Journal of Nuclear and Radiochemical Sciences,Vol. 3, No. 1, pp. 155–158, 2002

155

Rapid Chemical Separation for Bk
T. Maruyama,a D. Kaji,a T. Kaneko,a S. Goto,a K. Tsukada,b H. Haba,b M. Asai,b S. Ichikawa,bY. Nagame,b and H. Kudo∗,aaDepartment of Chemistry, Faculty of Science, Niigata University, Niigata 950-2181, JapanbAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195,
Japan
Received: March 5, 2002; In Final Form: April 29, 2002
An anion exchange in mineral acid and methanol system was examined in view of rapid chemical separation. An
elution behavior of Bk in hydrochloric acid–methanol system was obtained using 250 Bk. An elution behavior of Bk
in nitric acid–methanol system was predicted from the relationship between an elution position and an ionic radius.
The separation was completed for nitric acid–methanol system and for hydrochloric–methanol system within 40 and25 min, respectively.

1. Introduction
There are a number of nuclides which have not been discovered even though they are expected to have fairly long half-lives
especially in the neutron-rich region of actinides. Many newisotopes of actinides may be produced by use of neutron-richtargets such as 248 Cm, 249 Cf, and 254 Es. Neutron-rich Bk isotopes belong to such isotopes. The purpose of the present investigation is to develop a rapid separation method for the observation of neutron-rich berkelium isotopes. Discovery of sucha nuclide needs separation from many kinds of nuclides which
will be produced at the same time. Most separation methods forlanthanides and actinides have been based on the use of cationexchanger with eluents containing organic complexing agents.
These methods are fairly rapid and the mutual separation is also
good.1–4 However, measurement of α particles and fission fragments are obscured by the residue of the organic agents which
are not easily decomposed. Most solvent extraction methods
also utilize organic complexing agents.5 Therefore new chemical methods which enable the rapid separation of the actinide
elements and the immediate preparation of counting sources
suitable for α spectrometry are desired, so that we examinedan anion exchange in mineral acid–alcohol system in which noresidue and fast evaporation are expected.

particle measurement or into a plastic tube for γ-ray measurement.
An isotope of 250 Bk was used as a Bk tracer, which wasproduced from 248 Cm(18 O, X)250 Bk reaction by the tandem accelerator of Japan Atomic Energy Research Institute. About
400 µg/cm2 thick 248 Cm was electrodeposited together with
152
Gd-enriched Gd of 50 µg/cm2 thickness on a Be backing foil.
As the target was originally prepared for rutherfordium chemistry, gadolinium was mixed to check the chemical behavior ofrutherfordium homologue, Hf. The target was irradiated forabout 50 min with the 18 O beam of 300 pnA in current. Theincident energy of 18 O was 94 MeV on target. Nuclear reaction
products were transported with an aerosol loaded gas-jet system,and collected on membrane filter of a 0.1 µm pore diameter. After collection the membrane filter was washed with a loading
solution to prepare for the sample solution, to which 241 Am wasadded as a tracer.
An HPGe detector coupled with a multichannel pulse height
analyzer was used for the measurement of γ-ray radioactivity.
An automatic γ counting system with an NaI(Tl) scintillation
detector, COBRA (PACKARD), was also employed when only

2. Experimental
A strongly basic anion-exchange resin, MCI GEL CA08S(Mitsubishi Chemical Industries Ltd.), was used in the presentwork. The particle size of the resin is 11 ± 2 µm and the degree of cross-linking is 8%. The exchange capacity is larger
than 1.2 meq/mL. The Teflon tube column of 2 mm inner diameter filled with the resin is illustrated in Figure 1(a). As eluent,methanol was selected for its properties of low viscosity andhigh vapor pressure. Figure 1(b) shows a schematic diagramof loading a sample solution and passing the eluent through thecolumn. After conditioning the resin by methanol mixed witheither conc. HNO3 or conc. HCl in a volume ratio of 9 : 1, theeluent was stored in a reservoir, Spiral-II, by using a tube pump.
By manipulating valves, 300 µL of the sample solution was introduced into the top of the column. Then the eluent was passed
through the column and chromatograms were developed. The
flow rate was controlled by a nitrogen gas pressure.
The elution behaviors of lanthanide and actinide elements
were examined with varying the flow rate, methanol contents,and acid concentration. Tracers used in this work were 152 Eu,
148
Gd, 160 Tb, 241 Am, 242 Cm, 252 Cf, and fission products from252
Cf. The effluent was collected either on a Ta dish for α∗Corresponding author. E-mail: hkudo@curie.sc.niigata-u.ac.jp.

