Journal of Nuclear and Radiochemical Sciences, Vol. 18, pp. 24-31, 2018

ArticlesDevelopment of new methods for aqueous chemistry on element 104, rutherfordium: Batchtype solid-liquid extraction and coprecipitation
Yoshitaka Kasamatsu*
Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

Received February 28, 2018; Accepted November 27, 2018: Published online December 20, 2018
Rapid chemical experiment targeting single atoms combined with identification via alpha-particle measurement isrequired for superheavy element chemistry. Herein, successful development of two types of experimental methods of superheavy element chemistry: solid-liquid extraction and precipitation, is presented. The chemical behaviors of Zr and Hf (homologues of element 104, Rf ), and Th (pseudo homologue) were investigated using
carrier-free RI tracers. Through these studies, rapid chemical reaction systems were found and the comparative
data to discuss the chemical properties of Rf were obtained. In addition, automated chemistry apparatuses for
extraction and precipitation were developed and their performance was evaluated using the short-lived isotopes ofZr and Hf, which were transported online from the nuclear reaction chamber in the accelerator room by a He/KCl
gas-jet system. From those results, the newly developed methods were both found to be applicable to 261Rf experiments, and suitable experimental conditions to study the chloride complexation (solid-liquid extraction) andhydroxide complexation (coprecipitation) of Rf were determined.

1. Introduction
The elements with the atomic numbers Z ≥ 104; namely,
beyond actinide elements, are called superheavy elements(SHEs) or transactinide elements. The SHEs are relatively
new elements for us and major part of their chemical properties is unknown. Because the influence of relativistic effects
on electron orbital shells becomes significant for heavy elements, the chemical properties of the SHEs are expected todeviate from the periodicity of the lighter homologues in the
periodic table.1,2 Thus, it is important and interesting to clarify
their chemical properties. Some kinds of chemical studies on
the SHEs have been conducted since 1970’s.1,2 Because of theextremely low production rates and short half-lives (within a
few min) of these heavy nuclides, chemical evaluations of theSHEs must be conducted on a one-atom-at-a-time basis,3 andmust be rapidly completed. These difficulties limit the varietyof chemical investigation of SHEs. Indeed, simple chemical
behaviors such as adsorption and extraction have been mainly
investigated. In these experiments, the chemical separations
were repeated hundreds or thousands of times under identicalconditions to observe the chemical behavior of SHEs existingas single atoms. This approach requires two types of apparatuses: an online system having the capability for rapid transport of nuclear reaction products from the reaction chamber(in the accelerator room) to the chemistry laboratory, and a
rapid chemistry apparatus equipped with a radiation detection
system.1,2 Additionally, for unambiguous identification ofsuperheavy elements (single atoms), it is necessary to measure
the energies and lifetimes of α or sometimes spontaneous fission decays. Thus, it is difficult to clarify various chemical
properties of SHEs. In this paper, two types of newly developed experimental methods to study chemical properties ofSHEs are presented; one is the method to study time dependence of the solid-liquid extraction behavior (observation of*Corresponding author. E-mail: kasa@chem.sci.osaka-u.ac.jp, Tel:
+81-6-6850-5418; Fax: +81-6-6850-6999

the equilibrium of the chemical reactions) for SHEs,4 and theother is that to study coprecipitation behaviors of SHEs with
Sm hydroxide.5,6
In solution chemistry for SHEs, extraction behaviors tosolid phase or organic solution have been mainly investigatedon the lightest transactinide elements, rutherfordium (Rf, Z =104) and dubnium (Db, Z = 105).1,2,7–20 From the viewpoint of
the similarity of the extraction behavior of SHE to its homologues, chemical properties of the SHE were discussed. On
the other hand, equilibrium of the chemical reactions has notbeen confirmed for the short-lived SHEs, although this confirmation is important to investigate the detailed chemical properties of these elements such as complex formation. In the
fluoride complexation studies,11,13,15–17,19 the equilibrium distribution ratios were obtained for the lighter homologues inonline experiments, and an interesting result for Rf was found;
the Kd values of Rf obtained in the ion-exchange chromatography in hydrofluoric acid (HF) and HF/HNO3 mixture solutions
were clearly different from those of Zr and Hf.11,13,15,19
Investigation of the complex formation of Rf with otherligands is very important for an understanding of its chemical
properties. However, sufficiently fast chemical reaction systems for the fast chemical apparatus such as ARCA (AIDA)21,22
seem to be very limited. Thus, a new apparatus allowing alonger contact time between the two phases, AMBER, wasdeveloped,4 which is introduced herein. With this chemical
apparatus, the distribution behavior of Rf in equilibrium
would be observed to allow a discussion of the complex formation of Rf with various ligands. Furthermore, the time dependence of the distribution behavior for the SHEs is expected tobe observed for the first time.
On the other hand, a novel method to study chemical properties of SHEs is desirable to expand the research region ofSHE chemistry. Recently, the coprecipitation method using
Sm hydroxide was developed for SHE chemistry.5,6 It was suggested that the formation of hydroxide and ammine complexesof various elements would be investigated through the coprecipitation yields with Sm hydroxide.5© 2018 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/20/2018

