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The mass-energy distributions of fragments of the reaction 32S + 232Th leading to the formation of 264Sg (Z = 106) at energies of incident ions 32S of 165, 181 and 200 MeV are measured. The contribution from the quasifission process is found at energies below and above the Coulomb barrier in the region of symmetric masses (АCN/2 ± 20). A high-energy symmetric fission mode is found at an energy of 165 MeV, which corresponds to the excitation energy of the compound 264Sg nucleus 45 MeV.

Background: Observation of asymmetric fission of $^{180}\mathrm{Hg}$ has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region.Purpose: The study of asymmetric and symmetric fission modes of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei.Methods: Mass-energy distributions of fission fragments of $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$ formed in the $^{36}\mathrm{Ar}+^{144,154}\mathrm{Sm}$ and $^{40}\mathrm{Ca}+^{144}\mathrm{Sm}$ reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured $^{192,202}\mathrm{Pb}$ isotopes produced in the $^{48}\mathrm{Ca}+^{144,154}\mathrm{Sm}$ reactions. The mass distributions for $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ together with old data for $^{187}\mathrm{Ir}, ^{195}\mathrm{Au}, ^{198}\mathrm{Hg}, ^{201}\mathrm{Tl}, ^{205,207}\mathrm{Bi}, ^{210}\mathrm{Po}$, and $^{213}\mathrm{At}$ [J. Nucl. Phys. 53, 1225 (1991)] have been decomposed into symmetric and asymmetric fission modes. The total kinetic-energy distributions for different fission fragment mass regions have been analyzed for $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$.Results: The stabilization role of proton numbers at $Z\ensuremath{\approx}36$, 38, $Z\ensuremath{\approx}45$, 46, and $Z=28/50$ in asymmetric fission of excited preactinide nuclei has been observed. The high ($\ensuremath{\approx}145\text{\ensuremath{-}}\mathrm{MeV}$) and the low ($\ensuremath{\approx}128\text{\ensuremath{-}}\mathrm{MeV}$) energy components have been found in the total kinetic-energy distributions of $^{180,190}\mathrm{Hg}$ fission fragments corresponding to the fragments with proton numbers near $Z\ensuremath{\approx}46$ and $Z\ensuremath{\approx}36$, respectively. In the case of fission of $^{184}\mathrm{Pb}$ only the low-energy component ($\ensuremath{\approx}135\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$) for the fragments with masses corresponding to the proton numbers $Z\ensuremath{\approx}36$ and 46 has been found.Conclusions: The studied properties of asymmetric fission of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei point out the existence of well deformed proton shell at $Z\ensuremath{\approx}36$ and less deformed proton shell at $Z\ensuremath{\approx}46$.

A novel Monte Carlo technique has been developed to determine lifetimes of excited states in the tens-to-hundreds femtoseconds range in products of low-energy heavy-ion binary reactions, with complex velocity distributions. The method is based on a detailed study of Doppler-broadened $$\gamma $$ γ -ray lineshapes. Its relevance is demonstrated in connection with the $$^{18}\text {O}(7.0\, \text {MeV/u})+\,^{181}\text {Ta}$$ 18 O ( 7.0 MeV/u ) + 181 Ta experiment, performed at GANIL with the AGATA+VAMOS+PARIS setup, to study neutron-rich O, C, N, ... nuclei. Excited states in $$^{17}\text {O}$$ 17 O and $$^{19}\text {O}$$ 19 O , with known lifetimes, are used to validate the method over the $$\sim 20{-}400\,\text {fs}$$ ∼ 20 - 400 fs lifetime-sensitivity range. Emphasis is given to the unprecedented position resolution provided by $$\gamma $$ γ -tracking arrays, which turns out to be essential for reaching the required accuracy in Doppler-shift correction. The technique is anticipated to be an important tool for lifetime investigations in exotic neutron-rich nuclei, produced with intense ISOL-type beams.

The elastic scattering in the reaction $$^{7}$$ 7 Li+$$^{208}$$ 208 Pb was investigated in the bombarding energy range from 25 to 39 MeV. The real and imaginary parts of the optical potential were analyzed by using a phenomenological potential. A dispersion relation analysis is presented in order to investigate the threshold anomaly effect. It is concluded that $$^{7}$$ 7 Li has an intermediate behavior between the tightly bound nuclei such as $$^{16}$$ 16 O and the loosely bound nuclei such as $$^{6}$$ 6 Li where the lack of the threshold anomaly is unambiguously observed. Reaction cross sections are also extracted from the elastic scattering data and its comparison with the ones of other systems has been performed to draw hints on the effect of the breakup channel.

