Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 51 (2018)

A prototype novel laser-melting sampler for analyzing ice coreswith high depth resolution and high throughput
M. Maruyama,∗1 M. Yumoto,∗1 K. Kase,∗1 K. Takahashi,∗2 Y. Nakai,∗2 S. Wada,∗1 Y. Yano,∗2 and Y. Motizuki∗2A new facility for analyzing ice cores is being preparedjointly by the RIKEN Nishina Center Astro-Glaciology
Research Group (AGG) and the RIKEN Center for Advanced Photonics in Room B35 (50 m2 ) in the main research building at Wako. The mission of the facility is toanalyze ice cores with high depth (temporal) resolution
and high throughput to obtain concentration proﬁles ofvarious isotopes such as 18 O/16 O and various ions such
as SO4 2− and NO3 − . The ice cores that we study havebeen drilled by the Japanese Antarctic Research Expedition (JARE) at Dome Fuji station in East Antarctica.
From the data obtained, one can elucidate the long-term
history of climate changes, and even the history of solar activities and possible supernova explosions in ourgalaxy. Such astro-related research was initiated by theAGG and their activity so far was summarized in theRIKEN APR special issue.1)
One of the major components of our facility is a newly
installed prefabricated freezer container (3 m wide × 5 mlong × 3 m high). The temperature in the container iscontrolled at −20◦ C. The inside of this container is partitioned into two areas: a storage area where valuable ice
cores are kept clean and frozen, and an ice core samplingarea where a new system (under development) for applying the laser-melting technique will be installed. The
other components are isotope analyzers and ion chromatography systems for measuring the concentrationsof isotopes and ions in the samples collected automatically as described below. They will be placed outside
the container at room temperature.
Figure 1 depicts the schematic diagram of a prototype
laser-melting sampler. The sampler consists of a continuous wave ﬁber laser (λ =1.55 µm), optical switching
devices, optical ﬁbers (0.25 mm ϕ), needles (0.7 mm ϕ),and a computer that controls the positions of the sampling nozzles and the motorized stage on which an ice
core is placed. The laser beam delivered by the opticalﬁber is radiated on the target ice core surface, and themelted water of 1 mL (enough volume for precision analysis) thereby obtained is sucked up through the needle
and transported into a vial bottle by a peristaltic tube
pump at a pressure drop of 1 atm. The needle and thetube are kept over 0◦ C by the heater windings.
We conducted several performance tests for this prototype. Figure 2 shows one of the results: holes as small as
2 mm ϕ were made on ice 5 mm apart by laser-melting.
For this performance test, a laser beam with a power of
1 W was irradiated, and the sampling speed was measured to be 26 min/mL. We are optimizing the irradiation conditions via such performance tests. In addition,∗1∗2RIKEN Center for Advanced Photonics
RIKEN Nishina Center- 16 -Fig. 1. A schematic view of the ice-core laser-melting sampler. The bottom image shows a sampling nozzle.

Fig. 2. Photos of a performance test.

we are developing an automated multi-nozzle system torealize high throughput, which is the mission of our facility.
The new system obviously has advantages over our
previous work on ice core sampling, which was performed manually using electric band saw machines andceramic knifes. Our new technique is diﬀerent from theheater-melting continuous ﬂow analysis method2) for thefollowing reasons: 1) sampling zones, either holes or horizontal planes, are discrete to avoid mixing with eachother, and 2) the amount of sampling ice is adequately
minimized for precision analysis.
This system will make it possible to analyze ice coresat a high depth resolution of 1 mm scale, which corresponds to the temporal resolution of ∼1 month in thecase of a Dome Fuji ice core. Since the new JARE
ice core drilling project has been approved and is inprogress, it will become possible to study the correlations between climate and solar activity, and the galactic supernova rate of the past 1,000,000 years. We thankK. Eto and M. Kawada of Tokyo Denki Univ. for helping
us with our measurements.
References
1) Y. Motizuki, RIKEN Accel. Prog. Rep. 50, S-80 (2017).
2) e.g., R. Dallmayr et al., Bulletin of Glac. Res. 34, 11(2016).