Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Observation of resonances in 14 C with 10 Be+α resonant elastic
scattering at CRIB
H. Yamaguchi,∗1 D. Kahl,∗1 S. Hayakawa,∗1 Y. Sakaguchi,∗1 and K. Abe,∗1 for CRIB collaboration
A measurement of 10 Be+α resonant elastic scattering was conducted at CRIB on the interests of cluster structure in the 14 C nucleus1–3) . In 2015, themain measurement was performed using the thicktarget method in inverse kinematics. The 10 Be radioactive isotope (RI) beam was produced via the11B(d, 3 He)10 Be reaction in inverse kinematics using
a 1.2-mg/cm2 -thick deuterium gas target and a 11 B
beam at 5.0 MeV/u and 700 pnA accelerated with an
AVF cyclotron. The 10 Be beam was separated and puriﬁed by magnetic analysis and velocity selection witha Wien ﬁlter. The experimental setup at the ﬁnal focal plane was similar to the previous one in the 7 Be+αexperiment4) , but we placed an extra silicon detector
telescope instead of the NaI detectors, and we used
two parallel-plate avalanche counters (PPACs) as thebeam counter. The new setup enabled us to perform areliable analysis on the angular distribution with a better position sensing of the beam and recoiled particles.
The parallel-plate avalanche counters (PPACs) measured timing and position of the incoming 10 Be beamwith a position resolution of 1 mm or better. The
beam ﬁnally traveled into the gas target, a chamberﬁlled with helium gas at 700 Torr and covered with a
20-µm-thick Mylar ﬁlm as the beam entrance window.
The 10 Be beam energy at the entrance of the heliumgas target was 25 MeV, and the purity was better than95%, with a typical intensity of 104 pps. α particles
recoiling to the forward angles were detected by the∆E-E detector telescopes. We used two sets of detector telescopes in the gas-ﬁlled chamber, where eachtelescope consisted of two layers of silicon detectors,
which had thicknesses of 20 µm and 480 µm. The central telescope was located at 555 mm from the beam
entrance window, and the other telescope was at an angle of 9◦, looking from the entrance window position.
Each detector in the telescope had an active area of 50
× 50 mm, and 16 strips for one side, making pixels of
3 × 3 mm2 .
The dominant particle measured at the telescopes
was α particle, which was distinguished from other particles with the ∆E-E information. We selected eventsin which the beam particle was entering into the target and an α particle was detected at the telescope incoincidence with the 10 Be beam particle at the PPAC.
A precise energy loss function of the 10 Be beam in
the helium gas target was obtained by a direct energy
measurement at seven diﬀerent target pressures interpolated with a calculation using the SRIM code. The∗1

scattering position, or equivalently the center-of-massenergy Ecm , was determined by a kinematic reconstruction on event-by-event basis, which uses the energy loss function, the beam trajectory measured with
the PPACs, and the energy and position of the recoiled
α particle at the telescope. The number of events foreach small energy division was converted to the differential cross section dσ/dΩ, using the solid angle ofthe detector, the number of beam particles, and the effective target thickness. The number of beam particles
was precisely known by the single counting of the beam
particle with the PPAC, simultaneously recorded in themeasurement. The background contribution evaluatedby the argon-target run data was subtracted from thehelium-target spectrum. Finally we obtained the excitation function of the 10 Be+α resonant scattering for
14–19 MeV as shown in Fig. 1a, where events with thelaboratory angle of the recoiled α particle θlab =0–8◦(corresponding to the center-of-mass angle θcm =164–180◦) were selected. The excitation function obtained
here has a similar peak structure with a previous measurement5) . The resonant information including J πwill be obtained with an analysis with R-matrix calculation.
Differential cross section (mb/sr)

400350300250200150100500141516171819Excitation energy in 14C (MeV)

Fig. 1. Excitation function of the 10 Be+α resonant scattering for θlab =0–8◦.

References
1) T. Suhara and Y. Kanada-En’yo: Phys. Rev. C 82,044301 (2010).
2) T. Suhara and Y. Kanada-En’yo: Phys. Rev. C 84,024328 (2011).
3) H. Yamaguchi et al.: RIKEN Accelerator Progress Report 48, 67 (2015).
4) H. Yamaguchi et al.: Phys. Rev. C 87, 034303 (2013).
5) M. Freer et al.: Phys. Rev. C 90, 054324 (2014).

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