Search

The mechanism of reactions with weakly-bound proton-rich nuclei at energies near the Coulomb barrier is a long-standing open question owing to the paucity of experimental data. In this study, a complete kinematics measurement was performed for the proton drip-line nucleus 17F interacting with 58Ni at four energies near the Coulomb barrier. Thanks to the powerful performance of the detector array, exhaustive information on the reaction channels, such as the differential cross sections for quasielastic scattering, exclusive and inclusive breakup, as well as for fusion-evaporation protons and alphas, was derived for the first time. The angular distributions of quasielastic scattering and exclusive breakup can be described reasonably well by the continuum-discretized coupled-channels calculations. The inclusive breakup was investigated using the three-body model proposed by Ichimura, Austern, and Vincent, and results indicate the non-elastic breakup is the dominant component. The total fusion cross sections were determined by the fusion-evaporation protons and alphas. Based on the measured exclusive breakup data, the analysis of the classical dynamical simulation code PLATYPUS demonstrates that the incomplete fusion plays a minor role. Moreover, compared with 16O+58Ni, both the reaction and total fusion cross sections of 17F+58Ni exhibit an enhancement in the sub-barrier energy region, which mainly arises from couplings to the continuum states. This work indicates that the information of full reaction channels is crucially important to comprehensively understand the reaction mechanisms of weakly bound nuclear systems.

The elastic scattering process for the nuclear reactions induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target was measured for the first time in the energy range around the Coulomb barrier. Extensive theoretical calculations within the framework of the optical model were performed. An excellent agreement between experimental data and theoretical predictions was achieved for the reaction 7Be + 208Pb, while a comprehensive understanding of the reaction dynamics induced by the more exotic projectile 8B is still far to be reached. Predictions of the cross section for the breakup for both systems will also be given., The 8B experiment was performed at RI Beam Factory operated by RIKEN Nishina Center and CNS, University of Tokyo. This work was supported by the Polish National Science Centre under Contract No. 2014/14/M/ST2/00738 (COPIN-INFN Collaboration), by JSPS KAKENHI (Nos. 16K05369, and 19K03883) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and by the projects: CONACyT LN-294537 and DGAPA-PAPIIT IA103218.

We developed a Monte-Carlo code for describing the reaction kinematics of the two-body direct processes employed of the EXOTIC beam-line of the Laboratori Nazionali di Legnaro (LNL) for the production of light weakly bound radioactive ion beams at energies of a few MeV/u. The program calculates the phase-space distribution of both primary and secondary beams at the target exit and uses these quantities to optimize the secondary beam selection with the EXOTIC spectrometer. The calculations have been performed and compared with the available experimental data for two reactions: (1)H(2)((17)O, (17)F)n and (3)He((6)Li, (8)B)n. (c) 2008 Elsevier B.V. All rights reserved.

The low intensity (about 105-106 pps) of the presently available RNBs (Radioactive Nuclear Beams) requires detection apparatuses with large solid angle coverage and high granularity. Moreover, the utilization of highly segmented detectors needs unconventional read-out systems appositely designed and the development of electronic boards making use of highly miniaturized and integrated circuitry (ASIC chip). The EXODET (EXOtic DETector) apparatus has been designed and constructed following these guide lines. It consists of large-area silicon detectors segmented in 100 strips on a single side. The particle energy loss information is obtained from the unsegmented side using standard electronic chains, while for the read-out of the incident position information we found suitable a chip already developed for high-energy particle physics experiments. EXODET has been already successfully used in exotic nuclei experiments devoted to the study of the scattering of 17F on a 208Pb target and of 11Be on a 209Bi target at energies around the Coulomb barrier, performed at the Argonne National Laboratory (USA) and at the RIKEN Laboratory (Japan), respectively. The development of these modern and compact detection systems opens new and interesting perspectives for experimentation with RNBs.

