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The high explosive PBX 9502 undergoes irreversible expansion during thermal cycling ("ratchet growth"). Recent innovations in thermomechanical modeling via homogenization strategies are beginning to incorporate mesoscale information such as grain size, total porosity, and spatial distribution of voids and cracks. To generate a complete experimental data set to challenge and inform these models, PBX 9502 pellets were thermally cycled, cross-sectioned using ion polishing, and imaged in high resolution with scanning electron microscopy. Ratchet growth was found to drive expansion through microcracking. Microcracks were affected by agglomeration of crystals within the PBX. Virgin material showed greater ratchet growth than recycled material. [ABSTRACT FROM AUTHOR]

Low-to-medium temperature fluid reservoirs hosted in carbonate rocks are some of the most promising and unknown geothermal systems. Western Sicily is considered a key exploration area. This paper illustrate a multidisciplinary and integrated review of the existing geological, geochemical and geophysical data, mainly acquired during oil and gas explorations since the 1950s, specifically re-analyzed for geothermal purposes, has led to understanding the western Sicily geothermal system as a whole, and to reconstructing the modalities and particular features of the deep fluid circulation within the regional reservoir. The data review suggests the presence of wide groundwater flow systems in the reservoir beneath impervious cap rocks. We identified the main recharge areas, reconstructed the temperature distribution at depth, recognized zones of convective geothermal flow, and depicted the main geothermal fluid flow paths within the reservoir. We believe that our reconstruction of geothermal fluid circulation is an example of the general behavior of low-to-medium enthalpy geothermal systems hosted in carbonate units on a regional scale. Due to the recent technological developments of binary plants, these systems have become more profitable, not only for geothermal direct uses but also for power production. [ABSTRACT FROM AUTHOR]

The study of core samples and in-hole data of a 545 m deep well drilled in Mt. Amiata extinct volcano allowed a better characterization of the shallow volcanic reservoir, which is exploited for domestic utilization. The new discovery is that: 1) the water table level is at a depth of 302 m b.g.l. (783 m a.s.l.), in agreement with recent magnetotelluric surveys, and in disagreement with previous hydrogeological models; 2) there is no evidence of present or past interaction with geothermal fluids, the alteration minerals being present only in fractures within the volcanic rocks and indicating fluids of low temperature and relatively low pH due to gas inlets in the volcanic reservoir; and 3) the volcanic reservoir is characterized by fracture permeability, as shown by the fracture system along the well. On the base of these new data the previous geological and hydrogeological models of Mt. Amiata should be revised. In particular, the hypothesis of a catastrophic lowering of the water table in a short time span is unlikely. [ABSTRACT FROM AUTHOR]

An excitation function of one- and two-neutron transfer channels for the 60Ni+116Sn system has been measured with the magnetic spectrometer PRISMA in a wide energy range, from the Coulomb barrier to far below it. The experimental transfer probabilities are well reproduced, for the first time with heavy ions, in absolute values and in slope by microscopic calculations which incorporate nucleon-nucleon pairing correlations. [ABSTRACT FROM AUTHOR]

The γ decays of neutron-rich Ca isotopes around 48Ca were measured at Legnaro National Laboratory with the PRISMA-CLARA setup, using the heavy-ion transfer reactions 48Ca on MNi and 48Ca on 208Pb at ≈6 MeV/A. The work shows the feasibility to perform full in-beam y spectroscopy with heavy-ion transfer reactions (in terms of angular distributions, polarizations, and lifetimes analysis), providing a method that can be further exploited in the future with heavy targets and radioactive beams. For the one-neutron transfer channels, 49Ca and 47Ca, shell-model and particle-vibration coupling calculations are used to understand the nature of the states. In particular, in both nuclei evidence is found for particle-vibration coupled states based on the 3- phonon of 48Ca. In the two-neutron transfer channels, 46Ca and 50Ca, the experimental data are in global agreement with predictions based on full fp shell-model calculations. [ABSTRACT FROM AUTHOR]

Elastic, inelastic, one-nucleon transfer channels in the 48Ca + 64Ni reaction have been measured at ≈6 MeV/nucleon with the PRISMA-CLARA setup, at Legnaro National Laboratory, consisting of the coupling of a large solid angle magnetic spectrometer with a germanium array. By trajectory reconstruction the reaction products have been fully identified in mass, nuclear charge, kinetic energy, while coincident γ spectra of binary partners have been constructed after Doppler correction. Absolute differential cross sections have been extracted for the inelastic excitation and one-nucleon transfer, also for specific excited states. The data are in good agreement with semiclassical calculations and distorted wave Born approximation predictions. The work outlines an experimental method which can become valuable to extract structural information from heavy-ion reaction studies. [ABSTRACT FROM AUTHOR]

