Fusion Suppression Research Articles

Bivariate analysis of 3D structure for stereoscopic image quality assessment

Human visual system (HVS) identifies each unit of stereo-pair into binocular or monocular perception depending on distortions and depth perception. However, these HVS properties still have a large room for exploration in stereoscopic image quality assessment (SIQA) research field. In this paper, a bivariate natural scene statistics (NSS) model is proposed to capture image quality by extracting features from binocular and monocular perception regions, respectively. In the implementation details, the stereo-pair is first segmented into various regions based on spatial information of its disparity. Then the regions are classified into categories of binocular fusion, binocular rivalry and binocular suppression. Bivariate statistics of spatially adjacent Gabor response of image are extracted from each category of regions, based on which features are calculated for image quality representation. In particular, the extraction strategy depends on the type of image patch. Experimental results show that the proposed model is promising at handling the task of SIQA on LIVE 3D Image Quality Database.

Interplay of charge clustering and weak binding in reactions of Li8

In collisions of light, stable, weakly bound nuclides, complete fusion (capture of all of the projectile charge) has been found to be suppressed by $\ensuremath{\sim}30%$ at above-barrier energies. This is thought to be related to their low thresholds for breakup into charged clusters. The observation of fusion suppression in the neutron-rich radioactive nucleus $^{8}\mathrm{Li}$ is therefore puzzling: the lowest breakup threshold yields $^{7}\mathrm{Li}+n$ which cannot contribute to fusion suppression because $^{7}\mathrm{Li}$ retains all the projectile charge. In this work, the full characteristics of $^{8}\mathrm{Li}$ breakup in reactions with $^{209}\mathrm{Bi}$ are presented, including, for the first time, coincidence measurements of breakup into charged clusters. Correlations of cluster fragments show that most breakup occurs too slowly to significantly suppress fusion. However, a large cross section for unaccompanied $\ensuremath{\alpha}$ particles was found, suggesting that charge clustering, facilitating partial charge capture, rather than weak binding is the crucial factor in fusion suppression, which may therefore persist in exotic nuclides.

CDCC calculations of fusion of 6Li with targets 144Sm and 154Sm: effect of resonance states**A. Gómez Camacho from CONACYT, México, J. Lubian from CNPq, FAPERJ, Pronex, Brazil. S.G.Z was partly supported by the NSF of China (11120101005, 11275248, 11525524, 11621131001, 11647601, 11711540016), 973 Program of China (2013CB834400) and the Key Research Program of Frontier Sciences of CAS. H.Q.Z. from NSF

Continuum Discretized Coupled-Channel (CDCC) model calculations of total, complete and incomplete fusion cross sections for reactions of the weakly bound 6Li with 144,154Sm targets at energies around the Coulomb barrier are presented. In the cluster structure frame of 6Li→α+d, short-range absorption potentials are considered for the interactions between the ground state of the projectile 6Li and α-d fragments with the target. In order to separately calculate complete and incomplete fusion and to reduce double-counting, the corresponding absorption potentials are chosen to be of different range. Couplings to low-lying excited states 2+, 3− of 144Sm and 2+, 4+ of 154Sm are included. So, the effect on total fusion from the excited states of the target is investigated. Similarly, the effect on fusion due to couplings to resonance breakup states of 6Li, namely, l=2, Jπ=3+,2+,1+ is also calculated. The latter effect is determined by using two approaches, (a) by considering only resonance state couplings and (b) by omitting these states from the full discretized energy space. Among other things, it is found that both resonance and non-resonance continuum breakup couplings produce fusion suppression at all the energies considered.

Effect of breakup and resonance states of6Li on fusion

CDCC calculations of total fusion cross sections are presented for reactions of the weakly bound6Li with targets144Sm and154Sm at energies around the Coulomb barrier. Couplings to the low-lying excited states 2+, 3− of144Sm and 2+, 4+ of154Sm are included in the calculations. In the cluster structure frame of6Li → α + d, short range absorption potentials are considered for the interactions between α- and d- with the target to account for fusion. The effect of the excited states of the target on total fusion is investigated, as well as, that from couplings of resonance states of6Li, namely, l = 2, Jπ = 3+, 2+, 1+. The latter effect is calculated by two different approaches, (a) by considering only resonance states couplings and (b) by omitting these states from the full discretized energy space. Among other things, it is found that resonance and non-resonance continuum couplings give rise to small and similar fusion suppression at the higher energies.

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.

