Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 2, pp. N1-N3, 2005

Notes
Simultaneous Observation of Volatility of Zr, Hf, and Rf Chlorides
Tetsuya Kaneko Sato,*, a, b Kazuaki Tsukada,b Masato Asai,b Kazuhiko Akiyama,bHiromitsu Haba,c Atsushi Toyoshima,b, d Sawako Ono,a Toshiyuki Hirai,a Shin’ichi Goto,aShin’ichi Ichikawa,b Yuichiro Nagame,b and Hisaaki Kudoa
aDepartment of Chemistry, Faculty of Science, Niigata University, Niigata 950-2181, Japan
Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, JapancRIKEN, Wako, Saitama 351-0198, Japan
dGraduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japanb

Received: March 9, 2005; In Final Form: September 20, 2005
85

Zr, 169Hf, and 261Rf were produced simultaneously from natGe(18O, xn), natGd(18O, xn), and 248Cm(18O, 5n) reactions, respectively, and the volatility of their chlorides was examined using an isothermal gas chromatographicsystem. The observed gas chromatogram indicated that ZrCl4, HfCl4, and RfCl4 had almost similar volatility.

1. Introduction
The group 4 elements zirconium (Zr) and hafnium (Hf) havequite similar chemical properties and the chlorides of these twoelements in a macro amount have almost equal volatility.1 The
first transactinide rutherfordium (Rf) is a group 4 element of theperiodic table and is expected to have the chemical property
similar to those of Zr and Hf. The modern relativistic molecular orbital calculation2−4 predicts that RfCl4 is slightly morevolatile than ZrCl4 and HfCl4, whereas the simple extrapolationof classic periodic trend predicts a less volatile property for
RfCl4.5An isothermal gas chromatograph is a widely used tool toinspect the relative volatility of the chloride of the group 4 elements and used frequently to compare the volatility of transactinide elements with their homologues. Türler et al.6 reported
that the chlorides of Hf and Rf had quite similar volatility. On
the other hand, Kadkhodayan et al.7 reported that ZrCl4 and RfCl4
had almost equal volatility and HfCl4 was less volatile than ZrCl4
and RfCl4. These two experiments were carried out by using
tracer scale samples. Thus, the observed trend needs not coincidewith that shown in Reference 1. However, the two researchgroups claimed obviously the difierent trend of the volatility ofZr, Hf, and Rf. These two previous findings were obtained byobserving separately the volatility of each element. Therefore,
there is a doubt whether each experiment was carried out exactly
in the identical condition. Türler et al.8 re-investigated thevolatility of HfCl4 and RfCl4 by observing simultaneously theirisothermal chromatograms and reported that RfCl4 was morevolatile than HfCl4. But they did not observe the volatility ofZrCl4.
As described above, the volatility of the chlorides of the group
4 elements including Rf is a still challenging research target inmodern chemistry. The objective of this work is to examine thetrend of the volatility of ZrCl4, HfCl4, and RfCl4 by inspecting
simultaneously recorded their isothermal gas chromatograms.
2. Experimental

chromatographic apparatus, and an α-particle detection system.
In order to study the isothermal gas chromatographic behavior ofZr, Hf, and Rf chlorides under a strictly identical experimental
condition, the isotopes of these elements, 85Zr, 169Hf, and 261Rf,
were simultaneously produced and their volatility was inspected
simultaneously. For the production of these isotopes, we used
two targets; one is a 248Cm target and the other is a Ge and Gd
mixed target. The 248Cm target of 490 µg cm−2 in thickness and 5mm in diameter was prepared by electrodeposition of Cm(NO3)3
from isopropyl alcohol onto a 2.2 mg cm−2 thick beryllium
backing foil. The mixed target was prepared as follows. Initiallynat
Gd of 180 µg cm−2 in thickness and 5 mm in diameter was electrodeposited on a 2.07 mg cm−2 thick beryllium foil. Then natGeof 210 µg cm−2 in thickness was deposited on the surface of Gdby vacuum evaporation. The two targets were mounted in atarget chamber as shown in Figure 1.
The irradiation was performed at the JAERI tandem accelerator. The isotope 261 Rf (T 1/2 = 78 s) was produced in the248
Cm(18O, 5n) reaction, while 85Zr (T1/2 = 7.86 min) and 169Hf(T1/2 = 3.24 min) were produced in natGe(18O, xn) and natGd(18O,xn) reactions, respectively. The 18O6+ beam energy was 94
MeV at the middle of the 248Cm target. The average beam
intensity was about 200 particle nA. The nuclear reaction
products recoiling out of the targets were transported to the gas
chromatographic system via the He/KCl gas-jet transportsystem through a 2.2 mm inner diameter stainless steel capillary. The stainless steel capillary was employed in order toGe/Gd target

HAVAR foil
2.0 mg cm-2

18O beamwater cooledbeam stopper

HAVAR foil
2.0 mg cm-2248Cmtarget

He coolinggas
electric furnace

He cooling gas
He/KCl gas-jet

reclusteraluminum jacket chamber

reactionchamber

He/KCl gas-jetwith reaction products
quartz wool

An experimental set-up used in the present work is schematically shown in Figure 1. It consists of a target and recoil chamberarrangement with a He/KCl gas-jet system, an isothermal gas

heat sink

isothermal column

He/KClgas-jet

chlorinating agent(Cl2 /CCl4)
rotationg wheel

MANON
Si PIN photodiodes*Corresponding author. E-mail: sato.tetsuya@jaea.go.jp. FAX:
+81-29-282-5927.

He/KCl gas-jetwith chemicallyseparated isotopes

Figure 1. Schematic diagram of experimental set-up.

© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 11/07/2005

catcher foil
120 mg cm-2

SatoJ. Nucl. Radiochem. Sci., Vol. 6, No. 2, 2005

3. Results and Discussion
Volatile chlorides of Zr and Hf were efficiently formed in
the reaction chamber at the temperature of above 800 ˚C andthe chlorination yields for Zr and Hf were evaluated to beabout 80% at 1000 ˚C. After passing through the isothermalcolumn, about 25% of the volatile chlorides was transported tothe detection position. Lanthanides that were produced as
nuclear reaction by-products did not pass through the column.
As the chlorides of lanthanides are non-volatile under theexamined condition, only volatile species passed through thecolumn.
Figure 2 shows an α spectrum taken at the temperature of theisothermal column of 400 ˚C and the total beam dose of 2.5 ×1016 particles. The α-particle group in the energy range of
8.00 – 8.40 MeV was assigned to 261Rf and its daughter 257No(T1/2 = 26 s). The spectrum is contaminated by α-particles from211m,212m
Po which were produced by nucleon-transfer reaction
on a Pb impurity in the target and formed volatile compounds.
Due to much effort to remove the Pb impurity from the 248Cmtarget, the background was greatly reduced compared with thatby Kadkhodayan et al.7
In Figure 3 the measured relative yields of 261Rf together
with those of 85Zr and of 169Hf are shown as a function of thetemperature of the isothermal column. The yields at 400 ˚C arenormalized to 100%. Above the temperature of 300 ˚C, Zr, Hf,and Rf chlorides start to pass through the isothermal column.
The passing yields of those chlorides increase steeply with theincrease of the temperature, and reach the maximum around350 ˚C. This steep increase of the yield with the temperature

50

Po

261

Rft1/2=78 s

211m

40

257

30

No

20

Po

Rf + 257No

t1/2=26 s

10212m261

Number of Events

avoid oxygen entering through a capillary wall. The concentration of oxygen impurity in He gas was monitored with an
oxygen monitor and was kept to be less than 30 ppm.
Domanov et al.9 reported that in gas chromatographic experiments chlorination of Zr and Hf is not affected by oxygen inthis order of concentration. The flow rate of the He carrier gas
was 1.2 L min−1.
The isothermal gas chromatographic apparatus consists of areaction chamber, an isothermal column, and a re-clusteringchamber. Each section is made of quartz and connected in aseries. The isothermal column is a spiral tube of 2000 mm longand inner diameter of 3 mm. The reaction chamber and theisothermal column can be independently heated by electric
furnaces up to a maximum temperature of 1200 ˚C and 500 ˚C,respectively.
The transported nuclear reaction products were stopped atquartz wool in the reaction chamber and a mixture of chlorine(Cl2) gas and carbon tetrachloride (CCl4) vapor was introduced forchlorination. Volatile tetrachlorides of Zr, Hf, and Rf wereformed in the reaction chamber at 1000 ˚C and passed through theisothermal column. The volatile species, after leaving the column,
entered the reclustering chamber, where they were caught by new
KCl aerosols in He gas, and were transported to the detection
system. An HPGe γ-ray spectrometer system was employed forthe detection of characteristic γ-rays of 85Zr and 169Hf, and α-particles were measured with MANON (Measurement system for
Alpha-particle and spontaneous fissioN events ON-line),10, 11
having a rotating wheel detection system with an 80 cm diameter
wheel. The activity-laden aerosols were deposited on polyethylene terephthalate foils of 120 µg cm−2 in thickness and 20 mm indiameter at the periphery of an 80-position stainless steel wheel.
The wheel was periodically rotated to set each foil at the center of
one of the six pairs of Si PIN photodiodes. Each sample wascollected for 30 s and the spectrum was aquired for 30 s with one
detector pair, that is, 180 s in all. Each detector has an active areaof 18 × 18 mm2 and the detection efficiency was approximately
40% for α particles. The energy resolution (FWHM) was about
30 keV for the top detectors and 100 keV for the bottom ones.

0789101112Figure 2. α Spectrum after chemical separation.

Relative Yield / %N2

10085m Zr
169 Hf261Rf

500200300400

Isothermal Temperature / ˚CFigure 3. Relative yields for 85Zr, 167Hf, and 261Rf chlorides. Thecurves are the calculated results based on a Monte Carlo simulation.13
Zr: dot-dashed line, Hf: dashed line, Rf: solid line.

is characteristic of a simple adsorption-desorption transportmechanism12 and oxychlorides were not involved in chromatographic transportation because of low oxygen concentration in
the system.9 The lines in Figure 3 are the calculated results of aMonte Carlo simulation based on the Zvára’s model.13
In the present work, KCl aerosol was used for the transportation of nuclear reaction products, thus the surface of the chromatographic column would be partially coated with a thin layerof KCl. In such a case, the temperature at which the volatile
species pass through the column tends to be higher comparedwith those for pure quartz surface.14, 15 However, it may bereasonable to consider that the order of relative volatility for theelements of interest is not affected by materials of a columnsurface.
It was clearly shown that the volatility of Zr, Hf, and Rf chlorides closely resemble each other under the identical experimental conditions. From this result, we may conclude that thevolatility of Zr and Hf chlorides is quite similar to each other as
expected from the standard sublimation enthalpy of Zr and Hf
chlorides in macro scale and that the volatility of Rf chloride isnearly the same as those of Zr and Hf. The latter conclusion isqualitatively consistent with the prediction by the relativistic
calculations.2−4
Acknowledgement. This work was supported in part by theGrant-in-Aid for Scientific Research (13640556) of the Japan
Society for the Promotion of Science.

Simultaneous Observation of Volatility of Zr, Hf, and Rf Chlorides

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