A study is performed of the asymmetric fission of neutron-deficient mercury 180, 190Hg isotopes obtained in the reactions of 36Ar + 144, 154Sm and 68Zn + 112Sn at incident energies near and above the Coulomb barrier. The relative contributions from asymmetric and symmetric fission change along with the excitation energy of the fissile compound nucleus. The effect the characteristics of the entrance channel have on the dynamics of the reaction is studied.

International audience; The overlap in the mass symmetric region of the reaction products from fusion-fission and quasifission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The approach proposed here relies on the fact that fusion-fission and quasifission are characterized by different timescales. Within this framework, we performed a detailed study to find out how timescales can be probed via angular momentum transfer as measured via γ-ray multiplicities. The proof of principle was carried out by measuring the γ rays in coincidence with fusion-fission and quasielastic binary fragments in the reaction S32 + Au197 at beam energy near the Coulomb barrier. The experiment was performed at the Accélérateur Linéaire Tandem à Orsay (ALTO) facility at the Institut De Physique Nucléaire (IPN) in Orsay (France) using a detection setup consisting of ORGAM (ORsay GAMma) and PARIS (Photon Array Radioactive Ion Stable beams) γ-detectors arrays coupled with the CORSET (CORrelation SETup) time-of-flight spectrometer. Results of the sensitivity of this method to distinguish reaction channels with different dynamics are discussed.

The dynamics of the fission process is expected to affect the evaporation residue cross section because of the fission hindrance due to the nuclear viscosity. Systems of intermediate fissility constitute a suitable environment for testing such hypothesis, since they are characterized by evaporation residue cross sections comparable or larger than the fission ones. Observables related to emitted charged particle, due to their relatively high emission probability, can be used to put stringent constraints on models describing the excited nucleus decay and to recognize the effects of fission dynamics. In this work model simulations are compared with the experimental data collected via the ^{32}S + ^{100}Mo reaction at E_{lab}= 200 MeV. By comparing an extended set of evaporation channel observables the limits of the statistical model and the large improvement coming by using a dynamical model are evidenced. The importance of using a large angular covering apparatus to extract the observable is stressed. The opportunity to measure more sensitive observables by a new detection device in operation at LNL are also discussed., v1: 7 pages, 6 figures

Light charged particles emitted by the compound nucleus $^{158}\mathrm{Er}$ produced in the reaction $^{32}\mathrm{S}$ $(180 \mathrm{MeV})+^{126}\mathrm{Te}$, at the excitation energy ${E}_{x}=92$ MeV, have been measured at Laboratori Nazionali di Legnaro in coincidence with fission fragments and evaporation residues. The $4\ensuremath{\pi}$ detector array $8\ensuremath{\pi}\mathrm{LP}$ coupled to a system of parallel-plate avalanche counters to detect evaporation residues has been used. Data have been analyzed in the framework of the statistical model of evaporation with the code pace2_n11. This enlarged version of the code pace2 has been used to reproduce the large set of observables measured in the fusion-evaporation and fusion-fission channels along with experimental prescission neutron multiplicity and fission cross section taken from literature. It is found that the simultaneous reproduction of the prescission neutron, proton, and $\ensuremath{\alpha}$-particle multiplicities can be obtained with zero fission delay without dynamical effects. However, the same set of model input parameters does not allow us to reproduce proton and $\ensuremath{\alpha}$-particle multiplicities in the evaporation channel. Extensive calculations, with different sets of parameters, show the limits of the statistical model in reproducing the whole set of data. This work evidences the importance of measuring a large set of observables in order to obtain a reliable description of the decay of the compound nucleus, and in particular of the fission process.

