LUNA: Status and Prospects

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of $^{12}$C+$^{12}$C and of the two reactions which generate free neutrons inside stars: $^{13}$C($\alpha$,n)$^{16}$O and $^{22}$Ne($\alpha$,n)$^{25}$Mg.Comment: To be published in Progress in Particle and Nuclear Physics 98C (2018) pp. 55-8

Progettazione e preparazione di nuovi materiali per applicazioni sostenibili in chimica organica e ambientale

In recent years Green Chemistry has become a central area of research for chemists working in both industry and academia. The fundamental concepts of sustainable chemistry are, among others, atom efficiency, waste prevention, use of renewable materials and innocuous solvents, as well as design of safer products. Within this context, microreactor technology offers, on the one hand, safe, environmentally benign, and high throughput processes typically intensified by a fast postreaction phase (workup and purification) and direct scalability; on the other hand, asymmetric organocatalysis allows for new and unique opportunities towards efficient and highly stereoselective metal-free catalytic syntheses. In the first part of this thesis project it has been carried out the synthesis of new heterogeneous organocatalysts for their ultimate utilization in continuous-flow processes. Precisely, proline-like mimetics and thiazolium salt pre-catalysts have been immobilized on silica and polystyrene macroporous supports, respectively; next, these functionalized solid materials have been employed as packing material for the fabrication of fixed-bed microreactors in the form of either packed or monolithic columns. During this research, it has been demonstrated that operation of this type of organocatalytic microreactors results in flow processes with levels of stereoselectivity comparable to those of the corresponding homogeneous batch processes, allowing at the same time productivity enhancements thanks to the higher long-term stability of the heterogeneous organocatalytic species in flow regime. In the second part of this thesis project, the same techniques of support functionalization have been employed to prepare perfluorinated stationary phases for the determination of perfluorinated compounds (PFCs). These are emerging pollutants widely spread in the environment. They can be found in soils, sediments, superficial waters, particulate matter, as well as in animal and human tissues or organs. PFC are characterized by environmental persistence and have negative side effects for the biota where they accumulate. The chromatographic behavior of perfluorinated acid pollutants have been investigated on the basis of the specific fluorine-fluorine interactions (fluorophilicity) occurring between these analytes and the perfluoroalkyl groups of the newly prepared stationary phases. It has been demonstrated that the retention profile of perfluorinated acids is dependent on the composition of the mobile phase, thus permitting the use of the prepared fluorinated stationary phases as means of pre-concentration of PFCs from environmental and biological matrices

Strength of the EpE_{\text{p}}=1.842 MeV resonance in the 40^{40}Ca(p,γ\gamma)41^{41}Sc reaction revisited

The strength of the $E_{\rm p} = 1.842$ MeV resonance in the $^{40}$Ca(p,$\gamma$)$^{41}$Sc reaction is determined with two different methods: First, by an absolute strength measurement using calcium hydroxide targets, and second, relative to the well-determined strength of the resonance triplet at $E_\alpha$ = 4.5 MeV in the $^{40}$Ca($\alpha$,$\gamma$)$^{44}$Ti reaction. The present new value of $\omega\gamma=(0.192\pm0.017)$ eV is 37% (equivalent to $3.5\sigma$) higher than the evaluated literature value. In addition, the ratio of the strengths of the 1.842 MeV $^{40}$Ca(p,$\gamma$)$^{41}$Sc and 4.5 MeV $^{40}$Ca($\alpha$,$\gamma$)$^{44}$Ti resonances has been determined to be $0.0229\pm0.0018$. The newly corrected strength of the 1.842-MeV resonance can be used in the future as a normalization point for experiments with calcium targets.Comment: Submitted to Phys. Rev.

Determination of gamma-ray widths in 15^{15}N using nuclear resonance fluorescence