The excitation of the dynamical dipole mode along the fusion path was investigated in the formation of a heavy compound nucleus in the A=190 mass region. To form the compound nucleus, the 40 Ca + 152 Sm and 48 Ca + 144 Sm reactions were employed at Elab =11 and 10.1 MeV/nucleon, respectively. Both fusion–evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

The subbarrier fusion cross sections with radioactive ion beams in the systems 10,11 Be+ 209 Bi have been measured and compared also with the stable system 9 Be+ 209 Bi. All three cross sections are similar within experimental accuracy; this is somehow unexpected since, in particular, the fusion process with 11 Be should be influenced by its halo structure and small binding energy and could behave in a different way from the other two Be isotopes, in particular from 10 Be, well bound. Extensive calculations were undertaken within the formalism of continuum discretized coupled channel ( CDCC ) that considered only the coupling to two-body breakup, into n +core, of the projectile with excitation to continuum up to 10 MeV. The results are in agreement with the 11,10 Be experimental data except at low energy where the cross sections could be influenced by target/projectile collective excitations. The CCFULL theoretical approach, compared to CDCC , seems to reproduce better the subbarrier region and worse the above barrier one. The 9 Be cross sections are all underestimated by the CDCC approach while are well reproduced by CCFULL calculations. This suggests that, in this last case, the schematization of the breakup process into 2 only fragments maybe is not adequate and/or other excitations, properly handed by the CCFULL code, could be relevant.

From recent experimental data for the systems 9 Be+ 2 0 8 Pb, 2 0 9 Bi and 6 Li+ 2 0 8 Pb it results that the complete fusion process is hindered with respect to realistic theoretical predictions (CCFUSS). However the 9 Be+ 2 0 8 Pb, 2 0 9 Bi complete fusion cross sections are different from each other contrary to expectations. The 6 Li data show breakup of the projectile into two outgoing fragments, well reproduced by CDCC approach, as well as α or deuteron capture from the target; this is relevant for the theories on the reaction dynamics around the Coulomb barrier.

The prompt γ‐ray emission related with the dynamical dipole mode decay was investigated in the 192Pb mass region by means of the 40Ca+152Sm and 48Ca+144Sm fusion‐evaporation and fission reactions at Elab = 11 and 10.1 MeV/nucleon, respectively. The two reactions populate, through entrance channel having different charge asymmetries, the 192Pb compound nucleus at an excitation energy of 236 MeV with identical spin distribution. Preliminary results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole γ radiation could be of interest for the synthesis of super‐heavy elements through “hot” fusion reactions.

We studied the reaction dynamics induced at Coulomb barrier energies by the weakly-bound Radioactive Ion Beam 7Be (Sα = 1.586 MeV) on medium-mass (58Ni) and heavy (208Pb) targets. The experiments were performed at INFN-LNL (Italy), where a 2-3×105 pps 7Be secondary beam was produced with the RIB in-flight facility EXOTIC. Charged reaction products were detected by means of high-granularity silicon detectors in rather wide angular ranges. The contribution presents an up-to-date status of the data analysis and theoretical interpretation for both systems. European Commission, Seventh Framework Programme 600376

The 12C(α,γ)16O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for SE1(300) and 7 to 120 keVb for SE2(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi- elastic α scattering on 12C, α-transfer reactions to 16O, and 16N decay are usually included in the analysis. Here the β-delayed α decay of 16N i...

Elastic scattering of {sup 7}Be+{sup 28}Si was studied at several near barrier energies for probing the energy dependence of the optical potential. Our analysis at 17.2 MeV will be presented in this article and discussed, in terms of Continuum Coupled Channel Calculations (CDCC). This research is part of a long term plan concerning the energy dependence of the optical potential for weakly bound projectiles, at near barrier energies and for probing the potential threshold anomaly. The experiment took place at the EXOTIC facility - Laboratori Nationali di Legnaro (LNL), and refers to an angular distribution measurement, using the detector array EXPADES (Exotic Particle Detection System). Results at 9 MeV (Rutherford region) were also analyzed and were used for estimating the solid angle. Our analysis for other energies is under process.

The dynamical dipole mode was investigated in the mass region of the 192Pb compound nucleus, by using the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

In the framework of the European program to define a second generation Radioactive Ion Beam facility, LNL are proposing the construction in the next five–seven years of a specialized national facility for RIB originated by fission fragments produced by secondary neutrons. It consists on a two-accelerator ISOL-type facility to provide intense neutron-rich radioactive ion beams of highest quality, in the range of masses between 80 and 160. The conceptual design is based on a high intensity 50 MeV (100 kW) proton linac as driver and on the availability of the heavy-ion accelerator ALPI as post accelerator. The estimated neutron yield is 2×1014 n/s at 0°, high enough to satisfy the demand for an advanced RIB facility. An intense R&D program on different items is actually in progress in collaboration with other Laboratories and University groups and is moving in a European context.