Near and sub-barrier reactions of 8B

Four classes of measurements that are important for achieving a complete understanding of the reactions of exotic nuclei are identified and classified according to their degree of difficulty. Previously reported data for near- and sub-barrier fusion of 8 B+58 Ni are critically reviewed. The influence of breakup protons on the evaporation proton measurements for this system is shown to be small at all energies except for the lowest one measured, and corrections are made for this process. Model dependencies in the deduced fusion cross sections are assessed using three different evaporation codes. Data sets for targets of 58 Ni and 28 Si are shown to be consistent with each other, and with fusion enhancement up to energies that are greater than the Coulomb barrier Vb (Ec.m. ≲ Vb + 1.5×ћω ). An important difference with the behavior of neutron-halo systems is thereby confirmed. Possible fusion suppression beyond this energy is suggested by the 28 Si data. A proposal to measure the 8 B+40 Ar fusion cross section using an active-target time projection chamber is discussed.

Study of breakup and transfer of weakly bound nucleus 6Li to explore the low energy reaction dynamics

Investigation of the breakup and transfer effect of weakly bound nuclei on the fusion process has been an interesting research topic in the past several years. However, owing to the low intensities of the presently available radioactive ion beam (RIB), it is difficult to clearly explore the reaction mechanisms of nuclear systems with unstable nuclei. In comparison with RIB, the beam intensities of stable weakly bound nuclei such as 6,7 Li and 9 Be, which have significant breakup probability, are orders of magnitude higher. Precise fusion measurements have already been performed with those stable weakly bound nuclei, and the effect of breakup of those nuclei on the fusion process has been extensively studied. Those nuclei indicated large production cross sections for particles other than the α + x breakup. The particles are originated from non-capture breakup (NCBU), incomplete fusion (ICF) and transfer processes. However, the conclusion of reaction dynamics was not clear and has the contradiction.In our previous experiments we have performed 6 Li+96 Zr and 154 Sm at HI-13 Tandem accelerator of China Institute of Atomic Energy (CIAE) by using HPGe array. It is shown that there is a small complete fusion (CF) suppression on medium-mass target nucleus 96 Zr different from about 35% suppression on heavier target nucleus 154 Sm at near-barrier energies. It seems that the CF suppression factor depends on the charge of target nuclei. We also observed one neutron transfer process. However, the experimental data are scarce for medium-mass target nuclei.In order to have a proper understanding of the influence of breakup and transfer of weakly bound projectiles on the fusion process, we performed the 6 Li+89 Y experiment with incident energies of 22 MeV and 34 MeV on Galileo array in cooperation with Si-ball EUCLIDES at Legnaro National Laboratory (LNL) in Italy. Using particle-particle and particle-γ coincidences, the different reaction mechanisms can be clearly explored.

Negligible suppression of the complete fusion ofLi6,7on light targets, at energies above the barrier

Motivated by a recent work performed at Australian National University by S. Kalkal et al. [Phys. Rev. C 93, 044605 (2016)] on breakup and its time scale, where it was shown that the prompt (or near-target) breakup of $^{6,7}\mathrm{Li}$ is almost negligible and consequently the near-barrier complete fusion cross section induced by these weakly bound Li isotopes on light targets should not be suppressed by the breakup, as it is for heavier targets, we estimated the contributions of complete and incomplete fusion in the measured total fusions for several light systems available in the literature. The chosen systems were those for which the fusion cross sections had been measured using the $\ensuremath{\gamma}$-ray spectroscopy method and all evaporation channel cross sections were reported. For the estimation, we used, apart from the data, the predictions of the evaporation code cascade. The results show that, indeed, the complete fusion suppression is negligible for such systems at energies slightly above the barrier, in agreement with the above-mentioned recent measurements of breakup time scales.

Exploring contributions from incomplete fusion inLi6,7+Bi209andLi6,7+Pt198reactions

We use the breakup absorption model to simultaneously describe the measured cross-sections of the Complete fusion (CF), Incomplete fusion (ICF), and Total fusion (TF) in nuclear reactions induced by weakly bound nuclei $^{6,7}$Li on $^{209}$Bi and $^{198}$Pt targets. The absorption cross-sections are calculated using the Continuum Discretized Coupled Channels (CDCC) method with different choices of short range imaginary potentials to get the ICF, CF and TF cross-sections. It is observed that the cross-sections for deuteron-ICF/deuteron-capture are of similar magnitude as the $\alpha$-ICF/$\alpha$-capture, in case of $^{6}$Li projectile, while the cross-sections for triton-ICF/triton-capture is more dominant than $\alpha$-ICF/$\alpha$-capture in case of $^{7}$Li projectile. Both these observations are also corroborated by the experimental data. The ratio of ICF to TF cross-sections, which defines the value of fusion suppression factor is found to be in agreement with the data available from the literature. The cross-section ratio of CF/TF and ICF/TF show opposite behavior, the former decreases while the latter increases as the energy is lowered, which shows the dominance of ICF at below barrier energies. We have also studied the correlation of the ICF cross-sections with the non-capture breakup (NCBU) cross-sections as a function of energy, which shows that the NCBU is more significant than ICF at below barrier energies.

