Journal of Nuclear and Radiochemical Sciences, Vol. 5, No. 2, pp. 45-48, 2004

ArticlesElution Curve of Rutherfordium (Rf) in Anion-Exchange Chromatography with
Hydrofluoric Acid Solution
A. Toyoshima,*, a, b H. Haba,c K. Tsukada,a M. Asai,a K. Akiyama,a I. Nishinaka,a Y. Nagame,aD. Saika,b K. Matsuo,b W. Sato,b A. Shinohara,b H. Ishizu,d M. Ito,d J. Saito,d S. Goto,d H. Kudo,dH. Kikunaga,e N. Kinoshita,e C. Kato,e A. Yokoyama,e and K. Sueki faAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japanc
Cyclotron Center, RIKEN, Wako, Saitama 351-0198, JapandFaculty of Science, Niigata University, Niigata 950-2181, Japane
Graduate School of Science, Kanazawa University, Kanazawa 920-1192, Japanf
Department of Chemistry, University of Tsukuba, Tsukuba 305-8571, Japanb

Received: October 6, 2004; In Final Form: December 3, 2004
An elution curve of element 104, rutherfordium (Rf), in anion-exchange chromatography has been obtained forthe first time on an atom-at-a-time basis. The distribution coefficient in 5.4 M hydrofluoric acid solution has been
determined to be 28 ± 6 mL/g from the observed peak volume of the elution curve.

1. Introduction
In the study of aqueous chemistry of the transactinide elements,
partition experiments, such as liquid-liquid extraction, ionexchange chromatography, and reversed-phase extraction
chromatography, are generally performed on an atom-at-a-timescale.1, 2 The chromatographic systems with fast kinetics are
ideally suited for the dynamic partition of single atoms between
the stationary and mobile phases through rapid and multiple
sampling of chemical species of interest. To determine thermodynamic equilibrium constants of the transactinide elements,
quantitative data on chemical equilibria such as distribution
coefficients (Kd) are required. Because of the short half-lives
and low production yields of the transactinide elements,
however, reliable Kd values of those elements are little available
at present.
A few attempts have been made to determine the Kd valuesof element 104, Rf, by using the ion-exchange chromatographic
methods. Pfrepper et al.3 showed via the retention time with themulti-column technique that the Kd values of Rf on an anionexchange resin in mixed 0.27 M HF/0.1 M HNO3 and 0.27 M
HF/0.2 M HNO3 were identical with those of the lighter homologue Hf. The Kd values of Rf in HF/HNO3 were also measured
by the rapid ion-exchange separation method as a ratio of
specific radioactivities of Rf in the solid and liquid phases, inwhich the significant differences in the Kd values between Rf
and Hf were observed.4 The measurement of the Kd values of
Rf in the reversed-phase extraction chromatography from 8 M
HCl into tributylphosphate (TBP) was carried out and theextraction sequence among Rf, Zr, and Hf was establishedthrough the Kd values.5 In our previous report,6 the anionexchange behavior of Rf was studied together with its lighter
homologues, Zr and Hf, as a function of HF concentration in
1.9 – 13.9 M. The Kd values of Rf were deduced from the relationship between adsorption probability and the Kd values of Zr
and Hf by assuming that the kinetics in the fluoride complexation and the ion-exchange processes of Rf is the same as thoseof the homologues, Zr and Hf. However, no Kd values of Rf
directly measured from elution curves in chromatographic*Corresponding author. E-mail: toyosima@popsvr.tokai.jaeri.go.jp.
FAX: +81-29-282-5939.