International audience; The features of fission fragments formed in the near barrier reaction $^{32}\hbox {S}$ + $^{197}\hbox {Au}$ ($E^\mathrm{lab}_\mathrm{beam}=166\,\hbox {MeV}$) are investigated. The measurement was performed at the ALTO facility of IPN Orsay, France, with the aim of clarifying the quantitative contribution of the quasi-fission process to the total fission events. The mass and total kinetic energy of the fission fragments were compared to the expectations of the liquid drop model, revealing an asymmetric fission component which may be traced back to a quasi-fission process mixed with the fusion–fission events. The $\gamma $-rays and neutrons measured in coincidence with the fission fragments were used to yield additional information for the discrimination of the two aforementioned mechanisms. All observed trends are consistent and fairly well reproduced by the statistical model.

International audience; The mass, energy and angular distributions of binary fragments formed in the reactions $^{64}$Ni + $^{238}$U, $^{58}$Fe + $^{244}$Pu, $^{52}$Cr + $^{248}$Cm, $^{54}$Cr + $^{248}$Cm at energies near the Coulomb barrier have been measured. The analysis of energy distributions of the symmetric fragments with mass numbers ${{{{A}_{{{\text{CN}}}}}} \mathord{\left/ {\vphantom {{{{A}_{{{\text{CN}}}}}} 2}} \right. \kern-0em} 2} \pm 20$ formed in these reactions have been applied to separate compound nucleus fission and quasi-fission. The estimated fusion probability for the reactions Cr, Fe, and Ni ions with actinide targets shows an exponential dependence on the mean fissility parameter of the system and shows also that reaction with Cr ions is more favorable for production of the super heavy element with Z = 120.

For the 68Zn + 112Sn reaction the Coulomb parameter Z 1 Z 2 is equal to 1500 that is close to the threshold value for the appearance of quasifission process. It was found that mass-energy distributions of the reaction fragments differ significantly from those obtained in the 36Ar + 144Sm reaction leading to the formation of the same composite system of 180Hg at similar excitation energies of about 50 MeV. In the case of the reaction with 68Zn ions, the mass distribution of fissionlike fragments has a wide two-humped shape with maximum yields at 70 and 110 u for the light and heavy fragments, respectively, instead of 80 and 100 u observed in the fission of 180Hg formed in the 36Ar + 144Sm reaction. The difference is explained by an unexpectedly large contribution (more than 70%) of quasifission in the case of the 68Zn + 112Sn reaction.

International audience; The overlap in the mass symmetric region of the reaction products from fusion-fission and quasi-fission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The method proposed here relies on the fact that fusion-fission and quasifission are characterized by a different timescale. Within this framework we performed a detailed study to find out if timescales can be probed via angular momentum as measured via γ rays multiplicity. The proof of principle was carried out by measuring the γ rays in coincidence with two fragments in the reaction 32S + 197Au at beam energy near the Coulomb barrier. The experiment has been performed at the Tandem ALTO facility at IPN Orsay using a detection setup consisting of ORGAM and PARIS γ detector arrays coupled with the CORSET time-of-flight spectrometer. Preliminary results on the sensitivity of this method to distinguish reaction channels with different dynamics are discusses.

The fourth IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements 113, 115, 117 and 118 has reviewed the relevant literature pertaining to several claims. In accordance with the Criteria for the discovery of elements previously established by the 1991 IUPAC/IUPAP Transfermium Working Group (TWG), and reinforced in subsequent IUPAC/IUPAP JWP discussions, it was determined that the RIKEN collaboration has fulfilled those Criteria for element Z=113. The Dubna–Livermore–Oak Ridge collaborations claims for 115 and 117 are also in compliance. The discussion of element Z=118 will appear in a subsequent report. A synopsis of experiments and related efforts is presented along with some commentary guiding future applications of the Criteria.

Nuclear viscosity is an irreplaceable ingredient of nuclear fission collective dynamical models. It drives the exchange of energy between the collective variables and the thermal bath of single particle degrees of freedom. Its dependence on the shape and temperature is a matter of controversy. By using systems of intermediate fissility we have demonstrated in a recent study that the viscosity parameters is larger for compact shapes, and decreases for larger deformations of the fissioning system, at variance with the conclusions of the statistical model modified to include empirically viscosity and time scales. In this contribution we propose an experimental scenario to highlight the possible dependence of the viscosity from the temperature.