A new facility, named EXOTIC, for the in‐flight production of light low‐energy weakly bound Radioactive Ion Beams (RIBs) is now fully operational at the Laboratori Nazionali di Legnaro (LNL) of the INFN. In this contribution we will present the facility, the Monte‐Carlo code we developed to properly describe the reaction dynamics inside the production target, the experimental results achieved and a list of possible RIBs delivered from the facility EXOTIC in the next future.

"Beta Beams" produce collimated pure electron (anti-) neutrino beams by accelerating beta active ions to high energies and having them decay in a race track shaped storage ring of 7 km circumference, the Decay Ring. EUROnu Beta Beams are based on CERN infrastructures and existing machines. Using existing machines may be an advantage for the cost evaluation, however, this choice is also constraining the Beta Beams. The isotope pair of choice for the Beta Beam is 6He and 18Ne. However before the EUROnu studies one of the needed isotopes, 18Ne, could not be produced in rates that satisfy the needs for physics reach of the Beta Beam. Therefore, studies of alternative beta emitters, 8Li and 8B, with properties interesting for a Beta Beam have been proposed and have been studied within EUROnu. These alternative isotopes could be produced by using a small storage ring, in which the beam traverses a target, creating the 8Li and 8B isotopes. This Production Ring, the injection Linac and the target system have been evaluated. Measurements of the cross-section of the reactions to produce the Beta Beam isotopes show interesting results. A device to collect the produced isotopes from the target has been developed and tested. However, the obtained rates of the 8Li and 8B, using the Production Ring for production of 8Li and 8B, is not yet, according to simulations, giving the rates of isotopes that would be needed. Therefore, a new method of producing the 18Ne isotope has been developed and tested giving good production rates. The baseline presented for the Beta Beam is therefore now to use the 6He and 18Ne isotopes for neutrino production. A 60 GHz ECRIS prototype, the first in the world, was developed and tested with contributions from EUROnu. The Beta Beam has to take into account the modifications of the injectors planned in view of LHC-upgrades. The Decay Ring lattices for the 8Li and 8B have been developed, the lattice for 6He and 18Ne has been optimized also to ensure the high intensity ion beam stability.

A new beam line is now fully operational at Laboratori Nazionali di Legnaro (LNL) TANDEM/ALPI accelerator for the in-flight production of light low-energy Radioactive Nuclear Beams (RNBs). The RNBs are produced by inverse kinematics reactions induced by heavy ions, such as 17O and 6Li, on 1H and 3He gas targets. The beam line has a large solid angle acceptance ( Δ Ω = 10 msr ) and a high rejection capability of spurious beams due to the combined action of magnetic rigidity and velocity filtering. A very pure (100%) and high intensity ( 3.6 × 10 6 pps ) 17 F 9 + secondary beam at E lab = 86 ± 1 MeV has been produced and used for experiments. A 8 B 5 + beam at E lab = 33 MeV , with a production rate of ∼ 2 × 10 3 pps , is presently under commissioning.

A new detection apparatus, named EXPADES (EXotic PArticle DEtection System), has been expressly designed to be used in nuclear physics experiments involving exotic beams and devoted to the study of nuclear reactions (scattering, direct reactions, breakup…) at energies around the Coulomb barrier. It consists of double-side segmented silicon detectors arranged in a compact configuration around the target. A very large solid angle, a wide angular range, high granularity and a highly miniaturized readout electronics, based on a new production commercial ASIC chipset, are the main features of the system.

We present the new facility EXOTIC at Legnaro National Laboratories (LNL), dedicated to the in flight production of light exotic beams at near-barrier energies. The radioactive beams are produced via inverse kinematics mode of intense TANDEM beams hitting on light gas targets. The first beams, 17F and 8B, were produced with very low contaminant background and with an intensity of $\sim\kern-3pt 10^6$ and $\sim\kern-3pt 10^4$ pps, respectively. In the first measurement performed with the EXOTIC facility we studied the elastic scattering and the two-body breakup process of the 17F radioactive beam on a 208Pb target at Elab=86MeV. Preliminary results of this experiment, aiming at the investigation of the reaction mechanisms of the loosely bound 17F nucleus at subbarrier energies, show a rather small two-body breakup cross section.

