Fusion Evaporation Research Articles

Use of the facility EXOTIC for fusion–evaporation studies

The EXOTIC facility was developed to produce light radioactive beams and it is installed at Laboratori Nazionali di Legnaro (LNL) of INFN. We have explored the capabilities of EXOTIC as a beam separator for studies of heavy ion fusion–evaporation reactions. For this purpose, the facility has been slightly modified to allow the detection and identification of the fusion–evaporation residues (ER). We have measured fusion reactions for the two systems 32S + 48Ca and 32S + 64Ni where the cross sections are known from previous experiments at LNL. The ion optical parameters of EXOTIC have been set to maximize the ER yield in the detector system for the various cases. A good and clean separation of the ER from beam-like particles was obtained in the experimental Energy–Time of Flight correlation plots. These encouraging results have been compared with the performance of the electrostatic deflector set-up PISOLO, routinely used at LNL for sub-barrier fusion experiments. The beam rejection factor of EXOTIC at 0°is comparable to the one of PISOLO at 2°–3°, while a gain of overall efficiency up to a factor 3 has been obtained with EXOTIC. We briefly discuss possible ways of improving these results.

ENHANCEMENT OF SOLUBILITY AND DISSOLUTION OF IBUPROFEN BY SOLID DISPERSION TECHNIQUE AND FORMULATION OF SUSTAINED RELEASE TABLETS CONTAINING THE OPTIMISED BATCH OF SOLID DISPERSION

Objective: The present study was aimed to enhance the solubility of poorly water soluble drug Ibuprofen using solid dispersion technique and to develop sustained release tablets containing solid dispersion granules of the optimized batch. Ibuprofen is a non-steroidal anti-inflammatory drug (NSAID) with analgesic, antipyretic, and anti-inflammatory propertiesMethods: Solid dispersions of Ibuprofen were prepared by using PEG 20000 and Poloxamer 407 in different weight ratios by fusion and solvent evaporation method. Drug-carrier physical mixtures were also prepared. Solid dispersions were characterized by saturation solubility, drug content, in vitro dissolution, FTIR and DSC analysis. Solid dispersion formulation, SDF9 (PEG 20000 and Poloxamer 407, 1:3:3) prepared by solvent evaporation method was considered as the optimized batch. Sustained release tablets containing the solid dispersion granules of the optimized batch were prepared by direct compression method using HPMC K100M at three concentrations (10%, 14%, 18% w/w). The prepared formulations were evaluated for hardness, thickness, weight variation, friability, in vitro dissolution studies and release kinetics modelling.Results: Solid dispersion formulation, SDF9showed 95.09% drug release in 60 min and considered as the optimized batch. Tablet formulation, FT3 (HPMC K100M 18% w/w) showed 96% drug release for 12 h.Conclusion: Solid dispersions of ibuprofen using a combination of PEG 20000 and poloxamer 407 by solvent evaporation method may result in higher aqueous solubility of the drug. Also sustained release tablets containing solid dispersion granules of ibuprofen, using HPMC K100M may be a promising approach to extend the release rate of the drug from the solid dispersion for 12 h.

Spin distribution of evaporation residues formed in complete and incomplete fusion in 16O+154Sm system

Spin distributions for several evaporation residues populated in the 16O+154Sm system have been measured at projectile energy ≈ 6.2 MeV/A by using the charged particle–γ-coincidence technique. The measured spin distributions of the evaporation residues populated through incomplete fusion associated with ‘fast’ α and 2α-emission channels are found to be entirely different from fusion–evaporation channels. It is observed that the mean input angular momentum for the evaporation residues formed in incomplete fusion channel is relatively higher than that observed for evaporation residues in complete fusion channels. The feeding intensity profile of evaporation residues populated through complete fusion and incomplete fusion have also been studied. The incomplete fusion channels are found to have narrow range feeding only for high spin states, while complete fusion channels are strongly fed over a broad spin range and widely populated. Comparison of present results with earlier data suggests that the mean input angular momentum values are relatively smaller for spherical target than that of deformed target using the same projectile and incident energy highlighting the role of target deformation in incomplete fusion dynamics.