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Kasamatsu

2. Batch-type solid-liquid extraction
As a preliminary experiment of SHE chemistry, various solvent extraction and ion-exchange (solid-liquid extraction)
experiments with the homologues of objective SHEs have been
performed. 23–32 Some works also tried to develop the newchemistry apparatuses.24,25 Solid-liquid extraction experimentof Zr, Hf, and Th in the TIOA/HCl system is described below,
which was applied to the online extraction experiment using
AMBER.4
2.1. Solid-liquid extraction for Zr, Hf, and Th. In thesolid-liquid extraction experiment by conventional batch
method, the 18–57 wt% TIOA resin and 6.2–10.9 M HCl containing the 88Zr (T1/2 = 83.4 d), 175Hf (T1/2 = 70.0 d), and 234Th(T1/2 = 24.1 d) tracer solution were used. These were mixed ina polypropylene (PP) tube and the mixture was shaken for
2–120 min at 25 ± 1 °C with a vortex mixer. Then, the samples were subjected to γ-ray spectroscopy using a Ge semiconductor detector. In all solid-liquid extraction experiments,
control experiments without the resin were performed todetermine the radioactivity of the control solution. The R values were determined from the following eq 1,
R=

ArVs(Ac–As)Vs
=
Aswr
Aswr

(1)

where Ar and As are the radioactivities on the resin and in thesolution, respectively, Vs is the volume (mL) of the solution,
and wr is the mass (g) of the dry resin. Ac denotes the radioactivity of the control solution. The R value in equilibrium is
described as the Kd value in this solid-liquid extraction experiment.
As a result, the Kd values were determined from the dependences of the R values on the shaking time. The chemical
reactions were found to be fast in the TIOA/HCl extraction
when using TIOA resins with weight concentrations above 30
wt%.4 The dependences of the Kd values of Zr, Hf, and Th on
the HCl concentration are shown in Figure 1 together with theresults obtained in the online experiment. The results indicatethat the abundances of the anionic chloride complexes of Zr
and Hf increase with higher HCl concentrations, and that thesec omplexe s a s se mble w it h prot on at e d T IOA ion s a s(R3NH)2[MCl6] to be extracted into the solid phase,26 while thespecies of the pseudo homologue Th dominantly exist in HCl
solutions. Formation of the anionic chloride complexes of thegroup 4 elements was able to be investigated based on thesolid-liquid extraction behaviors in the TIOA/HCl system. As
the solid (organic) phase, 30–60 wt% TIOA resin and 7–11 M
HCl as the aqueous phase were proposed for the Rf experi-

89m

10

4

10

3

Zr (Online)88
Zr (Batch)
175

Hf (Online)
Hf (Batch)
234
Th (Batch)
175-1

To establish the experimental methods for SHE chemistry,
three steps of preliminary experiments using homologue samples are needed. First, the chemical behaviors of homologues
are investigated by conventional method using carrier-free RI
tracers. From these experiments, fast chemical reaction system is searched and suitable experimental conditions to study
objective chemical properties of the elements (homologues andSHEs) are determined. The distribution ratios in two phases atequilibrium are also obtained in this experiment by using
long-lived RI tracers of the homologues. In the next step, therapid chemistry apparatus for “online” use is developed and its
performance is evaluated using RI tracers. Finally, “online”
chemical experiment of homologues is performed using thedeveloped apparatus, accelerator, and the gas-jet transport system of nuclear reaction products. In the “online” experiment,
consistent data with those obtained by conventional method
must be obtained. Through those results, suitable conditions
for online experiment of SHE are determined.