Recent data on inclusive and exclusive breakup and on fusion at Coulomb barrier energies are presented and comparatively discussed for the systems 6Li,17F+208Pb. Both projectiles are very loosely bound and moreover 17F is an unstable beam. The breakup strength in 6Li, bound by 1.47 MeV, is one order of magnitude larger than in 17F, bound by 0.60 MeV; this is at contrary to simple expectations and suggests that other effects, maybe connected to the specific structure of the nuclei (e.g. 6Li cluster structure ?), in addition to the binding energies, influence the breakup process.

MeV/nucleon, with the aim to probe its evolution with incident energy. These reactions populate, through entrance channels having different charge asymmetries, the 132 Ce compound nucleus at an excitation energy of 117 MeV with identical spin distribution. Fusion events were selected by detecting high-energy γ-rays in coincidence with evaporation residues. The present results can be compared directly with those related to the same reactions at Elab � 9 MeV/nucleon where the compound nucleus excitation energy was equal to 173.5 MeV [1]. This study could be of aid in the formation of superheavy elements. In fact, the emission of pre-equilibrium dipole photons could represent an efficient new cooling mechanism of the composite system in charge asymmetric ”hot” fusion reactions, increasing thus its survival probability against fission [2]. EXPERIMENTAL SET-UP The experiment was performed by using the pulsed beams of 32 S and 36 S provided by the heavy-ion 15 MV Tandem-XTU accelerator of the Laboratori Nazionali di Legnaro (Italy) at Elab = 196 MeV and 214.2 MeV, respectively, impinging on 550 � g/cm 2 thick 100 Mo ( 97.42%) and 96 Mo ( 95.9%) self-supporting targets. The beam consisted of � 2 ns wide bunches with a 400 ns separation and it was measured in a Faraday cup shielded with lead and paraffin to reduce the background due to γ-rays and neutrons. Beam current was about 10 nA. The γ-rays were detected by using six seven-pack clusters of BaF2 scintillators situated at 28 cm from the target at different θ angles with respect to the beam direction. The total solid angle covered by all the clusters was 1.6 sr. Each cluster was surrounded by a 3 mm thick lead shield which reduced the counting rate due to the low energy γ-rays to 50% and stopped the charged particles. The evaporation residues were detected by means of four position sensitive Parallel Plate Avalanche Counters (PPAC’s) located at θ = 7 ◦ symmetrically around the beam direction at 70 cm from the target. The total solid angle covered by the PPAC’s was 0.089 sr. They provided the time of flight (TOF) with respect to the radiofrequency signal of the accelerator, the energy loss (�E) and the position of the reaction products. The energy calibration of the γ-ray detectors was obtained by using the sources 60 Co, 88 Y, the composite source of 241 Am+ 9 Be and the 15.1 MeV γ-rays from the p+ 12 C reaction. Down-scaled single events together with coincidence events between a PPAC and at least one fired BaF2 scintillator were collected during the experiment. A coincidence event was accepted if the deposited energy in a BaF2 cluster was greater than � 5 MeV. The threshold of each BaF2 scintillator was set at � 100 keV. The coincidence request eliminated any cosmic ray contamination of the γ-ray spectra.

The low intensity of the RIBS presently available at the first generation production facilities (10(5)-10(6) pps) and the necessity to reconstruct the event kinematics in RIB measurements require detection systems having both a large solid-angle coverage and a high granularity. The EXODET (EXOtic DETector) apparatus has been accomplished to respond to these requirements and the first experiment has been successfully performed studying the F-17 scattering on Pb-208 at 90.4 MeV.

The 9Be +209Bi fusion cross sections were measured in the range 37.5 MeV ≤ Elab≤ 45.0 MeV at the Munich Tandem via the observation of ground state α-decay of the evaporation residues. Fusion cross sections of 209Bi with the “halo”11Be unstable projectile in the region around the Coulomb barrier were deduced from an experiment done with the same technique at the RIKEN Ring Cyclotron. Above the Coulomb barrier the 11Be cross sections are larger than the 9Be ones in agreement with theoretical predictions based on the larger 11Be halo radius. Also below the barrier these theories foresee the same behavior in disagreement with the experimental results, since the two cross sections are rather similar.