Synthesis of 119292−303 superheavy elements using Ca- and Ti-induced reactions

The synthesis of superheavy element $Z=119$ in the fusion evaporation reactions $^{42,44,46,48}\mathrm{Ca}+^{252\ensuremath{-}255}\mathrm{Es}$ and $^{46\ensuremath{-}50}\mathrm{Ti}+^{246\ensuremath{-}249}\mathrm{Bk}$ in the $3n$-, $4n$-, and $5n$-channels leading to $^{294\ensuremath{-}303}119$ and $^{292\ensuremath{-}299}119$, respectively, is evaluated. It is observed that the $3n$-channel (952.173 fb) cross section is larger for the reaction $^{48}\mathrm{Ca}+^{252}\mathrm{Es}\ensuremath{\rightarrow}^{300}119$; the $4n$- (155.026 fb) and $5n$- (23.11 fb) channel cross sections are larger for $^{48}\mathrm{Ca}+^{254}\mathrm{Es}\ensuremath{\rightarrow}^{302}119$. For the reaction $^{50}\mathrm{Ti}+^{249}\mathrm{Bk}\ensuremath{\rightarrow}^{299}119$, the experimental upper limit of the cross section was about 50 fb, which is very close to our calculated value (40.86 fb for the $4n$-channel). Also, the isotopic dependence of both projectile and target for the production cross section is discussed. These studies will be useful for the experimentalists to produce isotopes of element $Z=119$.

Inclusive and exclusive measurements of alpha particle production mechanisms in the 7Li + 144Sm system

In this work we have studied the production of alpha particles emitted as a consequence of different reactions in the 7Li + 144Sm system at near-barrier energies. We have obtained absolute cross sections of the total yield at backward angles and at bombarding energies of 24 and 30 MeV. We have also performed complementary exclusive measurements of non-capture breakup processes at 30 MeV. In particular, the neutron transfer followed by non-capture breakup of the 6Li ejectile, which was found to be the dominant process in the studied region, could be accounted for by estimations of a classical dynamical model. This contribution, together with estimations for the incomplete fusion and alpha particle evaporation following compound-nucleus formation, are compared to the experimental inclusive angular distributions obtained in this work.

Near-barrier neutron transfer in reactions 6He + 45Sc, 64Zn, and 197Au

Experimental cross sections of formation of isotopes 46Sc (in reaction 6He + 45Sc), 196,198Au (in reaction 6He + 197Au), and 65Zn (in reaction 6He + 64Zn) are analyzed. The time-dependent Schrodinger equation for the outer neutrons of 6He and 197Au nuclei is solved numerically to calculate the probability of neutron transfer and transfer cross sections. In reaction 6He + 197Au, the contribution of fusion and subsequent evaporation to experimental data can be neglected, while the corresponding contributions to reactions 6He + 45Sc and 6He + 64Zn are considerable. Fusion–evaporation is taken into account using the computational code of the NRV knowledge base. The results of calculations are in satisfactory agreement with the experimental data.

Dynamical Dipole mode in heavy-ion fusion reactions

In this work we give evidence for the first time of the Dynamical Dipole mode in a heavy system in the A∼190 mass region, in both fusion–evaporation and fission events. The 40,48Ca + 152,144Sm reactions at Elab=11(10.1) MeV/nucleon were employed. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

Clustering effects in fusion evaporation reactions with light even-even N=Z nuclei

In the recent years, cluster structures have been evidenced in many ground and excited states of light nuclei [1, 2]. In the currently experimental campaign, the NUCL-EX collaboration has measured the12C+12C and14N+10B reactions at 95 MeV and 80 MeV respectively. The experimental data corresponding to complete fusion of target and projectile into an excited24Mg nucleus was compared to the results of a pure statistical model [3, 4]. In addition, data from12C+12C have been analyzed to investigate the decay of the Hoyle state of12C* [12] obtained as an intermediate step in the 6α decay channel of the24Mg* formed in central events.