K d / mL g

25

10 2
10 1
10 0
10 -1
5

6

7

8

9

10

11

HCl concentration / M
Figure 1. The Kd values of Zr (circles) and Hf (squares) obtained byonline experiment with AMBER as a function of HCl concentration
at 31 wt% of the TIOA resin and those obtained in off line batch
experiments with 10-min shaking (double circles and squares)
together with the Kd values of Th (double triangles).4

ment.
2.2. Development of the solid-liquid extraction apparatus. An AutoMated Batch-type solid-liquid Extraction apparatus for Repetitive experiments of transactinides (AMBER)
was developed, and a schematic diagram of AMBER is shownin Figure 2.4 Automated Slider-type dissOlution equipment(ASO) was based on the dissolution section of ARCA 21,22 .
Compressor supplies compressed air through a buffer tank to
air cylinders and chemical reaction containers. A compactDAQ dev ice a nd L abV I EW sof t wa re f rom Nat ion al
Instruments were used for operations of the valves and air cylinders, and all the operations were controlled with fixed timeintervals in online extraction experiments. Polytetrafluoroethylene (PTFE) tubes were used in all the passage ways forsolution. Because the PTFE tubes used downstream of the
dissolution apparatus had an internal diameter of 0.17 mm, thedead volume in these tubes was negligibly small. Chemical
reaction containers, in which the solution sample and resin
were mixed to extract the reaction products to the resin phase,were made of polychlorotetrafluoroethylene (PCTFE), and theinner volume of the container was about 0.6 mL. At the bottom of the container, a PTFE filter with a pore size of 5 or 10
μm was set to push out only the solution with compressed air
after the extraction. By this method, separation between thesolution and resin phases was accomplished within 10 s automatically.
2.3. Online solid-liquid extraction for Zr and Hf. In the
online experiment, the 89g,mZr (T1/2 = 3.27 d, 4.18 min) and 175Hf
nuclides were produced in the 89Y( p, n) 89g,m Zr and 175Lu( p,n)175Hf reactions, respectively, using the K70 AVF cyclotron at
RIKEN. The product nuclides were transported by the gas-jet
system to the chemistry laboratory and deposited on a collection site of ASO for 60 s. Then, the deposited sample was dissolved in 160–230 μL of 6–11 M HCl. The solution passed
through the valves, and then entered the chemical reaction
container containing the 31 wt% TIOA resin. After shaking
the container with a vortex mixer for 10–120 s, only the liquid
phase was pushed out of the container by the compressed air at
0.5 MPa, and was assayed by γ-ray spectroscopy. The residual
Zr and Hf species adsorbed on the resin were stripped bywashing the resin three times with about 220 μL of a mixture
solution of 5.1 M HNO3 and 0.01 M HF. The first two fractions of the stripping solution were analyzed γ-ray spectro-

Development of new methods for aqueous chemistry on element 104,

J. Nucl. Radiochem. Sci., Vol. 18, 201826

Figure 2. Schematic diagram of the online extraction experiment using the batch-type solid-liquid extraction apparatus AMBER.4 The nuclear
reaction products are continuously transported to the dissolution equipment in AMBER located in chemistry room. Eluate from the dissolution
equipment goes through two passage valves and a slider-type valve into a chemical reaction container. After the extraction, only the solution ispushed out from the container.