Near-barrier fusion of proton- and neutron-halo systems

It is shown that the behaviour of the fusion excitation functions for proton-halo and neutron-halo systems presents important differences, especially in the energy region slightly above the barrier. Measurements for 6He, 11Li and 11Be projectiles are discussed to exemplify the behaviour of neutron-halo systems, while experiments with 8B beams illustrate the situation for proton-halo nuclei. With respect to a standard benchmark, neutron- (proton-) halo systems show a fusion suppression (enhancement) above the barrier.

Fusion suppression/fusion enhancement around the Coulomb barrier

This work explored the fusion dynamics of 36Li+2759Co, 49Be+50124Sn, 49Be+82208Pb, 2040Ca+50124Sn and 612C+82208Pb reactions by using energy dependent Woods–Saxon potential model (EDWSP model) and coupled channel model. The roles of projectile breakup channel on fusion process are directly reflected from fusion mechanism of 36Li+2759Co, 49Be+50124Sn and 49Be+82208Pb reactions. Whereas, the impacts of collective excitations and/or nucleon transfer channels on fusion process are evident from analysis of 2040Ca+50124Sn and 612C+82208Pb reactions. The total fusion data (sum of complete and incomplete fusion data) of 36Li+2759Co reaction is reasonably recovered by the EDWSP model calculations which in turn indicate that total fusion excitation function data is not suppressed with reference to theoretical predictions. In contrast, for 49Be+50124Sn (49Be+82208Pb) reaction, the above barrier fusion data is suppressed with respect to the expectations of coupled channel approach and single barrier penetration model by 28% (32%). However, the EDWSP model based calculations reduce the magnitude of suppression factor by 8% (12%) for 49Be+50124Sn (49Be+82208Pb) reaction and consequently the fusion data at above barrier energies is inhibited for both reactions by 20% with reference to the EDWSP model calculations. This fusion suppression can be correlated with loosely bound nature of the projectile. On the other hand, the above barrier fusion data of 2040Ca+50124Sn and 612C+82208Pb reactions is not inhibited with respect to the predictions of coupled channel approach and EDWSP method, henceforth, confirms stability of projectiles against breakup effects.

Importance of lifetime effects in breakup and suppression of complete fusion in reactions of weakly bound nuclei

Complete fusion cross sections in collisions of light, weakly bound nuclei and high Z targets show above-barrier suppression of complete fusion. This has been interpreted as resulting from breakup of the weakly bound nucleus prior to reaching the fusion barrier, reducing the probability of complete fusion. This paper investigates how these conclusions are affected by lifetimes of the resonant states that are populated prior to breakup. If the mean life of a populated resonance is much longer than the fusion timescale, then its breakup cannot suppress complete fusion. For short-lived resonances, the situation is more complex. This work includes the mean life of the short-lived 2+ resonance in 8Be in classical dynamical model calculations to determine its effect on energy and angular correlations of the breakup fragments and on predictions of fusion suppression. Coincidence measurements of breakup fragments produced in reactions of 9Be with 144Sm, 168Er, 186W, 196Pt, 208Pb and 209Bi at energies below the barrier are re-analysed. Predictions of breakup observables and of complete and incomplete fusion at energies above the fusion barrier are made using the classical dynamical simulation code PLATYPUS, modified to include the lifetimes of short-lived resonant states. The agreement of the breakup observables is improved when lifetime effects are included. The predicted suppression of complete fusion due to breakup is nearly independent of Z, with an average value of 9%, below the experimentally determined fusion suppression of 30% in these systems. This more realistic treatment of breakup leads to the conclusion that the suppression of complete fusion cannot be fully explained by breakup prior to reaching the fusion barrier. Other mechanisms that can suppress complete fusion must be investigated. A candidate is cluster transfer that produces the same nuclei as incomplete fusion.

