The excited states of neutron-rich Fe isotopes have been studied through a multinucleon transfer reaction of a Zn-70 beam on a U-238 target. Unambiguous identification of prompt gamma rays belonging to each nucleus was performed by coincidence detection of the ions in a high-acceptance magnetic spectrometer. The observed spectra are compared with large-scale shell-model calculations in the fpgd model space.

In recent years a series of near- and sub-barrier transfer experiments have been carried out at LNL, with reaction products detected in inverse kinematics and at forward angles with the large solid angle magnetic spectrometer PRISMA. Nucleon-nucleon correlation properties have been studied by measuring transfer cross sections far below the Coulomb barrier, making excitation functions down to very low energies and corresponding to very large distances of closest approach where the nuclear absorption is small. Such kind of studies are of general interest since one probes the tails of the density distributions. One subtle case is the possible manifestation of a nuclear Josephson effect. Predictions have been made of a specific gamma strength function associated with the dipole oscillations generated by the, mainly successive, two neutron transfer process. The coupling of PRISMA to the AGATA gamma array, recently installed at LNL, offered a unique opportunity to study such an effect. In a very recent experiment we directly tested for the first time the possible manifestation of Cooper pair oscillations, observed to date only in condensed matter physics.

Abstract Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions $$E\sigma $$ E σ in relation to their first energy derivatives $$d(E\sigma )/dE$$ d ( E σ ) / d E . The relation between $$d(E\sigma )/dE$$ d ( E σ ) / d E and $$E\sigma $$ E σ removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.

In this Letter we report on effects of nucleon-nucleon correlations probed in nucleon transfer reactions with heavy ions. We measured with high efficiency and resolution a complete set of observables for neutron transfer channels in the 206Pb & thorn; 118Sn system employing a large solid angle magnetic spectrometer, which allowed us to study a wide range of internuclear distances via a detailed excitation function. The coupled channel theory, based on an independent particle transfer mechanism, follows the experimental transfer probabilities for one- and two-neutron pick-up and stripping channels. The experimental two-neutron transfer cross sections indicate that in reactions between pair-vibrational (closed shell) and pair-rotational (open shell) nuclei, correlations manifest via pair-addition and pair-removal modes, which constitute one of the elementary modes of excitations in nuclei.

The Advanced GAmma Tracking Array (AGATA) has been installed at Laboratori Nazionali di Legnaro (LNL), Italy. In this installation, AGATA will consist, at the beginning, of 13 AGATA triple clusters (ATCs) with an angular coverage of 1π, and progressively the number of ATCs will increase up to a 2π angular coverage. This setup will exploit both stable and radioactive ion beams delivered by the Tandem–PIAVE-ALPI accelerator complex and the SPES facility. The new implementation of AGATA at LNL will be used in two different configurations, firstly one coupled to the PRISMA large-acceptance magnetic spectrometer and lately a second one at Zero Degrees, along the beam line. These two configurations will allow us to cover a broad physics program, using different reaction mechanisms, such as Coulomb excitation, fusion-evaporation, transfer and fission at energies close to the Coulomb barrier. These setups have been designed to be coupled with a large variety of complementary detectors such as charged particle detectors, neutron detectors, heavy-ion detectors, high-energy γ-ray arrays, cryogenic and gasjet targets and the plunger device for lifetime measurements. We present in this paper the conceptual design, characteristics and performance figures of this implementation of AGATA at LNL.

Background: The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in C-12+ Mg-24 (with a positive Q value for fusion) at sigma(fus) similar or equal to 0.75 mb, misses a valid interpretation within current theoretical models. Purpose: Our aim has been to search evidence for fusion hindrances in the nearby system C-12+ Mg-26 also having Q(fus) greater than or similar to 0, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations. Methods: The experiment was performed in inverse kinematics using the Mg-26 beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin C-12 evaporations isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E-Delta E-ToF detector telescope following an electrostatic beam deflector. Results: The fusion excitation function of C-12+ Mg-26 has been measured down to approximate to 5 mu b. The astrophysical S factor shows a maximum at an energy where the cross section is approximate to 0.03 mb, significantly lower than for C-12+ Mg-24. This difference is confirmed by the comparison of the two S factors. coupled channel calculations give a good account of the data, but they overpredict the cross sections below approximate to 0.03 mb. The logarithmic slopes of the two excitation functions are superimposable to a large extent, with visible oscillations, more noticeable for C-12+ Mg-24. Conclusions: The hindrance phenomenon is clearly observed in C-12+ Mg-26. The difference between the corresponding threshold energies for C-12+ Mg-24,Mg-26 might (only qualitatively) be attributed to the alpha-like structure of Mg-24. In the Jiang's phenomenological systematics, the different behaviors of C-12+ (24,2)6Mg make the situation more complex, and call into question the extrapolation procedure toward the lighter systems of astrophysical interest.