scopically. A control extraction experiment without the resin
was also performed.
The online solid-liquid extraction experiment was successfully performed using AMBER. The R values of Zr and Hf
obtained with shaking times of 10–120 s were approximately
constant; very rapid achievement of the equilibrium of thechemical reactions within 10 s was observed in the present
extraction system. The averaged R value at each HCl concentration was consistent with the K d values obtained in theoffline batch experiment in 7–11 M HCl as shown in Figure 1.
Consequently, it was found that the Kd values of Zr and Hf
were able to be obtained in the online rapid experiment with
AMBER. In the extraction using AMBER with shaking for 10s, the solution sample for measurement was prepared about 35
s from the start of the dissolution of the products transportedby the gas-jet system. This result suggests that the present
extraction experiment is applicable to the 68-s 261Rf experiment. Indeed, solid-liquid extraction experiment of 261Rf with
AMBER at RIKEN was recently achieved and interesting
results were reported.33
3. Coprecipitation with Sm hydroxide
The precipitation property is one of the important chemical
properties and coprecipitation technique using carrier elements has been widely used for chemical separation and so on
in radiochemical researches.34 In 2009, a simple and rapid
coprecipitation method with Sm hydroxide, which facilitatesalpha spectrometry with high energy resolution, was established. 35 For the application of this method to SHEs, thecoprecipitation experiments of various elements including
homologues of SHEs and development of the suction filtration
apparatus for online use were conducted.5,6
3.1 Establishment of the experimental method of coprecipitation with Sm hydroxide for SHEs
To establish a new methodology for superheavy element
chemistry, the coprecipitation behaviors of 34 elements with
Sm hydroxide were investigated using multitracer (multiple
radionuclide source).5 The multitracer was produced by irradiating natTa targets (2-μm thickness × 30 foils) with 14N7+ ionsaccelerated to 135 MeV per nucleon by the RIKEN ring cyclotron for 40 h. The beam current was ~1.6 electric μA. Various
nuclides, namely various elements, with Z ≤ 73 (Ta) were produced by nuclear spallation reactions. Only the nuclear reaction products recoiling out of the target foils were transported
from the nuclear reaction chamber to the chemical laboratory
by a He/KCl gas-jet system through a PTFE capillary tube.36
The transported products were collected on glass filter paper,and were dissolved in 1 mL of 0.01 M HCl.
In a PP beaker, 20 μL of Sm standard solution (1000 mg L−1,
1 M HNO3) was added into 220 μL of the prepared multitracer
solution. The solution was stirred, and then, 2 mL of the basic
solution (dilute and concentrated aqueous NH3, and 0.10, 1.0,
6.0, or 12 M NaOH solutions) was added. The solution was
stirred for 10 s or 10 min at room temperature. Then, the solution containing the precipitate was filtrated by suction with a
PP membrane filter (eichrom, Resolve® Filters 0.1 μm). Boththe precipitate and filtrate were dried using a heater at 100 °C.
The precipitate, filtrate, and PP beaker used were subjected toJ. Nucl. Radiochem. Sci., Vol. 18, 201827

Kasamatsu
10 min, respectively. The variation of the yields for the prepared basic solutions qualitatively ref lects the ordinaryhydroxide precipitation properties (formation of ammine andhydroxide complexes) of the elements in macro amounts. For
example, the coprecipitation yields of group 1 elements, Na, K,
Rb, and Cs, were lower than 1.5% under all the conditions
studied. This result indicates that these elements do not form
coprecipitates with Sm hydroxide, which is consistent with thefact that group 1 elements in macro amounts hardly form precipitates in basic aqueous solutions, including NH 3 andNaOH.37 In addition, the coprecipitation yields of group 3 elements are almost 100% when using aqueous NH3 and 0.10 and
1.0 M NaOH solutions. These behaviors are consistent withthe well-known properties of these elements, i.e., hydroxide
precipitation in basic solutions.35 The yields of some elements
were low when using 6.0 and 12 M NaOH, and it was foundthat these elements form hydroxide complex ions such as[M(OH) 4]− (M3+ = metal ions) in high [OH−] solutions.38 See
ref. 5 for details. Anyway, the observed consistency between
the coprecipitation yields of various elements with Sm hydroxide and their individual hydroxide precipitation properties suggests that the coprecipitation behavior of an element whose
chemical properties are unknown can be investigated using thepresent coprecipitation method and from the coprecipitation
behaviors, general hydroxide precipitation properties of theelements can be discussed. Additionally, the chemical reactions for the majority of the elements in the multitracer are sufficiently fast to reach equilibrium within 10 s of stirring.

γ-ray spectrometry with Ge semiconductor detectors. The
standard activities of the radiotracers were also determined.
The precipitation yields, Y, were evaluated from these radioactivities according to eq 2.
Y=

Appt
× 100
Astd

(2)

In the above equation, Appt represents the radioactivity of the
precipitate and Astd represents the standard radioactivity.
The product nuclides were identified based on their characteristic γ-ray energies and corresponding half-lives. In total,
34 elements containing more than 60 nuclides were identified
as follows: 24Na, 42K, 82m Rb, 127,129Cs {group 1}, 28Mg, 47Ca,
128,(131)
Ba {group 2}, 44,47,48 Sc, (86),87g,(m)Y {group 3}, (132 La),
132,135
Ce, 145,146,(147) Eu, 146,147,149 Gd, 149-153,155 Tb, 152,155,157 Dy,(160m Ho), 161Er, 165,(166),167Tm, 166,(169)Yb, 169,(170),171,172Lu {group 3(lanthanides)}, (86,87)89Zr, 170,173Hf {group 4}, 90Nb, 176Ta {group5}, 93m Mo {group 6}, 96Tc {group 7}, 99m,100,(101m)Rh {group 9},65
Zn {group 12}, 67Ga, 110,111In {group 13}, 71,72As, 118m,120mSb{group 15}, 73Se, and 119mTe {group 16}. The nuclides listed inparentheses are ones for which the coprecipitation yields could
not be determined. Various elements belonging to various
groups in the periodic table (including the homologues of nine
SHEs (groups 4–18)) were found in the prepared multitracer
sample.
The coprecipitation yields of radionuclides of groups 1–7, 9,
12, 13, 15, 16 elements with Sm hydroxide were determinedand shown in Tables 1 and 2 with the stirring time of 10 s and