systemhave beendeduced. Comparisonoftheexperimentaldatawithtwodifferenttheoretical approaches strongly supports the direct breakup process description.1. INTRODUCTIONThe growing interest and effort of the nuclear physicists community for experimentsperformed with Radioactive Nuclear Beams (RIBs), has triggered several experimentsthat can be performed using stable beams and could give a first taste of what kind ofdifficulties and results we will face once RIBs will be available. In this perspective, it’snatural to choose stable beams that have characteristics very close to those of the RIBs.For example, if one considers the binding energy of the nuclei, it’s immediately clear thatsome stable light nuclei are weakly bound, like many light RIBs

The dynamical dipole mode was investigated in the mass region of the 192 Pb compound nucleus, by using the 40 Ca + 152 Sm and 48 Ca + 144 Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for thefirst time. Our results show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously, however, its yield is lower than that expected within BNV calculations.

Present experiments related to fusion and breakup processes in the energy region immediately above the Coulomb barrier are reviewed and discussed. The most of the material utilised concerns very recent experimental work not yet published, still subject to possible slight changes. These data involve skin, skin-like and halo nuclei with weakly bound outer nucleons. Skin nuclei: 1) the results on 4,6 He + 209 Bi represent a rather unsolved puzzle for their theoretical interpretation; 2) the data on 27,29,31 Al + 197 Au sub-barrier fusion do not show big singularities and suggest once more the influence of neutron transfer well expected for skin-like nuclei. Halo nuclei: 1) the system 9,10,11 Be + 209 Bi after a careful analysis, indicates that the contribution of the breakup-fusion process, under a certain schematization of the breakup, has only less than 25% probability; 2) the system 9,11 Li + Si indicates the existence of fast breakup neutrons in forward direction in coincidence with the evaporation residues originating from the fusion. Some of these data point out that new phenomena are slowly showing up with skin and halo nuclei.

The cross-section excitation functions for various neutron-evaporation channels have been measured in the 11,10,9 Be+ 209 Bi systems around the Coulomb barrier, for energies ranging from 35 to 70 MeV, in order to see any eventual effect from the expected breakup of the 11 Be unstable halo nucleus. Within the simplified reaction process considered, the data are consistent with a breakup of 11 Be at the top of the Coulomb barrier contributing to less than 25% to the total fusion cross-section; however contributions from other type of breakup mechanisms cannot be excluded.

The EXOTIC facility, installed at the INFN-Laboratori Nazionali di Legnaro (LNL), is devoted to the in-flight production of light Radioactive Ion Beams (RIBs) in the energy range between 3-5 MeV/nucleon. The research field accessible using the EXOTIC RIBs is the investigation of reaction mechanisms and nuclear structure, resonant scattering measurements and measurements of nuclear reaction cross sections of astrophysical interest.

C. PARASCANDOLO, D. PIERROUTSAKOU, C. AGODI, R. ALBA, V. BARAN, A. BOIANO, M. COLONNA, R. CONIGLIONE, E. DE FILIPPO, A. DEL ZOPPO, M. DI TORO, U. EMANUELE, F. FARINON, A. GUGLIELMETTI , M. LA COMMARA, C. MAIOLINO, B. MARTIN, M. MAZZOCCO, C. MAZZOCCHI , C. RIZZO, M. ROMOLI, D. SANTONOCITO, C. SIGNORINI, R. SILVESTRI, F. SORAMEL, E. STRANO, D. TORRESI, A. TRIFIRO AND M. TRIMARCHI a Dip. di Fisica e Astronomia, Universita di Padova and INFN, Sezione di Padova

The facility EXOTIC for the in-flight production of light weakly-bound Radioactive Ion Beams (RIBs) has been operating at INFN-LNL since 2004. RIBs are produced via two-body reactions induced by high intensity heavy-ion beams impinging on light gas targets and selected by means of a 30°-dipole bending magnet and a 1-m long Wien filter. The facility has been recently upgraded (i) by developing a cryogenic gas target, (ii) by replacing the power supplies of the middle lenses of the two quadrupole triplets, (iii) by installing two y-steerers and (iv) by placing two Parallel Plate Avalanche Counters upstream the secondary target to provide an event-by-event reconstruction of the position hit on the target. So far, RIBs of 7Be, 8B and 17F in the energy range 3–5 MeV/u have been produced with intensities about 3 × 105, 1.6 × 103 and 105 pps, respectively. Possible light RIBs (up to Z = 10) deliverable by the facility EXOTIC are also reviewed.