Abstract: Neutron rich nuclei around 48Ca have been measured with the CLARA–PRISMA setup, making use of 48Ca on 64Ni binary reactions, at 5.9 MeV/A. Angular distributions of γ rays give evidence, in several transfer channels, for a large spin alignment () perpendicular to the reaction plane, making it possible to firmly establish spin and parities of the excited states. In the case of 49Ca, states arising from different types of particle–core couplings are, for the first time, unambiguously identified on basis of angular distribution, polarization and lifetime measurements. Shell model and particle–vibration coupling calculations are used to pin down the nature of the states. Evidence is found for the presence, in the same excitation energy region, of two types of coupled states, i.e. single particle coupled to either 48Ca or 50Ca simple configurations, and particle–vibration coupled states based on the phonon of 48Ca. [Copyright &y& Elsevier]

The deep inelastic reaction 48Ca+64Ni at 6 MeV/A has been studied using the CLARA-PRISMA setup. Angular distributions for pure elastic scattering and total cross-sections of the most relevant transfer channels have been measured. The experimental results are compared with predictions from a semiclassical model, showing good agreement for the presently analyzed few neutrons transfer channels. The &gamm;-decay of the most intense reaction products has also been studied, giving indications of the population of states with very short lifetimes. [ABSTRACT FROM AUTHOR]

We performed a γ-particle coincidence experiment for the 60Ni+116Sn system to investigate whether the population of the two-neutron pickup channel leading to 62Ni is mainly concentrated in the ground-state transition, as has been found in a previous work [D. Montanari et al., Phys. Rev. Lett. 113, 052501 (2014)]. The experiment has been performed by employing the PRISMA magnetic spectrometer coupled to the Advanced Gamma Tracking Array (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one- and two-neutron transfer channels has been extracted. We found that in the two-neutron transfer channel the strength to excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtained results that the 2n channel is dominated by the ground-state to ground-state transition. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents analogue models for the emplacement of granitic magmas in upper crustal levels with different mechanical layering during shortening, extension and strike–slip deformation. In particular, we investigated how a weak layer embedded in the upper brittle crust can control the level of magma emplacement. The adopted experimental setup was used to examine the control of soft rocks on the movement of magma through a deforming brittle crust. Model results indicate that the occurrence of a weak (soft) layer embedded in brittle (stiff) material has an impact on the level of magma emplacement. The level of emplacement during both extension and shortening was systematically deeper for models with a soft layer than for purely brittle models. During strike–slip deformation the magma pierced the surface in both purely brittle and brittle–ductile models. [Copyright &y& Elsevier]

Abstract: A wide sector of the internal portion of the Central Apennines, which comprises the southern Lepini Mtns up to the northern Simbruini Mtns has been investigated through detailed field mapping and integrated with structural analyses. A few small productive oil fields and a large number of hydrocarbon seeps and oil impregnations are located in this sector. This area offers good opportunities for testing the use of structural fieldwork methodologies in order to highlight oil migrating paths, from Triassic source rocks, and prospecting chances for oil field exploitation. The main stages of the structural evolution of the area took place after deposition of the foredeep sediments (Frosinone Fm.), i.e. after Late Tortonian, under a stress field characterised by a NE–SW trending σ1, which was responsible for the early emplacement of major thrust faults present in the area. The Messinian-Early Pliocene thrust-top basin deposits allowed the reconstruction of an in-sequence evolution of the thrust system. The development of out-of-sequence thrusting post-dates these structures leading to a further strong shortening phase in the area during the Pliocene. This phase is characterised by a roughly NNE–SSW trending σ1. Some peculiar tectonic features evidenced by thrust faults with younger-over-older relationships and an inversion of the original stacking of thrust sheets developed during this phase. Successively, a block-faulting tectonic, mainly with NE–SW extension stress field, occurred and dismembered the compressive tectonic edifice. Later on up to the Middle Pleistocene, N–S to NNE–SSW trending dextral strike-slip faults also acted in the area. Associated to the strike-slip tectonics are local volcanic centres as well as necks, whose compositions show a mantle origin, thus indicating deep seating and a possible lithospheric significance of these structures. In the light of this study, the reduced extension of the productive oil area as well as the spotting of oil seeps, may indicate that the migration conditions are not tied to well defined structures but that likely the cross-cutting points among structures facilitate the conditions for an upwards rising of oil. These conditions in particular are achieved at least in two cases: (1) where the Late Triassic source rocks do not have great depth due to normal or reverse faults, or (2) at a major depth when encountered by transcurrent-oblique roughly N–S trending faults—in both cases oil can easily migrate along the damage zone associated to the fault plane. [Copyright &y& Elsevier]