Multi-Nucleon Transfer (MNT) reactions have been used for decades as a reaction mechanism, in order to populate excited states in nuclei far from stability and to perform nuclear structure studies. Nevertheless, the development of set-ups involving high acceptance tracking magnetic spectrometers (mainly existing in Europe), coupled with the Advanced GAmma Tracking Array (AGATA) opens new possibilities, especially if they are used in conjunction with high-intensity stable beams or ISOL RIBs. In this article, we will discuss the capabilities of such set-ups aiming at different goals, including complete information in high-resolution spectroscopy as well as lifetime measurements.

The measurement of the production cross sections of exotic neutron -rich heavy nuclei, in the uranium region, in the vicinity of the N = 152 deformed shell gap was carried out via multinucleon transfer reactions of 238U + 238U at 7.193 and 6.765 MeV/A using the VAMOS++ magnetic spectrometer coupled to the AGATA and ID-Fix photon detection arrays. This article reports on the status of the VAMOS++ data analysis and results on the population of the strongest (+/- 1n) transfer channels observed from the decay of long-lived products after irradiation.

The next years will see the completion of the radioactive ion beam facility SPES (Selective Production of Exotic Species) and the upgrade of the accelerators complex at Istituto Nazionale di Fisica Nucleare – Legnaro National Laboratories (LNL) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics, and applications. The nuclear physics community has organised a workshop to discuss the new physics opportunities that will be possible in the near future by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.

We measured multinucleon transfer reactions for the 206Pb + 118Sn system at Elab = 1200 MeV by employing the large solid angle magnetic spectrometer PRISMA. Differential and total cross sections and Q-value distri-butions have been obtained for a variety of neutron and proton pick-up and stripping channels. The Q-value distributions show how the quasielastic and deep inelastic processes depend on the mass and charge of the transfer products. The corresponding cross sections have been compared with calculations performed with the GRAZING code. An overall good agreement is found for most of the few nucleon transfer channels. The underestimation of the data for channels involving a large number of transferred nucleons indicates that more complicated processes populate the given isotopes.

The systematics of the lowest 2 ^+ energies of even-even nuclei, and the B(E2) rates connecting those levels to the ground states, give essential information about the degree of collectivity in various regions of the nuclide chart. The B(E2) rates provide crucial tests of theoretical predictions, such as the quenching of shell structure in neutron-rich nuclei. Measurements of such rates are in progress using multi-nucleon transfer reactions and radioactive ion beams. We have measured the fusion excitation functions for the three systems ^48 Ca + ^116 Cd, ^118 Sn, ^120 Te, in the relevant energy range from above to below the Coulomb barrier. The magic projectile ^48 Ca has been chosen in view of its spherical and rigid structure, while the three targets have proton numbers Z= 48,50,52 . We observe that the cross sections are smallest for the target ^118 Sn, thus indicating the effect on sub-barrier fusion of crossing the major shell closure at Z = 50. This suggests the possibility of using near-barrier fusion reactions of radioactive ion beams with suitable stable targets, as a complementary technique to evidence the low-lying nuclear structure of exotic nuclei, besides well established methods.

In the present work the fusion cross section of the 12 C+ 24 Mg system has been measured down to energies far below the coulomb barrier around 4μ b . This system is slightly heavier than those of astrophysical interest, like 12 C+ 12 C and 16 O+ 16 O. The data points highlight the presence of hindrance in 12 C+ 24 Mg because the excitation function is over-estimated by standard Coupled-Channels calculations, and a clear maximum of the S factor has been observed. The cross section at hindrance threshold is found to be remarkably large (σ ≈0.75mb). The S-factor maximum is nicely fitted using both an empirical interpolation in the spirit of the adiabatic model, and the hindrance parametrisation. The data far below the barrier may suggest that the coupling strengths gradually decrease and vanish, so that the excitation function seems to be well reproduced by a simple one-dimensional tunnelling through the potential barrier in that energy range. On the other hand, the equally good fit obtained with the hindrance model, indicates that discriminating between the two approaches would require further precise measurements at slightly lower energies.