Role of projectile breakup effects and intrinsic degrees of freedom on fusion dynamics**Supported by Dr. D. S. Kothari Post-Doctoral Fellowship Scheme sponsored by University Grants Commission (UGC), New Delhi, India

This article analyzes the fusion dynamics of loosely bound and stable projectiles with Zr-target isotopes within the context of the coupled channel approach and the energy-dependent Woods-Saxon potential model (EDWSP model). In the case of the 28Si + 90Zr reaction, the coupling to the inelastic surface excitations results in an adequate description of the observed fusion dynamics while in case of the 28Si + 94Zr reaction, the coupling to collective surface vibrational states as well as the neutron (multi-neutron) transfer channel is necessary in the coupled channel calculations to reproduce the below-barrier fusion data. However, the EDWSP model calculation provides an accurate explanation of the fusion data of 28Si + 90,94Zr reactions in the domain of the Coulomb barrier. In the fusion of the 6Li + 90Zr reaction, the inclusion of the nuclear structure degrees of freedom recovers the observed sub-barrier fusion enhancement but results in suppression of the above barrier fusion data by 34% with respect to the coupled channel calculations. Using EDWSP model calculations, this suppression factor is reduced by 14% and consequently, the above-barrier fusion data of 6Li + 90Zr reaction is suppressed by 20% with reference to the EDWSP model calculations. Such fusion suppression at above-barrier energies can be correlated with the breakup of the projectile (6Li) before reaching the fusion barrier, as a consequence of low binding energy.

Asymptotic and near-target direct breakup ofLi6andLi7

Background: $^{6,7}\mathrm{Li}$ and $^{9}\mathrm{Be}$ are weakly bound against breakup into their cluster constituents. Breakup location is important for determining the role of breakup in above-barrier complete fusion suppression. Recent works have pointed out that experimental observables can be used to separate near-target and asymptotic breakup.Purpose: Our purpose is to distinguish near-target and asymptotic direct breakup of $^{6,7}\mathrm{Li}$ in reactions with nuclei in different mass regions.Method: Charged particle coincidence measurements are carried out with pulsed $^{6,7}\mathrm{Li}$ beams on $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$ targets at sub-barrier energies and compared with previous measurements using $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$ targets. A detector array providing a large angular coverage is used, along with time-of-flight information to give definitive particle identification of the direct breakup fragments.Results: In interactions of $^{6}\mathrm{Li}$ with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$, direct breakup occurs only asymptotically far away from the target. However, in interactions with $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$, near-target breakup occurs in addition to asymptotic breakup. Direct breakup of $^{7}\mathrm{Li}$ into $\ensuremath{\alpha}\ensuremath{-}t$ is not observed in interactions with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$. However, near-target dominated direct breakup was observed in measurements with $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$. A modified version of the Monte Carlo classical trajectory model code platypus, which explicitly takes into account lifetimes associated with unbound states, is used to simulate sub-barrier breakup reactions.Conclusions: Near-target breakup in interactions with $^{6,7}\mathrm{Li}$ is an important mechanism only for the heavy targets $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$. There is insignificant near-target direct breakup of $^{6}\mathrm{Li}$ and no direct breakup of $^{7}\mathrm{Li}$ in reactions with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$. Therefore, direct breakup is unlikely to suppress the above-barrier fusion cross section in reactions of $^{6,7}\mathrm{Li}$ with $^{58}\mathrm{Ni}$ and $^{64}\mathrm{Zn}$ nuclei.

Amblyopia: neural basis and therapeutic approaches.

Abnormalities in visual processing caused by visual deprivation or abnormal binocular interaction may induce amblyopia, which is characterized by reduced visual acuity. Occlusion therapy, the conventional treatment, requires special attention as occlusion of the fellow normal eye may reduce its visual acuity and impair binocular vision. Besides recovering visual acuity, some researchers have recommended restoration of stereoacuity and motor fusion and reverse suppression in order to prevent diplopia. Recent studies have documented that the amblyopic visual cortex has a normal complement of cells but reduced spatial resolution and a disordered topographical map. Changes occurring in the late sensitive period selectively impact the parvocellular pathway. Distinct morphophysiologic and psychophysical deficits may demand individualization of therapy, which might provide greater and longer-lasting residual plasticity in some children.

