11,007 research outputs found
Feasibility of modifying the high resolution infrared radiation sounder (HIRS/2) for measuring spectral components of Earth radiation budget
The concept of adding four spectral channels to the 20 channel HIRS/2 instrument for the purpose of determining the origin and profile of radiant existence from the Earth's atmosphere is considered. Methods of addition of three channels at 0.5, 1.0 and 1.6 micron m to the present 0.7 micron m visible channel and an 18-25 micron m channel to the present 19 channels spaced from 3.7 micron m to 15 micron m are addressed. Optical components and physical positions were found that permit inclusion of these added channels with negligible effect on the performance of the present 20 channels. Data format changes permit inclusion of the ERB data in the 288 bits allocated to HIRS for each scan element. A lamp and collimating optic assembly may replace one of the on board radiometric black bodies to provide a reference source for the albedo channels. Some increase in instrument dimensions, weight and power will be required to accommodate the modifications
New Results on e+e- Line Emission in U+Ta Collisions
We present new results obtained from a series of follow-up e+e- coincidence
measurements in heavy-ion collisions, utilizing an improved experimental set-up
at the double-Orange beta-spectrometer of GSI. The collision system U+Ta was
reinvestigated in three independent runs at beam energies in the range
(6.0-6.4)xA MeV and different target thicknesses, with the objective to
reproduce a narrow sum-energy e+e- line at ~635 keV observed previously in this
collision system. At improved statistical accuracy, the line could not be found
in these new data. For the ''fission'' scenario, an upper limit (1 sigma) on
its production probability per collision of 1.3x10^{-8} can be set which has to
be compared to the previously reported value of [4.9 +- 0.8 (stat.) +- 1.0
(syst)]x10^{-7}. In the light of the new results, a reanalysis of the old data
shows that the continuous part of the spectrum at the line position is
significantly higher than previously assumed, thus reducing the production
probability of the line by a factor of two and its statistical significance to
< 3.4sigma.Comment: 15 pages, standard LaTeX with 3 included PS figures; Submitted to
Physics Letters
First Energy and Angle differential Measurements of e^+e^- -pairs emitted by Internal Pair Conversion of excited Heavy Nuclei
We present the first energy and angle resolved measurements of e+e- pairs
emitted from heavy nuclei (Z>=40) at rest by internal pair conversion (IPC) of
transitions with energies of less than 2MeV as well as recent theoretical
results using the DWBA method, which takes full account of relativistic
effects, magnetic substates and finite size of the nucleus. The 1.76MeV E0
transition in Zr90 (Sr source) and the 1.77MeV M1 transition in Pb207 (Bi
source) have been investigated experimentally using the essentially improved
set-up at the double-ORANGE beta-spectrometer of GSI. The measurements prove
the capability of the setup to cleanly identify the IPC pairs in the presence
of five orders of magnitude higher beta- and gamma background from the same
source and to yield essentially background-free sum spectra despite the large
background. Using the ability of the ORANGE setup to directly determine the
opening angle of the e+e- pairs, the angular correlation of the emitted pairs
was measured. In the Zr90 case the correlation could be deduced for a wide
range of energy differences of the pairs. The Zr90 results are in good
agreement with recent theory. The angular correlation deduced for the M1
transition in Pb207 is in strong disagreement with theoretical predictions
derived within the Born approximation and shows almost isotropic character.
This is again in agreement with the new theoretical results.Comment: LaTeX, 28 pages incl. 10 PS figures; Accepted by Z.Phys.
Positron spectra from internal pair conversion observed in {238}U + {181}Ta collisions
We present new results from measurements and simulations of positron spectra,
originating from 238U + 181Ta collisions at beam energies close to the Coulomb
barrier. The measurements were performed using an improved experimental setup
at the double-Orange spectrometer of GSI. Particular emphasis is put on the
signature of positrons from Internal-Pair-Conversion (IPC) processes in the
measured e+ energy spectra, following the de-excitation of electromagnetic
transitions in the moving Ta-like nucleus. It is shown by Monte Carlo
simulations that, for the chosen current sweeping procedure used in the present
experiments, positron emission from discrete IPC transitions can lead to rather
narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical
accuracy achieved, although expected from the intensities of the observed
transitions (E keV) and theoretical conversion
coefficients. This is due to the reduced detection efficiency for IPC
positrons, caused by the limited spatial and momentum acceptance of the
spectrometer. A comparison with previous results, in which lines have been
observed, is presented and the implications are discussed.Comment: LaTeX, 20 pages including 5 EPS figures; Accepted by Eur. Phys.Jour.
Laser and microwave spectroscopy of even-parity Rydberg states of neutral ytterbium and Multichannel Quantum Defect Theory analysis
New measurements of high-lying even parity and
levels of neutral Yb are presented in this paper.
Spectroscopy is performed by a two-step laser excitation from the ground state
, and the Rydberg levels are detected by using the
field ionization method. Additional two-photon microwave spectroscopy is used
to improve the relative energy accuracy where possible. The spectroscopic
measurements are complemented by a multichannel quantum defect theory (MQDT)
analysis for the J=0 and the two-coupled J=2 even parity series. We compare our
results with the previous analysis of Aymar {\it{et al}} \cite{Aymar_1980} and
analyze the observed differences. From the new MQDT models, a revised value for
the first ionization limit cm is proposed.Comment: 15 pages, 3 figure
Recent advances in laser-plasma experiments using foams
The paper discusses recent advances in the use of foams in
laser–plasma experiments, concerning in particular: (1)
the use of foam in order to get an efficient smoothing of laser
energy deposition, (2) the problem of hydrodynamics of layered
foam-payload targets, (3) the use of foam for shock pressure
amplification in equation-of-state experiments, (4) the study
of the equation of state of foams in the Megabar regime, and
(5) the use of foams for astrophysics relevant experiments,
here in particular shock acceleration experiments
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