RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Experimental investigation of a linear-chain structure in 14 C †H. Yamaguchi,∗1 D. Kahl,∗1 S. Hayakawa,∗1 Y. Sakaguchi,∗1 and K. Abe,∗1 for CRIB collaboration
Table 1. The resonance parameters in 14 C determined by
the present work, compared with the AMD calculation2) . Parameters in bold letters are for LCCS predicted in the calculation, and corresponding experimental resonances.

In 1956, Morinaga1) came up with the novel idea of aparticular cluster state: the linear-chain cluster state(LCCS). Now the LCCS is commonly considered as
extreme and exotic, due to its presumed propensity toexhibit bending conﬁgurations. A theoretical prediction of LCCS in 14 C was made by Suhara and En’yo2,3)
with an antisymmetrized molecular dynamics (AMD)calculation, yielding a prolate band (J π = 0+ , 2+ , 4+ )that has a conﬁguration of an LCCS at a few MeV ormore above the 10 Be+α threshold. In the present work
we applied the 10 Be+α resonant scattering method4–7)
in inverse kinematics to identify the predicted LCCSband in 14 C.
The present measurement was performed at the lowenergy radioactive isotope beam separator CRIB. The10Be beam had a typical intensity of 2 × 104 particles per second, and the beam purity was better than
95%. The 10 Be beam at 25.8 MeV impinged on the gas
target, which was a chamber ﬁlled with helium gas at
700 Torr (930 mbar) and covered with a 20-μm-thick
Mylar ﬁlm as the beam entrance window. The measured 10 Be beam energy at the entrance of the heliumgas target, after the Mylar ﬁlm, was 24.9±0.3 MeV. αparticles recoiling to the forward angles were detectedby ΔE-E detector telescopes.
Finally we obtained the excitation function of the10Be+α resonant elastic scattering for 13.8–19.1 MeV,
where events with θlab = 0–8◦ (θcm = 164–180◦ ) wereselected. We performed an R-matrix calculation todeduce the resonance parameters. The best ﬁt parameters obtained from the analysis are summarized in Table 1. Although the analysis was performed without
any assumption from the theoretical calculation, weidentiﬁed three resonances perfectly corresponded tothe predicted LCCS band; J π are identical, and theirenergies and spacings are consistent with the theoretical prediction. We claim this as the strongest indication of the LCCS ever found. It can be also shownthat both sets of level energies can be plotted almost
on a line, EJ = E0 + h̄2 /2(J(J + 1)), where  is themoment of inertia of the nucleus. The linearity allows
us to interpret the levels as a rotational band, and thelow h̄2 /2 = 0.19 MeV implies the nucleus could bestrongly deformed, consistent with the interpretationof an LCCS. The experimental Γα of these resonances
are also compared with the theoretical predictions interms of the dimensionless partial width θα2 in Table 1,
although the precision of both is quite limited. The
calculation qualitatively reproduces the feature thatthe experimental θα2 is anti-correlated with J.
†∗1

Eex (MeV)
14.21
14.50
15.07
16.22
16.37
16.93
17.25
18.02
18.63
18.87

Present WorkJπΓα (keV)
(2+ )
17(5)
1−45(14)0+760(250)
2+190(55)
(4+ )
15(4)
(2+ )
270(85)(1− )190(45)(3− )31(19)
5−72(48)
4+45(18)

2
θα
3.5%
4.5%
34(12)%
9.1(27)%
3.0%
10.3%
5.5%
1.3%
9.4%
2.4(9)%

Eex (MeV)
15.1
16.0
19.2

Suhara & En’yo2)
Jπ
0+
2+4+2
θα16%
15%
9%

As investigated in the theoretical calculation of theC system, the orthogonality between diﬀerent quantum mechanical states is considered to play a key rolein stabilizing the LCCS. Further studies may reveal
whether this mechanism is universal in nuclear systems
or particular to 14 C.

14References
1) H. Morinaga, Phys. Rev. 101, 254 (1956).
2) T. Suhara and Y. Kanada-En’yo: Phys. Rev. C 82,044301 (2010).
3) T. Suhara and Y. Kanada-En’yo: Phys. Rev. C 84,024328 (2011).
4) K. P. Artemov et al.: Sov. J. Nucl. Phys 52, 408(1990).
5) H. Yamaguchi et al.: Phys. Rev. C 87, 034303 (2013).
6) M. Freer et al.: Phys. Rev. C 90, 054324 (2014).
7) A. Fritsch et al.: Phys. Rev. C 93, 014321 (2016).

Condensed from the article in Phys. Lett. B 766, 11 (2017)
Center for Nuclear Study, University of Tokyo- 78 -