A detailed comparative study of the sub-barrier fusion of the two nearby systems 36S+50Ti,51V was performed at the National Laboratories of Legnaro (INFN). The experiment aimed to evidence possible effects of the non-zero spin of the ground state of the 51V nucleus on the sub-barrier excitation function and on the shape of the barrier distribution. The comparison of both excitation functions and barrier distributions showed a very similar behavior, down to the level of 20–30 μb. Coupled-channels calculations have been performed including the low-energy excitations of both projectile and the two targets, and the results are in very good agreement with the data. This indicates that the low-lying levels in 51V can be interpreted in the weak-coupling scheme and that the extra proton in the f7/2 shell does not have a significant influence on sub-barrier fusion. [ABSTRACT FROM AUTHOR]

Abstract The STELLA (STELlar LAboratory) experimental station for the measurement of deep sub-barrier light heavy-ion fusion cross sections has been installed at the Andromède accelerator at the Institut de Physique Nucléaire, Orsay (France). The setup is designed for the direct experimental determination of heavy-ion fusion cross sections as low as tens of picobarn. The detection concept is based on the coincident measurement of emitted gamma rays with the UK FATIMA (FAst TIMing Array) and evaporated charged particles using a silicon detector array. Key developments relevant to reaching the extreme sub-barrier fusion region are a rotating target mechanism to sustain beam intensities above 10 μ A, an ultra-high vacuum of 10−8 mbar to prevent carbon built-up and gamma charged-particle timing in the order of nanoseconds sufficient to separate proton and alpha particles. [ABSTRACT FROM AUTHOR]

A gas detection system has been developed for the identification in atomic number Z and the measurement of energy E , timing and scattering angles of the fragments produced in low-energy heavy-ion induced reactions. In particular, it has been designed to be used in kinematic coincidence measurements in conjunction with the large solid angle magnetic spectrometer PRISMA. The detection system is composed of a multiwire parallel plate avalanche counter (MWPPAC) followed by an axial field ionization chamber. Both detectors have been fully characterized with analog electronics by means of heavy-ion beams delivered by the Tandem-ALPI accelerator complex of LNL. Digital electronics has also been tested for the processing of anode signal of the ionization chamber. [ABSTRACT FROM AUTHOR]

Angular distributions of $ \gamma$ -rays for selected transitions in Ar isotopes have been studied with the PRISMA magnetic spectrometer coupled to the CLARA $ \gamma$ array. These transitions were populated in Ar isotopes reached via neutron transfer in the Ar + Pb reaction. By comparison with the shape of the experimental angular distribution of the known E2 transitions we established more firmly the spin and parity of excited states. In particular, in Ar for the $ (11/2^-)$ state through the $ (11/2^-) \rightarrow 7/2^-$ transition whose structure was discussed in terms of a phonon-fermion coupled state. The comparison with the expected fully aligned spin indicated that a high level of spin alignment has been reached. [ABSTRACT FROM AUTHOR]

In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180 °C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate change-induced increases in temperature or evaporation at the global scale. [ABSTRACT FROM AUTHOR]

An experiment was performed at LNL to obtain information concerning the yield distributions in both the 132Sn (N = 82) and the 208Pb (N = 126) regions of the nuclide chart. The experimental set-up was composed of the large-acceptance magnetic spectrometer PRISMA to detect the light partner of the reaction, in conjunction with a recently installed ancillary set-up to detect the heavy partner. [ABSTRACT FROM AUTHOR]

One and two proton transfer channels have been measured in 116Sn+60Ni with the magnetic spectrometer PRISMA by making an excitation function at several bombarding energies, from above to well below the Coulomb barrier. The total kinetic energy loss distributions show the predominance of quasi-elastic processes in the sub-barrier regime. The data have been compared with calculations performed with the GRAZING program, based on semiclassical formalism, and in the Distorted Wave Born Approximation (DWBA), which provided a good theoretical description of the extracted transfer probabilities for the one proton transfers. The much larger values of the experimental two proton transfers compared with those evaluated within an independent particle transfer mechanism, indicate the presence of strong proton-proton correlations. The results complement the ones of the previously analyzed one- and two-neutron transfers, providing significant new information on the subject compared to past works. [ABSTRACT FROM AUTHOR]

