Influence of the break-up on the fusion and scattering processes

Lubián, J.; Gomes, P. R. S.; Anjos, R. M.; Padron, I.; Muri, C.; Moraes, S B; Alves, J. J. S.; Maciel, Auterives; Neto, R. Liguori; Added, N.; Martí, G. V.; Ramírez, M.; Pacheco, A. J.; Capurro, O. A.; Niello, J. O. Fernández; Testoni, J. E.; Abriola, D.; Spinella, M. R.

doi:10.1590/s0103-97332003000200032

Cited by 5 publications

(5 citation statements)

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“…The influence of the break-up on the fusion cross section with medium -light mass nuclei was investigated by the comparison of the fusion excitation functions of several systems, at above barrier energies: the weakly bound 6,7 Li and 9 Be, and the tightly bound 16,17,18 Li was also measured. Several light systems measured by the gamma ray spectroscopy method by Mukherjee et al [19] were also analyzed.…”

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confidence: 99%

Does the break-up process influence the fusion cross section?

2004

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We give an overall picture of our present understanding of the effect of the break-up of stable weakly bound nuclei on their fusion cross section with light, medium and heavy mass nuclei, at energies above the Coulomb barrier. The discussion is based mostly on recent data obtained by our group in collaborative experiments with ANU, USP and Tandar Laboratories. We conclude that there is complete fusion suppression for heavy targets, due to the loss of flux, corresponding to the occurrence of incomplete fusion of one of the break-up fragments. For medium and light mass targets, the incomplete fusion is negligible and therefore is no complete fusion suppression.Fusion of heavy ions is a subject that has been extensively studied in the last decades. For energies not too much above the Coulomb barrier (the so-called "region I"), the fusion process has the major contribution to the reaction cross section. As the bombarding energy increases, the competition with other reaction mechanisms decreases the fraction of the reaction cross section corresponding to the fusion cross section, that becomes saturated (the so-called "region II"). At energies close and below the Coulomb barrier, the study of the fusion mechanism is particularly interesting, due to its dependence on the nuclear structure of the colliding nuclei and to its strong couplings with elastic, inelastic and transfer channels. Simultaneous analyses of fusion and elastic scattering data [1,2] have shown that the fusion process is decided at the Coulomb barrier position, or even outside the barrier. Transfer channels that have sharp form factors, and consequently a relative small average transfer distance, act as important doorway to fusion and enhance the fusion cross section at this energy regime [3,4].Nuclei that have small separation energies have a large probability of breaking-up when the colliding nuclei approach each other and their interactions convert potential and kinetic energy into relative kinetic energy between the two fragments. An important question that has been raised in the last years is: What is the effect of the break-up process on the fusion cross section? Although there has been many theoretical and experimental works on this subject, it is still far from being full understood. There is a special interest on this field due to the recently available radioactive beams of very weakly bound nuclei. Reactions of astrophysical interest are induced by weakly bound nuclei and, if the coupling with the break-up channel leads to remarkable enhancement of the fusion cross section, super-heavy nuclei could be more easily produced. Due to the low intensities of the radioactive beams, it is very convenient to produce fusion reactions with the high intensity stable beams that are weakly bound, and consequently should have a reasonable break-up probability. Such reactions are important reference for the understanding of reactions induced by radioactive proton and neutron rich beams, althoght the reactions with these stable nuclei do not cover all the phy...

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confidence: 99%

Does the break-up process influence the fusion cross section?

2004

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“…The reduced fusion excitation functions for the 6,7 Li, 9 Be, 16O + 64 Zn systems coincide. 30), 33) The same behavior is found when we compare the excitation functions of the 6,7 Li, 9 Be, 11 B, 16 O + 27 Al systems; 9 Be + 27 Al, 29 Si and 11 B + 27 Al systems (the last one leads to the same compound nucleus as 9 Be + 29 Si); 18 O + 10 B, 17 O + 11 B, 19 F + 9 Be (leading to the same compound nucleus); 19 F + 9 Be and 19 F + 12 C. 32), 33) The data for the 12 C + 7 Li reaction, 34) measured in inverse kinematics in order to minimize the problems of transmission of the low energy residues through the detector window, agree with those from the gamma spectroscopy method, 35)- 39) where no fusion suppression could be detected at energies above the Coulomb barrier. Therefore, we believe that there are strong signatures that the BU process does not affect the TF cross section, at above barrier energies, for these medium and light mass systems, and there is also some evidence that the ICF process is negligible, within the 10% uncertainties of the data, at this mass range.…”

Section: Discussion Of the Effect Of The Break-up On The Fusion Crossmentioning

confidence: 99%

“…23)-25) Barrier distributions were also derived. The total fusion (CF + ICF) cross sections of 6,7 Li + 64 Zn, 27 Al and 9 Be + 27 Al were measured at TANDAR by either time of flight 29), 33) or ionization chamber techniques. 32) The fusion of 9 Be + 64 Zn was measured at USP by the in-beam and off-beam gamma ray spectroscopy methods, 30), 31) and it was derived that the ICF cross section was smaller than 10% of the CF.…”

Section: Fusion Cross Section Data Obtained By Our Group In Collaboramentioning

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The Fusion of Stable Weakly Bound Nuclei

Gomes

Anjos

Lubián

2004

Prog. Theor. Phys. Suppl.