We measured for the first time the scattering process of 7Be nuclei from a 58Ni target at 23.2 MeV beam energy. The experiment was performed at the Laboratori Nazionali di Legnaro (LNL, Italy), where the 7Be Radioactive Ion Beam was in-flight produced with the facility EXOTIC. Charged reaction products were detected by means of the detector array DINEX, arranged in a cylindrical configuration around the target to ensure a polar angle coverage in the ranges θcm = 40°-80° and 110°-150°. The scattering differential cross section was analyzed within the optical model formalism with the coupled-channel code FRESCO to extract the total reaction cross section. The result was compared with those obtained at lower beam energies in an earlier experiment performed at the University of Notre Dame (USA). At the present stage of our analysis, the two data sets were found to be not fully consistent each other.

Fusion cross sections of 11 Be, 10 Be and 9 Be have been measured on 209 Bi target at 30–70 MeV. Due to the neutron halo effect of 11 Be, a large enhancement or suppression of the fusion cross section around the Coulomb barrier was theoretically predicted. Comparing the excitation function of 11 Be with 10 Be at near the Coulomb barrier region, no significant difference has been observed.

The high-spin states in 45 Sc were studied with the GASP multidetector array. The nuclei were excited by the 30 Si( 18 O,p2n) 45 Sc reaction at E LAB =60 MeV and separated with the Recoil Mass Spectrometer. Several new high-spin levels extending the known single-particle and collective structures were observed. Energies of the negative-parity states agree with the shell model predictions whereas the positive-parity-intruder rotational band extends up to very high rotational frequencies and continues beyond the maximum angular momentum available from the single-particle f 7 2 configuration.

In this work we present new data for the sub‐barrier fusion of the system 6He+206Pb obtained in the Centre de Recherches du Cyclotron (UCL), in Louvain‐la‐Neuve, Belgium. The preliminary results suggest the absence of fusion enhancement at sub‐barrier energies.

Fusion cross sections and mean angular momenta have been measured for 64 Ni + 92,96 Zr around the Coulomb barrier. The results are presented and systematically compared with the predictions of a schematic coupled-channel model, demonstrating the need of more refined calculations including higher-order coupling effects, and/or other degrees of freedom, beyond the usual inelastic and quasi-elastic transfer channels.

The11,9Be +209Bi subbarrier fusion cross-sections were measured. The good quality of the9Be data allowed also to extract the fusion barrier distribution. The data are in good agreement with the theoretical predictions above the barrier but not below, where the cross-sections are similar, in contradiction with present theories. The barrier distribution for9Be does not evidence fusion processes originating from breakup.

We investigated the prompt dipole γ‐ray emission, related with entrance channel charge asymmetry effects, in the 40Ar + 92Zr and 36Ar + 96Zr fusion reactions at Elab= 15 and 16 MeV/nucleon, respectively, with the aim to probe its evolution with incident energy. These reactions populate, through entrance channels having different charge asymmetries, the 132Ce compound nucleus at an average excitation energy of 304 MeV with identical spin distribution. Fusionlike events were selected by detecting high‐energy γ‐rays in coincidence with evaporation residues. By studying the differential γ‐ray multiplicity spectra of the considered reactions, it was shown that the dipole γ‐ray intensity increases by ∼14% for the more charge asymmetric system. This result, associated with those reported for the 32,36S + 100,96Mo reaction pair at lower beam energies, implies a “rise and fall” trend of the prompt dipole γ‐ray emission in the studied beam energy range with a maximum value at 9 MeV/nucleon.

The use of radioactive beams opens a new frontier for fusion studies. The coupling to the continuum can be explored with very loosely bound nuclei. Experiments were performed with beams of nuclei at or near the proton and neutron drip-lines to measure fusion and associated reactions in the vicinity of the Coulomb barrier. In addition, the fusion yield is predicted to be enhanced in reactions involving very neutron-rich unstable nuclei. Experimental measurements were carried out to investigate if it is feasible to use such beams to produce new heavy elements. The current status of these experimental activities is given in this review., Comment: 30 pages, 12 figures