In this study a new approach to geothermal potential assessment was set up and applied in four regions in southern Italy. Our procedure, VIGORThermoGIS, relies on the volume method of assessment and uses a 3D model of the subsurface to integrate thermal, geological and petro-physical data. The method thus produces 2D geothermal potential maps for three different uses: district heating, district heating and cooling, and electrical power production. Our study focused on carbonate reservoirs, which usually present an excellent natural permeability and important geothermal gradients at depth. Our computations were possible thanks to the large quantity of data available from hydrocarbon exploration that largely investigate deep-seated reservoirs. Based on geothermal potential available for power production we estimate the contribution of the geothermal energy in the CO 2 emissions reduction in the study regions. Moreover policy makers as well as investors can use our maps to establish new policies and to locate the most promising places for geothermal development, in line with the international low carbon strategy. [ABSTRACT FROM AUTHOR]

Background: No data on the fusion excitation function of 48Ti + 58Fe in the energy region near the Coulomb barrier existed prior to the present work, while fusion of 58Ni + 54Fe was investigated in detail some years ago, down to very low energies, and clear evidence of fusion hindrance was noticed at relatively high cross sections. 48Ti and 58Fe are soft and have a low-lying quadrupole excitation lying at ≈800-900 keV only. Instead, 58Ni and 54Fe have a closed shell (protons and neutrons, respectively) and are rather rigid. Purpose: We aim to investigate (1) the possible influence of the different structures of the involved nuclei on the fusion excitation functions far below the barrier and, in particular, (2) whether hindrance is observed in 48Ti + 58Fe, and to compare the results with current coupled-channels models. Methods: 48Ti beams from the XTU Tandem accelerator of INFN-Laboratori Nazionali di Legnaro were used. The experimental setup was based on an electrostatic beam separator, and fusion-evaporation residues (ERs) were detected at very forward angles. Angular distributions of ERs were measured. Results: Fusion cross sections of 48Ti + 58Fe have been obtained in a range of nearly six orders of magnitude around the Coulomb barrier, down to ≲2 μb. The sub-barrier cross sections of 48Ti + 58Fe are much larger than those of 58Ni + 45Fe. Significant differences are also observed in the logarithmic derivatives and astrophysical S factors. No evidence of hindrance is observed, because coupled-channels calculations using a standard Woods- Saxon potential are able to reproduce the data in the whole measured energy range. Analogous calculations for 58Ni + 45Fe predict clearly too large cross sections at low energies. The two fusion barrier distributions are wide and display a complex structure that is only qualitatively fit by calculations. Conclusions: It is pointed out that all these different trends originate from the dissimilar low-energy nuclear structures of the involved nuclei. In particular, the strong quadrupole excitations in 48Ti and 58Fe produce the relative cross section enhancement and make the barrier distribution ≈ 2 MeV wider, thus probably pushing the threshold for hindrance below the measured limit. [ABSTRACT FROM AUTHOR]

Absolute cross sections for isotopically identified products formed in multinucleon transfer in the 136Xe+198Pt system at ~8 MeV/nucleon are reported. The isotopic distributions obtained using a large acceptance spectrometer demonstrated the production of the "hard-to-reach" neutron-rich isotopes for Z<78 around the N=126 shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around N=126 which are crucial for understanding both astrophysically relevant processes and the evolution of "magic" numbers far from stability. [ABSTRACT FROM AUTHOR]

Nuclei produced via multineutron transfer channels have been studied in 90 Zr + 208 Pb close to the Coulomb barrier energy in a fragment- γ coincident measurement employing the PRISMA magnetic spectrometer coupled to the CLARA γ -array. The selective properties of the reaction mechanism have been discussed in terms of states and their strength excited in the neutron transfer channels leading to 89–94 Zr isotopes. A strong population of yrast states, with energies up to ∼7.5 MeV has been observed. [ABSTRACT FROM AUTHOR]

