359 research outputs found
Universality and Critical Behavior at the Critical-End-Point on Itinerant-Metamagnet UCoAl
We performed nuclear-magnetic-resonance (NMR) measurements on
itinerant-electron metamagnet UCoAl in order to investigate the critical
behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We
derived c-axis magnetization and its fluctuation from the
measurements of Knight shift and nuclear spin-lattice relaxation rate
as a function of the c-axis external field () and temperature (). We
developed contour plots of and on the - phase diagram,
and observed the strong divergence of at the CEP. The critical exponents
of and near the CEP are estimated, and found to be close to the
universal properties of a three-dimensional (3-D) Ising model. We indicate that
the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common
feature as a gas-liquid transition.Comment: 8 Pages, 14 figure
Candidate chiral doublet bands in the odd-odd nucleus Cs
The candidate chiral doublet bands recently observed in Cs have been
extended to higher spins, several new linking transitions between the two
partner members of the chiral doublet bands are observed, and
intensities related to the chiral doublet bands are presented by
analyzing the coincidence data collected earlier at the
NORDBALL through the CdN, 4nCs reaction at a beam
energy of 65 MeV. The intraband and interband
ratios and the energy staggering parameter, S(I), have
been deduced for these doublet bands. The results are found to be consistent
with the chiral interpretation for the two structures. Furthermore, the
observation of chiral doublet bands in Cs together with those in
Cs, Cs, Cs and Cs also indicates that the
chiral conditions do not change rapidly with decreasing neutron number in these
odd-odd Cesium isotopes
Equilibrium magnetisation structures in ferromagnetic nanorings
The ground state of the ring-shape magnetic nanoparticle is studied.
Depending on the geometrical and magnetic parameters of the nanoring, there
exist different magnetisation configurations (magnetic phases): two phases with
homogeneous magnetisation (easy-axis and easy-plane phases) and two
inhomogeneous (planar vortex phase and out-of-plane one). The existence of a
new intermediate out-of-plane vortex phase, where the inner magnetisation is
not strongly parallel to the easy axis, is predicted. Possible transitions
between different phases are analysed using the combination of analytical
calculations and micromagnetic simulations.Comment: LaTeX, 19 pages, 11 figure
First application of the Trojan Horse Method with a Radioactive Ion Beam: study of the F()O}} reaction at astrophysical energies
Measurement of nuclear cross sections at astrophysical energies involving
unstable species is one of the most challenging tasks in experimental nuclear
physics. The use of indirect methods is often unavoidable in this scenario. In
this paper the Trojan Horse Method is applied for the first time to a
radioactive ion beam induced reaction studying the
F()O process at low energies relevant to astrophysics
via the three body reaction H(F,O)n. The knowledge
of the F()O reaction rate is crucial to understand
the nova explosion phenomena. The cross section of this reaction is
characterized by the presence of several resonances in Ne and possibly
interference effects among them. The results reported in Literature are not
satisfactory and new investigations of the F()O
reaction cross section will be useful. In the present work the spin-parity
assignments of relevant levels have been discussed and the astrophysical
S-factor has been extracted considering also interference effectsComment: 7 pages, 4 figure
Further Evidence for the Decay K+ to pi+ neutrino-antineutrino
Additional evidence for the rare kaon decay K+ to pi+ neutrino-antineutrino
has been found in a new data set with comparable sensitivity to the previously
reported result. One new event was observed in the pion momentum region
examined, 211<P<229 MeV/c, bringing the total for the combined data set to two.
Including all data taken, the backgrounds were estimated to contribute 0.15 pm
0.05 events. The branching ratio is B=1.57^{+1.75}_{-0.82} 10^{-10}.Comment: 10 pages, 2 figure
Measurement of Direct Photon Emission in K^+ -> pi^+ pi^0 gamma Decay
We have performed a measurement of the K^+ -> pi^+ pi^0 gamma decay and have
observed 2 X 10^4 events. The best fit to the decay spectrum gives a branching
ratio for direct photon emission of (4.7\pm0.8\pm0.3) X 10^{-6} in the pi^+
kinetic energy region of 55 to 90 MeV and requires no component due to
interference with inner bremsstrahlung.Comment: 9 pages, 3 figures. To be submitted to PR
Search for the decay in the momentum region
We have searched for the decay in the kinematic
region with pion momentum below the peak. One event was
observed, consistent with the background estimate of . This
implies an upper limit on
(90% C.L.), consistent with the recently measured branching ratio of
, obtained using the standard model
spectrum and the kinematic region above the peak. The
same data were used to search for , where is a weakly
interacting neutral particle or system of particles with .Comment: 4 pages, 2 figure
Nuclear structure of 30S and its implications for nucleosynthesis in classical novae
The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature
range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude
due to the uncertain location of two previously unobserved 3+ and 2+ resonances
in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of
silicon isotopes synthesized in novae, which are relevant for the
identification of presolar grains of putative nova origin, were uncertain by a
factor of 3. To investigate the level structure of 30S above the proton
threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam
gamma-ray spectroscopy experiments were performed. Differential cross sections
of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born
approximation calculations were performed to constrain the spin-parity
assignments of the observed levels. An energy level scheme was deduced from
gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction.
Spin-parity assignments based on measurements of gamma-ray angular
distributions and gamma-gamma directional correlation from oriented nuclei were
made for most of the observed levels of 30S. As a result, the resonance
energies corresponding to the excited states in 4.5 MeV - 6 MeV region,
including the two astrophysically important states predicted previously, are
measured with significantly better precision than before. The uncertainty in
the rate of the 29P(p,gamma)30S reaction is substantially reduced over the
temperature range of interest. Finally, the influence of this rate on the
abundance ratios of silicon isotopes synthesized in novae are obtained via 1D
hydrodynamic nova simulations.Comment: 22 pages, 12 figure
The Magnetic Phase Diagram and the Pressure and Field Dependence of the Fermi Surface in UGe
The ac susceptibility and de Haas-van Alphen (dHvA) effect in UGe are
measured at pressures {\it P} up to 17.7 kbar for the magnetic field {\it B}
parallel to the {\it a} axis, which is the easy axis of magnetization. Two
anomalies are observed at {\it B}({\it P}) and {\it B}({\it P}) ({\it
B} {\it B} at any {\it P}), and the {\it P}-{\it B} phase diagram
is presented. The Fermi surface and quasiparticle mass are found to vary
smoothly with pressure up to 17.7 kbar unless the phase boundary {\it
B}({\it P}) is crossed. The observed dHvA frequencies may be grouped into
three according to their pressure dependences, which are largely positive,
nearly constant or negative. It is suggested that the quasiparticle mass
moderately increases as the boundary {\it B}({\it P}) is approached. DHvA
effect measurements are also performed across the boundary at 16.8 kbar.Comment: to be published in Phys. Rev.
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