Experimental Determination of η/s for Finite Nuclear Matter.

We present, for the first time, simultaneous determination of shear viscosity (η) and entropy density (s) and thus, η/s for equilibrated nuclear systems from A∼30 to A∼208 at different temperatures. At finite temperature, η is estimated by utilizing the γ decay of the isovector giant dipole resonance populated via fusion evaporation reaction, while s is evaluated from the nuclear level density parameter (a) and nuclear temperature (T), determined precisely by the simultaneous measurements of the evaporated neutron energy spectra and the compound nuclear angular momenta. The transport parameter η and the thermodynamic parameter s both increase with temperature, resulting in a mild decrease of η/s with temperature. The extracted η/s is also found to be independent of the neutron-proton asymmetry at a given temperature. Interestingly, the measured η/s values are comparable to that of the high-temperature quark-gluon plasma, pointing towards the fact that strong fluidity may be the universal feature of the strong interaction of many-body quantum systems.

Fusion and quasifission studies in reactions forming Rn via evaporation residue measurements

Background: Formation of the compound nucleus (CN) is highly suppressed by quasifission in heavy-ion collisions involving massive nuclei. Though considerable progress has been made in the understanding of fusion-fission and quasifission, the exact dependence of fusion probability on various entrance channel variables is not completely clear, which is very important for the synthesis of new heavy and superheavy elements.Purpose: To study the interplay between fusion and quasifission in reactions forming CN in the boundary region where the fusion probability starts to deviate from unity.Methods: Fusion evaporation residue cross sections were measured for the $^{28,30}\mathrm{Si}+^{180}\mathrm{Hf}$ reactions using the Hybrid Recoil Mass Analyser at IUAC, New Delhi. Experimental data were compared with data from other reactions forming the same CN or isotopes of the CN. Theoretical calculations were performed using the dinuclear system and statistical models.Results: Reduced evaporation residue cross sections were observed for the reactions studied compared with the asymmetric reaction forming the same CN, indicating fusion suppression in more symmetric systems. The observations are consistent with fission fragment measurements performed in the same or similar systems. Larger ER cross sections are observed with increase in mass in the isotopic chain of the CN.Conclusions: Fusion probability varies significantly with the entrance channels in reactions forming the same CN. While complete fusion occurs for the $^{16}\mathrm{O}+^{194}\mathrm{Pt}$ reaction, the fusion probability drops to approximately $60--70%$ for the $^{30}\mathrm{Si}+^{180}\mathrm{Hf}$ and less than $20%$ for the $^{50}\mathrm{Ti}+^{160}\mathrm{Gd}$ reactions, respectively, forming the same CN at similar excitation energies.

Observation of a novel stapler band in 75 As

Abstract The heavy ion fusion–evaporation reaction study for the high-spin spectroscopy of 75As has been performed via the reaction channel 70Zn(9Be, 1p3n)75As at a beam energy of 42 MeV. The collective structure especially a dipole band in 75As is established for the first time. The properties of this dipole band are investigated in terms of the self-consistent tilted axis cranking covariant density functional theory. Based on the theoretical description and the examination of the angular momentum components, this dipole band can be interpreted as a novel stapler band, where the valence neutrons in ( 1 g 9 / 2 ) orbital rather than the collective core are responsible for the closing of the stapler of angular momentum.

