Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 53

Study of quasielastic barrier distributions as a step towards thesynthesis of superheavy elements with hot fusion reactions†
T. Tanaka,∗1,∗2,∗3 K. Morita,∗1,∗2 K. Morimoto,∗1 D. Kaji,∗1 H. Haba,∗1 R. A. Boll,∗4 N. T. Brewer,∗4S. Van Cleve,∗4 D. J. Dean,∗4 S. Ishizawa,∗1,∗5 Y. Ito,∗1,∗6 Y. Komori,∗1 K. Nishio,∗1,∗6 T. Niwase,∗1,∗2
B. C. Rasco,∗4 J. B. Roberto,∗4 K. P. Rykaczewski,∗4 H. Sakai,∗1 D. W. Stracener,∗4 and K. Hagino∗7,∗8,∗9The excitation functions of quasielastic scatteringcross sections for reactions relevant to the syntheses of superheavy nuclei, that is, the 22 Ne+248 Cm,26
Mg+248 Cm, and 48 Ca+238 U systems, were measured
using the gas-ﬁlled recoil ion separator GARIS to understand systematically the reaction dynamics of thehot fusion reactions. From the measured cross sections,the barrier distribution was extracted, which shows adistribution of the barrier height in the entrance channel. The experimental data were well reproduced by
the coupled-cannels calculations.1) The calculated results indicate that the shape of barrier distribution isaﬀected dominantly by deformation of the actinide target nuclei, but also by vibrational/rotational excitations of the projectile nuclei as well as neutron transfer processes before capture. Contribution from eachcolliding angles to the barrier distribution is systematically shown in Fig. 1 (black thin solid curves) byshowing the barrier distribution from each collidingangle range with 10◦ interval. Here, the distribution
for the side collision 80–90◦ is highlighted by the reddashed curve. The total barrier distributions, which
are the sum of the black thin solid curves and the reddashed curves, are also shown by the blue solid curves.
The peak of the sum of the evaporation residue crosssections for Sg (Z = 106),2–6) Hs (108),7) Cn (112)8,9)
and Lv (116)8,10)a) coincide not only with the barrier
distribution for 80–90◦ , but also with that for 70–80◦
etc. However, the overlap with the barrier distribution
for the tip collision, such as 0◦ –20◦ , is negligibly small,indicating that these hot fusion reactions take advantage of the compact collision, where the projectile approaches along the short axis of a prolately deformednucleus, as was discussed in Refs. 11–13).
For hot fusion reactions, the optimum incident energy, at which the evaporation residue cross section
†
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8∗9a)

0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.02

-d(dσQE /dσR )/dE

22Ne+248Cm

26

σER (pb)

Sg (106)
102

101
100

110

120

48
Exp.
Ca+238U
Cal. (total)
Cal. (80 - 90 deg)Cal. (every 10 deg)

Mg+248Cm

Hs (108)101

10110010010-110-1

110 120 130 140
Ec.m. (MeV)

Upper limit Cn (112)
3n4n5n170 180 190 200 210

Fig. 1. A comparison between the measured quasielastic
barrier distributions (the upper panels) and the evaporation residue cross sections reported at diﬀerent centerof-mass energies for the syntheses of Sg, Hs, and Cn2–9)(the lower panels). The red symbols indicate the experimental data from this work. The detailed explanationsof the calculated results are described in main text.

is maximized, can be estimated by an experimentally
determined barrier distribution, if the trend of compact collision is not changed. Importantly, it would
take only about one day to measure a barrier distribution for one reaction, which is much shorter than atypical experiment to synthesize new superheavy element, e.g., more than one hundred days using one pµA
beam. This new method will signiﬁcantly contributeto future experiments to synthesize both new superheavy elements and superheavy nuclei in the island ofstability.
References
1) K. Hagino et al., Comput. Phys. Commun. 123, 143(1999).
2) Yu. A. Lazarev et al., Phys. Rev. Lett. 73, 624 (1994).
3) A. Türler et al., Phys. Rev. C 57, 1648 (1998).
4) R. Dressier et al., PSI Rep. 1, 130 (1999).
5) S. Hübener et al., Radiochimica Acta 89, 737 (2001).
6) H. Haba et al., Phys. Rev. C 85, 024611 (2012).
7) J. Dvorak et al., Phys. Rev. Lett. 100, 132503 (2008).
8) Y. T. Oganessian et al., Phys. Rev. C 70, 064609 (2004).
9) S. Hofmann et al., Eur. Phys. J. A 32, 251 (2007).
10) S. Hofmann et al., Eur. Phys. J. A 48, 62 (2012).
11) D. J. Hinde et al., Phys. Rev. Lett. 74, 1295 (1995).
12) K. Nishio et al., Phys. Rev. C 62, 014602 (2000).
13) T. Tanaka et al., J. Phys. Soc. Jpn. 87, 014201 (2018).

Condensed from the article in Phys. Rev. Lett. 124, 052502(2020)RIKEN Nishina Center
Department of Physics, Kyushu University
Department of Nuclear Physics, The Australian National
University
Oak Ridge National Laboratory
Graduate School of Science and Engineering, Yamagata University
Advanced Science Research Center, JAEA
Department of Physics, Tohoku University
Research Center for Electron Photon Science, Tohoku University
Department of Physics, Kyoto University
The result of 48 Ca+248 Cm→296 Lv* is omitted from theFig. 1 due to the space limit. See the original article.

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