160
C. H. Pyeon
(97% argon and 3% nitrogen). For measuring capture reaction rate ratio, a test foil
237 Np was set in the BTB fission chamber, and a reference foil gold-197 (
197 Au)
was attached to the Al sheath containing the chamber. The reference foil
197 Au was
a normalization factor that has the capture reactions
197 Au(n, γ)
198 Au, to obtain
capture reaction rate ratio:
237 Np/
197 Au.
The BTB fission chamber was set at the special void element position in HEU-Pb
zone (15, O; Fig. 6.4a), whereas in HEU-PE zone the position was (15, K; Fig. 6.4b).
The hard and intermediate spectra are shown in Fig. 6.5. As shown in Fig. 6.4a,
b, one and five normal fuel assemblies were added to the cores, respectively, when
comparing with reference core shown in Fig. 6.1. Further fuel assemblies were added
to reach criticality for two irradiation experiments at the critical state shown in
Table 6.1. A series of critical irradiation experiments on
237 Np and
241 Am foils was
conducted under the following core conditions: irradiation time 1 h; reactor power
3.5 W; neutron flux (4.73 ± 0.24) × 10
7 s
−1 cm
−2 .
6.1.1.3
237 Np and
241 Am Foils
Two
237 Np and
241 Am thin test foils (both 99.99% purity, 20 mm diameter, and
4 nm thick), electro-deposited on Al backing (28 mm diameter and 0.2 mm thick),
had an isotopic mass, respectively, equal to 89 and 15 μg as shown in Table 6.2.
Thin
235 U reference foils (20 mm diameter and 0.6 nm thick, 5 or 10 μg weight),
used to determine the fission reaction rate ratios, had a 99.91% enrichment. Test and
reference
237 Np and
197 Au foils (8 mm diameter and 0.05 mm thick) were used to
determine the capture reaction rate ratio. After the irradiation at critical state,
237 Np
and
197 Au capture reaction rates were deduced by the saturated radioactivity obtained
from the γ-ray spectra of irradiated test and reference foils, respectively, with the
use of a high-purity germanium (HPGe) detector. The γ-ray energy generated by
the capture reactions was as follows: 984.45, 1025.87, and 1028.53 keV in
237 Np;
411.80 keV in
197 Au, as shown in Table 6.3.
6.1.2 Experimental Analyses
6.1.2.1 Experimental Analyses
During the irradiation experiments, the pulsed-height signals (voltage) induced by
fission reactions were stored by the use of a multi-channel analyzer to discriminate
the signals originated from fission products generated by fission reactions. In the
HEU-Pb zone, pulsed-height distributions were clearly observed at two peaks of
237 Np (2.0 V and 5.0 V) and
235 U (1.6 V and 3.4 V) foils attributed to light and heavy
fragments in fission products, as shown in Fig. 6.6, demonstrating the counts by their
fission reactions. For
241 Am, one peak (0.1 V) was observed in the pulsed-height
distribution shown in Fig. 6.7, and the counts by fission reactions were obtained by
C. H. Pyeon
(97% argon and 3% nitrogen). For measuring capture reaction rate ratio, a test foil
237 Np was set in the BTB fission chamber, and a reference foil gold-197 (
197 Au)
was attached to the Al sheath containing the chamber. The reference foil
197 Au was
a normalization factor that has the capture reactions
197 Au(n, γ)
198 Au, to obtain
capture reaction rate ratio:
237 Np/
197 Au.
The BTB fission chamber was set at the special void element position in HEU-Pb
zone (15, O; Fig. 6.4a), whereas in HEU-PE zone the position was (15, K; Fig. 6.4b).
The hard and intermediate spectra are shown in Fig. 6.5. As shown in Fig. 6.4a,
b, one and five normal fuel assemblies were added to the cores, respectively, when
comparing with reference core shown in Fig. 6.1. Further fuel assemblies were added
to reach criticality for two irradiation experiments at the critical state shown in
Table 6.1. A series of critical irradiation experiments on
237 Np and
241 Am foils was
conducted under the following core conditions: irradiation time 1 h; reactor power
3.5 W; neutron flux (4.73 ± 0.24) × 10
7 s
−1 cm
−2 .
6.1.1.3
237 Np and
241 Am Foils
Two
237 Np and
241 Am thin test foils (both 99.99% purity, 20 mm diameter, and
4 nm thick), electro-deposited on Al backing (28 mm diameter and 0.2 mm thick),
had an isotopic mass, respectively, equal to 89 and 15 μg as shown in Table 6.2.
Thin
235 U reference foils (20 mm diameter and 0.6 nm thick, 5 or 10 μg weight),
used to determine the fission reaction rate ratios, had a 99.91% enrichment. Test and
reference
237 Np and
197 Au foils (8 mm diameter and 0.05 mm thick) were used to
determine the capture reaction rate ratio. After the irradiation at critical state,
237 Np
and
197 Au capture reaction rates were deduced by the saturated radioactivity obtained
from the γ-ray spectra of irradiated test and reference foils, respectively, with the
use of a high-purity germanium (HPGe) detector. The γ-ray energy generated by
the capture reactions was as follows: 984.45, 1025.87, and 1028.53 keV in
237 Np;
411.80 keV in
197 Au, as shown in Table 6.3.
6.1.2 Experimental Analyses
6.1.2.1 Experimental Analyses
During the irradiation experiments, the pulsed-height signals (voltage) induced by
fission reactions were stored by the use of a multi-channel analyzer to discriminate
the signals originated from fission products generated by fission reactions. In the
HEU-Pb zone, pulsed-height distributions were clearly observed at two peaks of
237 Np (2.0 V and 5.0 V) and
235 U (1.6 V and 3.4 V) foils attributed to light and heavy
fragments in fission products, as shown in Fig. 6.6, demonstrating the counts by their
fission reactions. For
241 Am, one peak (0.1 V) was observed in the pulsed-height
distribution shown in Fig. 6.7, and the counts by fission reactions were obtained by