Ⅱ-1. Nuclear Physics

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

Barrier distribution measurement of the 51 V + 159 Tb system
P. Brionnet,∗1 M. Forge,∗2,∗1 T. Fukatsu,∗3 H. Haba,∗1 D. Kaji,∗1 S. Kimura,∗1 K. Morimoto,∗1Y. Michimoto,∗3,∗1 T. Niwase,∗4,∗1 S. Sakaguchi,∗3,∗1 H. Sakai,∗1 M. Tanaka,∗1 and Y. Yamanouchi∗3 for thenSHE Collaboration
With the discovery of elements up to oganesson (Z= 118), all reactions based on the 48 Ca beam leading to a new element have already been performed.
The next step forward to produce new element Z =119 and beyond needs to rely on 50 Ti, 51 V, or 54 Cr
beam on trans-actinium targets. However, in the super heavy mass region, the reactions using these beams
have only been studied on spherical targets (208 Pb and209Bi). Thus, very little information regarding the reaction parameters on deform targets is currently available with these beams. Most of the information usedby the predictions is extrapolated from the 48 Ca results. Systematic studies of reaction using these beams
on deform targets are thus needed to improve the predictive power of the diﬀerent models.
One of these important parameters is the beam energy selected for the search for new elements. The
search of the element Z = 119 is currently ongoingat RIKEN using the 51 V + 248 Cm reaction. The optimal beam energy was selected by studying the barrier distribution of this reaction.1) We decided to begin the systematic measurement of the same parameters extracted in Refs. 1) and 2) with lighter deformed
targets, starting with the 159 Tb. The relation between the maximum cross-section of production andthe QuasiElastic (QE) barrier distribution is directly
linked to the reaction dynamics.
The 51 V13+ beam was provided by the newly upgraded SRILAC accelerator.3) Similarly to the reports,1,2) we used the GARIS-III separator to transport the QE backscattering. These events correspondto the recoil of target-like events at 180◦ (or a beamlike event at 0◦ ). Using the information from our detector array located at the end of GARIS-III,3) we can use
the time-of-ﬂight telescope to select the target-like recoil nuclei. Then, by using the dose estimated throughelastic scattering of the 51 V beam onto the 159 Tb at
the target position, we can extract the barrier distribution as shown in Fig. 1 (bottom panel). The toppanel represents the reﬂection probability R(E), whichis the normalized ratio of target-like events detected
at the focal plane to the number of elastic scatterings
detected at the target position. The bottom panel represents the barrier distribution D(E) deﬁned as:

Fig. 1. Reﬂection probability (top panel) and barrier distribution (bottom panel) of the 51 V+159 Tb reaction.
The points (blue, red/orange, and green) are the measured data and the several curves CCFULL calculations4) with diﬀerent input parameters.

in the R(E) distribution. It is determined as 164.12 ±0.3 MeV (blue arrow in Fig. 1). This value is related tothe maximum of the cross-section of production in thecase of reaction on spherical targets. However, in thecase of the deformed targets, the side collision energy
is more important, as has been pointed out.1,2)
This side collision corresponds to the collision of theprojectile and target at a 90◦ angle in a compact conﬁguration. In order to extract this side collision energy,
we need to perform the Coupled Channels calculation(CCFULL4) ).
The dashed orange line in Fig. 1 represents the optimized CCFULL calculations,4) and the orange dots
represent the contribution of the side collision to theD(E) ≡ −dR/dE
The average barrier height is deﬁned at the 0.5 crossing
∗1
∗2
∗3
∗4

RIKEN Nishina Center
IPHC Strasbourg
Department of Physics, Kyushu University
Wako Nuclear Science Center (WNSC), IPNS, KEK- 14 -Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 56 (2023)

overall barrier distribution. We optimized the parameters of the CCFULL calculation to reproduce both thereﬂection probability and the barrier distribution. We
can then extract from these calculations the side collision energy as 171.5 ± 0.5 MeV (orange dot and arrow
in Fig. 1 bottom panel). These results will be compared and correlated with the precise excitation function we simultaneously measured for this reaction.5)
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) H. Sakai et al., Eur. Phys. J. A 58, 238 (2022).
4) K. Hagino et al., Comput. Phys. Commun. 123, 143(1999).
5) P. Brionnet, in this report.

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