International audience; Compound nucleus fission and quasi-fission are both binary decay channels whose common properties make the experimental separation between them difficult. A way to achieve this separation could be to probe the angular momentum of the binary fragments. This can be done detecting gamma rays in coincidence with the two fragments. As a case study, the reaction 32S + 197Au near the Coulomb barrier has been performed at the Tandem ALTO facility at IPN ORSAY. ORGAM and PARIS, two different gamma detectors arrays, are coupled with the CORSET detector, a two-arm time-of-flight spectrometer. TOF-TOF data were analyzed to reconstruct the mass-energy distribution of the primary fragments coupled with gamma multiplicity and spectroscopic analysis. Preliminary results of will be shown.

Multi-nucleon transfer reactions are nowadays the only known mean to produce neutron-rich nuclei in the Terra Incognita. The closed-shell region N=126 is crucial for both studying shell-quenching in exotic nuclei and the r-process, being its last "waiting-point". The choice of suitable reactions is challenging and a favorable case is 136Xe+208Pb, near the Coulomb barrier, because their neutron shell-closures play a stabilizing role, favoring the proton-transfer from lead to xenon. TOF-TOF data were analyzed to reconstruct the mass-energy distribution of the primary fragments. Preliminary results of an experiment held at Laboratori Nazionali di Legnaro with PRISMA, aimed at A and Z identification of the products, will be shown. peerReviewed

Background: Low-energy multinucleon transfer reactions may be used for production of new neutron-enriched heavy nuclei.Purpose: Our aim is to investigate the influence of proton ($Z=82$) and neutron ($N=82$, 126) shells as well as orientation effects on the formation of reaction products in the inverse quasifission process in the reactions $^{156,160}\mathrm{Gd}+^{186}\mathrm{W}$.Methods: Mass, energy, and angular distributions of primary binary fragments formed in the reactions $^{156}\mathrm{Gd}+^{186}\mathrm{W}$ at an energy of 878 MeV, and $^{160}\mathrm{Gd}+^{186}\mathrm{W}$ at 860 and 935 MeV, have been measured using the double-arm time-of-flight spectrometer CORSET at the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research (JINR), Dubna.Results: Enhancement in the yield of products with masses 200--215 u has been found for both reactions. The cross sections of the formation of trans-target fragments with masses around 208 u are found to be about 10 \ensuremath{\mu}b at the Coulomb barrier energy and reach the level of 0.5 mb at the energy above the barrier for side-to-side collision.Conclusions: The enhanced yield of products with masses heavier than the target mass confirms the important role of the closed shells at $Z=82$ and $N=82$, 126 in the inverse quasifission process in low-energy damped collisions. The orientation effect caused by the strong deformation of colliding nuclei can result in a gain in the yield of heavy target-like fragments.

It is well accepted that fission is a slow process dominated by nuclear viscosity. This is demonstrated by experimental observations, mainly based on measurements of fission fragment TKE, pre-scission light particles and GDR γ-ray multiplicities, energy spectra. The fission time-scale, as well as the nature of energy dissipation during the process and its dependence on the nuclear shape and temperature are the main aspects which have often been addressed. In spite of the extensive work, there are still many open questions on the dynamics of the fission process, mainly due to the lack of constraints on the models and to the different probes used. Intermediate fissily systems are particularly suited for this study as they present comparable cross sections in the fusion-fission and fusion-evaporation channels, allowing to measure observables in both channels, and therefore to further constrain the models. Furthermore, the path from equilibrium to saddle configuration is expected to dominate with respect to saddle-to-scission one, reducing the complexity of the physical process to be studied. We present here an in depth review of a study performed on the nucleus 132Ce, which shows the limits of the statistical model in accounting for an extended set of observables. We further present the analysis of the same data with a 3D Langevin dynamical approach which proves to be capable of reproducing the values of the whole set of observables. Our analysis reinforce the fact that extended data sets are essential to achieve reliable simulations to address the open questions on fission dynamics and strongly suggest the use of setups of high efficiency.

The pathway toward the production of superheavy elements (SHE) crosses with the one of an in-depth study of the fission and quasifission processes. Quasifission affects the probability of forming a compound nucleus (CN) after capture and fission plays a decisive role during the cooling of the CN. To search for optimal reactions to produce SHE in fusion reactions and to provide an estimate of their production cross section measurements of the capture and fusion cross sections along with the survival probabilities are a mandatory task. Here an overview of the impact of fission and quasifission over the synthesis of SHE is discussed along with the need to perform measurements over a wide range of masses and energies.

