Resonant tunneling in a schematic model

Tunneling of an harmonically bound two-body system through an external Gaussian barrier is studied in a schematic model which allows for a better understanding of intricate quantum phenomena. The role of finite size and internal structure is investigated in a consistent treatment. The excitation of internal degrees of freedom gives rise to a peaked structure in the penetration factor. The model results indicate that for soft systems the adiabatic limit is not necessarily reached although often assumed in fusion of nuclei and in electron screening effects at astrophysical energies.Comment: 7 pages, 7 figure

Case study: calculation of a narrow resonance with the LIT method

The possibility to resolve narrow structures in reaction cross sections in calculations with the Lorentz integral transform (LIT) method is studied. To this end we consider a fictitious two-nucleon problem with a low-lying and narrow resonance in the $^3P_1$ nucleon-nucleon partial wave and calculate the corresponding ``deuteron photoabsorption cross section''. In the LIT method the use of continuum wave functions is avoided and one works instead with a localized function \tilde\Psi. In this case study it is investigated how far into the asymptotic region \tilde\Psi has to be determined in order to obtain a precise resolution of the artificially introduced E1 resonance. Comparing with the results of a conventional calculation with explicit neutron-proton continuum wave functions it is shown that the LIT approach leads to an excellent reproduction of the cross section in the resonance region and of further finer cross section details at higher energies. To this end, however, for \tilde\Psi one has to take into account two-nucleon distances up to at least 30 fm.Comment: 18 pages, 11 figure

Effects of three-nucleon forces and two-body currents on Gamow-Teller strengths

We optimize chiral interactions at next-to-next-to leading order to observables in two- and three-nucleon systems, and compute Gamow-Teller transitions in carbon-14, oxygen-22 and oxygen-24 using consistent two-body currents. We compute spectra of the daughter nuclei nitrogen-14, fluorine-22 and fluorine-24 via an isospin-breaking coupled-cluster technique, with several predictions. The two-body currents reduce the Ikeda sum rule, corresponding to a quenching factor q^2 ~ 0.84-0.92 of the axial-vector coupling. The half life of carbon-14 depends on the energy of the first excited 1+ state, the three-nucleon force, and the two-body current

On the Accuracy of Hyperspherical Harmonics Approaches to Photonuclear Reactions

Using the Lorentz Integral Transform (LIT) method we compare the results for the triton total photodisintegration cross section obtained using the Correlated Hyperspherical Harmonics (CHH) and the Effective Interaction Hyperspherical Harmonics (EIHH) techniques. We show that these two approaches, while rather different both conceptually and computationally, lead to results which coincide within high accuracy. The calculations which include two- and three-body forces are of the same high quality in both cases. We also discuss the comparison of the two approaches in terms of computational efficiency. These results are of major importance in view of applications to the much debated case of the four-nucleon photoabsorption.Comment: 12 pages, 3 figure

Continuous flow adsorption of phenolic compounds from olive mill wastewater with resin XAD16N: life cycle assessment, cost\u2013benefit analysis and process optimization

BACKGROUND: Olive mill wastewaters (OMWs) represent a major environmental concern due to their high organic load and phytotoxic activity. The selective recovery of phenolic compounds (PCs) from OMW is promising, thanks to the antioxidant and antimicrobial properties of PCs. The goal of this work was to perform a life cycle assessment (LCA) and cost\u2013benefit analysis (CBA) of a full-scale process of PC adsorption/desorption on resin Amberlite XAD16N. The industrial process was designed on the basis of laboratory tests aimed at performing a preliminary process optimization. RESULTS: Adsorption tests were conducted at different velocities in a 1.8-m column packed with XAD16N. The optimal superficial velocity and retention time (2.78 m h \u20131 and 0.56 h) allowed the attainment of satisfactory performances in terms of resin operating capacity (0.46), PC adsorption yield (0.92), PC mass fraction in the sorbed product (0.50 g PC /g VS ) and specific antioxidant activity (3\u20136 g ascorbic acid /g PC ). Six consecutive adsorption/desorption cycles, operated with the same resin load, resulted in stable process performances. The LCA indicated that the environmental impact of the process could be decreased markedly through the addition of an anaerobic digestion step for the production of irrigation-quality water and fertilizers from the dephenolized OMW. The PC market price required for the generation of a positive business case resulted relatively low (\u20ac1.7\u201313.5 kg PC\u20131 ). CONCLUSION: The results indicate that the proposed PC adsorption/desorption technology, if integrated with an anaerobic digestion step, represents a promising solution for the treatment and valorization of OMW, a major agro-industrial waste in Mediterranean countries

Total Photoabsorption Cross Sections of A=6 Nuclei with Complete Final State Interaction

The total photoabsorption cross sections of 6He and 6Li are calculated microscopically with full inclusion of the six-nucleon final state interaction using semirealistic nucleon-nucleon potentials. The Lorentz Integral Transform (LIT) method and the effective interaction approach for the hyperspherical formalism are employed. While 6Li has a single broad giant resonance peak, there are two well separated peaks for 6He corresponding to the breakup of the neutron halo and the alpha core, respectively. The comparison with the few available experimental data is discussed.Comment: LaTeX, 8 pages, 3 ps figure

First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He

The first direct mass-measurement of $^{6}$He has been performed with the TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the mass of $^{8}$He was determined with improved precision over our previous measurement. The obtained masses are $m$($^{6}$He) = 6.018 885 883(57) u and $m$($^{8}$He) = 8.033 934 44(11) u. The $^{6}$He value shows a deviation from the literature of 4$\sigma$. With these new mass values and the previously measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and 1.959(16) fm for $^{6}$He and $^{8}$He respectively. We present a detailed comparison to nuclear theory for $^6$He, including new hyperspherical harmonics results. A correlation plot of the point-proton radius with the two-neutron separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure

Electromagnetic Excitations and Responses in Nuclei from First Principles

We discuss the role of clustering on monopole, dipole, and quadrupole excitations in nuclei in the framework of the ab initio symmetry-adapted no-core shell model (SA-NCSM). The SA-NCSM starts from nucleon-nucleon potentials and, by exploring symmetries known to dominate the nuclear dynamics, can reach nuclei up through the calcium region by accommodating ultra-large model spaces critical to descriptions of clustering and collectivity. The results are based on calculations of electromagnetic sum rules and discretized responses using the Lanczos algorithm, that can be used to determine response functions, and for 4He are benchmarked against exact solutions of the hyperspherical harmonics method. In particular, we focus on He, Be, and O isotopes, including giant resonances and monopole sum rules.Comment: 6 pages, 4 figures, Proceedings of the Fourth International Workshop on State of the Art in Nuclear Cluster Physics, Galveston, TX, USA, May 13-18, 201