Experiments on astrophysical reactions with low-energy unstable nuclei beams at CRIB

Two experimental techniques have been developed at GANIL using resonant elastic and inelastic scattering reactions in inverse kinematics. These techniques were used to study the structure of unstable nuclei. A brief description of the methods is presented through two examples of application in astrophysics. Moreover, new ideas and simple questions are put forward: what happens in the low energy tail of unbound nuclei ground state resonances?

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Application of the THM to the investigation of reactions induced by unstable nuclei: the 18F(p,α)15O case

EPJ Web of Conferences ◽

10.1051/epjconf/201922301030 ◽

2019 ◽

Vol 223 ◽

pp. 01030

Author(s):

Marco La Cognata ◽

Rosario G. Pizzone ◽

Jordi José ◽

Margarita Hernanz ◽

Silvio Cherubini ◽

...

Keyword(s):

Reaction Mechanism ◽

Cross Section ◽

Energy Resolution ◽

Low Energy ◽

Radioactive Nucleus ◽

Exit Channel ◽

Unstable Nuclei ◽

Trojan Horse Method ◽

Astrophysical Factor ◽

First Time

The Trojan Horse Method is applied to the investigation of the 18F(p,α)15O reaction, by extracting the quasi free contribution to the 2H(18F,α15O)n process. For the first time the method is applied to a reaction of astrophysical importance involving a radioactive nucleus. After investigating the reaction mechanism populating the a + 15O + n exit channel, we could extract the 18F(p,α)15O cross section and calculate the astrophysical factor over the 0 – 1 MeV energy interval. The possibility of exploring the cross section with no need of extrapolation allowed us to to point out the possible occurrence of a 7/2+ state at 126 keV, which would strongly influence the trend of the astrophysical factor at the energies of astrophysical interest. However, the low energy resolution prevents us to draw definite conclusions. Possible astrophysical consequences are also discussed, motivating further work on this reaction.

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Dissociated Σ=27 boundaries in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105187 ◽

1988 ◽

Vol 46 ◽

pp. 624-625

Author(s):

A. Garg ◽

W.A.T. Clark ◽

J.P. Hirth

Keyword(s):

Electron Diffraction ◽

Local Minimum ◽

Boundary Energy ◽

Coincidence Site Lattice ◽

Boundary Plane ◽

Low Energy ◽

Theoretical Understanding ◽

Site Lattice ◽

Kikuchi Pattern ◽

Analysis Techniques

In the last twenty years, a significant amount of work has been done in the theoretical understanding of grain boundaries. The various proposed grain boundary models suggest the existence of coincidence site lattice (CSL) boundaries at specific misorientations where a periodic structure representing a local minimum of energy exists between the two crystals. In general, the boundary energy depends not only upon the density of CSL sites but also upon the boundary plane, so that different facets of the same boundary have different energy. Here we describe TEM observations of the dissociation of a Σ=27 boundary in silicon in order to reduce its surface energy and attain a low energy configuration.The boundary was identified as near CSL Σ=27 {255} having a misorientation of (38.7±0.2)°/[011] by standard Kikuchi pattern, electron diffraction and trace analysis techniques. Although the boundary appeared planar, in the TEM it was found to be dissociated in some regions into a Σ=3 {111} and a Σ=9 {122} boundary, as shown in Fig. 1.

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Transfer optics for high spatial resolution electron spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105394 ◽

1988 ◽

Vol 46 ◽

pp. 666-667

Author(s):

G. G. Hembree ◽

Luo Chuan Hong ◽

P.A. Bennett ◽

J.A. Venables

Keyword(s):

Magnetic Field ◽

Scanning Transmission Electron Microscope ◽

Low Energy ◽

Objective Lens ◽

State University ◽

Arizona State University ◽

Initial Field ◽

Resolution Electron ◽

Scanning Transmission ◽

Low Energy Electrons

A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.

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Performance Evaluation of a Novel Type of Low-Energy Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180525 ◽

1990 ◽

Vol 48 (1) ◽

pp. 354-355

Author(s):

Bertholdand Senftinger ◽

Helmut Liebl

Keyword(s):

Electron Microscope ◽

High Resolution ◽

Field Strength ◽

Numerical Aperture ◽

Low Energy ◽

Energy Electron ◽

High Resolution Imaging ◽

Lens System ◽

Resolution Imaging ◽

Low Energy Electron

During the last few years the investigation of clean and adsorbate-covered solid surfaces as well as thin-film growth and molecular dynamics have given rise to a constant demand for high-resolution imaging microscopy with reflected and diffracted low energy electrons as well as photo-electrons. A recent successful implementation of a UHV low-energy electron microscope by Bauer and Telieps encouraged us to construct such a low energy electron microscope (LEEM) for high-resolution imaging incorporating several novel design features, which is described more detailed elsewhere.The constraint of high field strength at the surface required to keep the aberrations caused by the accelerating field small and high UV photon intensity to get an improved signal-to-noise ratio for photoemission led to the design of a tetrode emission lens system capable of also focusing the UV light at the surface through an integrated Schwarzschild-type objective. Fig. 1 shows an axial section of the emission lens in the LEEM with sample (28) and part of the sample holder (29). The integrated mirror objective (50a, 50b) is used for visual in situ microscopic observation of the sample as well as for UV illumination. The electron optical components and the sample with accelerating field followed by an einzel lens form a tetrode system. In order to keep the field strength high, the sample is separated from the first element of the einzel lens by only 1.6 mm. With a numerical aperture of 0.5 for the Schwarzschild objective the orifice in the first element of the einzel lens has to be about 3.0 mm in diameter. Considering the much smaller distance to the sample one can expect intense distortions of the accelerating field in front of the sample. Because the achievable lateral resolution depends mainly on the quality of the first imaging step, careful investigation of the aberrations caused by the emission lens system had to be done in order to avoid sacrificing high lateral resolution for larger numerical aperture.

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