Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Excitation functions for the 51 V + 159 Tb fusion evaporation reaction
P. Brionnet,∗1 M. Forge,∗2,∗1 T. Fukatsu,∗3 H. Haba,∗1 D. Kaji,∗1 K. Morimoto,∗1 Y. Michimoto,∗3,∗1T. Niwase,∗4,∗1 S. Sakaguchi,∗3,∗1 H. Sakai,∗1 and Y. Yamanouchi∗3,∗1 for the nSHE Collaboration
an average density of 365 ± 16 µg/cm2 and beam intensities ranging from 152 particle nA to 345 particle nA. The ER nuclei were implanted into a Doublesided Strip Silicon Detector4) that was also used forthe detection of the subsequent α-decays.
The identiﬁcation of reaction channels was only
based on the known α-decay energies and branchingratios, without any timing selection. The overall ﬁtof the α-spectrum accumulated over 24 hours at eachenergy was used to extract the individual yield of ERs
produced. Considering the transmission and detection
eﬃciency, the cross section of various exit channels wasextracted from those yields. Figure 1 shows the measured cross section of the xn, pxn, and αxn exit channels for the 51 V + 159 Tb → 210 Ra∗ reaction.

Syntheses of elements from ﬂerovium (Z = 114) tilloganesson (Z = 118) were made using the hot-fusion
reactions with 48 Ca beams on actinide targets. To
synthesize the elements beyond Z = 118, reactions
with either 50 Ti, 51 V, or 54 Cr beam on actinide targets are necessary. However, these beams have, sofar, only been used on spherical targets around 208 Pb.
Thus, any information regarding the reaction mechanisms using these beams on actinide targets will provide valuable information for the success of current andfuture searches for new elements. Unfortunately, thedirect systematic study of reaction mechanisms on actinides target is unrealistic due to the too-small fusionevaporation cross-sections (pb–fb range). Thus, theuse of a lighter surrogate system based on deformed
targets with similar deformation characteristics aroundlanthanide nuclei may give insight and valuable information regarding reaction mechanisms with 50 Ti,
51
V, or 54 Cr beams, especially regarding the side collision eﬀect.1,2) The reaction of 51 V beam on 159 Tb target presents much higher production rates (µb range)
while being an excellent surrogate reaction. Indeed,
the 159 Tb deformation parameters (β2 = 0.271, β4 =0.066) are similar to the one of the 248 Cm (β2 = 0.286,β4 = 0.039) that is currently used in the search for thenew element Z = 119 at RIKEN.
This similarity in deformation parameters allows forthe study of the side collision eﬀect using 51 V beam on
deformed target. Has it been pointed out in Refs. 1)
and 2). this side collision eﬀect is involved in the relation between the barrier distribution and the maximum production cross-section of production for thesuper heavy elements. This relation also shows surprising diﬀerences between spherical and deformed targets
as indicated in Refs. 1) and 2). Furthermore, these
relations were derived using beams lighter than 48 Ca
and never had been directly extracted for 50 Ti, 51 V, or54
Cr beams.
The 51 V + 159 Tb → 210 Ra∗ reaction was selected
as the ﬁrst test surrogate reaction, measuring a wide
range of excitation energies from 32 to 66 MeV. Thebarrier distribution was also measured separately andreported elsewhere.3)
The GARIS-III separator was set to transport theEvaporation Residue (ER) nuclei to the focal planedetector array.4) The 51 V13+ beam was provided by
the newly upgraded SRILAC accelerator.4) The experiment used a rotating target of metallic 159 Tb with
∗1
∗2
∗3
∗4

RIKEN Nishina Center
IPHC Strasbourg
Department of Physics, Kyushu University
Wako Nuclear Science Center (WNSC), IPNS, KEKFig. 1. Excitation function of the reaction 51 V + 159 Tb:(a) αxn exit channel, (b) pxn exit channel, (c) xn exit
channel.

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RIKEN Accel. Prog. Rep. 56 (2023)

The maximum cross-sections are the p3n with 33.1±
8.9 µb, followed by the α3n at 27.2 ± 7.3 µb and thenthe 3n at 4.4 ± 0.9 µb. The increase of the charged
particle exit channel has been observed in this lower
mass region but are not yet well reproduced by models. Discussions with the team of M. Kowal in Poland
are ongoing to reproduce this behavior and our data
based on their model.5) It also seems that the side collision eﬀect is not as present as expected for the xn
exit channel and is under discussion with K. Hagino.6)
References
1) M. Tanaka et al., J. Phys. Soc. Jpn. 91, 084201 (2022).
2) T. Tanaka et al., Phys. Rev. Lett. 124, 052502 (2020).
3) P. Brionnet et al., in this report.
4) H. Sakai et al., Eur. Phys. J. A 58, 238 (2022).
5) T. Cap et al., Eur. Phys. J. A 58, 231 (2022).
6) K. Hagino et al., Comput. Phys. Commun. 123, 143(1999).

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