Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Zeeman resonance spectroscopy of 84−87 Rb in superfluid helium
X.F. Yang,∗1,∗2 T. Furukawa,∗1,∗3 T. Wakui,∗1,∗4 K. Imamura,∗1,∗5 T. Fujita,∗1,∗6 Y. Mitsuya,∗1,∗5M. Hayasaka,∗1,∗7 Y. Ichikawa,∗1 Y. Ishibashi,∗1,∗9 H. Shirai,∗1,∗8 T. Suzuki,∗1,∗8 Y. Ebara,∗3 A. Hatakeyama,∗10M. Wada,∗1 T. Sonoda,∗1 Y. Ito,∗1 T. Kobayashi,∗11 S. Nishimura,∗1 M. Kurata-Nishimura,∗1 Y. Kondo,∗1,∗8K. Yoneda,∗1 H. Ueno,∗1 T.Shinozuka,∗4 T. Shimoda,∗6 K. Asahi,∗1,∗8 and Y. Matsuo∗1,∗12
OROCHI is a newly developed laser spectroscopy
method for optical determination of nuclear spins andmoments of exotic radioisotopes (RIs)1) . It aims toovercome several experimental limitations due to thelow yield of RIs and large contaminations in the production of RIs by taking advantages of the characteristic properties of atoms in superﬂuid helium (He II). Firstly, it utilizes condensed He II as the trapping
medium for the RI beam and the matrix of in situ
laser spectroscopy of trapped atoms. Subsequently, bymeasuring the hyperﬁne and Zeeman splitting energies
of atoms using optical pumping and laser microwave(MW)/radiofrequency (RF) double resonance method,
nuclear moments and spins of RIs can be determined.
Initial studies with the OROCHI method were concentrated in ﬁeld of the technological research and development with a considerable number of oﬀ-line experiments, which conﬁrmed the feasibility of the OROCHI
method1) . Recently, after extensive tests and calculations, the ﬁrst on-line experiments with the 84−87 Rbbeam have been successfully performed. In this experiment, the primary 85,87 Rb and secondary 84,86 Rb
beams produced from RIPS were precisely trapped inHe II. Optical pumping and Zeeman resonance (ZR)
for 84−87 Rb and the isomer state 84m Rb have been successfully observed.
Figure 1 shows the measured spectra for 84m,84−87
Rb isotopes, which are recorded by scanning the applied magnetic ﬁeld (B0 ) with a ﬁxed-frequency RF
ﬁeld. The corresponding beam for each spectrum andisotopes for each observed ZR are marked in Fig. 1.
Note that in the case of 86 Rb, to reduce the deformation of the observed spectra owing to beam instability,
the recording time for one cycle is changed to 1 s (10s for 84,85,87 Rb). The detailed measurement method
is explained in an early report2) . Conventionally, nuclear spin can be directly deduced from the resonancepeaks with the relation (for the ground state of an alkali atom) I = µBν B − 12 , where ν is the RF frequency
and B is the magnetic ﬁeld. In practice, the accuracy of the deduced nuclear spin is degraded by theresidual magnetic ﬁeld (BL ). The detailed information about how BL aﬀects the results can be foundin a recent article3) . In this work, to eliminate theeﬀects of BL , we used a combination relation of theBell-Bloom equation4) , which describes optical pumping in longitudinal (B∥ : B0 + BL∥ (parallel componentof BL )) and transverse magnetic ﬁelds (B⊥ : perpendicular component of BL ) (for details, see Yang et al.3) )and ILIF ∝ Natom (1 − Pz ) to ﬁt the peaks at B0 = 0,
while the ZR peaks are ﬁtted with the Lorentz function(red curve in Fig. 1).
From the ZR, after eliminating the eﬀect of BL , nuclear spins were deduced as 1.9(1) for the 84 Rb, 6.2(1)for 84m Rb, 2.5(1) for 85 Rb, 1.9(2) for 86 Rb, and 1.53(6)for 87 Rb. The inaccuracy of the B0 and the estimated
BL is supposed to be the main experimental error. In
addition, 3.3% of error arises from the ﬁeld inhomogeneity within the observation region and uncertainty of the observation region (1 mm). Taking all thefactors into account, the nuclear spins of 84m,84−87 Rb
were correctly deduced within the experimental error,
which are consistent with the literature values.
Consequently, we have successfully observed the ZR
spectra for 84−87 Rb isotopes and their nuclear spin canbe determined with a good accuracy, which directly
conﬁrms the feasibility of the OROCHI method. It
is worth emphasizing here that the measured spectra
were recorded in 30 minutes or less with a beam intensity of ∼104 pps. All the results suggest that, after
further being developed and improved, the OROCHI
method can be established as a promising method toprecisely measure nuclear spins and moments of various nuclear species near the drip line with a low yield.

∗1RIKEN Nishina Center
School of Physics, Peking University∗3 Department of Physics, Tokyo Metropolitan University∗4 Cyclotron Radioisotope Center, Tohoku University∗5 Department of Physics, Meiji University∗6 Department of Physics, Osaka University∗7 Department of Physics, Tokyo Gakugei University∗8 Department of Physics, Tokyo Institute of Technology∗9 Department of Physics, University of Tsukuba∗10 Department of Applied Physics, Tokyo University of Agriculture and Technology∗11 Laser Technology Laboratory, RIKEN∗12 Department of Advanced Science, Hosei University∗2Fig. 1.: Zeeman resonance spectra for 84m,84−87 Rb.
References
1) T. Furukawa et al.: Hyp. Int. 196, 191 (2010).
2) T. Furukawa et al.: RIKEN. APR. 46, xi(2013).
3) X.F. Yang et al.: Hyp. Int. 227, 147 (2014)4) M. Arndt et al.: Phys. Rev. Lett 74, 1359(1995)- 37 -