II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

One proton removal cross section of 25 F with a carbon target
Y. Yoshitome,∗1,∗2 Y. Kondo,∗1,∗2 T. Nakamura,∗1,∗2 J. A. Tostevin,∗3 R. Tanaka,∗1,∗2 R. Minakata,∗1,∗2S. Ogoshi,∗1,∗2 N. A. Orr,∗4 N. L. Achouri,∗4 T. Aumann,∗5,∗6 H. Baba,∗2 F. Delaunay,∗4 P. Doornenbal,∗2N. Fukuda,∗2 J. Gibelin,∗4 J. W. Hwang,∗7 N. Inabe,∗2 T. Isobe,∗2 D. Kameda,∗2 D. Kanno,∗1,∗2 S. Kim,∗7N. Kobayashi,∗1,∗2 T. Kobayashi,∗8,∗2 T. Kubo,∗3 S. Leblond,∗4 J. Lee,∗2 F. M. Marqués,∗4 T. Motobayashi,∗2D. Murai,∗9 T. Murakami,∗10 K. Muto,∗8 T. Nakashima,∗1,∗2 N. Nakatsuka,∗10,∗2 A. Navin,∗11,∗14 S. Nishi,∗1,∗2H. Otsu,∗2 H. Sato,∗2 Y. Satou,∗7 Y. Shimizu,∗2 H. Suzuki,∗2 K. Takahashi,∗8 H. Takeda,∗2 S. Takeuchi,∗2Y. Togano,∗9 A. G. Tuﬀ,∗12 M. Vandebrouck,∗13 and K. Yoneda∗2target was measured using the SAMURAI device atRIBF, as a by-product of the measurement of the oneproton removal of 26 F and 27 F into 25 O and 26 O,
respectively.5) For details of the experimental setup
and method, see Ref. 5). The 25 F secondary beam
was produced by the projectile-fragmentation of 48 Ca
at 345 MeV/nucleon with a thick beryllium target.
The beam intensity of 25 F reached 1.1×103 particles/s with a purity of 3.4%. The 25 F projectile thenimpinged on the carbon target with a thickness of
1.8 g/cm2 . The mean energy at the middle of thetarget was 218 MeV/nucleon, with momentum acceptance of |∆P/P | ≤ 0.6%. The particle identiﬁcation(PID) for 25 F was obtained by the standard method atthe BigRIPS.5) The PID of the 24 O residue was madeby the measurements of the time of ﬂight (TOF), andenergy loss ∆E at the hodoscope (HODF), with themagnetic rigidity (Bρ) obtained by the tracking withthe two multi-wire drift chambers, FDC1 and FDC2,
at the entrance and exit of the SAMURAI superconducting magnet, respectively.5,6) The central ﬁeld ofthe magnet was 3.0 T.
The 25 F(−p) removal cross section was extracted using the ratio of the counts of the outgoing 24 O to thoseof 25 F, where the background events measured withthe empty target were subtracted. The eﬀect of reaction loss in the thick target was incorporated using
the procedure in Ref. 7). The obtained preliminary
value of the one-proton removal cross section of 25 F is
7.1(8) mb. usdb-interaction shell- and eikonal-model
calculations give the theoretical cross section 14.9 mb,
resulting in the reduction factor Rs = 0.48(5). Further
evaluation of nucleon removal cross sections in neighboring neutron-rich isotopes is in progress.

Experimental one-proton (neutron) removal crosssections σ−1p (σ−1n ) with light target nuclei (Be andC) at intermediate energies have been shown to behindered with respect to the corresponding theoreticalvalues. Their ratio Rs = σexp /σth (reduction factor)
shows a strong linear dependence on the diﬀerence between the 1p and 1n separation energies, ∆S = Sp −Sn(Sn −Sp ).1,2) This dependence has been recognized as a
key to understand correlations beyond the shell-modelbased picture of atomic nuclei. The theoretical crosssections are evaluated using shell-model spectroscopic
factors C 2 S combined with an established reaction theory at intermediate energies, such as eikonal and impulse approximation. The reduction factor depends on
the reaction used and the reduction mechanisms are
yet to be clariﬁed.3)
We report a preliminary result of the one-proton
removal cross section of 25 F with a carbon target at218 MeV/nucleon. This data point is a useful addition
to the systematics of the one-nucleon removal cross sections. It should be noted that 25 F has one proton morethan doubly-magic 24 O. Accordingly, we expect thatthe spectroscopic factor for proton removal from 25 F isclose to unity. However, the recent 25 F(p, 2p) measurement at SHARAQ at RIBF4) obtained a much-reduced
value of 0.36(13) from 25 F to the bound 24 O. We also
note that the ∆S value of 10.17(24) MeV for 25 F lies
between those of the stable nuclei (|∆S| < 8 MeV) anddrip-line nuclei (|∆S| = 15–30 MeV). As such, the onenucleon removal cross section from 25 F on the carbon
target is a valuable addition.
The 25 F(−p) removal cross section on the carbon∗1Department of Physics, Tokyo Institute of Technology
RIKEN Nishina Center∗3 Department of Physics, University of Surrey∗4 LPC-Caen, ENSICAEN, Université de Caen, CNRS/IN2P3∗5 Institut für Kernphysik, Technische Universität Darmstadt∗6 ExtreMe Matter Institute (EMMI) and Research Division,GSI∗7 Department of Physics and Astronomy, Seoul National University∗8 Department of Physics, Tohoku University∗9 Department of Physics, Rikkyo University∗10 Department of Physics, Kyoto University∗11 GANIL, CEA/DSM-CNRS/IN2P3∗12 Department of Physics, University of York
∗13 Institut de Physique Nucléaire, Université Paris-Sud,
IN2P3-CNRS∗14 Present address: GANIL CEA/DRF-CNRSI/N2P3∗2References
1) A. Gade et al., Phys. Rev. C 77, 044306 (2008).
2) J. A. Tostevin, A. Gade, Phys. Rev. C 90, 057602(2014).
3) T. Aumann et al., Prog. Part. Nucl. Phys., in press.
4) T. L. Tang et al., Phys. Rev. Lett. 124, 212502 (2020).
5) Y. Kondo et al., Phys. Rev. Lett. 116, 102503 (2016).
6) T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 294 (2013).
7) N. Kobayashi et al., Phys. Rev. C 86, 054604 (2012).

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