RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-1. Nuclear Physics

On-line test of rotating magnetic ﬁeld system for β-NMR method
Y. Ishibashi,∗1,∗2 D. Nagae,∗1 Y. Abe,∗1,∗2 Y.E. Ichikawa,∗1 K. Sawahata,∗1 A. Ozawa,∗1 and H. Ueno∗2∗1∗2

Institute of Physics, Univ. of Tsukuba
RIKEN Nishina Centeris written as Aβ P =Tank circuit (a)Phaseshifter Attenuator
Amp᳸
F.G.

√√
(R0 /R) − 1/ (R0 /R) + 1.
Variable
capacitorCable
delay

Ferrite core

Tank circuit (b)5)
Magnet poleStatic
magnetic field5)

β-ray counter
telescope&D)FU\VWDO

Pickupcoil 1

Pickupcoil 2

Staticmagneticfield

Spin polarizedbeam

RF coil

Spin polarizedbeam
Oscilloscope

Fig. 1. Block diagram of the RF system for the rotating
magnetic ﬁeld and a schematic layout of the β-NMR
setup.

−→The d beam was pulsed with beam-on and beamoﬀ periods of 16 s and 22.02 s, respectively. In thebeam-oﬀ period of a cycle, RF was applied for the ﬁrst
10 ms. Subsequently, the β-rays were counted for 22s, and in the last 10 ms of the beam-oﬀ period RF wasapplied again to restore the spin direction. First, wemeasured R0 without RF and then, we measured Rwith RF. This cycle was repeated until the required
measurement statistics were attained.
In this experiment, we ﬁrst measured a µ moment
by using β-NMR applied to the linear RF using tankcircuit (a); then, measured it using another one. Figure 2 shows obtained Aβ P values. Next, we attempted
to measure the sign of µ(20 F) by applying a rotating
RF. Analysis of the results is in progress.
0.5
0.40.3AP [%]The β-ray detected nuclear magnetic resonance (βNMR) method1) is an eﬃcient method to measure thenuclear magnetic (µ) moment of unstable nuclei. Theabsolute value of µ moments are measured for various nuclei by using β-NMR. However, the sign of µmoments are rarely measured in experiment. In the βNMR method, a linear oscillating magnetic ﬁeld (RF),which can be a superposition of a right- and leftrotating RF, is applied to invert the direction of spinpolarization. Thus, only the absolute value of µ moments is estimated from the applied frequency of thelinear RF. Therefore, to determine the sign of a µ moment, applying a rotating RF is necessary. A rotating
RF system has been under development2,3) to determine the sign of a µ moment by using the β-NMR
method. The rotating magnetic ﬁeld is obtained using two Helmholtz-like coils with axes crossed at rightangles. The experimental apparatus to produce the rotating RF is shown in Fig. 1, and a detailed description
is given in Ref. 2 and 3.
In the present work, the performance of the system
was studied with spin-polarized 20 F (I π = 2+ , T1/2
= 11.163 s, µ(20 F) = +2.09335(9) µN ) nuclei at theResearch Center for Nuclear Physics, Osaka University. A spin-polarized 20 F nucleus was produced in−→the 19 F( d , p)20 F reaction. In this reaction, the polarization of the beam particles is transferred to each−→nucleus. The d beam was produced using a polarized ion source4) , and accelerated at E/A = 10 MeV
using the AVF cyclotron. The polarized beams wereimpinged on a CaF2 crystal (0.5 mmt ) to produce thepolarized 20 F. The crystal was placed at the center ofthe β-NMR apparatus (See Fig. 1.) at room temperature with a static magnetic ﬁeld B0 = 500 mT applied.
The β-rays emitted from 20 F nuclei were detectedwith plastic scintillator telescopes located above andbelow the crystal. The up/down ratio R of the β-ray
counts is written as R0 ≈ a(1+Aβ P )/(1−Aβ P ), wherea denotes a constant factor representing asymmetries
in counter solid angles and eﬃciencies and Aβ and P
denote the β-ray asymmetry parameter and the degreeof spin-polarization, respectively. A rotating RF perpendicular to B0 is applied to 20 F by using the twopairs of coils. If the frequency and direction of the rotating RF correspond to the resonance values, the direction of the spin polarization is inverted (P → −P )by the NMR. Thus, the up/down ratio is changed asR ≈ a(1 − Aβ P )/(1 + Aβ P ). When the polarization isaltered because of the resonant spin change, a change
appears in the ratio R0 /R. The β-ray asymmetry Aβ P0.2
0.1
0Linear RF Field1

Linear RF Field2

Fig. 2. Obtained Aβ P value of 20 F with applied linear RFﬁeld.

References
1) K. Sugimoto et al.: J. Phys. Soc. Jpn. 21, 213 (1966)
2) T. Niwa et al.: UTTAC 81, 5 (2012)3) D. Nagae et al.: Hype. Int. 220, 65 (2013)
4) K. Hatanaka et al.: Nucl. Instr. and Meth. 217, 397(1983)- 76 -完全版2014_本文.indd 76

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