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We discuss our present understanding of the effect of the break-up of stable weakly bound nuclei on the fusion cross section of these projectiles with light, medium and heavy mass targets, at energies above the Coulomb barrier. The discussion is based mostly on data obtained by our group in collaborative experiments. We show that for heavy targets there is complete fusion suppression, corresponding to the occurrence of incomplete fusion of one of the break-up fragments, whereas for medium and light mass targets, there is no such effect, due to the negligible incomplete fusion process. §1. The fusion versus break-up problem Fusion reactions induced by weakly bound nuclei have been extensively studied in the last years. Nuclei that have small separation energies have a large probability of breaking up when the colliding nuclei approach each other, and their interactions convert potential and kinetic energy into relative kinetic energy between the two fragments. The main question on this subject is: What is the effect of the break-up process on the fusion cross section? Although there has been many theoretical and experimental works, this subject is still far from being full understood. There is a special interest on this field due to the recent availability of radioactive beams of very weakly bound nuclei. 1)-6) Reactions of astrophysical interest are induced by weakly bound nuclei and, if the great size of radioactive nuclei leads to remarkable enhancement of the fusion cross section, super-heavy nuclei could be more easily produced. Due to the low intensities of the radioactive beams, it is very convenient to produce fusion reactions induced by high intensity stable beams that are weakly bound, and consequently should have a reasonable break-up probability. The full understanding of the fusion and break-up processes induced by stable weakly bound nuclei is an important reference for similar studies involving radioactive proton and neutron rich beams. The suitable stable nuclei for this kind of study are 9 Be, 6 Li and 7 Li, that have different structures and threshold break-up energies (from 1.48 MeV to 2.45 MeV). Measurements of fusion induced by these three nuclei may test theoretical models and may be useful when compared with fusion measurements involving unstable halo nuclei.The main general questions which have to be answered concerning this subject are: (i) -Does the break-up channel (BU) enhance or suppress the fusion cross section? (ii) -Is this effect concerned with the complete fusion (CF) cross section or with the total fusion (TF) cross section, corresponding to the sum of the usual complete fusion (CF n ) cross section with the fusion cross sections following the breakup process (by one (ICF) or all (CF BU ) the BU fragments)? (iii) -What are the effects of the BU on the fusion at different energy regimes? (iv) -What are the by guest on March 13, 2015 http://ptps.oxfordjournals.org/ Downloaded from

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“…At São Paulo, the elastic scattering was measured with the same set of nine surface barrier detectors used in previous work on the investigation of the threshold anomaly in the scattering of weakly [9,20,23,24] and tightly [28,29] bound nuclei. The detectors were placed at 40 cm from the target, with 5°angular separations between two adjacent detectors and a resolution of the order of 350 keV.…”

Section: Methodsmentioning

confidence: 99%

“…Important differences between these two lithium isotopes are the strong deformation of 7 Li, the much higher break-up ͑␣ + t͒ threshold energy, 2.47 MeV, and one bound excited state at 0.48 MeV. Keeley et al [18,19] suggested that the presence of the anomaly is due to inelastic and transfer channels, when reacting with 208 Pb, whereas Lubian et al [20] have shown that the anomaly disappears when only the coupling of the 7 Li excited state is considered in the scattering on 138 Ba. Recently, the scattering of radioactive 8 Li on 208 Pb was studied [21,22], and there were no signatures for the presence of the anomaly.…”

Section: Introductionmentioning

confidence: 99%

Threshold anomaly with weakly bound projectiles: Elastic scattering ofBe9+Al27

et al. 2004

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Elastic scattering of the weakly bound 9 Be on 27 Al was measured at near barrier energies. The optical model data analysis with the real and imaginary parts of a global double-folding potential does not show strong evidence of the usual threshold anomaly. The same result was obtained by using a Woods-Saxon shape optical potential and calculating the potential strengths at the strong absorption radius. The reason for this behavior may be explained by the presence of break-up and/or transfer channels at low energies.

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Influence of the break-up on the fusion and scattering processes

Cited by 5 publications

References 11 publications

Does the break-up process influence the fusion cross section?

Does the break-up process influence the fusion cross section?

The Fusion of Stable Weakly Bound Nuclei

Threshold anomaly with weakly bound projectiles: Elastic scattering ofBe9+Al27

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