Background: The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in $^{12}\mathrm{C}+^{24}\mathrm{Mg}$ (with a positive $Q$ value for fusion) at ${\ensuremath{\sigma}}_{\mathrm{fus}}\ensuremath{\simeq}0.75$ mb, misses a valid interpretation within current theoretical models.Purpose: Our aim has been to search evidence for fusion hindrances in the nearby system $^{12}\mathrm{C}+^{26}\mathrm{Mg}$ also having ${Q}_{\mathrm{fus}}>0$, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations.Methods: The experiment was performed in inverse kinematics using the $^{26}\mathrm{Mg}$ beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin $^{12}\mathrm{C}$ evaporations isotopically enriched to $99.9%$. The fusion-evaporation residues were detected at small angles by a $E\ensuremath{-}\mathrm{\ensuremath{\Delta}}E$-ToF detector telescope following an electrostatic beam deflector.Results: The fusion excitation function of $^{12}\mathrm{C}+^{26}\mathrm{Mg}$ has been measured down to $\ensuremath{\approx}5\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{b}$. The astrophysical $S$ factor shows a maximum at an energy where the cross section is $\ensuremath{\approx}0.03$ mb, significantly lower than for $^{12}\mathrm{C}+^{24}\mathrm{Mg}$. This difference is confirmed by the comparison of the two $S$ factors. coupled channel calculations give a good account of the data, but they overpredict the cross sections below $\ensuremath{\approx}0.03$ mb. The logarithmic slopes of the two excitation functions are superimposable to a large extent, with visible oscillations, more noticeable for $^{12}\mathrm{C}+^{24}\mathrm{Mg}$.Conclusions: The hindrance phenomenon is clearly observed in $^{12}\mathrm{C}+^{26}\mathrm{Mg}$. The difference between the corresponding threshold energies for $^{12}\mathrm{C}+^{24,26}\mathrm{Mg}$ might (only qualitatively) be attributed to the $\ensuremath{\alpha}$-like structure of $^{24}\mathrm{Mg}$. In the Jiang's phenomenological systematics, the different behaviors of $^{12}\mathrm{C}+^{24,26}\mathrm{Mg}$ make the situation more complex, and call into question the extrapolation procedure toward the lighter systems of astrophysical interest.

We measured multinucleon transfer reactions for the $^{206}\mathrm{Pb}+^{118}\mathrm{Sn}$ system at ${E}_{\mathrm{lab}}=1200$ MeV by employing the large solid angle magnetic spectrometer PRISMA. Differential and total cross sections and $Q$-value distributions have been obtained for a variety of neutron and proton pick-up and stripping channels. The $Q$-value distributions show how the quasielastic and deep inelastic processes depend on the mass and charge of the transfer products. The corresponding cross sections have been compared with calculations performed with the grazing code. An overall good agreement is found for most of the few nucleon transfer channels. The underestimation of the data for channels involving a large number of transferred nucleons indicates that more complicated processes populate the given isotopes.

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.

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers $A=35$, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of $^{36}\mathrm{S}$ ions of energy 225 MeV incident on a thin $^{208}\mathrm{Pb}$ target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA $\ensuremath{\gamma}$-ray tracking array was used to detect $\ensuremath{\gamma}$ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For $^{35}\mathrm{S}$, the lifetime was determined for the first $1/{2}^{+}$ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the ${3}^{\ensuremath{-}}$ state of $^{36}\mathrm{S}$ at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (${6}^{+}$) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For $^{37}\mathrm{S}$, the states for which lifetime limits were established were those at 646 keV with ${J}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}}$ and at 2776 keV with ${J}^{\ensuremath{\pi}}=11/{2}^{\ensuremath{-}}$; there are no previously published lifetime values for excited states of $^{37}\mathrm{S}$. Finally, a lifetime limit was established for the ${J}^{\ensuremath{\pi}}=({6}^{+})$ state of $^{38}\mathrm{S}$ at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers A = 35, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of S-36 ions of energy 225 MeV incident on a thin Pb-208 target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA gamma-ray tracking array was used to detect gamma rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For S-35, the lifetime was determined for the first 1/2(+) state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the 3(-) state of S-36 at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (6(+)) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For S-37, the states for which lifetime limits were established were those at 646 keV with J(pi)=3/2(-) and at 2776 keV with J(pi)=11/2(-); there are no previously published lifetime values for excited states of 37S. Finally, a lifetime limit was established for the J(pi )= (6(+)) state of S-38 at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.

Multinucleon transfer reactions in 90 Zr+ 208 Pb have been studied via fragment- γ coincidences, employing the PRISMA magnetic spectrometer coupled to the CLARA γ -array. An analysis on Y isotopes has been carried out incorporating spectroscopic as well as reaction mechanism aspects. New γ transitions have been observed in 94 Y, confirming the findings of recent studies where nuclei were produced via fission of uranium, and a comparison with near-by 90,92 Y isotopes populated in the same reaction has been discussed. Experimental cross sections have been extracted and compared with the GRAZING calculations, showing a fair agreement along the neutron pick-up side. The results confirm how multinucleon transfer reactions are a suitable mechanism for the study of neutron-rich nuclei.

We present some of the recent experimental results in heavy-ion transfer reactions obtained with the large solid angle magnetic spectrometer PRISMA at energies close to the Coulomb barrier. We focus on a series of experiments that have been carried out to study the nucleon-nucleon correlations for closed shell and superfluid systems. They are discussed together with the newest results concerning the proton transfer channels above and below the Coulomb barrier. The second set of the experiments was performed to study the production mechanism of heavy neutron-rich nuclei and the related effects of secondary processes.