TABLE 1: Coprecipitation yields, Y, with stirring time of 10 s. 5
Added basic solution
Nuclide
24

Na
K
82m
Rb
127
Cs
28
Mg
47
Ca
128
Ba
48
Sc
87
Y
132
Ce
145
Eu
146
Gd
150
Tb
152
Dy
161
Er
165
Tm
166
Yb
169
Lu
89
Zr
173
Hf
90
Nb
176
Ta
93m
Mo
42

96

Tc
Rh
65
Zn
67
Ga
111
In
71
As
118m
Sb
73
Se
119m
Te
99m

dil. NH3

conc. NH3

0.10 M NaOH

1.0 M NaOH

6.0 M NaOH

12 M NaOH

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

9.0E-04
1.0E-03
1.9E-03
1.9E-04
6.1E-0358.0
1.2E-03
92.4
98.1
83.2
100
98.0
94.3
91.1
94.4
96.3
94.1
102
97.3
90.6
98.4
93.1
74.2

3.E-05
1.E-04
2.E-04
1.E-05
4.E-049.0
2.E-04
6.0
4.0
5.9
5
17.4
5.7
9.0
1.6
5.8
5.6
6
3.7
5.4
6.4
8.0
7.3

1.11
1.0E-03
1.9E-03
1.9E-04
13.8
58.0
69.6
89.1
96.8
91.5
97.0
99.0
96.6
98.6
97.0
102
89.3
97.0
95.9
90.4
91.0
74.2
26.8

0.93
1.E-04
2.E-04
1.E-05
5.9
11.4
17.0
6.0
4.5
8.1
4.0
16.4
6.2
7.7
1.6
4
5.5
6.3
3.7
5.3
6.5
7.0
5.4

9.0E-04
1.0E-03
1.9E-03
1.9E-04
109
86.1
36.0
83.7
100
88.2
101
101
104
96.4
103
100
89.7
99.3
99.9
88.9
94.4
65.8
9.9

3.E-05
1.E-04
2.E-04
1.E-05
11
12.7
5.6
6.3
4
14.7
3
16
6
9.2
2
4
5.5
6.4
3.4
5.1
6.4
6.6
4.7

9.0E-04
1.0E-03
1.9E-03
1.9E-04101
72.5
1.2E-03
83.8
98.1
98.6
95.0
101
97.0
92.5
101
101
88.3
95.3
95.5
98.3
88.5
60.3
0

3.E-05
1.E-04
2.E-04
1.E-0511
16.0
2.E-04
6.2
3.7
16.0
5.0
16
9.1
11.5
3
4
5.7
6.6
3.5
8.0
6.3
6.5

1.34
1.0E-03
1.9E-03
1.9E-04
17.8
88.4
1.2E-03
63.2
86.0
101
92.9
97.3
102
87.4
91.8
77.4
66.5
71.4
40.5
34.4
97.1
56.0
0

1.41
1.E-04
2.E-04
1.E-058.0
13.7
2.E-04
4.6
3.1
17
4.5
14.9
8
11.3
2.9
3.5
4.7
4.3
2.1
2.9
7.0
6.7

1.07
1.0E-03
1.9E-03
1.9E-04
7.8
116
1.2E-03
26.9
42.1
84.5
85.5
83.1
73.8
54.6
47.5
40.0
31.3
37.0
32.6
24.0
77.8
52.1
0

