Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 49 (2016)

Development of magnetic field coils
for laser spectroscopy of atoms in He IIT. Fujita,∗1,∗2 K. Imamura,∗1,∗3 D. Tominaga,∗4,∗1 T. Kawaguchi,∗4,∗1 T. Egami,∗4,∗1 T. Nishizaka,∗4,∗1T. Kobayashi,∗5 A. Takamine,∗1 T. Furukawa,∗6,∗1 H. Ueno,∗1 T. Shimoda,∗2 and Y. Matsuo∗4,∗1

∗1
∗2
∗3
∗4
∗5
∗6

due to limitations of space inside the cryostat5) . In
our new setup, we constructed a set of large squarecoils, which can be placed outside the cryostat. Thecoils are represented in orange in Fig. 1. Figure 2
shows the resonance spectrum obtained using the newcoils. The measurement precision was improved by
one order of magnitude as compared with the previous work5) owing to the reduced inhomogeneities in
the applied magnetic ﬁeld as well as the increment of
the LIF counts. The achieved precision is satisfactory
for the discussion of hyperﬁne anomaly. However, theobtained spectrum was slightly distorted by the inhomogeneities of the magnetic ﬁelds, presumably due toenvironmental magnetic ﬁelds.



Nuclear spins and electromagnetic moments are important properties for investigating nuclear structures.
To determine these properties of low yield exotic
nuclei, we have been developing OROCHI (OpticalRI-atom Observation in Condensed Helium as Ioncatcher) method, which is a laser spectroscopic method
using superﬂuid helium (He II) as a stopping material for energetic ion beams. In this method, we measure the atomic Zeeman and hyperﬁne structure (HFS)
splitting energies of neutralized atoms in He II using
laser-radio frequency (RF)/microwave (MW) double
resonance method1) . Then, the nuclear spins and moments are deduced. The eﬀectiveness of the OROCHI
method was conﬁrmed by the experiments using energetic 84−87 Rb beams at the RIPS beam line, RIKEN2) .
In addition, the Zeeman and HFS splittings of stable
Rb, Cs, and Au atoms in He II have been observedin oﬄine experiments. Improvement of measurement
accuracy and precision leads us to discuss higher order eﬀects such as hyperﬁne anomaly. Recently, themeasurement accuracy is successfully improved by oneorder of magnitude by scanning the MW frequency using phase-locking3) . In order to increase the precision,
we installed a new set of magnetic ﬁeld coils to suppress the inhomogeneity of an applied magnetic ﬁeld.
We here report the current status of HFS measurementof stable Au atoms.
Figure 1 shows our oﬄine experimental apparatus.
An open-topped cubic quartz cell was fully ﬁlled withHe II. The Au sample was placed 1 cm above theHe II surface. The Au atoms were prepared in He
II by laser sputtering of the sample with two pulsedlasers4) . The atoms were optically pumped by irradiation with the frequency-quadrupled laser radiationof an LD-pumped pulsed 1054 nm Nd:YLF laser at a
3 kHz repetition rate. We set RF coils and an MW
loop antenna for the double resonance method. The
emitted laser-induced-ﬂuorescence (LIF) photons werefocused onto a photomultiplier tube (PMT) through a
monochromator for wavelength selection.
In the previous experiments, a pair of circular coils
was located near the quartz cell. The obtained resonance peaks, which are expected to be Lorentzian
shapes, were distorted because it was diﬃcult to apply a uniform magnetic ﬁeld in the observation region

Fig. 1. Experimental apparatus.

   

Fig. 2. MW resonance spectrum of 197 Au.

Next, we plan to measure HFS splittings using threeaxis coils for canceling environmental magnetic ﬁelds,
shown as gray coils in Fig. 1. After the test experiment, we will start the measurement for stable Ag
atoms, which belong to the same group of atom as Au
and have two stable isotopes.
References1) S. Lang et al.: Europhys. Lett. 30(4), 233 (1995).
2) X.F. Yang et al.: Phys. Rev. A 90, 052516 (2014).
3) K. Imamura et al.: Hype. Interact. 230, 73 (2015).
4) T. Furukawa et al.: Phys. Rev. Lett. 96, 095301 (2006).
5) T. Fujita et al.: RIKEN Accel. Prog. Rep. 47, 212(2014).

RIKEN Nishina Center
Department of Physics, Osaka University
Department of Physics, Meiji University
Department of Physics, Hosei University
RIKEN Center for Advanced Photonics
Department of Physics, Tokyo Metropolitan University- 191 -