898 research outputs found
Necessary conditions for accurate computations of three-body partial decay widths
The partial width for decay of a resonance into three fragments is largely
determined at distances where the energy is smaller than the effective
potential producing the corresponding wave function. At short distances the
many-body properties are accounted for by preformation or spectroscopic
factors. We use the adiabatic expansion method combined with the WKB
approximation to obtain the indispensable cluster model wave functions at
intermediate and larger distances. We test the concept by deriving conditions
for the minimal basis expressed in terms of partial waves and radial nodes. We
compare results for different effective interactions and methods. Agreement is
found with experimental values for a sufficiently large basis. We illustrate
the ideas with realistic examples from -emission of C and
two-proton emission of Ne. Basis requirements for accurate momentum
distributions are briefly discussed.Comment: To be published in Physical Review
Recommendations for Care of the Asymptomatic Patient
We present a set of reasonable guidelines for the care of healthy, asymptomatic individuals based upon recommendations prepared by an Internal Medicine review committee of Henry Ford Hospital. There recommendations have four goals: to prevent disease, to detect disease in an asymptomatic and potentially curable state, to enhance the patient\u27s quality of life, and to help physicians teach patients good health habits. Recommendations are made for infectious diseases, cancer, metabolic diseases, neurosensory conditions like visual and hearing loss, and general health habits. Some recommendations are at variance with those of well recognized authorities and should be viewed only as a suggested protocol for the care of the asymptomatic patient. Results of ongoing studies may alter our understanding of some areas of controversy and mandate revision of these guidelines periodically
Intermediate energy Coulomb excitation as a probe of nuclear structure at radioactive beam facilities
The effects of retardation in the Coulomb excitation of radioactive nuclei in
intermediate energy collisions (Elab ~100 MeV/nucleon) are investigated. We
show that the excitation cross sections of low-lying states in 11Be,
{38,40,42}S and {44,46}Ar projectiles incident on gold and lead targets are
modified by as much as 20% due to these effects. The angular distributions of
decaying gamma-rays are also appreciably modified.Comment: 21 pages, 3 figures, Phys. Rev. C, in pres
Beta decay radiation signature from neutron-rich gamma-ray bursts?
Core collapse of massive stars and binary neutron stars or black hole-neutron
star binary mergers are likely progenitors of long and short duration gamma-ray
bursts respectively. Neutronized material in the former and neutron star
material in the latter are ejected by the central engine implying a
neutron-rich jet outflow. A free neutron, however, beta decays to a proton, an
electron (beta) and an anti-neutrino in about fifteen minutes in its rest
frame. Sudden creation of a relativistic electron is accompanied by radiation
with unique temporal and spectral signature. We calculate here this radiation
signature collectively emitted by all beta decay electrons from neutron-rich
outflow. Detection of this signature may thus provide strong evidence for not
only neutron but also for proton content in the relativistic gamma-ray burst
jets.Comment: 11 pages, 2 figures, reference added, published versio
Identification of mixed-symmetry states in an odd-mass nearly-spherical nucleus
The low-spin structure of 93Nb has been studied using the (n,n' gamma)
reaction at neutron energies ranging from 1.5 to 3.0 MeV and the 94Zr(p,2n
gamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at
1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states
associated with the coupling of a proton hole in the p_1/2 orbit to the 2+_1,ms
state in 94Mo. These assignments are derived from the observed M1 and E2
transition strengths to the symmetric one-phonon states, energy systematics,
spins and parities, and comparison with shell model calculations.Comment: 5 pages, 3 figure
Physics at a Neutrino Factory
In response to the growing interest in building a Neutrino Factory to produce
high intensity beams of electron- and muon-neutrinos and antineutrinos, in
October 1999 the Fermilab Directorate initiated two six-month studies. The
first study, organized by N. Holtkamp and D. Finley, was to investigate the
technical feasibility of an intense neutrino source based on a muon storage
ring. This design study has produced a report in which the basic conclusion is
that a Neutrino Factory is technically feasible, although it requires an
aggressive R&D program. The second study, which is the subject of this report,
was to explore the physics potential of a Neutrino Factory as a function of the
muon beam energy and intensity, and for oscillation physics, the potential as a
function of baseline.Comment: 133 pages, 64 figures. Report to the Fermilab Directorate. Available
from http://www.fnal.gov/projects/muon_collider/ This version fixes some
printing problem
A new parametric equation of state and quark stars
It is still a matter of debate to understand the equation of state of cold
supra-nuclear matter in compact stars because of unknown on-perturbative strong
interaction between quarks. Nevertheless, it is speculated from an
astrophysical view point that quark clusters could form in cold quark matter
due to strong coupling at realistic baryon densities. Although it is hard to
calculate this conjectured matter from first principles, one can expect the
inter-cluster interaction to share some general features to nucleon-nucleon
interaction. We adopt a two-Gaussian component soft-core potential with these
general features and show that quark clusters can form stable simple cubic
crystal structure if we assume Gaussian form wave function. With this
parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable
constrained parameter space to give mass-radius relation of crystalline solid
quark star. With baryon densities truncated at 2 times nuclear density at
surface and range of interaction fixed at 2fm we can reproduce similar
mass-radius relation to that obtained with bag model equations of state. The
maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar
mass (about 2 solar mass) is then used to constrain parameters of this simple
interaction potential.Comment: 5 pages, 2 figure
A Deeper Look at Student Learning of Quantum Mechanics: the Case of Tunneling
We report on a large-scale study of student learning of quantum tunneling in
4 traditional and 4 transformed modern physics courses. In the transformed
courses, which were designed to address student difficulties found in previous
research, students still struggle with many of the same issues found in other
courses. However, the reasons for these difficulties are more subtle, and many
new issues are brought to the surface. By explicitly addressing how to build
models of wave functions and energy and how to relate these models to real
physical systems, we have opened up a floodgate of deep and difficult questions
as students struggle to make sense of these models. We conclude that the
difficulties found in previous research are the tip of the iceberg, and the
real issue at the heart of student difficulties in learning quantum tunneling
is the struggle to build the complex models that are implicit in experts'
understanding but often not explicitly addressed in instruction.Comment: v2, v3 updated with more detailed analysis of data and discussion;
submitted to Phys. Rev. ST: PE
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