RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

β-NMR measurements of 21 O
A. Gladkov,∗1,∗2 Y. Ishibashi,∗1,∗3 H. Yamazaki,∗1 Y. Ichikawa,∗1 A. Takamine,∗1 H. Nishibata,∗1 K. Asahi,∗1T. Sato,∗1 W. Y. Kim,∗2 T. Fujita,∗1,∗4 L. C. Tao,∗1,∗5 T. Egami,∗1,∗6 D. Tominaga,∗1,∗6 T. Kawaguchi,∗1,∗6M. Sanjo,∗1,∗6 W. Kobayashi,∗1,∗6 K. Imamura,∗1,∗7 Y. Nakamura,∗1,∗7 G. Georgiev,∗8 J. M. Daugas,∗1,∗9and H. Ueno∗1Oxygen nuclear magnetic resonance (NMR) servesas a powerful tool to realize the atomic-scale properties of a vast variety of oxygen-containing materials.
Such studies, however, have been so far complicatedby diﬀerent objective limitations such as low natural abundance of the NMR-active 17 O isotope, anddiﬃculties and costliness of the isotopic enrichment.
Alternatively, the 13 O and 19 O isotopes with known
values of nuclear moments would seem appropriate to
be used in β-ray-detected nuclear magnetic resonance(β-NMR) studies. However, the use of these isotopes
also has strong disadvantages such as low beam purity in case of proton-rich 13 O and relatively long lifetime of 19 O(T1/2 = 26.5 s) leading to the insuﬃcient
NMR-signal intensity. All these aspects make 21 O agood candidate to be used as a probe to investigate
the structure and properties of oxide-based systems.
As a ﬁrst step for such studies, the electromagnetic
moments of this isotope must be determined.
In the present research, we measured the groundstate magnetic dipole moment and electric quadrupole
moment of the 21 O isotope. The experiment was carried out using the projectile-fragment separator RIPS
at the RIBF facility. A secondary beam of 21 O wasproduced in the projectile fragmentation reaction involving one neutron pick-up reaction of a 22 Ne beamat 69A MeV on a 1.0-mm-thick Be target. The twostage isotope separation through the momentum andmomentum-loss analyses by RIPS was applied to purify the 21 O beam. The momentum window and emission angle of the primary beam were selected to bepF = p0 × (0.97 ± 0.03) and θF > 2.1◦ , respectively.
Electromagnetic moments were measured by meansof the β-NMR/NQR method in combination with the?) 1)
adiabatic
fast passage
passage (AFP)(AFP)technique
technique. . In theadiabatic fastg-factor measurements the beam was implanted into
the 0.5-mm-thick CaO stopper placed at the centerof the dipole magnet of the β-NMR system that provided a static magnetic ﬁeld of ∼500 mT. Some ofthe obtained NMR spectra are presented in Fig. 1.
The NQR measurements, in turn, require the presenceof the electric ﬁeld gradient (EFG) in the medium.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9Ron/ Roff

1.06
1.04
1.02
10.98
2250

2300

2350

2400

2450

Frequency [kHz]Fig. 1. β-NMR spectra of 21 O in a CaO crystal. Frequency
sweeps with the widths of 35 kHz, 14 kHz and 3 kHz
are plotted with blue circles, red triangles and green
squares, respectively. During the experiment the total frequency range from 1956 kHz to 2445 kHz wasscanned.

1.02

Ron/ Roff

1.015
1.01
1.005
10.995
0100

200

300

400

500

600

700

800900vQ [kHz]Fig. 2. β-NQR spectrum of 21 O in the TiO2 single crystal.
The dashed curve is a guide to the eye representing theexpected ﬁtting curve shape. The actual ﬁtting analysis
is work-in-progress. ForFor the definitiondeﬁnition ofof ννQQ,, seesee Ref.
Ref?)2..

For this purpose the 0.5-mm-thick TiO2 single crystal with a known value of EFG was used as a stopperand placed in the same magnetic ﬁeld of ∼500 mT.
The obtained NQR spectrum is shown in Fig. 2. Ron
and Roﬀ in Figs. 1 and 2 represent the U/D ratios
between the counts of upper and lower plastic scintillators with and without the application of oscillating
magnetic ﬁeld, respectively.
The analysis of the obtained NMR/NQR spectra isin progress.

RIKEN Nishina Center
Department of Physics, Kyungpook National University
Cyclotron and Radioisotope Center, Tohoku University
Department of Physics, Osaka University
School of Physics, Peking University
Department of Physics, Hosei University
Department of Physics, Meiji University
CSNSM, CNRS/IN2P3, Université Paris-Sud
CEA, DAM, DIF

References
1) A. Abragam: The Principles of Nuclear Magnetism(Springer, Oxford, 1961).
2) H. Izumi et al., Hyperﬁne Int. 97/98, 509 (1996).

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