Development of an Automated Solvent Extraction Apparatus Using

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					Development of an Automated Solvent Extraction Apparatus Using
            Microchip for Heavy Element Chemistry
H. Fujisawa, K. Ooe, Y. Komori, A. Kuriyama, R. Takayama, Y. Kikutani, H. Kikunaga, Y.
 Kasamatsu, T. Yoshimura, N. Takahashi, H. Habaa , Y. Kudoua , Y. Ezakia , A. Shinohara
                       Nishina Center for AcceleratorBased Science, RIKEN

1   Introduction
Studies of chemical properties of superheavy elements and heavy actinides with atomic numbers
≥ 100 require rapid analytical techniques with repeatability because of the low production rates
and short lifetimes of these nuclides. We have so far developed solvent extraction technique
with a micro-chemical chip (MCC) and successfully applied to an on-line experiment[1]. In
this study, we have automated this apparatus and applied to a solvent-extraction experiment
for nobelium.

2   Experimental
Figure 1 shows a schematic diagram of the developed solvent extraction apparatus. Nuclear
reaction products are transported to the chemistry laboratory with a He/KCl gas-jet transport
system. The transported products are deposited on the collection site of a polychlorotrifluo-
roethylene slider, are dissolved in aqueous solution, and are then subsequently fed into MCC
(ICC-DY15, Institute of Microchemical Technology Co., Ltd.). An organic solution is fed from
the other inlet of MCC. The aqueous and organic effluents from MCC are separately collected
on Ta discs. After evaporation to dryness, the samples are subjected to α spectrometry with
Si detectors. The series of the operations is automated by using a LabView system (National
Instruments Co.).
    Off-line tests of this apparatus were carried out with multitracers produced at the RIKEN
Ring Cyclotron and single radiotracers produced at the RCNP AVF Cyclotron in Osaka Uni-
versity. The radiotracers were stored in acetic acid/ammonium acetate solutions with pH of
approximately 5.8. Batch experiments were performed as follows. 100 µL of the aqueous so-
lution with various pH values and 100 µL of 0.01 M di(2-ethylhexyl) phosphoric acid-CCl4
solution was mixed in a test tube. The mixture was shaken for 10 min using a vortex mixer
and was then centrifuged for 2 min. After phase separation, each phase was assayed for γ
radioactivity. The off-line extractions with the apparatus were performed with the same solu-
tions as those in batch experiments. Aqueous and organic solutions were fed into MCC with a
flow rate of 5 µL/min. Each phase from MCC was separately collected in test tubes and was
assayed for γ radioactivity.

3   Results and Discussion
The distribution ratio D is obtained by the following equation: D = Vaq Aorg /Vorg Aaq , where
V shows volume and A is radioactivity. For MCC, V is replaced by the flow rate. The log D
values of strontium, which is a divalent cation as with nobelium, as a function of a pH value
in the aqueous phase are shown in Fig. 2. The D values obtained with the apparatus were
consistent with those by the batch experiments.
    The on-line extraction experiment of nobelium was performed using the apparatus described
above. The 255 No (T1/2 = 3.1 min) isotope was produced in the 248 Cm(12 C, 5n) reaction at
the RIKEN AVF Cyclotron. In this experiment, the AIDA system[2] was used for α detection.
The elapsed time from the dissolution of the reaction products to the start of measurement
was approximately 4 min. As a result, we have obtained the D value of nobelium in the extrac-
tion system although thorough corrections for such as cross-contamination between aqueous
and organic phases are required. To perform chemical experiments of superheavy elements
with atomic numbers ≥ 104, we will further improve the present apparatus for a more rapid

                                                                  Microchip extraction                     Evaporation with IR heater
                                           Organic solution

                                            Aqueous solution                                                                                                Alpha detection
                       Dissolution unit                                                                                                                        (AIDA)

                                 Switching gas-jet line                   slider

                                              by He/KCl Gas-jet          Gas exhaust
                                                                                                                                                 Collection site

                                                                                                             Aqueous solution
                                          nuclear reaction

                                                                                          He/KCl gas-jet

                                                                                                                                He/KCl gas-jet

        Figure 1: Schematic diagram of the automated solvent extraction apparatus.



                                                                                   batch experiments
                                                                                   apparatus tests
                              5.4                     5.6                     5.8                                                                6                  6.2

 Figure 2: Plot of log D vs. pH for strontium with 0.01 M di(2-ethylhexyl) phosphoric acid.

 [1] K. Ooe et al.: J. Nucl. Radiochem. Sci. 8, 59 (2007).
 [2] H. Haba et al.: J. Nucl. Radiochem. Sci. 3, 143 (2002).

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