The study of nuclear cluster states bound by valence neutrons is a field of recent large interest. In particular, it is interesting to study the pre-formation of α-clusters in α-conjugate nuclei and the dynamical condensation of clusters during nuclear reactions. The NUCL-EX collaboration (INFN, Italy) is carrying out a research campaign studying preequilibrium emission of light charged particles and cluster properties of light and medium mass nuclei. For this purpose, a comparative study of the three nuclear reactions: O 16 + Si 30 , O 18 + Si 28 and F 19 + 27Al, has been recently carried out using the GARFIELD+RCo 4π setup. After a general introduction on the experimental campaign, the preliminary results for the three systems are presented.

Selected experiments in fundamental physics have been proposed for many years at the Tandem Accelerator of the University of Napoli 'Federico II's Department of Physics as a part of a one-semester laboratory course for graduate students. The aim of this paper is to highlight the educational value of the experimental realization of the nuclear reaction 19F(p,α)16O. With the purpose of verifying the mass–energy equivalence principle, different aspects of both classical and modern physics can be investigated, e.g. conservation laws, atomic models, nuclear physics applications to compositional analysis, nuclear cross-section, Q-value and nuclear spectroscopic analysis.

International audience; The study of nuclear cluster states bound by valence neutrons is a field of recent large interest. In particular, it is important to study the pre-formation of α-clusters in α-conjugate nuclei and the dynamical condensation of clusters during nuclear reactions [1–5]. The NUCL–EX collaboration has recently initiated an experimental campaign of exclusive measurements of fusion–evaporation reactions with light nuclei as interacting partners. In collisions involving light systems, the low expected multiplicity of fragments increases the probability of achieving a quasi-complete reconstruction of the event. In particular the formation and decay modes of an excited 24Mg system have been studied through two different reactions, 12C (95 MeV)+ 12C and 14N (80.7 MeV)+ 10B, which have been used to produce fused systems with nearly the same mass and excitation energy (~60 MeV). In particular, even the de-excitation of the Hoyle state in 12C have been studied, both in peripheral (projectiles de-excitation) and in central collisions (six α-particles channel). Moreover, a research campaign studying pre-equilibrium emission of light charged particles and cluster properties of light and medium-mass nuclei has been carried out. For this purpose, a comparative study of the three nuclear systems 18O+28Si, 16O+30Si and 19F+27Al has been recently studied using the GARFIELD+RCo 4π setup [6]. The experimental data are compared with the predictions of simulated events generated with the statistical models (GEMINI++ and HFl) and through dynamical models like Stochastic Mean Field (SMF) and Antisymmetrized Molecular Dynamics (AMD) and filtered with a software replica of our apparatus in order to take into account the experimental conditions.

Pre-equilibrium emissions affect the production of excited systems in nuclear reactions, thus modifying their properties which enter as input parameters in the comparison with statistical models. In this contribution, we discuss this subject referring to recent results from experiments performed at Legnaro National Laboratories (Italy) with the GARFIELD apparatus complemented with other detectors. ispartof: Acta Physica Polonica B vol:48 issue:3 pages:635-639 ispartof: location:Zakopane: POLAND status: published

In the study of the effectiveness of shielding materials against radiations, one of the main steps concerns with the validation of models describing the interaction processes of the radiation of interest with the material chosen for the shielding. This paper shows the results of the validation of electromagnetic and hadronic processes with the aim to contribute to the study of protection for astronauts against the radiations due to the Solar Particle Events, in particular to the selection of the optimal material for radiation shielding. The physics case deals with the interaction of a proton beam with an aluminum slab about 20 g/cm 2 thick. Two specific applications, STP and DOSE, were developed by using Geant4 package. STP computes the radiations produced in the interaction and their stopping power; DOSE computes the absorbed dose from the stopping power calculated by STP. The validation process was performed in two steps. In the first one, the output of the STP code is compared to data available on NIST database; in the second one, the absorbed dose computed with DOSE is compared to the dose gathered during an experiment performed at the NASA Space Radiation Laboratory involving the bombardment of an aluminum slab with a 1 GeV proton beam. The computing model has allowed us to correlate the size of the impinging beam profile to the dose measured before and after an Al slab. The sharp increase of the dose in the position right after the slab might be due to the stochastic nature of the trajectories of charged ions in matter which makes the radiation to emerge with non-zero transverse linear momentum. From the case examined here, we conclude that aluminum is not an efficient material for Solar Particle Event shielding.