Background: Multinucleon transfer reactions (MNT) are a competitive tool to populate exotic neutron-rich nuclei in a wide region of nuclei, where other production methods have severe limitations or cannot be used at all. Purpose: Experimental information on the yields of MNT reactions in comparison with theoretical calculations are necessary to make predictions for the production of neutron-rich heavy nuclei. It is crucial to determine the fraction of MNT reaction products which are surviving neutron emission or fission at the high excitation energy after the nucleon exchange. Method: Multinucleon transfer reactions in 136Xe + 238U have been measured in a high-resolution γ-ray/particle coincidence experiment. The large solid-angle magnetic spectrometer PRISMA coupled to the high-resolution Advanced Gamma Tracking Array (AGATA) has been employed. Beamlike reaction products after multinucleon transfer in the Xe region were identified and selected with the PRISMA spectrometer. Coincident particles were tagged by multichannel plate detectors placed at the grazing angle of the targetlike recoils inside the scattering chamber. Results: Mass yields have been extracted and compared with calculations based on the grazing model for MNT reactions. Kinematic coincidences between the binary reaction products, i.e., beamlike and targetlike nuclei, were exploited to obtain population yields for nuclei in the actinide region and compared to x-ray yields measured by AGATA. Conclusions: No sizable yield of actinide nuclei beyond Z=93 is found to perform nuclear structure investigations. In-beam γ-ray spectroscopy is feasible for few-neutron transfer channels in U and the -2p channel populating Th isotopes. [ABSTRACT FROM AUTHOR]

Fusion cross sections of 28 Si + 28 Si have been measured in a range above the barrier with a very small energy step ( Δ E lab = 0.5 MeV ). Regular oscillations have been observed, best evidenced in the first derivative of the energy-weighted excitation function. For the first time, quite different behaviors (the appearance of oscillations and the trend of sub-barrier cross sections) have been reproduced within the same theoretical frame, i.e., the coupled-channel model using the shallow M3Y + repulsion potential. The calculations suggest that channel couplings play an important role in the appearance of the oscillations, and that the simple relation between a peak in the derivative of the energy-weighted cross section and the height of a centrifugal barrier is lost, and so is the interpretation of the second derivative of the excitation function as a barrier distribution for this system, at energies above the Coulomb barrier. [ABSTRACT FROM AUTHOR]

The discovery of argon from deep underground sources with significantly less 39 Ar than atmospheric argon was an important step in the development of direct dark matter detection experiments using argon as the active target. We report on the design and operation of a low-background single-phase liquid argon detector that was built to study the 39 Ar content of this underground argon. Underground argon from the Kinder Morgan CO 2 plant in Cortez, Colorado was determined to have less than 0.65% of the 39 Ar activity in atmospheric argon, or 6.6 mBq/kg specific 39 Ar activity. [ABSTRACT FROM AUTHOR]

Measurements of fusion excitation functions of 58Ni + 124Sn and 64Ni + 124Sn are extended towards lower energy to cross sections of 1 fib and are compared to detailed coupled-channels calculations. The calculations clearly show the importance of including transfer reactions in a coupled-channels treatment for such heavy systems. This result is different from the conclusion made in a previous article which claimed that the influence of transfer on fusion is not important for fusion reactions of Ni + Sn. In the energy region studied in this experiment no indication of fusion hindrance has been observed, which is consistent with a systematic study of this behavior. [ABSTRACT FROM AUTHOR]

The 40Ar + 208Pb multinucleon transfer reaction has been studied at Elab = 255 MeV with the large solid angle magnetic spectrometer PRISMA. Mass and charge yields, differential and total cross sections, total kinetic energy loss distributions of different channels were simultaneously measured. Angular distributions were measured in a wide angular range by matching different spectrometer angular settings. Absolute cross sections were obtained by careful evaluation of the spectrometer response function. These cross sections for different transfer channels allow the discussion of the role played by nucleon-nucleon correlations. [ABSTRACT FROM AUTHOR]