Analysis of fusion dynamics of colliding systems involving stable, loosely bound and halo nuclei

This article analyzed the fusion dynamics of stable nuclei, loosely bound nuclei and halo nuclei within the view of coupled channel approach and the energy dependent Woods–Saxon potential model (EDWSP model). The different projectiles ( and are bombarded onto common spherical target isotope ( wherein target isotope exhibits inelastic surface excitations as dominant mode of coupling. The fusion dynamics of reactions, wherein there is no signature of fusion suppression at above barrier energies, are adequately explained by both theoretical approaches in domain of Coulomb barrier. In case of reactions, the couplings of inelastic surface excitations of colliding systems remove the discrepancies between below barrier fusion data and expectations of one-dimensional barrier penetration model. However, at above barrier energies, the fusion excitation function data are suppressed in comparison to the theoretical predictions of both approaches. Interestingly, this suppression of above barrier fusion data is minimized by the present model calculation by a factor of 7% with respect to a value reported in literature. Within the view of the EDWSP model calculations, the above barrier fusion data of reaction are hindered by a factor of 25% and by a factor of 17% for reaction which is smaller than a value as pointed out in literature. The observed sub-barrier fusion dynamics of and reactions are reasonably described by the coupled channel model and the EDWSP model. Furthermore, the applicability of the EDWSP model has been tested for exploration of the fusion of reaction and hence due to barrier modification effects, the EDWSP model successfully explains the observed fusion enhancement of reaction. The present calculations clearly indicate that different theoretical approaches (coupled channel formulation and EDWSP model) induce similar kinds of barrier modification effects in the heavy ion fusion reactions.

Dispositional mindfulness in trauma recovery: Prospective relations and mediating mechanisms

This study examined the protective properties and candidate mediating processes (cognitive fusion and cognitive suppression) linking dispositional mindfulness to distal risk factors (negative affect, anxiety sensitivity, rumination) and psychopathology symptom outcomes (depression and posttraumatic stress symptoms) following trauma exposure. To do so, a community-based sample of adults was longitudinally studied in the six-months following exposure – within 30-days (T1), 3-months (T2), and 6-months (T3) – to a shared disaster-related potentially traumatic event (PTE). Specifically, we found that cognitive fusion predicted, and mediated, the effect of mindfulness on outcomes related to distress post-trauma including negative affect, depression and posttraumatic stress symptoms. Complementary to these effects, we found that cognitive suppression predicted, and mediated, the effect of mindfulness on distal risk factors linked to negative self-referential processes including rumination and anxiety sensitivity. Findings are discussed with respect to their theoretical and clinical implications for the potential role and mechanisms of mindfulness in recovery following trauma.

Nuclear matter incompressibility effect on the cross-section of fusion reactions with a weakly bound projectile

Fusion reactions with a weakly bound projectile are studied using the double-folding model along with a repulsive interaction modifying term. Using this modified potential, including nuclear matter incompressibility effects, the fusion reaction cross sections and suppression parameters are calculated for 9Be+ 209Bi, 208Pb, 29Si and 27Al reactions. The results show that applying these effects at energies near the Coulomb barrier improves the agreement between the calculated and experimental cross sections, and modifies the mean values of the suppression parameter.

Role of Surface Energy Coefficients and Temperature in the Fusion Reactions Induced by Weakly Bound Projectiles

A systematic study is provided to analyze the behaviors of the interaction potential and complete fusion cross section which are influenced by the effects of the surface energy coefficients γ and temperature T. Our framework is restricted to the proximity formalism for fusion reactions induced by weakly bound projectiles 6Li, 7Li and 9Be. The different surface energy coefficients (γ-MN76, γ-MN95, γ-MS00 and γ-PD03) are used to study the role of the parameter γ in the proximity potentials AW 95 and BW 91. Comparison of the theoretical and the experimental values of the barrier characteristics (barrier heights and its positions) indicates that the modified versions AW 95 (γ-MS00) and BW 91 (γ-MS00) give the least deviations for fusion barrier heights. Moreover, it is shown that the temperature-dependence improves the calculated barrier heights based on the potentials AW 95 and BW 91. In the present study, the analysis of the mentioned effects on the complete fusion cross sections has been also discussed for the systems of interest. The obtained results reveal that the above-modified versions provide a more accurate description for behavior of the complete fusion cross sections than the original potentials at above-barrier energies. It is demonstrated that the increase of the temperature T enhances the complete fusion suppression at this energy range.

Search of a systematic behaviour for the weakly bound complete fusion suppression caused by breakup

We discuss the effect of breakup on the complete and total fusion cross sections of weakly bound nuclei, both stable and radioactive, at near barrier energies. We show that there is suppression of the complete fusion of non-halo nuclei and total fusion of neutron- halo nuclei at energies above the barrier, whereas there is some enhancement at sub-barrier energies. We investigate a systematic behaviourfor this effect for several weakly bound systems.