Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Spectroscopy of unbound oxygen isotopes IIY. Kondo,∗1,∗2 T. Nakamura,∗1,∗2 N. L. Achouri,∗3 L. Atar,∗4 T. Aumann,∗4 H. Baba,∗2 K. Boretzky,∗5,∗2C. Caesar,∗5,∗2 D. Calvet,∗6,∗2 H. Chae,∗7 N. Chiga,∗2 A. Corsi,∗6,∗2 H. L. Crawford,∗8 F. Delaunay,∗3A. Delbart,∗6,∗2 Q. Deshayes,∗3 Zs. Dombrádi,∗9,∗2 C. Douma,∗10 Z. Elekes,∗9,∗2 P. Fallon,∗8 H. Al. Falou,∗11I. Gašparić,∗12,∗2 J. -M. Gheller,∗6,∗2 J. Gibelin,∗3 A. Gillibert,∗6,∗2 M. N. Harakeh,∗10 A. Hirayama,∗1,∗2C. R. Hoﬀman,∗13 M. Holl,∗4,∗2 A. Horvat,∗4 A. Horváth,∗14 J. W. Hwang,∗7 T. Isobe,∗2 J. Kahlbow,∗4,∗2
N. Kalantar-Nayestanaki,∗10 S. Kawase,∗15 S. Kim,∗7 K. Kisamori,∗2 T. Kobayashi,∗16,∗2 D. Körper,∗5,∗2
S. Koyama,∗17,∗2 I. Kuti,∗9,∗2 V. Lapoux,∗6,∗2 S. Lindberg,∗18,∗2 F. M. Marqués,∗3 S. Masuoka,∗19 J. Mayer,∗20,∗2K. Miki,∗21,∗2 T. Murakami,∗22,∗2 M. A. Najaﬁ,∗10 K. Nakano,∗15,∗2 N. Nakatsuka,∗22,∗2 T. Nilsson,∗18A. Obertelli,∗6,∗2 F. de Oliveira Santos,∗23 N. A. Orr,∗3 H. Otsu,∗2 T. Ozaki,∗1,∗2 V. Panin,∗2 S. Paschalis,∗4A. Revel,∗23 D. Rossi,∗4 A. T. Saito,∗1,∗2 T. Saito,∗17,∗2 M. Sasano,∗2 H. Sato,∗2 Y. Satou,∗24 H. Scheit,∗4F. Schindler,∗4 P. Schrock,∗19 M. Shikata,∗1,∗2 Y. Shimizu,∗2 H. Simon,∗5,∗2 D. Sohler,∗9,∗2 O. Sorlin,∗23L. Stuhl,∗2 S. Takeuchi,∗1,∗2 M. Tanaka,∗25,∗2 M. Thoennessen,∗21 H. Törnqvist,∗4,∗2 Y. Togano,∗1,∗2T. Tomai,∗1,∗2 J. Tscheuschner,∗4 J. Tsubota,∗1,∗2 T. Uesaka,∗2 H. Wang,∗2 Z. Yang,∗2 and K. Yoneda∗2a 48 Ca primary beam at 345 MeV/nucleon on a 15mm thick beryllium target, and they were puriﬁed byBigRIPS. In addition to a 15-mm thick aluminum degrader at the ﬁrst momentum dispersive focal plane(F1) of BigRIPS, a 7-mm thick aluminum degrader
was installed at the second dispersive focal plane F5
to reduce the large amounts of light-ion background inthe secondary beam. Plastic scintillators with a thickness of 3 mm were installed at the focal planes F3, F5,and F7 for particle identiﬁcation.
A 15-cm length MINOS4) target cell ﬁlled with liquid hydrogen was installed 4.4 m upstream from thecenter of the SAMURAI magnet, surrounded by theMINOS TPC and the DALI2 γ-ray detector array.5)
The incident beam was detected by two 1-mm thickplastic scintillators (SBTs) and two drift chambers(BDC1 and BDC2) placed before the MINOS target. The outgoing charged particle and neutrons wereseparated by the SAMURAI dipole magnet with a
2.9 Tesla ﬁeld at the center. Standard drift chambers(FDC1 and FDC2) and a plastic scintillator hodoscope(HODF24) were used for the detection of charged fragments. HODF24 was expanded from the existing hodoscope (HODF) by adding eight new paddles, to cover
the whole eﬀective area of FDC2. For neutron detection, NeuLAND6) (new Large Area Neutron Detector
for R3B at FAIR) was combined with NEBULA to increase the eﬃciency for multiple neutron detection.
Data analysis is now in progress.

The NP1312-SAMURAI21 experiment, entitled“Spectroscopy of unbound oxygen isotopes II”, wascarried out in November-December 2015, aiming atidentifying resonance states of the extremely neutronrich oxygen isotopes 27 O and 28 O, following theNP1106-SAMURAI02 experiment for 25 O and 26 O1)
in 2012. The motivation for this series of experiments
is exploring the shell evolution towards the possibly
doubly magic nucleus 28 O (Z=8 and N =20), which isessential to understand the mechanism of the suddenchange of the neutron drip line from oxygen to ﬂuorine (Z=9), called “oxygen anomaly.”2) The invariant
mass method is applied to reconstruct the decay energies of 27 O and 28 O, produced by two- and one-proton
removal reactions from 29 Ne and 29 F, respectively.
The experiment was performed using the SAMURAIfacility3) at RIBF. The secondary beams of 29 Ne and29
F were produced by the projectile fragmentation of∗1

Tokyo Institute of Technology
RIKEN Nishina Center∗3 LPC-Caen∗4 Technical University Darmstadt∗5 GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt∗6 CEA Saclay∗7 Seoul National University∗8 Lawrence Berkeley National Laboratory∗9 ATOMKI∗10 KVI-CART∗11 Lebanese-French University of Technology and Applied Science∗12 Ruer Bošković Institute, Zagreb∗13 Argonne National Laboratory∗14 Eötvös Loránd University∗15 Kyushu University∗16 Tohoku University∗17 University of Tokyo∗18 Chalmers University of Technology∗19 Center for Nuclear Studies (CNS), University of Tokyo∗20 University of Cologne, Köln∗21 NSCL, Michigan State University∗22 Kyoto University∗23 GANIL∗24 Institure for Basic Science∗25 Osaka University∗2References
1) Y. Kondo et al., RIKEN Accel. Prog. Rep. 46, 6 (2013).
2) T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010).
3) T. Kobayashi et al., Nucl. Instrum. and Methods inPhys. Res. Sect. B317, 294 (2013).
4) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).
5) S. Takeuchi et al., Nucl. Instrum. and Methods in Phys.
Res. Sect. A763, 596 (2014).
6) NeuLAND Technical Design Report, http://www.faircenter.de/fileadmin/fair/experiments/NUSTAR/Pdf/TDRs/NeuLAND-TDR-Web.pdf- 42 -