Breakup effects of weakly bound nuclei on the fusion reactions

1. Breakup effects of weakly bound nuclei on thefusion reactions C.J. Lin, H.Q. Zhang, F. Yang, Z.H. Liu, X.K. Wu, P. Zhou, C.L. Zhang, G.L. Zhang, G.P. An, H.M. Jia, and X.X. Xu (China Institute of Atomic Energy)

2. §Dynamics of both fusion and elastic scattering are influenced by coupling to direct-reaction channels (including breakup if the projectile and/or target nuclei are weakly bounded); §These couplings generate a distribution of potential barriers; §Barrier distributions can derived from the excitation functions of fusion and elastic (or quasielastic) scattering.

3. Barrier distributions extracted from fusion excitation functions N. Rowley et al., Phys. Lett. B254, 25(1991)

4. 48Ca+90,96Zr fusion ◆The experiment was carried out at the XTU Tandem accelerator of Legnaro National Laboratory, Legnaro Italy; ◆ The evaporation residues (ER) were separated from the background of beam and beam-like particles by means of an electrostatic deflector;

5. The energy ranges are : for 48Ca+90Zr for 48Ca+96Zr in 0.5 MeV energy steps.

9. Barrier distribution deduced from quasielastic scatering ※is the transmission coefficient for angular momentum ; ※the reflection coefficient of .

10. ※is the quasielastic differential cross section at back angles. • H. Timmer et al., Nucl. Phys. A584, 190(1995)

11. Barrier distributions from elastic scattering • N. Rowley et al., Phys. Lett. B373, 23 (1995)

12. Barrier distributions for tightly-bound projectiles

13. The results of tightly bound projectile can be taken as a reference for probing the break-up effects of weakly bound-projectiles on fusion

14. Barrier distributions for 16O+152Sm quasielastic scattering ※ The experiment was carried out with 16O beam from the HI-13 tandem accelerator at CIAE, Beijing; ※ Three gas-ionization chambers set at 1560,1600,1640 were used to measure scattering particles.

19. 32S+90,96Zr experiment ※ The excitation functions of quasielastic scattering were measured at back angles. ※ The barrier distributions for these two systems are compared. ※ The influence of neutron transfer on the barrier of 32S+96Zr are observed. This system have positive Q-values for 1n, 2n, and 4n neutron transfer.

21. Structures are very similar at high energies.

22. Comparison of the barrier height distributions obtained from excitation functions of fusion and elastic scattering for more systems. (N. Rowley et al., Phys. Lett. B 373(1996)23)

27. Conclusion 1: Except some details, the barrier distributions derived from the data of fusion and elastic/quasielastic scattering are almost the same.

28. Barrier distributions for weakly bound projectiles • The experiments were carried out at the HI-13 tandem accelerator at CIAE, Beijing;

29. 6,7Li are weakly bound stable light nuclei.

30. 6Li+208Pb fusion • The compound nucleus 214At formed following complete fusion de-excites dominantly through 1n, 2n, 3n, 4n evaporation resulting residue 213-210At. These Nuclei are particle emitters. Their half-life time and energies are known.

31. On-line measurements

32. Off-line measurements

34. Elastic and breakup experiment The experiments were carried out at the HI-13 tandem accelerator at CIAE, Beijing with 6,7Li beams bombarding 208Pb target. The detector system arrangement is similar to 16O+152Sm experiment.

35. E=33MeV

38. Conclusion 2: For the weakly bound projectiles, the Barrier distributions extracted from the data of (complete) fusion and scattering are different, but nearly the same if the contributions of breakup are added into the differential cross sections of quasielastic scattering.

39. Possible Reason Barrier distribution is a good probe for the breakup effects on fusion and elastic scattering.

40. Complete fusion of weakly bound nuclei at above barrier energies Fusion cross section of tightly-bound nuclei can be satisfactory described with the semi-classical approach formula at above barrier energies:

41. The tightly bound system 16O+208Pb can be taken as a reference for study of breakup effects.

48. Complete fusion and total fusion ※ For weakly bound-projectile, the total fusion cross section is the sum of the complete fusion and partial fusion cross sections, . ※ The fusion of weakly bound nuclei is suppressed at the above barrier energies.

50. Conclusion 3: ◆ The complete fusion of weakly bound projectile with heavy target is suppressed, whereas in most cases breakup has very little effects on the total fusion at the above barrier energies; ◆ This result indicates that partial fusion of weakly bound nuclei most likely takes place near the absorption region.