The stable nucleus $^{15}$N is the mirror of $^{15}$O, the bottleneck in the hydrogen burning CNO cycle. Most of the $^{15}$N level widths below the proton emission threshold are known from just one nuclear resonance fluorescence (NRF) measurement, with limited precision in some cases. A recent experiment with the AGATA demonstrator array determined level lifetimes using the Doppler Shift Attenuation Method (DSAM) in $^{15}$O. As a reference and for testing the method, level lifetimes in $^{15}$N have also been determined in the same experiment. The latest compilation of $^{15}$N level properties dates back to 1991. The limited precision in some cases in the compilation calls for a new measurement in order to enable a comparison to the AGATA demonstrator data. The widths of several $^{15}$N levels have been studied with the NRF method. The solid nitrogen compounds enriched in $^{15}$N have been irradiated with bremsstrahlung. The $\gamma$-rays following the deexcitation of the excited nuclear levels were detected with four HPGe detectors. Integrated photon-scattering cross sections of ten levels below the proton emission threshold have been measured. Partial gamma-ray widths of ground-state transitions were deduced and compared to the literature. The photon scattering cross sections of two levels above the proton emission threshold, but still below other particle emission energies have also been measured, and proton resonance strengths and proton widths were deduced. Gamma and proton widths consistent with the literature values were obtained, but with greatly improved precision.Comment: Final published version, minor grammar changes, 10 pages, 4 figures, 8 tables; An addendum is published where the last section is revised: T. Sz\"ucs and P. Mohr, Phys. Rev. C 92, 044328 (2015) [arXiv:1510.04956

Effusion Cooling Plates for Combustor Liners: Experimental and Numerical Investigations on the Effect of Density Ratio

AbstractEffusion cooling represents the state-of-the-art of liner cooling technology for modern combustors. The present paper describes experimental tests aiming at evaluating the cooling performance of a multi-perforated plate in real engine representative fluid- dynamic conditions. Adiabatic effectiveness maps were obtained following the mass transfer analogy by the use of Pressure Sensitive Paint. In addition, a CFD campaign was performed in order to benchmark the reliability in estimating the cooling performance of effusion cooling liners. In order to include anisotropic diffusion effects, the k − ω SST turbulence model was corrected considering a tensorial definition of the eddy viscosity with an algebraic correction to dope its stream-span components

A new study of 25^{25}Mg(α\alpha,n)28^{28}Si angular distributions at EαE_\alpha = 3 - 5 MeV

The observation of $^{26}$Al gives us the proof of active nucleosynthesis in the Milky Way. However the identification of the main producers of $^{26}$Al is still a matter of debate. Many sites have been proposed, but our poor knowledge of the nuclear processes involved introduces high uncertainties. In particular, the limited accuracy on the $^{25}$Mg($\alpha$,n)$^{28}$Si reaction cross section has been identified as the main source of nuclear uncertainty in the production of $^{26}$Al in C/Ne explosive burning in massive stars, which has been suggested to be the main source of $^{26}$Al in the Galaxy. We studied this reaction through neutron spectroscopy at the CN Van de Graaff accelerator of the Legnaro National Laboratories. Thanks to this technique we are able to discriminate the ($\alpha$,n) events from possible contamination arising from parasitic reactions. In particular, we measured the neutron angular distributions at 5 different beam energies (between 3 and 5 MeV) in the \ang{17.5}-\ang{106} laboratory system angular range. The presented results disagree with the assumptions introduced in the analysis of a previous experiment.Comment: 9 pages, 9 figures - accepted by EPJ

A new FSA approach for in situ γ\gamma-ray spectroscopy

An increasing demand of environmental radioactivity monitoring comes both from the scientific community and from the society. This requires accurate, reliable and fast response preferably from portable radiation detectors. Thanks to recent improvements in the technology, $\gamma$-spectroscopy with sodium iodide scintillators has been proved to be an excellent tool for in-situ measurements for the identification and quantitative determination of $\gamma$-ray emitting radioisotopes, reducing time and costs. Both for geological and civil purposes not only $^{40}$K, $^{238}$U, and $^{232}$Th have to be measured, but there is also a growing interest to determine the abundances of anthropic elements, like $^{137}$Cs and $^{131}$I, which are used to monitor the effect of nuclear accidents or other human activities. The Full Spectrum Analysis (FSA) approach has been chosen to analyze the $\gamma$-spectra. The Non Negative Least Square (NNLS) and the energy calibration adjustment have been implemented in this method for the first time in order to correct the intrinsic problem related with the $\chi ^2$ minimization which could lead to artifacts and non physical results in the analysis. A new calibration procedure has been developed for the FSA method by using in situ $\gamma$-spectra instead of calibration pad spectra. Finally, the new method has been validated by acquiring $\gamma$-spectra with a 10.16 cm x 10.16 cm sodium iodide detector in 80 different sites in the Ombrone basin, in Tuscany. The results from the FSA method have been compared with the laboratory measurements by using HPGe detectors on soil samples collected in the different sites, showing a satisfactory agreement between them. In particular, the $^{137}$Cs isotopes has been implemented in the analysis since it has been found not negligible during the in-situ measurements.Comment: accepted by Science of Total Environment: 8 pages, 10 figures, 3 table