391 research outputs found
Drag-free estimation feasibility study
A drag compensation system for solar probes and other spacecraft that require a drag-free capability is presented. Estimation techniques, derived from modern control theory, are proposed
Planetary benchmarks
Design criteria and technology requirements for a system of radar reference devices to be fixed to the surfaces of the inner planets are discussed. Offshoot applications include the use of radar corner reflectors as landing beacons on the planetary surfaces and some deep space applications that may yield a greatly enhanced knowledge of the gravitational and electromagnetic structure of the solar system. Passive retroreflectors with dimensions of about 4 meters and weighing about 10 kg are feasible for use with orbiting radar at Venus and Mars. Earth-based observation of passive reflectors, however, would require very large and complex structures to be delivered to the surfaces. For Earth-based measurements, surface transponders offer a distinct advantage in accuracy over passive reflectors. A conceptual design for a high temperature transponder is presented. The design appears feasible for the Venus surface using existing electronics and power components
Kabul Times (April 11, 1964, vol. 3, no. 37)
High-resolution photon scattering experiments have been performed on the nucleus 45Sc at the Darmstadt superconducting electron accelerator S-DALINAC using bremsstrahlung beams with end point energies of 5.0 and 7.0MeV. Energies, absolute cross-sections and decay widths of 50 states, most of them previously unknown, have been determined. The results are compared to (γ,) experiments on the neighbouring closed proton shell isotope 44Ca
High precision Y(,)Y scattering at low energies
Elastic scattering cross sections of the Y(,)Y
reaction have been measured at energies E = 15.51 and 18.63 MeV. The
high precision data for the semi-magic nucleus Y are used to
derive a local potential and to evaluate the predictions of global and regional
-nucleus potentials. The variation of the elastic alpha scattering
cross sections along the isotonic chain is investigated by a study of
the ratios of angular distributions for Y(,)Y and
Mo(,)Mo at E 15.51 and 18.63
MeV. This ratio is a very sensitive probe at energies close to the Coulomb
barrier, where scattering data alone is usually not enough to characterize the
different potentials. Furthermore, -cluster states in Nb =
Y are investigated
How important is the Family? : Alpha nuclear potentials and p-process nucleosynthesis
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike LicenceIn this work we present the results from the analysis of the experimentally measured angular distributions of the reaction 106Cd(α , α )106 Cd at several different energies around the Coulomb barrier. The difficulties that arise in the study of 106Cd-α -nuclear potential and the so called Family Problem are addressed in this work
Re(\gamm,n) cross section close to and above the neutron threshold
The neutron capture cross section of the unstable nucleus Re is
studied by investigating the inverse photodisintegration reaction
Re(,n). The special interest of the {\it s}-process branching
point Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}^{186}\gamma^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres
Investigation of alpha-nuclear potential families from elastic scattering experiments
In this work we present the continuation of the reported analysis [1] of the experimentally measured angular distributions of the reaction Cd-106(alpha, alpha)Cd-106 at several different energies around the Coulomb barrier. The difficulties that arise in the study of Cd-106-alpha-nuclear potential and the so called Family Problem are addressed
The s-process branching at 185W
The neutron capture cross section of the unstable nucleus 185W has been
derived from experimental photoactivation data of the inverse reaction
186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the
theoretically predicted neutron capture cross section of 185W of sigma = 700
mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n =
(3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching.
In a stellar s-process model one finds a significant overproduction of the
residual s-only nucleus 186Os.Comment: ApJ, in pres
Fragmentation and systematics of the Pygmy Dipole Resonance in the stable N=82 isotones
The low-lying electric dipole (E1) strength in the semi-magic nucleus 136Xe
has been measured which finalizes the systematic survey to investigate the
so-called pygmy dipole resonance (PDR) in all stable even N=82 isotones with
the method of nuclear resonance fluorescence using real photons in the entrance
channel. In all cases, a fragmented resonance-like structure of E1 strength is
observed in the energy region 5 MeV to 8 MeV. An analysis of the fragmentation
of the strength reveals that the degree of fragmentation decreases towards the
proton-deficient isotones while the total integrated strength increases
indicating a dependence of the total strength on the neutron-to-proton ratio.
The experimental results are compared to microscopic calculations within the
quasi-particle phonon model (QPM). The calculation includes complex
configurations of up to three phonons and is able to reproduce also the
fragmentation of the E1 strength which allows to draw conclusions on the
damping of the PDR. Calculations and experimental data are in good agreement in
the degree of fragmentation and also in the integrated strength if the
sensitivity limit of the experiments is taken into account
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