FAX: +81-25-262-6171.

20 mm

50 mm

gaFigure 1. (a) Anion exchange column used in this work. (b) Schematic
drawing of apparatus for anion exchange separation.

c 2002 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 6/30/2002

156 J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

Maruyama

8Elution position /mL

Eu64Tb20012345Concentration of nitric acid /M

6Figure 3. Peak position vs. nitric acid concentration. The attachederror bars indicate the widths (FWHM) of the elution curves.

Figure 2. Effect of methanol content in 3.2 M HNO3 –methanol anion
exchange system.

a single tracer was used. A silicon surface barrier detector witha multichannel pulse height analyzer was used for the measurement of α radioactivity.
3. Results and Discussion
3.1. Nitric Acid–Methanol System. It is known that theelution positions for lanthanide and actinide elements are correlated with their ionic radii in an anion exchange in the nitricacid–methanol system.6 This means that the elution position ofa given element of actinide is easily predictable, if its trivalentionic radius is known. Therefore, the nitric acid–methanol system was firstly examined by using several tracers. Essentially arapid separation requires fast flow rate, so that the effect of theflow rate was examined. The peak position was found to be notinfluenced by the change of the flow rate, but the elution curves
became broader as the flow rate got faster. The optimum flowrate was determined from the elution time and the peak broadening to be around 0.5–0.8 mL/min.
When the column temperature was kept at room temperature, peak broadening, serious tailings, and overlapping elution
curves were observed in the chromatograms. This is caused byslow attainment of an exchange equilibrium at room temperature. In addition, the flow rate was slow compared with thecases at elevated temperatures under the same pressure. This isbecause the viscosity of the eluent is higher at low temperature.
Therefore, the column temperature was kept at 80–85 ◦ C. Although this temperature was almost an upper limit for the resin,
the deterioration of the resin was not recognized after more than
20 runs of experiments.

Figure 4. Elution curves of some lanthanides and actinides in nitricacid–methanol anion exchange system. The estimated elution curves
for Bk and Sm are also shown.

In general, ions are more strongly adsorbed at higher
methanol content,7 so that good separation is expected at higher
methanol content. On the other hand, the stronger the adsorption, the longer the elution time. In this point of view, the effectof methanol content was examined using 152 Eu and 148 Gd tracers. The results are shown in Figure 2. As is expected, higher
methanol content gives a stronger adsorption. But at the highest methanol content examined, the width of the elution curveis considerably large. We define the figure of merit (FOM) as
the difference of the peak positions divided by the sum of thewidths of two elution curves. The best FOM was obtained at95% methanol content. At this methanol content, the elution
time for Eu was fairly short, about 20 min.
It was reported that adsorption on the resin is enhanced byan increase in nitric acid concentration.7 Considering the separation time, the concentration of nitric acid was examined up
to 4.7 M at 95% of methanol content. The results are shownin Figure 3. The best separation was achieved at the highest
concentration of nitric acid. The elution time for Eu was about
25 min in 4.7 M nitric acid. This value of the elution time is still
applicable to the separation for nuclides of a few tens minutes
half-life.
Under the best condition obtained in nitric acid–methanol
system, the chromatograms for several lanthanide and actinide
elements were developed and displayed in Figure 4. The
sequence of the elution was Tb < Gd < Cf < Eu < Cm < Am.
Americium remained on the resin under the present condition.
As the peak positions and the widths of the elution curves arefound to be well correlated with the ionic radii of trivalent ions,8
the chromatogram for Bk was predicted from these correlations

Rapid Chemical Separation for Bk

Figure 5. Effect of methanol content in 12 M HCl–methanol anion
exchange system.