0.94
1.E-04
2.E-04
1.E-053.6
12
2.E-04
3.0
1.7
7.5
3.0
12.2
6.0
8.5
1.8
2.1
1.7
3.0
1.3
1.6
11.2
6.7

1.8
101
200
21.3
96.6
99.0
101
50.2
101

1.9
7
90
6.3
10.5
7.5
16
13.0
9

0
71.0
3.2E-02
24.8
91.1
97.8
66.3
21
104

5.3
3.E-03
3.5
8.6
6.9
13.8
12
9

0
79.8
120
29.7
96.0
61.0
24.4
2.4E-04
57.1

6.3
60
4.7
8.9
4.8
9.8
3.E-05
5.9

0
55.1
91
22.9
93.5
35.8
15
2.4E-04
43.5

6.0
47
5.2
8.6
2.9
13
3.E-05
5.4

0
43.4
58
16.8
48.9
46.0
3.8
2.4E-04
51.4

4.3
32
3.2
5.3
5.4
13.9
3.E-05
5.4

0
15.4
36
17.7
24.2
22.4
27.1
2.4E-05
42.8

2.8
7
1.5
2.4
2.4
9.6
3.E-06
3.8

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Development of new methods for aqueous chemistry on element 104,

28

TABLE 2: Coprecipitation yields, Y, with stirring time of 10 min. 5
Added basic solution
Nuclide
24

Na
42
K
82m
Rb
127
Cs
28
Mg
47
Ca
128
Ba
48
Sc
87
Y
132
Ce
145
Eu
146
Gd
150
Tb
152
Dy
161
Er
165
Tm
166
Yb
169
Lu
89
Zr
173
Hf
90
Nb
176
Ta
93m
Mo
96
Tc
99m
Rh
65
Zn
67
Ga
111
In
71
As
118m
Sb
73
Se
119m
Te

dil. NH3

conc. NH3

0.10 M NaOH

1.0 M NaOH

6.0 M NaOH

12 M NaOH

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

Y (%)

error

4.9E-04
4.9E-03
7.2E-04
6.7E-05
3.1E-03
48.2
18.8
80.4
86.3
73.3
83.9
84.1
86.4
77.3
77.5
91.0
93.7
103
88.4
77.9
106
74.6
1.1E-03
4.1E-03
84.9
60.7
16.6
85.7
85.7
77.1
17
81.9

2.E-05
6.E-04
5.E-05
1.E-06
2.E-04
5.1
1.4
6.6
2.4
1.9
3.1
4.5
5.8
2.8
4.0
2.6
6.2
5
2.8
8.3
6
7.2
1.E-04
2.E-04
7.3
11.5
2.7
5.0
7.3
8.9
11
4.4

4.9E-04
4.9E-03
7.2E-04
6.7E-05
38.6
90.1
106
96.0
96.9
87.2
92.2
95.7
94.4
88.8
86.4
97.1
94.6
107
96.4
80.1
88.3
75.5
1.1E-03
4.1E-03
52.0
35
15.5
84.3
87.3
85.0
1.1E-0385.0

2.E-05
6.E-04
5.E-05
1.E-06
4.8
10.3
6.0
7.7
3.0
2.3
3.7
4.4
6.6
3.3
4.5
2.6
7.3
9
3.6
8.1
4.9
7.8
1.E-04
2.E-04
4.5
18
2.3
5.3
8.0
9.7
1.E-046.3

4.9E-04
4.9E-03
7.2E-04
6.7E-05
93.9
92.3
36.3
85.5
99.8
103
93.6
100
108
91.6
98.8
104
99.4
112
102
97.3
104
68.5
1.1E-03
4.1E-03
107
68.7
25.9
96.2
47.7
17.9
1.1E-0348.9

2.E-05
6.E-04
5.E-05
1.E-06
10.2
12.3
3.6
8.2
3.2
2
3.8
5
8
3.8
6.4
2
8.1
13
4
11.2
6
7.6
1.E-04
2.E-04
9
18.3
4.2
5.6
6.4
5.6
1.E-044.6

4.9E-04
4.9E-03
7.2E-04
6.7E-05
79.3
40.9
6.7E-04
100
102
102
96.7
96.3
109
90.5
101
102
93.3
104
93.3
63.4
94.6
76.3
1.1E-03
4.1E-03
99.2
49.7
26.3
95.7
30.0
3.1E-03
1.1E-0342.4

2.E-05
6.E-04
5.E-05
1.E-06
9.4
7.2
3.E-05
8
3
2
4.0
4.6
10
3.6
7
2
6.3
5
3.3
6.8
5.4
8.3
1.E-04
2.E-04
7.2
11.8
4.3
5.6
5.3
2.E-04
1.E-044.2

4.9E-04
4.9E-03
7.2E-04
6.7E-05
22.5
53.1
6.7E-04
61.9
92.1
113
107
107
112
94.3
97.8
78.9
75.0
81.4
44.4
38.1
99.6
84.7
1.1E-03
4.1E-03
63.8
60.7
29.9
52.9
28.2
20
1.1E-0344.4