Background: The nuclear structure of colliding nuclei is known to influence the fusion process. Couplings of the relative motion to nuclear shape deformations and vibrations lead to an enhancement of the sub-barrier fusion cross section in comparison with the predictions of one-dimensional barrier penetration models. This enhancement is explained by coupled-channels calculations including these couplings. The sub-barrier fusion cross section is also affected by nucleon transfer channels between the colliding nuclei. Purpose: The aim of the present experiment is to investigate the influence of the projectile and target nuclear structures on the fusion cross sections in the 40Ca+58Ni and 40Ca+64Ni systems. Methods: The experimental and theoretical fusion excitation functions as well as the barrier distributions were compared for these two systems. Coupled-channels calculations were performed using the ccfull code. Results: Good agreement was found between the measured and calculated fusion cross sections for the 40Ca + 58Ni system. The situation is different for the 40Ca + 64Ni system where the coupled-channels calculations with no nucleon transfer clearly underestimate the fusion cross sections below the Coulomb barrier. The fusion excitation function was, however, well reproduced at low and high energies by including the coupling to the neutron pair-transfer channel in the calculations. Conclusions: The nuclear structure of the colliding nuclei influences the fusion cross sections below the Coulomb barrier for both 40Ca + 58,64Ni systems. Moreover, we highlighted the effect of the neutron pair-transfer channel on the fusion cross sections in 40Ca + 64Ni. [ABSTRACT FROM AUTHOR]

Background: The fusion excitation function of the system 28Si + 28 at energies near and below the Coulomb barrier is known only down to ≃ 15 µb. This precludes any information on both coupling effects on sub-barrier cross sections and the possible appearance of hindrance. For 28Si + 30 even if the fusion cross section is measured down to ≃50 µb, the evidence of hindrance is marginal. Both systems have positive fusion Q values. While 28Si has a deformed oblate shape, 30Si is spherical. Purpose: We investigate 1. the possible influence of the different structure of the two Si isotopes on the fusion excitation functions in the deep sub-barrier region and 2. whether hindrance exists in the Si+Si systems and whether it is strong enough to generate an S-factor maximum, thus allowing a comparison with lighter heavy-ion systems of astrophysical interest. Methods: 28Si beams from the XTU Tandem accelerator of the INFN Laboratori Nazionali di Legnaro were used. The setup was based on an electrostatic beam separator, and fusion evaporation residues (ER) were detected at very forward angles. Angular distributions of ER were measured. Results: Fusion cross sections of 28Si + 28 have been obtained down to ≃600 nb. The slope of the excitation function has a clear irregularity below the barrier, but no indication of a S-factor maximum is found. For 28Si + 30 the previous data have been confirmed and two smaller cross sections have been measured down to ≃4 µb. The trend of the S-factor reinforces the previous weak evidence of hindrance. Conclusions: The sub-barrier cross sections for 28Si + 28 are overestimated by coupled-channels calculations based on a standard Woods-Saxon potential, except for the lowest energies. Calculations using the M3Y+repulsion potential are adjusted to fit the 28Si + 28 and the existing 30Si + 30 data. An additional weak imaginary potential (probably simulating the effect of the oblate 28Si deformation) is required to fit the low-energy trend of 28Si + 28. The parameters of these calculations are applied to predict the ion-ion potential for 28Si + 30. Its cross sections are well reproduced by also including one- and successive two-neutron transfer channels, besides the low-lying surface excitations. [ABSTRACT FROM AUTHOR]

Measurements of the excitation function for the fusion of 24Mg + 30Si (Q = 17.89 MeV)have been extended toward lower energies with respect to previous experimental data. The 5-factor maximum observed in this large, positive-Q-value system is the most pronounced among such systems studied thus far. The significance and the systematics of an S-factor maximum in systems with positive fusion Q values are discussed. This result would strongly impact the extrapolated cross sections and reaction rates in the carbon and oxygen burnings and, thus, the study of the history of stellar evolution. [ABSTRACT FROM AUTHOR]

Abstract: The sub-barrier fusion excitation function of 40Ca + 96Zr has been measured down to cross sections ≃2.4 μb, i.e. two orders of magnitude smaller than obtained in a previous experiment, where the sub-barrier fusion of this system was found to be greatly enhanced with respect to 40Ca + 90Zr, and the need of coupling to transfer channels was suggested relying on coupled-channels calculations. The purpose of this work has been to investigate the behavior of 40Ca + 96Zr fusion far below the barrier, thereby disentangling the elusive interplay of effects due to inelastic couplings, transfer couplings and, possibly, the appearance of the fusion hindrance. The smooth trend of the excitation function has been found to continue, and the logarithmic slope increases very slowly. No indication of hindrance shows up, and a comparison with 48Ca + 96Zr is illuminating in this respect. A new CC analysis of the complete excitation function has been performed, including explicitly one- and two-nucleon transfer channels. Such transfer couplings bring significant cross section enhancements, even at the level of a few μb. Locating the hindrance threshold, if any, in 40Ca + 96Zr would require challenging measurements of cross sections in the sub-μb range. [Copyright &y& Elsevier]