experiments have not been reported yet.
In this paper, we present the first observation of the elution
curve of Rf in anion-exchange chromatography with 5.4 M HF
on an atom-at-a-time basis. The Kd values of Rf was directly
determined from the peak volume.
2. Experiment
The isotope 78-s 261Rf (Ref. 7) was produced in the 248Cm(18O,5n) reaction with a 94-MeV 18O6+ beam delivered from theJapan Atomic Energy Research Institute (JAERI) tandem
accelerator. The 248Cm target of 610 µg/cm2 in thickness was
prepared by electrodeposition of Cm(NO3)3 in 2-propanol onto
a 2.4-mg/cm2-thick beryllium backing foil. The beam intensity
was 250 – 300 particle nA. The production cross section of261
Rf through the reaction was 13 nb,8 resulting in a production
rate of about 2 atoms/min under the given condition. The
target included 36-µg/cm2 enriched 152Gd (the isotopic composition was: 39.3% 152 Gd, 5.9% 154 Gd, 16.7% 155 Gd, 13.8%
156
Gd, 7.7% 157Gd, 10.0% 158Gd, and 6.6% 160Gd) to simultaneously produce the short-lived 169Hf isotope (T1/2 = 3.24 min)via Gd(18O, xn) that was used for monitoring on-line elution
behavior of the homologue Hf under strictly identical experimental condition. Reaction products recoiling out of the target
were stopped in a volume of He gas (~ 1 bar) which had been
loaded with KCl aerosols generated by sublimation from thesurface of KCl powder at 640˚C. The products attached to theaerosols were swept out of the recoil chamber with the He gas
flow (2.0 L/min) and were transported through a Teflon capillary (2.0 mm i.d., 20 m long) by a He/KCl gas-jet system to a
rapid chemical separation apparatus. The transport efficiencyof the products through the gas-jet system was estimated to beapproximately 35%.8
To perform fast and repetitive anion-exchange chromatography of Rf, we employed an apparatus AIDA (AutomatedIon-exchange separation apparatus coupled with the Detection
system for Alpha spectroscopy) 9, 10 that consists of a modified
ARCA (Automated Rapid Chemistry Apparatus)11 which is aminiaturized computer controlled liquid chromatographysystem and an automated on-line α-particle detection system.
In the present study, AIDA was used to collect consecutive 4
effluent fractions as schematically shown in Figure 1. The© 2004 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/22/2004

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J. Nucl. Radiochem. Sci., Vol. 5, No. 2, 2004
Front view

30

Side view

He/KCl Gas-Jet inCollection site

Toyoshima

Eluent in

2nd Eluent(4.0 M HCl)

255 No1st Eluent(5.4 M HF)

244 Cm25

252,254,255 Fm

Gas out

20

Column Magazine

15

10

4th fraction
1st – 4th fractions%ads

Slider20 micro-columns(1.6 mm i.d. × 7.0 mm)

5
1st – 3rd fractions
5 cm

0Figure 1. Schematic diagram of the AIDA.

0

5

10

15

20

[HF] / M

nuclear reaction products transported by the gas-jet system were
deposited on the collection site of AIDA. After collection for
182 s, the site was mechanically moved onto the microcolumn
packed with an anion-exchange resin, MCI GEL CA08Y,
Mitsubishi Chemical Corporation. The resin, a strongly basic
quaternary-amine polymer with a particle size of 22 ± 2 µm ina chloride form, was converted to a fluoride form by washingin a column with 26 M HF, washed thoroughly by the batch
method with pure water and dried to a constant weight at 80˚Cin a vacuum oven.
The collected products were dissolved with 5.4 M HF andwere fed onto the 1.6 mm i.d. × 7 mm anion-exchange column
at a flow rate of 0.8 mL/min. The effluent from the column
was consecutively collected on three separate Ta disks with avolume of 170, 130, and 130 µL as fraction 1, 2, and 3, respectively. Then, the remaining products in the column were
eluted with 260 µL of 4.0 M HCl at a flow rate of 1.4 mL/min
through the second path after one-step forward movement of
the column magazine (see Figure 1). The effluent wascollected on the other Ta disk as fraction 4. Each fraction was
evaporated to dryness with hot He gas and halogen heat lamps.
These 4 Ta disks were in turn subjected to α-spectroscopy witheight 600 mm2 passivated ion-implanted planar silicon (PIPS)
detectors. The counting efficiency of each detector was 35%
and its α-particle energy resolution was 110 – 200 keV FWHM.
All events were registered event-by-event together with time
information. After the α-particle measurement, the 493 keV γray of 169Hf was measured with Ge detectors for every third or
fourth set of the samples to monitor the elution behavior of Hfand its chemical yield. Counting durations for the α−particle
and γ-ray measurements were 222 s and 297 s, respectively.
The chemical yield of Hf including deposition and dissolution
efficiencies of the aerosols was 55% on the average.
In order to evaluate the contribution of “primordial 257No” 4
formed from the α decay of 261 Rf between the start of thecollection at AIDA and the end of the 5.4 M HF elution to theeluted radioactivities of 261Rf in anion-exchange chromatography, adsorption behavior of No on the same anion-exchange
resin was examined using 255No, because the α-particle energies of 261Rf (Eα = 8.28 MeV) and of its daughter 257No (Eα =8.22, 8.27, 8.32 MeV) are indistinguishable.13 The isotope 3.1min 255No was produced in the 77-MeV 12C-induced reactionof 248Cm through 248Cm(12C, 5n) with the cross section of about
500 nb.14 The reaction products recoiling out of the target
were transported by the He/KCl gas-jet system to the collection site of AIDA. After deposition for 300 s, the products
were dissolved with 270 µL of 3.9 and 13.9 M HF solution andwere fed onto the 1.6 mm i.d. × 7 mm chromatographic
column filled with the anion-exchange resin, MCI GELCA08Y, at a flow rate of 1.0 mL/min. The effluent collected
on a Ta disk as fraction 1 was evaporated to dryness with hot

