Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Production of 179mW in the form of a carbonyl complex
M. Huang,＊1 J. Kanaya,＊1 M. Murakami,＊1 H. Haba,＊1 and S. Shibata＊1
We are developing a CO gas-jet technique and plan to
apply it to the separation of neutron-rich isotopes of Sg
produced in the transfer reaction 248Cm + 48Ca. In thispreliminary investigation, we successfully separated 179mW,
the lighter homologue element of Sg, from other heavy ions(89mZr, 28Al et al.) in the form of a volatile carbonylcomplex.
A 24-MeV d beam was extracted from the AVF cyclotronof the RIKEN RI Beam Factory. Five natTa targets werestacked with one natNb target in the sequence
Ta/Nb/Ta/Ta/Ta/Ta. All targets were fixed in an Al holder
with 5-mm distance between each other. The thicknesses ofnat
Ta and natNb target were 7.62 and 0.917 mg/cm2,respectively. Reaction products emitted from the targets
were thermalized and stopped in the He/CO mixed gas.
Elements that could form volatile complexes with the CO
reagent, e.g. W(CO)6, were flushed out from the target
chamber and extracted along capillaries of inner diameter(i.d.) 1.59 or 2.0 mm. After the volatiles were passed
through a PTFE filter (SMC SFB 300-02) mounted at theoutlet of the target chamber and a 2.1-m quartz column(2.0-mm i.d.) immersed in a chiller, they were collectedusing a charcoal filter (ADVANTEC CP20) and subjectedto γ-ray spectrometry with a Ge detector. Because of thebeam irradiation, CO molecules would be decomposed into
carbon and oxygen. Most products adhered to the carbon
particles and were removed by the PTFE filter. The lengthfrom the PTFE filter to the collection site was about 17 m.
Flow rates of He and CO were controlled independently toadjust their concentrations in the target chamber. The lowest
flow rate controlled by the mass-flow meter was 0.2 L/min.
As explained above, reaction products could betransported out in the form of volatile molecules or by using
aerosols. First, to check all the products, a high-intensity
beam with 2.9 particle μA (pμA) as well as 1.2(He)+0.2(CO)L/min mixed gas was used to generate many carbon
aerosols. All nuclear products were efficiently carried to thecharcoal filter by carbon particles without selectivity when
the PTFE filter was removed. The 6.4-min 179mW and4.16-min 89mZr were identified by their γ-energies anddecay curves. The production yields after 1-min collection
were deduced to be 9.86±0.84 and 0.40±0.04 kBq/pμA for179m
W and 89mZr, respectively. By changing the i.d. of thecapillary and increasing the He/CO flow rate, the yield
could not be improved further.
After the PTFE filter was installed, the 221.5-keV γ-lineof 179mW was observed subsequent to 7-min beamirradiation under 0.03 pμA (See Fig.1). Other nuclides,
which could not form volatiles in a CO atmosphere, were＊1

RIKEN Nishina Center- 276 -removed, such as 89mZr. The transport efficiency for 179mW
in the carbonyl form was decreased with the beam intensity
and CO flow rate, but it could be improved by increasing
the He gas flow rate. By changing the i.d. of capillary from1.59 to 2.0 mm, the maximum flow rate of He gas wasincreased from 1.2 to 4.0 L/min, corresponding to about 1
atm in the target chamber. Under 4.0 L/min He flow rate,
the count of 221.5-keV γ-line was improved by a factor of 4(see Fig. 1). The optimal relative transport efficiency for
179m
W was 13.1±2.2%, which was obtained by normalizing
to the production yield of using carbon aerosols as thetransmission medium under 2.9-pμA beam intensity. The
yield of 179mW that passed through an isothermal column atdifferent temperatures was measured, and the results aredisplayed in Fig. 2. By fitting the breakthrough curve with aMonte-Carlo simulation1), the adsorption enthalpy of thecarbonyl complex was determined to be -47±1 kJ/mol,which agrees well with the 46.5±2.5 kJ/mol reported forW(CO)6 in Reference2).

Fig. 1. γ-ray spectra obtained for 179W in the form of avolatile carbonyl complex.

Fig. 2. Yields of 179mW passing through the quartz column.
References
1) I. Zvara: Radiochim. Acta 38, 95-102 (1985)
2) J. Even et al.: Inorg. Chem. 51, 6431-5433 (2012).