Fusion hindrance in light nuclear systems: binding energy and/or surface diffuseness effect?

Toledo, A. Szanto de; Added, N.; Cárdenas, W. H. Z.; Carlin, N.; Moura, M. M. de; Munhoz, M. G.; Suaide, Alexandre Alarcon Do Passo; Szanto, E.M.; Takahashi, J.

doi:10.1016/s0375-9474(00)00346-8

Cited by 14 publications

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References 21 publications

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“…The cross section enhancement generally observed at sub-barrier energies is understood in terms of dynamical processes arising from couplings to collective inelastic excitations of the target and/or projectile [1]. However, in the case of reactions where at least one of the colliding nuclei has a sufficient low binding energy so that breakup becomes an important process, conflicting experimental and theoretical results are reported in recent papers [2][3][4][5][6][7][8][9][10].The 6,7 Li + 12 C, 59 Co fusion reactions are used to investigate the effect of breakup on the fusion cross section [11]. These measurements help to establish the influence of the projectile breakup on the fusion process at near-barrier energies and contribute to the determination of how the mass of the target affects the process, as well as the influence of the incomplete fusion yield.…”

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“…However, in the case of reactions where at least one of the colliding nuclei has a sufficient low binding energy so that breakup becomes an important process, conflicting experimental and theoretical results are reported in recent papers [2][3][4][5][6][7][8][9][10].…”

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confidence: 99%

“…It is important to have clear the reference used when an enhancement and/or a suppression is defined [5][6][7]. A final tuning for the coupling of the breakup channel, as well as the correct description of the reaction dynamics, requires the explicit measurement of precise elastic scattering data as well as yields leading to breakup itself [12][13][14].…”

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Direct measurement of the breakup process

et al. 2005

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In order to better understand the breakup contribution to fusion, we perfomed light particle coincidence measurements for the systems 6,7 Li+ 12 C, 59 Co at energies near and above the barrier. A three body kinematics analysis is performed with the objective of separating the contributions of different reaction mechanisms. For small angular differences between the light particles, the sequential and direct breakup seem to dominate. On the other hand, for large detector separations, a sequential decay following transfer is likely to dominate.The recent availability of radioactive nuclei beams motivated the investigation of fusion reactions involving weakly bound nuclei. The cross section enhancement generally observed at sub-barrier energies is understood in terms of dynamical processes arising from couplings to collective inelastic excitations of the target and/or projectile [1]. However, in the case of reactions where at least one of the colliding nuclei has a sufficient low binding energy so that breakup becomes an important process, conflicting experimental and theoretical results are reported in recent papers [2][3][4][5][6][7][8][9][10].The 6,7 Li + 12 C, 59 Co fusion reactions are used to investigate the effect of breakup on the fusion cross section [11]. These measurements help to establish the influence of the projectile breakup on the fusion process at near-barrier energies and contribute to the determination of how the mass of the target affects the process, as well as the influence of the incomplete fusion yield.It is important to have clear the reference used when an enhancement and/or a suppression is defined [5][6][7]. A final tuning for the coupling of the breakup channel, as well as the correct description of the reaction dynamics, requires the explicit measurement of precise elastic scattering data as well as yields leading to breakup itself [12][13][14].Bidimensional plot E αd xE α , both at E lab = 26MeV for the 6 Li + 12 C system. The lines represents the loci for events leaving 12 C in the ground state and the first excited state.The identification of the breakup products has been achieved measuring the three body final state correlations. Coincidence data displayed in Fig. 1a show the identification of the process Q-value in order to gate exclusively on the projectile breakup channel. Furthermore, the system excitation energy as well as the projectile fragment relative energy (see Fig. 1b) are used to identify the exit channel with no ambiguity. Based on those filters, angular correlations (see Fig. 2) are obtained to identify the several processes. This is complemented by measurements of relative energy of the fragments using different rest frame references (target like, projectile, target + fragment) in order to disentangle the contribution of breakup, incomplete fusion and/or transfer-reemission process. These experimental results are compared to three body kinematics calculations. As an example Fig. 3 displays the relative energy between α − d for the 6 Li breakup on a 12 C

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Direct measurement of the breakup process

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“…One directly related to the lowest binding energy for particle or cluster breakup, and another related to the size of the system by the ratio of skin / core volume. (14). Conflicting interpretations reported in the litterature, are, in part, originated from the use of different references to state that an inhibition is observed: reaction cross section, predictions based on one dimentional barrier penetration model (1BPM), fusion cross section of similar systems, and others.…”

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Is the inhibition/enhancement of fusion due to breakup still a puzzle?

et al. 2003

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The effect of breakup in the fusion cross section in terms of suppression versus enhancement, discussed in a conflicting way in the literature, is addressed. Data and theoretical predictions available in the literature are compared. Excitation functions of the sub-and near-barrier fusion cross-sections for a wide variety of light and heavy systems are presented and interpreted. We have measured fusion excitation functions and breakup correlation functions for the medium weight systems 6 Li + 59 Co and 7 Li + 59 Co. These measurements help to establish the influence of the projectile breakup on the fusion process at near-barrier energies and contribute to the determination of how the mass of the target affects the breakup role. The results indicate a light fusion enhancement at sub-barrier energies and a geometry dominated cross section at barrier energies.Systematic experimental and theoretical studies on the effect of the coupling of collective degrees of freedom to the fusion process, which lead to a significant enhancement of sub-barrier fusion cross-section when compared to predictions of one dimensional barrier penetration models, have been, so far, widely reported in the literature (ref 1-3). The dynamical process leading to this enhancement seems to be well understood (3). However, in the case of reactions where at least one of the colliding nuclei has a very low binding energy, and the breakup process may become an important reaction channel, conflicting model predictions and experimental results are found (4-7).Many questions regarding this feature became more relevant due to the large impact they may have on the investigations made possible with the recent availability of radioactive beams and the renewed interest in superheavy elements. It is so far established that the coupling of collective additional degrees of freedom to the sub-barrier fusion channel systematically enhances the Complete Fusion (CF) cross section. However, the theoretically expected decrease of the survival probability of weakly bound nuclei at barrier energies suggests an inhibition of the CF cross section. Experimental results have shown that the nuclear breakup channel may be a major limiting process for the fusion probability above the barrier energy when light weakly bound nuclei (8,9) are involved. On the other hand, the Coulomb breakup may also be important when weakly bound nuclei interact with very massive heavy-ions systems (10)(11)(12). One open and interesting question that remains in the case involving medium weight nuclei is whether the breakup process hinders or enhances fusion cross sections in different energy regimes.Recently a systematic study of the fusion process in systems as light as 6,7 Li+ 12 C and 6,7 Li+ 9 Be has been (8,13,14) presented reporting, at energies E above the barrier V B , (E > 2V B ), a correlation between the participants binding energy, the size of the system and the degree of inhibition of the fusion probability. This study indicated that the degree of inhibition of the fusion probabilit...

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Mapping Below-Barrier Breakup Probabilities to Above-Barrier Complete Fusion Suppression

Cook

2018

Zeptosecond Dynamics of Transfer‐Triggered Breakup

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Fusion hindrance in light nuclear systems: binding energy and/or surface diffuseness effect?

Cited by 14 publications

References 21 publications

Direct measurement of the breakup process

Direct measurement of the breakup process

Is the inhibition/enhancement of fusion due to breakup still a puzzle?

Mapping Below-Barrier Breakup Probabilities to Above-Barrier Complete Fusion Suppression

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