E. Kolbe

Earthshine observations of the Earth's reflectance

Regular photometric observations of the moons “ashen light” (earthshine) from the Big Bear Solar Observatory (BBSO) since December 1998 have quantified the earths optical reflectance. We find large (∼5%) daily variations in the reflectance due to large-scale weather changes on the other side of the globe. Separately, we find comparable hourly variations during the course of many nights as the earths rotation changes that portion of the earth in view. Our data imply an average terrestrial albedo of 0.297±0.005, which agrees with that from simulations based upon both changing snow and ice cover and satellite-derived cloud cover (0.296±0.002). However, we find seasonal variations roughly twice those of the simulation, with the earth being brightest in the spring. Our results suggest that long-term earthshine observations are a useful monitor of the earths albedo. Comparison with more limited earthshine observations during 1994–1995 show a marginally higher albedo then.

Neutrino–nucleus reactions and nuclear structure

The methods used in the evaluation of the neutrino–nucleus cross section are reviewed. Results are shown for a variety of targets of practical importance. Many of the described reactions are accessible in future experiments with neutrino sources from the pion and muon decays at rest, which might be available at the neutron spallation facilities. Detailed comparison between the experimental and theoretical results would establish benchmarks needed for verification and/or parameter adjustment of the nuclear models. Having a reliable tool for such calculation is of great importance in a variety of applications, e.g. the neutrino oscillation studies, detection of supernova neutrinos, description of the neutrino transport in supernovae and description of the r-process nucleosynthesis.

Calculations of fission rates for r-process nucleosynthesis

Abstract Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that nevertheless fission leads to the termination of the r-process. Furthermore, it is discussed that the probability of triple fission could be high for A > 260 and have an effect on the formation of the abundances of heavy nuclei. Fission after beta-delayed neutron emission is discussed as well as different aspects of the influence of fission upon r-process calculations.

Weak reactions on 12C within the continuum random phase approximation with partial occupancies

Abstract We extend our previous studies of the neutrino-induced reactions on 12 C and muon capture to include partial occupation of nuclear subshells in the framework of the continuum random phase approximation. We find, in contrast to the work by Auerbach et al., that a partial occupation of the p 1 2 subshell reduces the inclusive cross sections only slightly. The extended model describes the muon capture rate and the 12 C( ν e , e − ) 12 N cross section very well. The recently updated flux and the improved model bring the calculated 12 C( ν μ , μ − ) 12 N cross section (≈ 17.5 × 10 −40 cm 2 ) and the data ((12.4 ± 0.3(stat.) ± 1.8(syst.) × 10 −40 cm 2 ) closer together, but does not remove the discrepancy fully.

Inelastic neutrino scattering on 12C and 16O above the particle emission threshold

Recently a new formalism has been developed to described nuclear electromagnetic response within the continuum RPA theory. This model is extended in order to calculate cross sections for weak interactions in nuclei, in particular for inelastic neutrino scattering. The results of a numerical analysis are presented for 12C and 16O. We consider neutrino spectra like those generated in muon decay (relevant for terrestrial experiments) or in a supernova explosion. For the latter case we calculate neutral current cross sections for various neutrino-induced particle reactions on 12C and 16O, relevant for the ν-nucleosynthesis.

Element synthesis in stars

Except for H-1, H-2, He-3, He-4, and Li-7, originating from the Big Bang, all heavier elements are made in stellar evolution and stellar explosions. Nuclear physics, and in many cases nuclear structure far from stability, enters in a crucial way. Therefore, we examine in this review the role of nuclear physics in astrophysics in general and in particular how it affects stellar events and the resulting nucleosynthesis. Stellar modeling addresses four major aspects: 1. energy generation and nucleosynthesis, 2. energy transport via conduction, radiation or possibly convection, 3. hydrodynamics/hydrostatics, and finally 4. thermodynamic properties of the matter involved. Nuclear Physics enters via nuclear reaction cross sections and nuclear structure (affecting the composition changes and nuclear energy generation), neutrino-nucleon and neutrino-nucleus cross sections (affecting neutrino opacities and transport), and e.g. the equation of state at and beyond nuclear densities which creates a relation between the nuclear many body problem and and hydrodynamic response like pressure and entropy. In the following we review these four topics by highlighting the role and impact of nuclear physics in each of these aspects of stellar modeling. The main emphasis is put on the connection to element synthesis.

Unblocking of the Gamow-Teller Strength in Stellar Electron Capture on Neutron-Rich Germanium Isotopes

We propose a new model to calculate stellar electron capture rates for neutron-rich nuclei. These nuclei are encountered in the core-collapse of a massive star. Using the Shell Model Monte Carlo approach, we first calculate the finite temperature occupation numbers in the parent nucleus. We then use these occupation numbers as a starting point for calculations using the random phase approximation. Using the RPA approach, we calculate electron capture rates including both allowed and forbidden transitions. Such a hybrid model is particularly useful for nuclei with proton numbers Z 40, where allowed Gamow-Teller transitions are only possible due to configuration mixing by the residual interaction and by thermal unblocking of

Strange quark contributions to neutrino induced quasielastic scattering

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Muon capture, continuum random phase approximation, and in-medium renormalization of the axial-vector coupling constant

-shell single-particle states. Using the even germanium isotopes Ge-68 to Ge-76 as examples, we demonstrate that the configuration mixing is strong enough to unblock the Gamow-Teller transitions at all temperatures relevant to core-collapse supernovae.

Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem

Abstract We propose that measuring the ratio of proton-to-neutron neutrino-induced quasielastic yield is a sensitive way to determine the strange quark axial form factor of the nucleon. This form factor is determined by the ss contribution to the nucleon spin.