151 research outputs found
All Coronal Loops are the Same: Evidence to the Contrary
The 1998 April 20 spectral line data from the Coronal Diagnostics
Spectrometer (CDS) on the {\it Solar and Heliospheric Observatory} (\SOHO)
shows a coronal loop on the solar limb. Our original analysis of these data
showed that the plasma was multi-thermal, both along the length of the loop and
along the line of sight. However, more recent results by other authors indicate
that background subtraction might change these conclusions, so we consider the
effect of background subtraction on our analysis. We show Emission Measure (EM)
Loci plots of three representative pixels: loop apex, upper leg, and lower leg.
Comparisons of the original and background-subtracted intensities show that the
EM Loci are more tightly clustered after background subtraction, but that the
plasma is still not well represented by an isothermal model. Our results taken
together with those of other authors indicate that a variety of temperature
structures may be present within loops.Comment: Accepted for publication in ApJ Letter
Probing the isovector transition strength of the low-lying nuclear excitations induced by inverse kinematics proton scattering
A compact approach based on the folding model is suggested for the
determination of the isoscalar and isovector transition strengths of the
low-lying () excitations induced by inelastic proton
scattering measured with exotic beams. Our analysis of the recently measured
inelastic O+p scattering data at and 43 MeV/nucleon
has given for the first time an accurate estimate of the isoscalar
and isovector deformation parameters (which cannot be determined from
the (p,p') data alone by standard methods) for 2 and excited
states in O. Quite strong isovector mixing was found in the 2
inelastic O+p scattering channel, where the strength of the isovector
form factor (prototype of the Lane potential) corresponds to a
value almost 3 times larger than and a ratio of nuclear transition
matrix elements .Comment: 5 pages, 3 figure
Plasma Panel Sensors for Particle and Beam Detection
The plasma panel sensor (PPS) is an inherently digital, high gain, novel
variant of micropattern gas detectors inspired by many operational and
fabrication principles common to plasma display panels (PDPs). The PPS is
comprised of a dense array of small, plasma discharge, gas cells within a
hermetically-sealed glass panel, and is assembled from non-reactive,
intrinsically radiation-hard materials such as glass substrates, metal
electrodes and mostly inert gas mixtures. We are developing the technology to
fabricate these devices with very low mass and small thickness, using gas gaps
of at least a few hundred micrometers. Our tests with these devices demonstrate
a spatial resolution of about 1 mm. We intend to make PPS devices with much
smaller cells and the potential for much finer position resolutions. Our PPS
tests also show response times of several nanoseconds. We report here our
results in detecting betas, cosmic-ray muons, and our first proton beam tests.Comment: 2012 IEEE NS
Fusion of radioactive Sn with Ni
Evaporation residue and fission cross sections of radioactive Sn on
Ni were measured near the Coulomb barrier. A large sub-barrier fusion
enhancement was observed. Coupled-channel calculations including inelastic
excitation of the projectile and target, and neutron transfer are in good
agreement with the measured fusion excitation function. When the change in
nuclear size and shift in barrier height are accounted for, there is no extra
fusion enhancement in Sn+Ni with respect to stable Sn+Ni.
A systematic comparison of evaporation residue cross sections for the fusion of
even Sn and Sn with Ni is presented.Comment: 9 pages, 11 figure
Double-magic nature of 132Sn and 208Pb through lifetime and cross-section measurements
Single-neutron states in Sn133 and Pb209, which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the (Be9, Be8) one-neutron transfer reaction in inverse kinematics using particle-γ coincidence s
Elastic scattering and breakup of 17^F at 10 MeV/nucleon
Angular distributions of fluorine and oxygen produced from 170 MeV 17^F
incident on 208^Pb were measured. The elastic scattering data are in good
agreement with optical model calculations using a double-folding potential and
parameters similar to those obtained from 16^O+208^Pb. A large yield of oxygen
was observed near \theta_lab=36 deg. It is reproduced fairly well by a
calculation of the (17^F,16^O) breakup, which is dominated by one-proton
stripping reactions. The discrepancy between our previous coincidence
measurement and theoretical predictions was resolved by including core
absorption in the present calculation.Comment: 9 pages, 5 figure
Electromagnetic properties of the 21+ state in 134Te: Influence of core excitation on single-particle orbits beyond 132Sn
The g factor and B(E2) of the first excited 2+ state have been measured following Coulomb excitation of the neutron-rich semimagic nuclide 134Te (two protons outside 132Sn) produced as a radioactive beam. The precision achieved matches related g-factor m
Isospin structure of one- and two-phonon GDR excitations
Isospin is included in the description of Coulomb excitation of multiple
giant isovector dipole resonances. In the excitation of even-even nuclei, a
relevant portion of the excitation strength is shown to be associated with 1+
two-phonon states, which tends to be hindered or completely supressed in
calculations in which the isospin degree of freedom is not considered. We find
that the excitation cross sections is strongly dependent on the ground state
isospin.Comment: 8 pages, 2 figure
Breakup of F on Pb near the Coulomb barrier
Angular distributions of oxygen produced in the breakup of F incident
on a Pb target have been measured around the grazing angle at beam
energies of 98 and 120 MeV. The data are dominated by the proton stripping
mechanism and are well reproduced by dynamical calculations. The measured
breakup cross section is approximately a factor of 3 less than that of fusion
at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure
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