Near-barrier Fusion Evaporation and Fission of 28Si+174Yb and 32S+170Er

Fusion evaporation residues and fission fragments have been measured, respectively, at energies around the Coulomb barrier for the 28 Si+ 174 Yb and 32 S+ 170 Er systems forming the same compound nucleus 202 Po. The excitation function of fusion evaporation, fission as well as capture reactions were deduced. Coupled-channels analyses reveal that couplings to the deformations of targets and the two-phonon states of projectiles contribute much to the enhancement of capture cross sections at sub-barrier energies. The mass and total kinetic energy of fission fragments were deduced by the time-difference method assuming full momentum transfer in a two-body kinematics. The mass-energy and mass-angle distributions were obtained and no obvious quasi-fission components were observed in this bombarding energy range. Further, mass distributions of fission fragments were fitted to extract their widths. Results show that the mass widths decrease monotonically with decreasing energy, but might start to increase when E c.m. / V B < 0.95 for both systems.

Dynamical Dipole mode in heavy-ion fusion reactions

The excitation of the Dynamical Dipole mode along the fusion path was investigated for the first time in the formation of a heavy compound nucleus in the A~190 mass region. The compound nucleus was formed at identical conditions of excitation energy and spin from two entrance channels having different charge asymmetry: the charge asymmetric 40 Ca + 152 Sm and the nearly charge symmetric 48 Ca + 144 Sm at Elab =11 and 10.1 MeV/nucleon, respectively. Both fusion–evaporation and fission events were studied simultaneously for the first time. The Dynamical Dipole mode excitation in the charge asymmetric channel was evidenced, in a model-independent way, by comparing the γ -ray multiplicity spectra and angular distributions of the two entrance channels with each other.

Clustering in light nuclei and their effects on fusion and pre – equilibrium processes.

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 24 Mg system have been studied through two different reactions, 12 C (95 MeV)+ 12 C and 14 N (80.7 MeV)+ 10 B, 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 12 C 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 18 O+28 Si, 16 O+30 Si and 19 F+27 Al 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.

Sub-barrier fusion of Si+Si systems

The near- and sub-barrier fusion excitation function has been measured for the system 30 Si+30 Si at the Laboratori Nazionali di Legnaro of INFN, using the 30 Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28 Si+28 Si and Coupled Channels (CC) calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3− excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28 Si+28 Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30 Si is a spherical nucleus, 30 Si+30 Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28 Si+28 Si is not observed for 30 Si+30 Si, probably due to the weaker couplings in last case.

Towards saturation of the electron-capture delayed fission probability: The new isotopes 240 Es and 236 Bk

Abstract The new neutron-deficient nuclei 240 Es and 236 Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240 Es produced in the fusion–evaporation reaction 209 Bi( 34 S,3n) 240 Es. Half-lives of 6 ( 2 ) s and 22 − 6 + 13 s were obtained for 240 Es and 236 Bk, respectively. Two groups of α particles with energies E α = 8.19 ( 3 ) MeV and 8.09 ( 3 ) MeV were unambiguously assigned to 240 Es. Electron-capture delayed fission branches with probabilities of 0.16 ( 6 ) and 0.04 ( 2 ) were measured for 240 Es and 236 Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes.

Simulation of microexplosion hydrodynamics in heavy ion fusion reactor chamber with wetted first wall

Thermonuclear fusion flare, fireball expansion, and evaporation of the liquid-film chamber wall are simulated by combining two one-dimensional (1D) codes DEIRA and RAMPHY. The considered process is divided into two phases: the DEIRA code is used to simulate the fast ignition and burn of a cylindrical target with DT fuel and a lead tamper, while the RAMPHY code is applied to describe the subsequent quasi-spherical expansion of the fireball. By the end of the first phase, the neutron and X-ray output from the target as well as the debris motion are determined. The fast ions are practically fully absorbed by the lead tamper of the fusion target. At the second stage, which starts with the arrival of the main shock at the target surface, the fireball expansion and the behavior of the wall liquid film are considered. The fireball front propagates with a velocity close to the self-similar value. The liquid film is first evaporated by the X-ray pulse, and then by the heat flux generated when the fireball collides with the primary vapor layer. Mechanical loading on the liquid film remains within the 100-MPa range.