International audience; Clustering structural properties in medium-mass systems have been investigated studying the competition between the evaporation and pre-equilibrium particle emission in central collisions. At variance with light nuclei, in the case of heavier nuclei there are no experimental evidences of such structure effects, since the determination of pre-formed clusters within nuclear matter is less obvious.The two systems 16O + 65Cu and 19F + 62Ni, leading to the same compound system 81Rb*, have been studied at the same beam velocity (16 AMeV). The experiments have been performed using the GARFIELD + RCo multi-detection system at the Legnaro National Laboratories.Recent results of the data analysis and of the comparison of the experimental data with different statistical and dynamical model calculations are reported in this contribution.

The correlations between mass distributions of the binary fragments, total kinetic energy (TKE), and neutron multiplicity have been investigated for the reaction $^{50}\text{Ti}+\phantom{\rule{0.16em}{0ex}}^{208}\text{Pb}$ at 294 MeV bombarding energy. Although this reaction has been used to synthesize the Rf ($Z=104$) superheavy element, a complete study of its fragmentation dynamics is still not available in the literature. In this work, average neutron multiplicities were extracted as a function of different fragment mass splits and TKE windows. A weak increase of the prescission neutron multiplicity is observed going from asymmetric to symmetric mass splits. A fission delay time of $4.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}$ s has been extracted for the symmetric fission. The neutron multiplicity extracted for the symmetric mass split was used to derive the average number of neutrons emitted in the spontaneous fission of $^{258}\text{Rf}$. The extrapolated value of $4.7\ifmmode\pm\else\textpm\fi{}1.4$ is found to be consistent with systematics of spontaneous and neutron-induced fission in heavy nuclei and with the results of previous works for superheavy nuclei with $Z=116$ and $Z=124$.

International audience; The path to the synthesis of super heavy elements is strongly hindered by the competition between fusion and quasi-fission in heavy ions reactions at near barrier energies. We report on a recent experimental investigation performed at the ALTO facility of IPN Orsay, France on the heavy-ion collision around the Coulomb barrier of 32S+197Au. The fission-fragment mass and total kinetic energy were measured by the double arm mass spectrometer for binary fragments CORSET, using the double time of flight approach. The asymmetric structure on top of the predominant symmetric one may suggests the contribution from either quasi-fission or pre-equilibrium fission or might be driven by shell effects in the compound nucleus fission. To get further insight on such puzzling cases situated at the crossroads of the various opened channels, we extended the measurement to coincident prompt γ -rays, of low and high energy. For this purpose, the prompt γ-rays following fission were detected by the coupled high efficiency ORGAM array consisting of 10 Compton suppressed Germanium detectors (BGO shielded), located at backward angles and the first cluster of the future PARIS calorimeter consisting of 9 close packed phoswich detectors and another single phoswich, together covering a wide angular and energy range.

The current status of fission dynamics studies in heavy-ion collisions around the Coulomb barrier is illustrated with the 34S + 186W reaction. The fission-fragment mass and total kinetic energy were measured at the ALTO facility at IPN Orsay, France, with a dedicated set-up using the (v, E) approach. The measurement reveals the presence of an asymmetric fission component on top of a predominantly symmetric distribution. The asymmetric structure, pointed out for the first time, is discussed along with results of previous experiments studying the same reaction. While these analyses suggested the contribution from either quasi-fission or pre-equilibrium fission, we offer an alternative interpretation, in terms of shell-driven compound-nucleus fission. The present measurement demonstrates the critical influence of resolution when addressing puzzling cases, situated at the crossroads of the various channels opened in a heavy-ion collision. Current status in the field clearly calls for innovative measurements involving manifold correlations and new observables. The outcome of the attempt done in this work in this direction, based on the coincident measurement of prompt \( \gamma\)-rays is reported, and encouraging perspectives are discussed.

