. All commercial mounts showed greater angular movement than the simpler National Aeronautics and Space Administration Lidar Atmospheric Sensing Experiment (NASA LASE) custom mirror mounts
Three-body correlations in the ground-state decay of 26O
Background: Theoretical calculations have shown that the energy and angular
correlations in the three-body decay of the two-neutron unbound O26 can provide
information on the ground-state wave function, which has been predicted to have
a dineutron configuration and 2n halo structure.
Purpose: To use the experimentally measured three-body correlations to gain
insight into the properties of O26, including the decay mechanism and
ground-state resonance energy.
Method: O26 was produced in a one-proton knockout reaction from F27 and the
O24+n+n decay products were measured using the MoNA-Sweeper setup. The
three-body correlations from the O26 ground-state resonance decay were
extracted. The experimental results were compared to Monte Carlo simulations in
which the resonance energy and decay mechanism were varied.
Results: The measured three-body correlations were well reproduced by the
Monte Carlo simulations but were not sensitive to the decay mechanism due to
the experimental resolutions. However, the three-body correlations were found
to be sensitive to the resonance energy of O26. A 1{\sigma} upper limit of 53
keV was extracted for the ground-state resonance energy of O26.
Conclusions: Future attempts to measure the three-body correlations from the
ground-state decay of O26 will be very challenging due to the need for a
precise measurement of the O24 momentum at the reaction point in the target
Status of neutrino astronomy
Astrophysical neutrinos can be produced in proton interactions of charged
cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in
balloon, satellite and air shower experiments every day, from below 1e9 eV up
to macroscopic energies of 1e21 eV. The observation of different photon fields
has been done ever since, today with detections ranging from radio wavelengths
up to very high-energy photons in the TeV range. The leading question for
neutrino astronomers is now which sources provide a combination of efficient
proton acceleration with sufficiently high photon fields or baryonic targets at
the same time in order to produce a neutrino flux that is high enough to exceed
the background of atmospheric neutrinos. There are only two confirmed
astrophysical neutrino sources up to today: the sun and SuperNova 1987A emit
and emitted neutrinos at MeV energies. The aim of large underground Cherenkov
telescopes like IceCube and KM3NeT is the detection of neutrinos at energies
above 100 GeV. In this paper, recent developments of neutrino flux modeling for
the most promising extragalactic sources, gamma ray bursts and active galactic
nuclei, are presented.Comment: Talk given at Neutrino 2008, Christchurch (New Zealand) 6 pages, 4
figures, 1 tabl
Search for unbound 15Be states in the 3n+12Be channel
15Be is expected to have low-lying 3/2+ and 5/2+ states. A first search did
not observe the 3/2+ [A. Spyrou et al., Phys. Rev. C 84, 044309 (2011)],
however, a resonance in 15Be was populated in a second attempt and determined
to be unbound with respect to 14Be by 1.8(1) MeV with a tentative spin-parity
assignment of 5/2+ [J. Snyder et al., Phys. Rev. C 88, 031303(R) (2013)].
Search for the predicted 15Be 3/2+ state in the three-neutron decay channel. A
two-proton removal reaction from a 55 MeV/u 17C beam was used to populate
neutron-unbound states in 15Be. The two-, three-, and four-body decay energies
of the 12Be + neutron(s) detected in coincidence were reconstructed using
invariant mass spectroscopy. Monte Carlo simulations were performed to extract
the resonance and decay properties from the observed spectra. The low-energy
regions of the decay energy spectra can be described with the first excited
unbound state of 14Be (E_x=1.54 MeV, E_r=0.28 MeV). Including a state in 15Be
that decays through the first excited 14Be state slightly improves the fit at
higher energies though the cross section is small. A 15Be component is not
needed to describe the data. If the 3/2+ state in 15Be is populated, the decay
by three-neutron emission through 14Be is weak, less than or equal to 11% up to
4 MeV. In the best fit, 15Be is unbound with respect to 12Be by 1.4 MeV
(unbound with respect to $14Be by 2.66 MeV) with a strength of 7%.Comment: 6 pages, 5 figures, accepted in Physical Review
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