Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Collinear laser spectroscopy of Ba+ in 6s 2 S1/2 -6p 2 P3/2 transition
Y. Sasaki,∗1,∗2 M. Tajima,∗1 A. Takamine,∗1 H. Iimura,∗1,∗3 M. Wada,∗4 Y. Matsuo,∗1,∗2 and H. Ueno∗1
The nuclear electromagnetic properties in nuclear
ground states and long-life isomeric states for a wide
range of nuclides have been determined using collinear
laser spectroscopy (CLS).1) We are developing a CLS
apparatus for the slow RI beams that will be provided
from the SLOWRI facility2) in the near future, with thegoal of realizing CLS for RIs that are diﬃcult to obtainthrough the isotope separation on-line (ISOL) method.
We have started oﬀ-line CLS test. As a ﬁrst step, weselected stable Ba+ isotope ions since their high intensity ion beams can be produced with a compact surface
ionization source.
This report describes the oﬀ-line CLS experiment for
the transition from the ground state 6s 2 S1/2 to theexcited state 6p 2 P3/2 . Tajima et al. report on theCLS test for the transition from 4d 2 D5/2 to 6p 2 P3/2
in this progress report.3) The excitation wavelength forthe 6s 2 S1/2 → 6p 2 P3/2 transition for Ba+ is 455 nm.
We built an external cavity diode laser (ECDL), which
was assembled with an anti-reﬂection-coated laser diodeNDBA116T (peak wavelength range: 450 to 470 nm;
manufactured by Nichia Corporation) and a 2400/mm
holographic grating (Thorlabs GH13-24V) in a Littrow
conﬁguration. The wavelength of the ECDL was locked
to a desired wavelength using a feedback system of ahigh-precision wavemeter (HighFiness WS-U-10). The
resulting time variation of the center frequency of thelaser was narrowed to 4 MHz in full width at half maximum (Fig. 1).
The CLS test was performed using a home-built
ECDL. Figure 2 shows a schematic of our CLS apparatus. Barium ions generated from the surface ionizer
were accelerated by a high voltage of 10 to 20 keV. The
accelerated ions were transported to an observation region after mass separation by a mass analyzing magnet.

Fig. 1. Frequency locking result for our ECDL.
∗1
∗2
∗3
∗4

RIKEN Nishina Center
Department of Advanced Science, Hosei UniversityJAEA
Wako Nuclear Science Center (WNSC), KEK

Fig. 2. Schematic diagram of our collinear laser spectroscopy
apparatus.

Fig. 3. Collinear laser spectroscopy spectra for 136–138 Ba+ .

A series of electrodes to control the Doppler shift wasplaced around the observation region. Laser-induced
ﬂuorescence (LIF) from the ions was collected in a photomultiplier tube in front of the electrodes, as shownin Fig. 2. We observed resonance spectra while scanning the voltage of the electrodes to control the Doppler
shift of the ions, instead of scanning the laser frequency.
Figure 3 shows the observed spectra for 136, 137, 138 Ba+ .
At this time, the ions were accelerated to 10.51 keV,
the laser frequency was locked to 658.372682 THz, andthe laser power was 0.1 mW. The beam intensities were
200 pA, 350 pA, and 1.4 nA for 136 Ba+ , 137 Ba+ , and138
Ba+ , respectively. We successfully observed ﬁve resonance peaks for the transition between the hyperﬁnesublevels of 137 Ba+ , and only the peaks for the 6s 2 S1/2state (F = 1) → 6p 2 P3/2 state (F = 0, 1) transition
were not resolved, because the spacing is 32 MHz atmost.
We continue systematic measurements under various
experimental conditions such as diﬀerent laser powers,acceleration voltages, and laser light path alignments
for resolution improvement. We will also improve thesensitivity using a coincidence method,4) aiming at thespectroscopy for low-yield nuclei obtained at online experiments.
References

1) P. Campbell et al., Prog. Part. Nucl. Phys. 86, 127 (2016).
2) M. Wada, Nucl. Instrum. Methods Phys. Res. B 317, 450(2013).
3) M. Tajima et al., in this report.
4) D. A. Eastham et al., Opt. Commun. 60, 293 (1986).

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