The nuclear properties of $^{48}\mathrm{Cr}$ composite $\ensuremath{\alpha}$-like nuclei produced at 60 MeV of excitation energy via the $^{24}\mathrm{Mg}+^{24}\mathrm{Mg}$ reaction were investigated. This excitation energy corresponds to a resonance with a narrow width (170 keV) observed in the elastic and inelastic channels, which was interpreted as a highly deformed state. To gain insight on the deformation of this state exclusive measurements of light charged particles were carried out with $8\ensuremath{\pi}\mathrm{LP}$ apparatus at Laboratori Nazionali di Legnaro and compared to statistical model predictions. The measured of $\ensuremath{\alpha}$-particle energy spectra, $\ensuremath{\alpha}$-evaporation residues, $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}$, and $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\alpha}$ correlations indicate the limitation of the rotating liquid drop model in describing the nuclear shape of the compound nucleus along the decay cascade. To reproduce the full set of experimental data very elongated nuclear shapes had to be considered, with an axis ratio $3:1$ at the resonance angular momentum. This large deformation is consistent with previous findings for $\ensuremath{\alpha}$-like nuclei and with the predictions of the cranked cluster model.

The study of materials suitable for radiation protection of astronauts in space missions is always a topic of fundamental importance. This paper shows the results of the comparison of the effectiveness of different materials in cutting down the radiation dose and is intended as a contribution to the search of the most appropriate material for radiation protection against the Solar Particle Events. The physics case deals with the interaction of a 1 GeV proton beam with slabs of different materials having a thickness of 20 g cm - 2 . The study was conducted with a simulation tool based on the well-known simulation package Geant4. We focus in this work only on impinging protons with the energy of 1 GeV, and not on the whole energy spectrum of Solar Particle Events, because the simulated dose can be easily verified under strict experimental conditions thus providing the benefit of the validation of the prediction capabilities of the simulation tool developed. We conclude that the Nomex material, with the inclusion of a percentage of air, is more efficient than aluminum for what it concerns the shielding of the 1 GeV proton component of the Solar Particle Events.

One-dimensional and three-dimensional dynamical fission calculations based on Langevin equations are performed for the compound nuclei 194 Pb, 200 Pb, 206 Pb, 182 Hg, and 204 Hg to investigate the influence of the compound nucleus isospin on the prescission particle multiplicities and on the fission fragment mass–energy distribution. It is found that the prescission neutron, proton, and alpha particle multiplicities have approximately the same sensitivity to the dissipation strength for a given nucleus. This is at variance with conclusions of recent papers. The sensitivity of the calculated prescission particle multiplicities to the dissipation strength becomes higher with decreasing isospin of fissioning compound nucleus, and the increase of prescission particle multiplicities could reach 200%, when the reduction coefficient of one-body viscosity k s increases from 0.1 to 1, for the most neutron deficient nuclei considered. The variances of fission fragment mass and kinetic energy distributions are less sensitive to the change of dissipation strength than the prescission light particle multiplicities. A comparison to experimental data concerning 200 Pb nucleus is also presented.

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 fourth IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements 113, 115, 117 and 118 has reviewed the relevant literature pertaining to several claims. In accordance with the criteria for the discovery of elements previously established by the 1991 IUPAC/IUPAP Transfermium Working Group (TWG), and reinforced in subsequent IUPAC/IUPAP JWP discussions, it was determined that the Dubna-Livermore collaboration has fulfilled those criteria for element Z=118. A synopsis of experiments and related efforts is presented.

Expérience LNL/PRISMA; International audience; The unexplored area of heavy neutron rich nuclei is extremely important for nuclearastrophysics investigations and, in particular, for the understanding of the r-process ofastrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along theneutron closed shell N=126 (probably the last "waiting point" in the r-process of nucleosynthesis)the low-energy multi-nucleon transfer reaction 136Xe+208Pb at Elab=870MeV was explored.Due to the stabilizing eect of the closed neutron shells in both nuclei, N=82 and N=126, andthe rather favorable proton transfer from lead to xenon, the light fragments formed in this processare well bound and the Q-value of the reaction is nearly zero.Measurements were performed with the PRISMA spectrometer in coincidence with an additionaltime-of-flight (ToF) arm on the +20 beam line of the PIAVE-ALPI accelerator in Legnaro, Italy.The PRISMA spectrometer allows identication of the A, Z and velocity of the projectile-likefragments (PLF), while the second arm gives access to the target-like fragments (TLF).Details on the experimental setup and preliminary results are reported.

