JAEA-Conf 2011-002 - 日本原子力研究開発機構
JAEA-Conf 2011-002 - 日本原子力研究開発機構
JAEA-Conf 2011-002 - 日本原子力研究開発機構
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<strong>JAEA</strong>-<strong>Conf</strong> <strong>2011</strong>-<strong>002</strong><br />
was large. The activation method is not applicable for thermal neutron capture cross section<br />
measurements since the residual nuclei are stable. Recently, Nakamura et al. measured the<br />
thermal neutron capture cross sections of 93Zr and 107Pd with a prompt -ray spectroscopy<br />
[5,6] and gave the only available datum for 107Pd. Though Pomerance also measured the<br />
thermal capture cross section of 93Zr with a pile oscillator method [7,8], there is a large<br />
discrepancy between two data with different methods. For 99Tc and 129I, a number of<br />
experimental data with the activation, lead spectrometer, prompt -ray and TOF methods<br />
were reported. However, the accuracy of experimental data for 99Tc and 129I was not enough<br />
since those were considered as the first priority nuclei for a transmutation.<br />
As mentioned above, the current status of experimental data is not sufficient both in<br />
quality and in quantity. This is because it is not easy to prepare enough amount of sample<br />
with a high purity. To overcome the difficulty, we have started a series of experimental studies<br />
for LLFPs using the Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI)<br />
which was installed at the neutron Beam Line No.4 (BL04) of the Material and Life science<br />
experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC) [9].<br />
Neutron capture rays from a sample were measured with a 4 Ge spectrometer using the<br />
TOF method. A high intensity pulsed neutron source makes it possible to measure the capture<br />
rays accurately with a small amount of sample. Moreover, the background due to impurities<br />
contained in a sample can be removed from the observed events using Ge detectors with a<br />
high energy resolution. In this paper, the preliminary results of 93Zr, 99Tc and 107Pd are<br />
reported.<br />
2. Experimental Procedure<br />
The samples of 93Zr, 99Tc and 107Pd were purchased from the Oak Ridge National<br />
Laboratory (ORNL) of USA, the Research Institute of Atomic Reactors (RIAR) of Russia and<br />
the Nuclear Research and consultancy Group (NRG) of Netherlands, respectively. The metal<br />
or oxide powder of 93Zr, 99Tc and 107Pd were encapsulated in aluminum disk-shaped containers.<br />
A sintered natural boron sample was used for the measurement of the incident neutron flux<br />
on the sample. A crystal of NaCl sample which emits well-known rays from the neutron<br />
capture of chlorine was also used as a standard -ray source. The characteristics of samples<br />
and containers are shown in Table 1. Isotopic purities of LLFP samples were determined with<br />
a Thermal Ionization Mass Spectrometer (TIMS) as shown in Table 1 except for 99Tc sample<br />
which contains no isotopic impurities. The net weight of 99Tc was 78 mg. The net weights of<br />
93Zr and 107Pd were determined as 470 and 20 mg using the weights of powder and the<br />
isotopic purities, respectively.<br />
The neutron capture cross section measurements have been performed at the ANNRI.<br />
The pulsed-neutron beam was produced by spallation of 3-GeV proton beam at the Japan<br />
Spallation Neutron Source (JSNS) [10] of MLF. The accelerator was operated in a<br />
double-bunched mode at a power of 120 kW and repetition rate of 25 Hz. The 4 Ge<br />
spectrometer composed of two cluster and eight coaxial Ge detectors surrounded by BGO<br />
Compton suppression detectors was placed at a distance of 21.5 m from the pulsed neutron<br />
source. In this work, we used only two cluster Ge detectors. Each sample was set at the center