2.E-05
6.E-04
5.E-05
1.E-065.3
8.5
3.E-05
6.1
2.6
2
4
5
8
4.1
6.3
1.9
4.8
3.6
1.8
3.6
5.2
7.7
1.E-04
2.E-04
5.3
5.7
4.0
3.4
4.4
15
1.E-042.3

3.6
4.9E-03
7.2E-04
6.7E-05
3.1E-03
68.9
12.4
36.2
81.9
98.7
93.9
95.4
101
84.6
84.5
62.6
60.2
52.3
9.06
6.9
19.0
18.3
1.1E-03
4.1E-03
37.3
110
53.7
4.58
52.5
3.1E-03
1.1E-03
16.4

1.4
6.E-04
5.E-05
1.E-06
2.E-04
9.5
0.9
4.5
2.6
2.2
3.8
4.5
9.0
3.8
6.7
2.1
4.0
7.8
0.93
1.4
1.6
9.2
1.E-04
2.E-04
3.1
13
14.7
0.84
8.8
2.E-04
1.E-04
4.6

120

These results indicate that the present coprecipitation methodwith Sm hydroxide is applicable to SHE chemistry. Note that,for actual SHE chemistry, detailed preliminary experimentusing the homologues of the objective SHE and search for suitable conditions are necessary.

(a)

100
80
60
40
20

Zr-88

0
Y / %

3.2. Coprecipitation experiment for Zr, Hf, and Th with
Sm hydroxide. For coprecipitation experiment of Rf, detailed
coprecipitation experiment with Sm hydroxide was performed
with 88Zr, 175Hf, and 228Th (T1/2 = 1.91 y) tracers.6 Coprecipitatedsamples with Sm hydroxide were prepared using various basic
solutions: dilute and concentrated aqueous NH3 and 0.1, 1.0,
6.0, and 12.0 M NaOH solutions. A 20 μL aliquot of the Sm
standard solution was added into 220 μL of an aqueous solution (~0.4 M HCl) containing the radiotracers in a PP beaker.
The solution was stirred and 2 mL of the basic solution wasthen added to produce the precipitate. After aging the precipitate for 10 s or 10 min at 25 °C, the precipitate sample wassubjected to suction filtration with a PP membrane filter. The
obtained sample was dried on a heater at 100 °C, and was subjected to γ-ray and α-particle measurements. The radioactivities of the filtrate and PP beakers used were also measured.
The standard radioactivities of 88Zr, 175 Hf, and 228Th were
determined at the same detection efficiency. Precipitation
yields, Y, were determined from these radioactivities. The
errors in the yields were determined by taking into account thestandard deviation in each γ or α count and in the variation of
the precipitation yield.
The coprecipitation yields of Zr, Hf, and Th when 10-min

120

(b)

100

Hf-175
Th-228

80
60
40
20
0
dilute
NH3

conc.
NH3

0.1 M
NaOH

1.0 M
NaOH

6.0 M
NaOH

12.0 M
NaOH

Figure 3. Coprecipitation yields of Zr, Hf, and Th based on the
addition of various basic solutions. Yields obtained with stirring for
10 min are shown in (a) and for 10 s in (b).6

aging was employed are shown in Figure 3(a), and thoseobtained with 10-s aging are displayed in Figure 3(b). Figures
3(a) and 3(b) demonstrate that the yields obtained with 10-min
and 10-s aging are in good agreement with each other. This

29

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Kasamatsu

Solution sample
FilterFilter stick

Valve

Suction

Cylinders
Figure 4. A photograph of CHIN (upper) and schematic illustration of the filtration section of CHIN (lower).6

