Лаборатория ядерных реакций им. Г.Н. Флерова

Семинар физических секторов

Дата и время: среда, 14 ноября 2018 г., в 15:30

Место: Конференц-зал, Лаборатория ядерных реакций им. Г.Н.Флерова

Тема доклада: «Determination of Fusion Barrier Distributions from Quasielastic Scattering Cross Sections towards Superheavy Nuclei Synthesis»

Докладчик: Таики Танака (RIKEN, Университет Кюсю)

Аннотация:

In order to study the nucleus-nucleus interaction for synthesis of superheavy nuclei, we have measured excitation functions for Quasielastic (QE) scattering cross section relative to the Rutherford cross section dσ_QE/dσ_R of ⁴⁸Ca+²⁰⁸Pb, ^50Ti+²⁰⁸Pb, ²²Ne+²⁴⁸Cm, ²⁶Mg+²⁴⁸Cm, ⁴⁸Ca+²³⁸U and ⁴⁸Ca+²⁴⁸Cm using gas-filled type recoil ion separator GARIS^[1]. In contrast to previous QE barrier distribution studies^[2-3], which measured the recoiled projectile nuclei at back side (θ ∼ 170°), this work could measure the QE scattering cross section for angular momentum l = 0 by measurement of the target nuclei which recoiled at completely forward side with using the gas-filled-type recoil ion separator GARIS. The QE scattering events were clearly separated from deep-inelastic events by using GARIS and its focal plan detectors. The QE barrier distributions were successfully extracted, and compared with coupled-channels calculations^[4]. The results of the calculations indicate that vibrational and rotational excitations of the colliding nuclei, deformation of the actinide target, as well as neutron transfers before contact, strongly affect the structure of the barrier distribution. For the reactions of ⁴⁸Ca+²⁰⁸Pb and ⁵⁰Ti+²⁰⁸Pb, a local maximum of the barrier distribution occurred at the same energy as the peak of the 2n evaporation (ER) cross section^[5-8] of the system. On the other hand, for the hot fusion reactions of ²²Ne+²⁴⁸Cm, ²⁶Mg+²⁴⁸Cm, ⁴⁸Ca+²³⁸U and ⁴⁸Ca+²⁴⁸Cm, we found that the peaks of ER cross section^[9-16] appear between the experimental average Coulomb barrier height B0 (the energy point at dσ_QE/dσ_R = 0.5) and the Coulomb barrier of side collision Bside. This indicates that the ER cross sections are largely determined by using the advantage of the compact collision. In the compound nucleus (CN) formation process, the probability of CN formation increases for side collision because of the shorter distance of the center of nuclei in the touching configuration^[17]. Moreover, increasing the fusion hindrance, such as ⁴⁸Ca+²⁴⁸Cm (Z₁Z₂ = 1920), the peak of the σ_ER is close to the Coulomb barrier of side collision Bside. A few experimental groups will attempt (have attempted) to syntheses new elements Z > 118 by using the combinations of the ⁵⁰Ti, ⁵⁴Cr projectiles with ²⁴⁸Cm, ²⁴⁹Bk, ^249-251Cf targets, in hot fusion reactions^[18-20]. In that case, our study strongly implies that the incident energy of maximum σ_ER will appear at the energy of B_side.

References

[1] T. Tanaka et. al., J. Phys. Soc. Jpn. 87, 014201 (2018).
[2] S. Mitsuoka et. al., Phys. Rev. Lett. 99, 182701 (2007).
[3] S. S. Ntshangase et. al., Phys. Lett. B 651, 27 (2007).
[4] K. Hagino et. al., Comput. Phys. Commun. 123, 143 (1999).
[5] A. V. Belozerov et. al., Eur. Phys. J. A 16, 447 (2003).
[6] H. W. Gaggeler et. al., Nucl. Phys. A 502, 561c (1989).
[7] Yu. Ts. Oganessian et. al., Phys. Rev. C 64, 054606 (2001).
[8] F. P. Hesberger et. al., Eur. Phys. J. A 16, 57 (2001).
[9] Yu. A. Lazarev et. al., Phys. Rev. Lett. 73, 624 (1994).
[10] A. Turler et. al., Phys. Rev. C 57, 1648 (1998).
[11] R. Dressier et. al., PSI Rep. 1, p.130 (1999).
[12] S. Hubener et. al., Radiochimica Acta 89, 737 (2001).
[13] H. Haba et. al., Phys. Rev. C 85, 024611 (2012).
[14] J. Dvorak et. al., Phys. Rev. Lett. 100, 132503 (2008).
[15] Yu. Ts. Oganessian et. al., Phys. Rev. C 70, 064609 (2004).
[16] S. Hofmann et. al., Eur. Phys. J. A 48, 62 (2012). [17] K. Hagino, Phys. Rev. C 98, 014607 (2018).
[18] S. Dmitriev et. al., EPJ Web of Conf. 131, 08001(2016).
[19] C. E. Dullmann et. al., EPJ Web of Conf. 131, 08004 (2016).
[20] S. Hofmann, et. al., Eur. Phys. J. A 52, 180 (2016).