No abstract

The T(α,γ)Li7 reaction has been observed using thin targets of tritium absorbed in zirconium bombarded by singly charged helium ions of energy from 0.5 Mev to 1.9 Mev. The cross section rises smoothly with energy in a fashion characteristic of a direct radiative capture process. The ratio of the intensities of transitions to the first excited state at 478 kev and to the ground state is 0.40 ± 0.05. The angular distribution is, to within errors, isotropic at Eα = 0.8 Mev but is significantly higher at 0° than at 90° for Eα = 1.6 Mev. The total capture cross section at a mean alpha-particle energy in the target of 1.32 Mev is 3.58 ± 0.60 microbarns and the corresponding astrophysical S factor is 0.064 ± 0.016 kev barn in the center of mass system. The results are compared with recent theoretical results on the direct radiative capture process.

Context. The structure of the white-light and emission solar coronas and their MHD modelling are the context of our work. Aims. A comparison is made between the structure of the solar corona as observed during the 2008 August 1 total eclipse from Mongolia and that predicted by an MHD model. Methods. The model has an improved energy formulation, including the effect of coronal heating, conduction of heat parallel to the magnetic field, radiative losses, and acceleration by Alfvén waves. Results. The white-light corona, which was visible up to 20 solar radii, was of an intermediate type with well-pronounced helmet streamers situated above a chain of prominences at position angles of 48, 130, 241, and 322 degrees. Two polar coronal holes, filled with a plethora of thin polar plumes, were observed. High-quality pictures of the green (530.3 nm, Fe XIV) corona were obtained with the help of two narrow-passband filters (centered at the line itself and the vicinity of 529.1 nm background), with a FWHM of 0.15 nm. Conclusions. The large-scale shape of both the white-light and green corona was found to agree well with that predicted by the model. In this paper we describe the morphological properties of the observed corona, and how it compares with that predicted by the model. A more detailed analysis of the quantitative properties of the corona will be addressed in a future publication.

The s andw variations of the np charge-exchange (np-*pn) cross section are measured to be relatively smooth and without structure at intermediate energies-in sharp contast to previous results.

The prediction of the background global solar wind is a necessary part of space weather forecasting. Several coronal and heliospheric models have been installed and/or recently upgraded at the Community Coordinated Modeling Center (CCMC), including the Wang‐Sheely‐Arge (WSA)‐Enlil model, MHD‐Around‐a‐Sphere (MAS)‐Enlil model, Space Weather Modeling Framework (SWMF), and heliospheric tomography using interplanetary scintillation data. Ulysses recorded the last fast latitudinal scan from southern to northern poles in 2007. By comparing the modeling results with Ulysses observations over seven Carrington rotations, we have extended our third‐party validation from the previous near‐Earth solar wind to middle to high latitudes, in the same late declining phase of solar cycle 23. Besides visual comparison, we have quantitatively assessed the models' capabilities in reproducing the time series, statistics, and latitudinal variations of solar wind parameters for a specific range of model parameter settings, inputs, and grid configurations available at CCMC. The WSA‐Enlil model results vary with three different magnetogram inputs. The MAS‐Enlil model captures the solar wind parameters well, despite its underestimation of the speed at middle to high latitudes. The new version of SWMF misses many solar wind variations probably because it uses lower grid resolution than other models. The interplanetary scintillation‐tomography cannot capture the latitudinal variations of solar wind well yet. Because the model performance varies with parameter settings which are optimized for different epochs or flow states, the performance metric study provided here can serve as a template that researchers can use to validate the models for the time periods and conditions of interest to them.