Reorientation-effect measurement of the first 2+ state in 12C : Confirmation of oblate deformation

A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ−ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the 〈21 +‖E2ˆ‖21 +〉 diagonal matrix element in 12C from particle−γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (21 +) states in 12C have been calculated using chiral NN N4LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 21 + state at 4.439 MeV. The polarizability of the 21 + state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12C. Spectroscopic quadrupole moments of QS(21 +)=+0.053(44) eb and QS(21 +)=+0.08(3) eb are determined, respectively, yielding a weighted average of QS(21 +)=+0.071(25) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 21 + state of 12C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

International audienceA detailed chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, and methyl palmitate, are large methyl ester molecules, some with carbon-carbon double bonds, and kinetic mechanisms for them as a family of fuels have not previously been available. Of particular importance in these mechanisms are models for alkylperoxy radical isomerization reactions in which a C=C double bond is embedded in the transition state ring. The resulting kinetic model is validated through comparisons between predicted results and a relatively small experimental literature. The model is also used in simulations of biodiesel oxidation in jet-stirred reactor and intermediate shock tube ignition and oxidation conditions to demonstrate the capabilities and limitations of these mechanisms. Differences in combustion properties between the two biodiesel fuels, derived from soy and rapeseed oils, are traced to the differences in the relative amounts of the same five methyl ester components

Seniority structure of 136^{136}Xe82_{82}

International audienceThe level structure of the N=82 nucleus Xe136 was studied with the inelastic neutron scattering reaction followed by γ-ray detection. A number of the spins and parities were reassigned, and many level lifetimes were determined for the first time using the Doppler-shift attenuation method. New shell-model calculations were also performed using both the full Z=50–82 model space, and a reduced model space including only the 1d5/2 and 0g7/2 orbitals. This new information characterizing Xe136 was used to identify the seniority structure of the low-lying levels and to assign (π0g7/2)υ=04, (π0g7/2)υ=24, (π0g7/2)υ=44, (π1d5/2)(π0g7/2)υ=13, and (π1d5/2)2(π0g7/2)υ=02 configurations to describe all observed states below 2.8 MeV