Near-barrier neutron transfer in reactions 3,6He + 45Sc and 3,6He + 197Au

Experimental cross sections for formation of 196,198Au isotopes in reactions 3,6He + 197Au and cross sections for formation of 44,46Sc isotopes in reactions 3,6He + 45Sc have been analyzed. To calculate neutron transfer probabilities and cross sections the time- dependent Schrödinger equation for external neutrons of 3He, 6He, 45Sc and 197Au nuclei has been solved numerically. It is shown that the contribution of fusion and subsequent evaporation is significant in the case of reactions 3,6He + 45Sc, whereas in the case of reactions 3,6He + 197Au, it is negligible. Fusion-evaporation was taken into account using NRV evaporation code. Results of calculations demonstrate overall satisfactory agreement with experimental data.

Nanosecond lifetime measurements of Iπ=9/2- intrinsic excited states and low-lying B(E1) strengths in 183Re using combined HPGe-LaBr3 coincidence spectroscopy

This paper presents precision measurements of electromagnetic decay probabilities associated with electric dipole transitions in the prolate-deformed nucleus 183Re. The nucleus of interest was formed using the fusion evaporation reaction 180Hf(7Li,4n)183Re at a beam energy of 30MeV at the tandem accelerator at the HH-IFIN Institute, Bucharest Romania. Coincident decay gamma rays from near-yrast cascades were detected using the combined HPGe-LaBr3 detector array ROSPHERE. The time differences between cascade gamma rays were measured using the LaBr3 detectors to determine the half-lives of the two lowest lying spin-parity 9/2- states at excitation energies of 496 and 617keV to be 5.65(5) and 2.08(3) ns respectively. The deduced E1 transition rates from these two states are discussed in terms of the K-hindrance between the low-lying structures in this prolate-deformed nucleus.

&amp;lt;x content-type=&amp;quot;symbol&amp;quot;&amp;gt;&amp;alpha;&amp;lt;/x&amp;gt; decay studies of the neutron-deficient uranium isotopes &amp;lt;sup&amp;gt;215&amp;lt;x content-type=&amp;quot;symbol&amp;quot;&amp;gt;-&amp;lt;/x&amp;gt;217&amp;lt;/sup&amp;gt;U

The α -decay study is an important tool for obtaining information on the nuclear structure of heavy neutron-deficient nuclei. For the N =126 and 124 isotones with even proton number, an intruder state ( π h 9/2 π f 7/2)8+ based on the attractive interaction of f 7/2 protons and f 5/2 neutrons was observed, which increases the binding energy of this configuration with increasing proton number. Additionally, taking into account the octupole correlations, a large-scale shell model calculations predict that the ( π h 9/2 π f 7/2)8+ state lies close or below the ( π h 9 / 2 2 ) 6+ state in the 216Th and 218U. To extend the systematic of the I π =8+ isomeric state in N =124 isotones and search for the most neutron-deficient uranium isotopes, an experiment for the α -decay studies of 215 - 217U was performed at the gas-filled recoil separator SHANS at the Heavy Ion Research Facility in Lanzhou (HIRFL). Heavy ion induced fusion evaporation reactions of the 180W(40Ar, x n)220 - x U ( x =3 - 5) were used to synthesize these neutron-deficient uranium isotopes. The 40Ar beam was delivered by the sector focusing cyclotron of the HIRFL. The evaporation residues recoiled from the thin target were separated in-flight from the primary beam particles by the gas-filled recoil separator SHANS. After passing through two multi-wire proportional counters, the residues were planted into a focal plane detection system. Based on the energy-position-time correlation measurement, the isotopes 215 - 217U were identified. At a beam energy of 187.2 MeV, two α -decaying states were observed in 216U with E α =8.384(30) MeV, T 1/2=