TRIAC Progress Report - KEK

container of ion source and uranyl nitrate ( nat UO2(NO3)2 / 3M HNO3) solution was
impregnated. After drying in air atmosphere for the formation of UO2(NO3)2-6H2O, the
nitrates were out-gassed and converted to oxides such as U3O8 at about 900 K for about
1.5 hours in argon atmosphere. Then the target container of the oxides is loaded in the
target-ion source system, where the oxides are converted into UCx by in-situ sintering at
about 1800 K for about a half day. The target container (9 mm in diameter and 11-mm
long in case of FEBIAD-B2) is heated by electron bombardment (EB-heating). The
electrons were generated from the filament of the target heater. The potential difference
between the filament and the target container is about 200 V. A certain variation of the
target temperature does not affect the discharge parameters since the target chamber is
equipotential with the anode. The electric power of about 120 W (160 V / 0.75 A) was
supplied for the anode, about 180 W (220 V / 0.8 A) for EB-heating the target container,
when operating at the temperature of 1850 ± 50 K and 1800 ± 50 K, respectively. The
temperatures at the anode and the target were measured with an optical pyrometer and
the corresponding input powers were calibrated with the temperatures. Along this way,
in-situ preparation of UCx target was performed and the typical thickness of the carbide
target corresponds to the thickness of 600-800 mg/cm 2 of nat U. The process for target
preparation is summarized in Fig. 2-3.
Fig. 2-3. Target processing and photograph of the target base material.
The target/ion source was operated at temperature of about 1800 K and at the
pressure approximately 2 x10 -4 Pa. During the operation, ionization efficiencies for
stable xenon and krypton isotopes were periodically checked by using calibrated leaks
of 2.3 x 10 -7 and 4.6 x10 -7 atm cm 3 /s, respectively. The separation yields and
efficiencies for typical uranium fission fragments were summarized in Table 2-2. The
separation efficiency for an isotope is defined as the ratio of the yield mass-separated to
the calculated yield of production.
Although high separation efficiency was observed in the FEBIAD-B2 type ion
source, short-lived isotopes with half-lives shorter than 0.5 s such as 130, 131 In were
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