A new pixel-structure detector array with a large solid angle coverage has been used for the first time to study the elastic scattering of exotic $^{17}\mathrm{F}$ nuclei from a $^{208}\mathrm{Pb}$ target at $90.4\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The experimental data have been analyzed in the framework of the optical model potential and the real and imaginary strong absorption radii have been evaluated. These quantities have been compared with those obtained for the system $^{19}\mathrm{F}+^{208}\mathrm{Pb}$ at the same energy in the center of mass frame. The $^{17}\mathrm{F}+^{208}\mathrm{Pb}$ reaction cross section is more similar to those of the systems $^{16,17}\mathrm{O}+^{208}\mathrm{Pb}$ rather than to the one of the system $^{19}\mathrm{F}+^{208}\mathrm{Pb}$ at similar energies: this indicates that in the energy range around the Coulomb barrier the breakup channel is still weak. The exclusive breakup cross section $^{17}\mathrm{F}\ensuremath{\rightarrow}^{16}\mathrm{O}+p$ has been measured for the first time at energy below the Coulomb barrier.

The subbarrier fusion cross section has been measured in the system 11,10Be+209Bi. The data were collected at the RIKEN Ring Cyclotron with a total beam intensity of ∼10+5 Hz typical for such radioactive nuclear beams of first generation. The cross section accuracy is around 10 to 15 %. The two excitation functions look, within the statistical uncertainty very similar as well as the 9Be+209Bi one at difference with the expectations. This is triggering further theoretical analysis.

The prompt γ radiation originating from the dynamical dipole mode decay was investigated in the 192Pb composite system employing the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. The γ-ray energy spectra at various polar angles were obtained for fusion-evaporation and fission events by detecting the high energy γ rays with the MEDEA experimental apparatus in coincidence with evaporation residues and fission fragments. Preliminary results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole γ radiation could be of interest for the synthesis of super-heavy elements through "hot" fusion reactions.

The experimental results recently obtained for fusion reactions at energies close to the Coulomb barrier with light radioactive (loosely bound) beams are reviewed and critically discussed. There have been two conflicting views on the effect of the loose binding of the projectile on the fusion cross section. On the one hand one expects an enhancement of the fusion cross section due to the loose binding while, on the other hand, the easy breakup of the projectile is expected to inhibit the fusion cross section. We critically discuss these two aspects of loose binding by comparing the experimental results for a number of radioactive beams. The data for 17 F (where the last neutron binding energy S n =0.601 MeV), neither show breakup effects nor enhancement when compared with the fusion of the nucleus 19 F. The data for a 6 He beam ( S 2n =0.975 MeV) show enhancement, very strong in one case, and the strong breakup (BU) + transfer cross section may be related to this. The fusion data obtained with the halo nucleus 11 Be ( S n =0.504 MeV) do not show enhancement below the barrier, compared with 9 Be, and show moderate effects above the barrier. Moreover, 9 Be ( S n =1.665 MeV) shows a very strong BU + transfer cross section as in the case of 6 He, but this apparently has no direct effect on fusion. The data with the neutron-rich 38 S, 29,31 Al radioactive beams do not differ much from data with the stable 32 S, 27 Al, respectively. In conclusion we observe: (i) effects of loose binding in neutron skin nuclei but not with other halo nuclei, (ii) a reduction of the fusion cross section above the barrier due to breakup effects. The various theoretical approaches developed up to now based on “simple” assumptions give opposite predictions for fusion, with some expecting enhancement of the cross section while others expect a hindrance of the cross section. However, most of these approaches do not correctly treat the transitions to the continuum which are expected to be induced easily in these weakly bound nuclei. It is necessary to develop a more complete and possibly “simple” theoretical treatment that incorporates the continuum coupling which will play an important role in subbarrier fusion.

We report the first measurement, at the XTU Tandem+LINAC accelerator of the Laboratori Nazionali di Legnaro, of the decay of the very neutron deficient nucleus 117La using a 310 MeV 58Ni beam on a 64Zn target; the 117La nucleus was populated via the (p, 4n) evaporation channel. The Recoil Mass Spectrometer (RMS) was used to select M/q=117/30 recoils that were implanted in a (40×40) mm2 Double Sided Silicon Strip Detector (DSSD) detector. The analysis has revealed that 117La decays to 116Ba via proton emission with Ep=(783±6)keV and T1/2=(20±5) ms. From this result deformation parameters of β2=0.3 and β4=0.1 have been deduced for the 117La ground state which was assigned to Jπ=3/2+.