result suggests that the chemical reactions during coprecipitation of Zr, Hf, and Th are fast, and the present conditions are
suitable for evaluating the coprecipitation behavior of 68-s
261
Rf.
Almost complete coprecipitation of Zr and Hf with Smhydroxide was achieved when aqueous NH3 solutions and 0.1
M NaOH were used. These results are consistent with thoseobtained for multitracer (Tables 1 and 2) and with the inherent
properties of these elements, i.e., hydroxide precipitation inbasic solutions.39,40 With the use of more highly concentrated
NaOH solutions, the yields of Zr and Hf decreased as the OH−
concentration increased, whereas the Th yields were constantat ca. 100%. These behaviors are attributed to the fact that Zr
and Hf form hydroxide complex ions such as [M(OH)5]− (M4+
= Zr4+ and Hf4+)38,41 in solutions with high hydroxide concentration. The yields of Hf were consistently lower than those of
Zr in the same solutions. These results are qualitatively consistent with the larger solubility product of [Hf(OH)5]− (logKs5= −3.2) than that of [Zr(OH)5]− (logKs5 = −3.6).41 In addition,
the highest yields of Th compared with those of Zr and Hf isconsistent with the smallest solubility product of Th (logKs5 =−5.8).41 The ~100% coprecipitation yields of Zr, Hf, and Th
with the use of aqueous NH3 indicate that the ammine-coordinated complex ions, which dissolve in aqueous solution (e.g.,
Zn, Cu, and Ag hydroxide dissolve in concentrated NH3 solutions), are not dominantly formed even in concentrated NH3
solution. The obtained results indicate that the hydroxide andammine complexation properties of group 4 elements can bequalitatively investigated through their coprecipitation behaviors with Sm hydroxide under the present experimental conditions.
In addition, it was found in this study6 that well-resolved
alpha spectra can be obtained for coprecipitated samples without compromising the yield by aging the hydroxide precipitate
for only 10 s at 25 °C.
3.3. Development of the apparatus and online coprecipitation experiment. A computer-controlled suction filtration
apparatus for the preparation of precipitated samples of heavy
elements, CHIN, was developed using cylinders operated bycompressed air, valves operated by on/off operation of 24 V
DC power and so on as shown in Figure 4.6 This apparatus
enables rapid and repetitive filtration. Filter sticks were fabricated using PTFE to prevent the adsorption of the radiotracers
on the wall of the stick, and the stick was washed after eachusage.
The online experiment using CHIN was performed withrelatively short-lived nuclides 89m,g Zr and 173Hf (T1/2 = 23.6 h)
produced using the AVF cyclotron at the Research Center of
Nuclear Physics (RCNP).6 These nuclides produced in thereactions of natSr(α,xn)89m,gZr and natYb(α,xn)173Hf were rapidly
and continuously transported from the nuclear reaction chamber to the chemistry laboratory using the He/KCl gas-jet system. The products were collected on the collection site of the
dissolution apparatus, ASO. After dissolution by 200 μL of
dilute HCl for 12 s, the precipitate samples were prepared at

J. Nucl. Radiochem. Sci., Vol. 18, 2018

Development of new methods for aqueous chemistry on element 104,

4. Conclusion
In the present paper, two types of newly developed experimental methods for SHE chemistry are introduced. In boththe studies, preliminary chemical experiments using thehomologues of 104Rf and development of the apparatuses areachieved, and substantial applicability for Rf experiment was
indicated. Feasibility to study the chloride complexation of Rf
was represented through the solid-liquid extraction in the
TIOA/HCl system using the apparatus AMBER. This methodology also has a possibility of the first observation of theequilibrium of the chemical reactions for SHE.33 In coprecipitation study, the coprecipitation method was proposed toinvestigate the hydroxide and ammine complexation of SHEs
as a quite new method for SHE chemistry. In addition, goodenergy resolution in alpha spectroscopy was confirmed for
precipitated samples.
It is very difficult to clarify the chemical properties of newelements (SHEs) owning to their characteristics such as shortlife, low production rate, and single atom situation. For the
breakthrough in the research field of SHE chemistry, developments of various new experimental methods would be necessary. It is hoped that the methods introduced herein will
provide such valuable findings.
Acknowledgement
These works were car ried out by group members of
Shinohara laboratory in Osaka University. We would like toappreciate all our colleagues of Osaka University, RIKEN,
Tohoku University, and Kyoto University. The author especially acknowledges Prof. Atsuhi Shinohara and Dr. Hiromitsu
Haba for constant supervision. The author also appreciates Dr.
Yuichiro Nagame and Prof. Kosuke Morita for continuous support. The author would like to thank Mr. Keigo Toyomura andMiss Aiko Kino for their great contributions to the present
works. We express our gratitude to the staff of RIBF and
RCNP for the support in RI production using the accelerators.
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Zr-89m100

Hf-17380

Y/%room temperature in a manner similar to that used in the tracer
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30

60
40
20
0
dilute
NH 3

0.1 M
NaOH

1.0 M
NaOH

6.0 M
NaOH

12.0 M
NaOH

Figure 5. Coprecipitation yields of Zr and Hf obtained in the online
experiment.6

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