Figure 2. Percent adsorption (%ads) of No, Cm, and Fm on the anionexchange resin CA08Y as a function of HF concentration, [HF].

He gas and a halogen heat lamp. The remaining products inthe column were eluted with 250 µL of 4.0 M HCl. The
effluent was collected on another Ta disk and was evaporated
to dryness as fraction 2. The pair of Ta disks were assayed by
α-spectroscopy with the eight 600-mm2 PIPS detectors. The
α-decay events were accumulated for 937 and 904 s for the
first and second fractions, respectively.
3. Results and Discussion
The adsorption on the anion-exchange resin of 255No together
with that of 244Cm, recoil products of the target (the 248Cm target
contains 1.12% 244Cm and 1.31% 246Cm) and of 252,254,255Fm
produced in the nucleon transfer reactions is shown in Figure 2.
The ordinate indicates the percent adsorption expressed as, %ads
= 100 A2/(A1 + A2), where A1 and A2 are the eluted radioactivities observed in fractions 1 and 2, respectively. It has beenfound that the %ads values of 255No are almost independent of
the HF concentration. The %ads values of Cm and Fm wereapproximately 20% and 7%, respectively.
The results on the elution behavior of 261Rf and 169Hf aresummarized in Table 1, where the fraction number, the elapsed
time T from the end of aerosol collection at AIDA to the start ofthe α-particle measurement, the volume of eluted solutions, thenumber of observed α particles (α) of 261Rf and of its daughter
25-s 257No and correlated α particle pairs (α-α) of 261Rf and
257
No, and the relative eluted radioactivities of 261Rf and 169Hf
are listed. From the 511 cycles of the anion-exchange experiments, a total of 48 α events from 261Rf and 257No were registered in the energy range of 8.00 – 8.36 MeV, including 6 α − αtime-correlated α pairs of 261Rf and 257No. The expected event
ratio between α singles and α − α correlations is to be 45 : 5evaluated by taking into account the counting efficiency of thedetectors (35%), the recoil effect of 257No and the decay of
TABLE 1: Relative Eluted Activities of 261Rf and 169Hf in
Each Fraction
FractionNo.

T/s*

Volume/µL

α (α−α)count

Relative
Relative
activity of activity of
261
169
Rf/%
Hf/%

1
2
3
4

68.5
81.6
95.5
108.3

133 ± 12130 ± 9129 ± 10259 ± 128 (1)20 (1)
12 (3)8 (1)13 ± 539 ± 928 ± 820 ± 8000100*Elapsed time from the end of aerosol collection at AIDA to thestart of the α-particle measurement.