The mass-energy distributions and cross sections of proton-induced fission of Th-232 have been measured at the proton energies of 7, 10, 13, 20, 40, and 55 MeV. Experiments were carried out at the proton beam of the K-130 cyclotron of the JYFL Accelerator Laboratory of the University of Jyvakyla and U-150m cyclotron of the Institute of Nuclear Physics, Ministry of Energy of the Republic of Kazakhstan. The yields of fission fragments in the mass range A = 60- 170 a.m.u. have been measured up to the level of 10(-4)%. The three humped shape of the mass distribution up has been observed at higher proton energies. The contribution of the symmetric component grows up with increasing proton incident energy; although even at 55 MeV of proton energy the shoulders in the mass energy distribution clearly indicate the asymmetric fission peaks. Evolution of shell structure was observed in the fission fragment mass distributions even at high excitation energy.

Tunnelling of α particles through the Coulomb barrier is considered. The main attention is given to the effect of sharp peaks arising in the case of coincidence of the α energy with that of a quasistaionary state within the barrier. The question of the α-nucleus potential is discussed in this light. The method is applied to the α decay of a compound nucleus of 135Pr. The appearance of the peaks in the spectrum of emitted particles is predicted. They can give rise to ‘anomalous’ properties of some neutron resonances. The peaks can also be observed in the incoming α-nucleus channel. Observation of the peaks would give unique information about the α-nucleus potential.

The system of intermediate fissility Ce-132 has been studied experimentally and theoretically to investigate the dissipation properties of nuclear matter. Cross sections of fusion-fission and evaporation-residue channels together with light charged particle multiplicities in both channels, their spectra, light charged particle-evaporation residue angular correlations, and mass-energy distribution of fission fragments have been measured. Theoretical analysis has been performed using a multidimensional stochastic approach coupled with a Hauser-Feshbach treatment of particle evaporation. The main conclusions are that the full one-body shape-dependent dissipation mechanism allows the reproduction of the full set of experimental data and that after a time tau(d) = 5 x 10(-21) s from the equilibrium configuration of the compound nucleus, fission decay can occur in a time that can span several orders of magnitude.

The dynamics of the excited superheavy system with Z = 118 in the reaction Kr-86 + Pb-208 at E-Kr = 460, 500, and 600 MeV has been investigated. The mass and kinetic energy of binary fragments were measured by the time-of-flight method. Double-differential distributions of protons and a particles were measured in coincidence with fragments. The proton spectra can be described considering only evaporation from fragments. Evidence of the neck fragmentation was obtained from analysis of double-differential a spectra. Properties of the alpha-particle neck fragmentation component are close to those known from the tertiary fission of actinide nuclei, but the multiplicity is much larger than can be expected from extrapolation of the ternary fission data.

We have studied the elastic scattering of the exotic 17 F nuclei from 208 Pb at Coulomb barrier energies. For the measurement we used a new detector array with pixel structure and a large solid angle. Optical potential analysis shows that 17 F has an imaginary potential much less deep than 19 F. Information on the exclusive 17 F breakup cross section has been deduced too.

Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV 28 Si on 232 Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5 +7 −3 ×10 −20 s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10 −20 s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission.

A 4pi light charged particle spectrometer, named 8pLP, is in operation at the Laboratori Nazionali di Legnaro (Italy) for the study of the reaction mechanisms produced in low-energy heavy-ion reactions. The spectrometer has recently been used in a study of fission dynamics that involves the detection of light charged particles in the fission and evaporation residue channel in a system of intermediate fissility, as well as in a study of multinucleon transfer to heavy target. Data on the system 240 MeV S-32 + Mo-100 are presented. Dynamical effects extracted as a consequence of the comparison of the data to the statistical model calculations are discussed.

Light particles in coincidence with evaporation residues and heavy fragments have been measured by a 4pi charged-particle detector at the INFN Laboratori Nazionali di Legnaro (Padua) for the 240 MeV S-32+Mo-100 reaction leading to the Ce-132 composite system at 152 MeV of excitation energy. Energy spectra of the alpha-particles in coincidence with fission fragments were extracted for many correlation angles both in plane and out of plane. A prominent out-of-plane emission was observed, consistent with the pattern for the near-scission emission. From the fit to the spectra, the pre-scission alpha-particle multiplicity of 0.040 +/- 0.006 was obtained. This value is reproduced by the code PACE2 without the inclusion of a delay time for fission. The presence of fast fission, which could be responsible for this result, is discussed.