J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

157

change in the hydrochloric acid–methanol system.10 And it wasreported that in the hydrochloric acid–methanol system is efficient the separation of Bk from other actinides. However, theelution time is quite long and the reported separation scheme
cannot be used for a rapid separation as it is.
In the present work the fast flow rate for this system was examined whether it is applicable in rapid separation. The elution curves at fast flow rate over 1.0 mL/min became broad
remarkably. It was found that the flow rate should be below
0.7 mL/min. At room temperature, demerits similar to those in
the nitric acid system were encountered. All the neighboring
elution curves overlapped each other and the tailing was considerably large. Therefore the experiments should be performed atabout 85 ◦ C. When the concentration of hydrochloric acid wasless than 12 M, the adsorption on the resin was too weak andAm and Cf could not be separated. The concentration of hydrochloric acid was fixed to 12 M thereafter.
The effects of methanol content are shown in Figure 5, where
the chromatographic behaviors of Am and Cf were displayed. It
is clear from the figure that the best result was obtained at 90%
of methanol content. In this condition, Am and Cf were well
separated and the elution time for Bk was expected to be about
25 min judging from the elution position in Reference 7. The
hydrochloric acid–methanol system seems to be more suited for
the Bk separation, because no contamination from lanthanides
and actinides were expected.
In order to examine the behaviors of other elements, such asfission products which will be produced at the same time with
the Bk production, fission products from 252 Cf spontaneous fission were used as tracers. It was found that lanthanides (La, Ce,Nd, Pm, Sm), Ba, and Rh were observed only for the first fraction in a similar manner as seen in Figure 5, while Ru, Cd, andTe remained in the column. Small amounts of Ru were observed
for all fractions. The elution curves of such elements as Zr, Ag,and I, were seen near the expected position of Bk. Accordingly
the Bk fraction may be contaminated with small amounts of Ru,Zr, Ag, and I. However Bk can be separated from most of elements in this system.
Under the optimum condition in the HCl–methanol system,
the chromatographic behavior of Bk was examined using 250 Bk
which was produced from 248 Cm + 18 O reaction. The elution
curve for Bk is shown in Figure 6 together with that for 241 Am
which was added as a tracer. The elution curve of Cf which
was obtained under the same conditions in the tracer experiment
was also depicted in the figure. The elution curve for Hf is alsodepicted in the figure. Hafnium isotopes were produced fromGd + 18 O reaction. As is expected, the Hf behavior is about thesame with that of its homologue, Zr. The chemical yield forwhole procedure was about 80% including a wash-out efficiency
from the membrane filter which was used as a collector in thegas-jet transport system. The Bk fraction was measured within
30 min from the end of bombardment. As the separation time
is comparable to the theoretically predicted half-lives11 of 252 Bk(23.3 min) and 253 Bk (51.3 min), the present separation method
can be utilized to the observation of these nuclides.
4. Conclusion

Figure 6. Elution curves of Hf, Am, Cf, and Bk in hydrochloric acid–methanol system.

and depicted in Figure 4. The values of the ionic radii given by
Shannon9 were used. As the ionic radius of Sm is close to thatof Bk, the predicted chromatogram for Sm is also drawn in thefigure. It is expected that the separation for Bk is completed inabout 35 min and the separated fraction of Bk will be contaminated by small amounts of Cf, Eu, and Sm if exist.
3.2. Hydrochloric–Methanol System. Group separationof actinides from lanthanides has been made by an anion ex-Hydrochloric acid–methanol system is found to be more efficient compared with nitric acid–methanol system for the rapid
separation of Bk. The elution behavior of Bk in the anion exchange with hydrochloric acid–methanol was obtained, which
can be effectively utilized to the observation of unknown isotopes of Bk.
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158 J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002
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