JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
Table 1. Characteristics of samples
Sample
Chemical
Form
Isotopic
Compsition [%]
weight of
sample [g]
Diameter of
sample [mm]
Outer diameter of
container [mm]
93
Zr ZrO2 18.9 3.31 20.0 30.0
99 Tc Tc 100 0.078 6.3 9.0
107 Pd Pd 15.3 0.137 4.5 9.0
10 B B 19.9 0.083 10.0 ---
35 Cl NaCl 75.8 0.500 10.0 ---
of the spectrometer and in a neutron beam duct. The neutron beam was collimated to a
diameter of 3 or 7 mm at the sample position using a rotary collimator system [11].
The signals from the Ge crystals were stored using a data acquisition (DAQ) system
[12,13] with event-by-event mode as three-dimensional data of -ray pulse height, TOF, and
time-interval between coincidence signals. Random timing pulses were also fed into every
pre-amplifier from a random generator for making a dead-time correction [14].
The measurement times for 93Zr, 99Tc and 107Pd samples were about 52, 25 and 31 hours,
respectively. In order to estimate the background, a measurement with an empty aluminum
container was also done.
3. Data Processing and Analysis
The neutron flux at the sample position was deduced from the TOF spectrum
corresponding to the 478-keV ray emitted via the 10B(n,) 7Li reaction. The neutron capture
cross section data were taken from JENDL-3.3 [15].
For TOF spectrum of 99Tc, the background subtraction was performed using the capture
-ray yields from an empty aluminum container. The normalization of the background TOF
spectrum was performed on the basis of the prompt -ray emitted from the neutron capture
reaction of 27Al. For 93Zr and 107Pd which contain a large amount of impurities, the events
related to an objective nuclide were extracted with a ground-state transition method [16,17].
In the case of 93Zr, five ground-state transitions from the 919-, 1671-, 2846-, 2908-keV states
and the capture state were clearly observed in the -ray pulse-height spectrum. Especially, the
very strong ground-state transition at 919 keV is remarkable and the intensity amounts to
about 83 % of the total intensity of five ground-state transitions. We have gated on those -ray
peaks corresponding to the ground-state transitions and derived the net TOF spectrum for
93Zr. The background component was estimated from the TOF spectra for the continuous
region around the -ray peaks of ground-state transitions. The absolute neutron capture
yields were derived with the full-energy peak efficiency curve for the 4 Ge spectrometer. In
the case of 107Pd, it is summarized how to reject the contribution due to impurities. The
details of analysis have been described in Ref.[18]. The components due to 105Pd mainly
contained in the sample were extracted by gating on the ground-state transition ray peak at
512 keV.
The neutron capture cross sections of 93Zr, 99Tc and 107Pd were derived from the neutron
flux and the net TOF spectra. The corrections were made for the self-shielding and
multiple-scattering of neutron in the sample, dead time, and so on.