Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 52 (2019)

Microgram-order palladium isotope separation by odd-mass-selective
photoionization
T. Sonoda,∗1 T. Kobayashi,∗2 T. Fujiwara,∗2 Y. Nagata,∗2 H. Ishiyama,∗1 V. Sonnenschein,∗3 M. Oohashi,∗3A. Takamine,∗1 M. Rosenbusch,∗1 I. Katayama,∗1 H. Tomita,∗3 T. M. Kojima,∗1 P. Schury,∗4 and K. Midorikawa∗2High-level radioactive wastes generated from nuclear
power plants contain small percentages of platinumgroup metals such as palladium, rhodium, zirconium,
and plutonium, which are valuable resources for industrial applications. A novel research project has been
started by the Impulsing Paradigm Change through Disruptive Technologies Program (ImPACT, Project manager: R. Fujita), which includes (1) the separation of
those valuable metals from ﬁssion waste, (2) the separation of long-lived and short-lived nuclei, and (3) the nuclear mutation from long-lived to short-lived nuclei. Oneof the key techniques in (2) was successfully advanced in
the method using odd-mass-selective laser excitation.1)
The separation of even- and odd-mass-number isotopesof Pd using orthogonally polarized lasers was demonstrated with ionization that was 10,000 times more efﬁcient1) than the scheme used so far. From a practicalperspective, the yields on the separation of even- andodd-mass-number isotopes must be comparable to Avogadro’s number of atoms for a large amount of nuclear
waste.
We demonstrated stable Pd isotope separation on a
microgram order by photoionization using a high-power,
high repetition rate pulsed laser system.2) The experimental apparatus is shown in Fig. 1. The Pd vapor wasproduced by an electron beam that irradiated Pd samples in a crucible. Two linearly polarized beams withparallel polarization were applied for the selectively resonant ionization of odd-mass Pd isotopes among stable
six isotopes (102, 104, 105, 106, 108, 110 Pd). We succeeded in
the dominant photoionization of the105 Pd.
Two Frequency doubled Nd:YAG InnOSlab lasers(EdgeWave) individually pumped two dye lasers having a pulse width of 10 ns and repetition rate of 10 kHz.
Thickness meter
Photoionization zone

Gold plate
Current meter

10-4PaNd:YAG

Dye laserBBO

Nd:YAG

Dye laserBBO

Nd:YAG∗1∗2∗3∗4Ti:Sapphire -BBO

APowersupplyDichroic mirror

Deflector fornon-photoionized ions
Alternative

Pd

Heat shield
EB-Gunoriginal gold color

Gold color was changed due to photoionized Pd collection.

Fig. 2. The gold plate implanted by selectively ionized 105 Pd(total deposition time is 3 h 23 min).

Also, there is an intra-cavity SHG in a Ti:Sapphire laser
system pumped by Nd:YAG, whose repetition rate andpulse width are 10 kHz and 35 ns, respectively. Theﬁrst excitation wavelength (λ1 ) of 244.9 nm was produced by the ﬁrst dye laser after frequency doublingin a BBO crystal, which excites Pd atoms into the4d9 (2 D3/2 )5p[1/2] state. The typical power of λ1 was
100 mW. The second dye laser or Ti:Sa laser produces
the second excitation wavelength (λ2 ) of 361.023 nm via
frequency doubling in a BBO crystal placed at the external (dye) and internal (Ti:Sa) cavity conﬁguration. The
λ2 excites Pd atoms to the Rydberg autoionizing state4d9 (2 D3/2 )9d[3/2]. We used dye or Ti:Sa, depending on
the situation. The typical power of λ2 in the case ofTi:Sa was 2 W, while that in the case of dye was 1.5 W.
Photoionized 105 Pd ions were collected on the gold plateon which a collection voltage of −50 V was applied. The
distance between the gold plate and the ionization area
was about 5 cm. We conﬁrmed the yields of Pd ionsand identiﬁed the Pd element from the oﬀ/on resonant
frequency by monitoring with a current meter. The typical current level attributed to the photoionized Pd was
10 µA.
Figure 2 shows the gold plate after collecting photoionized 105 Pd ions for 3 h and 23 min. From the valueof the total deposition current, we deduce the total number of 105 Pd to be 3.0 × 1017 , which corresponds to aweight of 50 µg. For the ﬁrst time, we conﬁrmed Pd
isotope separation in microgram orders by using oddmass-selective laser excitation.
References

RIKEN Nishina Center
RIKEN Center for Advanced Photonics
Faculty of Engineering, Nagoya University
High Energy Accelerator Research Organization (KEK)1) C. Locke et al., Appl. Phys. B 123, 240 (2017).
2) T. Sonoda et al., Nucl. Instrum. Methods Phys. Res. A
877, 118 (2018).

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