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Study of one stellar outburst called Nova : measurement of spectroscopic properties of 19Ne by a new method of inelastic scattering

By F. Boulay (GANIL)

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When 2013-01-22
from 11:30 am à 12:00 pm
Where salle gamma
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Classical novae occur in close binary star systems consisting of white dwarf accreting matter from its companion, main sequence or red giant star. The accreting material provides fuel and the conditions necessary to initiate a thermonuclear explosion on the White Dwarf surface, leading to the synthesis of some heavier types of nuclei and the ejection of material into space.

Among else, novae produce radioactive isotopes, such as 18F, that could be detected by their gamma–ray emission (one of the scientific objective of the INTEGRAL satellite). Why do we focus on 18F? Because the annihilation of positrons generated by its β+ decay is the dominant source of gamma rays during the first hours of a nova explosion. So, The knowledge of the abundance of the 18F in novae is essential because its gamma rays (≤511 keV) are one of the observables, which give insight into nuclear processes of novae.

Depending on the temperature, the β+ decay and two nuclear reactions are in competition for the destruction of 18F : 18F(p,α)15O and 18F(p,γ)19Ne. Unfortunately, present radioactive beams intensities are not sufficient for a direct measurement of those reactions. Nevertheless, these two reactions rates strongly depend on the structure of 19Ne. In particular, the energies, spins, and decay widths of important 19Ne resonances must be determined in order to reduce their uncertainty. Today, only a few intrinsic properties of states have been measured yet experimentally in the excitation energy range of astrophysical interest (commonly called the Gamow window).

A code has been elaborated to calculate the reaction rate, underlying the sensibility on the spectroscopic properties, such as the spin of states.

Based on the success of the experiment performed at Louvain-La-Neuve (Belgium) in the past, we will realize soon at GANIL a new and accurate spectroscopy of 19Ne inside the Gamow window via an improved p,p’ inelastic scattering reaction. The experimental setup combines an annular silicon detector and the magnetic spectrometer VAMOS. The latter will be used for the first time to detect protons at zero degree, on the spectrograph mode.

In November 2012, a preparatory experiment was lead in Czech Republic to determine the optimal values of the pressure and the voltage of the drift chambers of VAMOS to detect protons with an energy about 25 MeV, using the Mayaito prototype. Results will be presented.

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