J. Nucl. Radiochem. Sci., Vol. 5, No. 2, 2004

Elution Curve of Rutherfordium (Rf)
10 3

100

5.4 M HF

80

4.0 M HCl

Zr

Rf
60

40

10 2

261

Rf (Eluted radioactivities)

261

Rf (Cumulative radioactivities)169

Hf (Eluted radioactivities)169

Hf (Cumulative radioactivities)

Hf

Kd /mL g -1

Eluted and cumulative radioactivities / %

47

10 1

This work

20

Rf
Zr
Hf

0
0

200

400

600

800

1000

Volume /µL
261

123

261
Rf and 257No, that is reasonably consistent with the experimental ratio (48 : 6) within the counting statistics. Relative
eluted radioactivities of 261Rf in Table 1 were corrected for the
decay of 261Rf and the contributions from the background andfrom “primordial 257No”. The average background count in eachfraction was estimated as 0.36. The contribution of “primordial 257No” to the relative eluted radioactivity of 261Rf, which
was taken into consideration on the basis of the standard equations of growth and decay and the adsorption behavior of No(Figure 1), is evaluated to be less than 5% for the 1st fraction
and is negligible for the others in the present experimental
condition.
In Figure 3, the relative eluted radioactivities of 261Rf and169
Hf are plotted by closed circles and closed squares, respectively, as a function of the half volume of each effluent, while
the cumulative radioactivities of 261Rf and 169Hf are indicatedby open circles and open squares, respectively, against the
cumulative eluted volume. As shown in Figure 3, the peakvolume of the elution curve for 261Rf is observed at around 200µL while the isotope 169Hf was eluted only in the 4th fraction,
indicating that the Kd value of Rf is much smaller than that of
Hf. The present result is consistent with the previous resultsthat the adsorption of Rf is much weaker than those of Zr and
Hf at the same concentration of HF.6
The elution curve of 261 Rf is analyzed by the Glueckaufmodel15 which is based on the theoretical plate concept assuming
a continuous flow and local equilibrium. The eluted radioactivity A(v) with the effluent volume v is represented as

678

10 1

[HF] / M

169

Figure 3. Elutions of Rf and Hf with 5.4 M HF. Closed circles
and squares are the relative eluted radioactivities for 261Rf and 169Hf,
respectively. The open symbols show the cumulative ones. The
dashed line is the fitted curve by the Glueckauf equation 15 and thesolid line indicates the integral curve (see text).

A(v) = Amax exp – N
2

10 0
10 0

(vp – v)2
vpv

(1)

where parameters Amax, N, and vp are the maximum peak height,
the number of theoretical plates, and the peak volume, respectively. The values of v and vp are corrected for the dead volumeof 40 µL. The dashed line shows the integrated curve of eq 1
to fit the experimental cumulative yields of 261Rf except for thedata of the 4th fraction (4.0 M HCl) with vp = 186 ± 35 µL and
N = 2.6 ± 1.5. The solid line in Figure 3 is the differential
curve of the dashed line, i.e., the theoretical fit of the eq 1.
The smaller value of N = 2.6 ± 1.5 for Rf than that for Zr andHf (4.8 ± 0.5)6 would be due to low statistics of the present
experiment. Although the statistics of Rf acquired in this study
is not enough to determine the details of the elution curve,
such as a peak width and a peak height, the peak volume canbe roughly obtained.
In the chromatographic system, the Kd value is described as,

Figure 4. The distribution coefficient K d of 261 Rf on the anionexchange resin at 5.4 M HF is shown in the log Kd vs. log [HF] plot bya closed square. For comparison, dependence of the Kd values of Rf
and those of Zr and Hf evaluated in Reference 6 are also depicted.

v
Kd = mp(2)

rwhere m r is the mass of the dry resin. The Kd value of Rf inanion-exchange chromatography with 5.4 M HF was determined to be 28 ± 6 mL/g with m r = 6.6 ± 0.3 mg. In Figure 4,
the Kd value of Rf in this study is plotted together with those ofRf, Zr, and Hf evaluated in our previous study.6 It is foundthat the previously deduced Kd values6 agree well with thepresent one obtained from the peak volume.
Acknowledgment. We would like to acknowledge the crewof the JAERI tandem accelerator for providing the stable 18O
beam. This work was partly supported by the JAERI tandem
accelerator collaboration program.
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