実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report
2016/05/25

課題番号 Project No.

装置責任者 Name of responsible person

2015A0160

Toh Yosuke

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Measurements of Total Cross Sections of Np-237

BL04 ANNRI

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Kazushi Terada

2016/03/08-2015/03/30

所属 Affiliation
JAEA
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Neputunium-237 sample were moved to Kyoto university research reactor, so we used an 241Am sample withactivity of 950 MBq for this experiment. Chemical formula of the Am sample is AmO2 , and net weight of Am is
7.5 mg. The powder of AmO2 formed in a disk by mixing Y2O3 powder. Then, the Am disk was completely
sealed in Al container with a thickness of 0.1 mm. Figure 1. shows the Am sample.

Figure 1. Am sample.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Measurements of neutron total cross sections of 241Am have been performed by the time-of-flight (TOF)
method with a 6Li-glass neutron detector. The 6Li-glass detector manufactured by OKEN with dimensions of 10cm x 10 cm and thickness of 1 cm using enriched 6Li (6Li>90%) was used to obtain transmission neutron TOF
spectra. Transmitted neutrons from the sample are detected by the 6Li-glass detector via the 6Li(n,α)3H reaction.
The distance between the 6Li-glass detector and the neutron source was 29 m. Signals from the 6Li-glass detector
were amplified with the ORTEC 474 timing filter amplifier, and the TOF and the Pulse Height (PH) of each
event were recorded event-by-event in a list data format file. We repeated the measurements of the 241Am
sample (Am run) and Am sample container except for Am (dummy run) to obtain the neutron transmission ratio.
Total cross sections of Au are well known. Hence, measurements of Au samples with thicknesses of 10 and 100
m (Au run) were carried out to check validity of the data analysis. Lead shielding with a thickness of 10 cm
was placed on the neutron beam axis to reduce the dead time of the Li-glass detector caused by intense gamma
flash from the spallation neutron source. Neutron notch filters of natMn, natCo, natIn and natAg were utilized toestimate the backgrounds from the TOF spectra obtained by the 6Li-glass detector by the black resonancetechnique.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Total cross sections are calculated from the equation as follows:exp(  n total ) Am
AmC Foreground CBackground
Dummy
DummyC Foreground CBackgroundwhere σtotal is total cross section, n is sample thickness, C is count from TOF spectrum normalized by neutron
intensity for the Am and dummy runs. In the beginning, dead time corrections were made for TOF spectra
assuming that the measurement system has a fixed dead time of 708 ns for each signal. Figure 2. shows
time-difference between two signals recorded by the measurement system and live-time ratio for the TOF spectrafrom the Au run. A rising edge of the time-difference spectrum is 177 ch., and the channel width is equal to 4 ns.
Dead time corrections were less than 5% in the TOF region after 1.2x104 ns. Then, we are conducting backgroundestimation of the TOF spectra due to gamma flash and scattered neutrons.

Figure 2. Time-difference between two signals was represented in the left figure. Ratio of live-time and TOF
spectrum for the Au run were described in the right figure.
Additionally, measurements of capture cross sections of 241Am have been performed with Ge
detectors at the ANNRI. The Ge detectors consist of two cluster Ge detectors and 8 coaxial Gedetectors. The distance between the neutron source and the Ge detectors was 21.5 m. The sample
was placed at the sample position of the Ge detectors. Lead sheets with a thickness of 5 mm wereplaced in front of the cluster Ge detectors in order to reduce the background caused by gamma-rays
from the decay of 241Am. Gamma-rays emitted from the sample were measured with the Gedetectors. Signals from the Ge detectors were amplified with the amplifier, and the TOF and the PH of each
event were recorded event-by-event. We carried out Am, dummy and blank (no sample) measurements
to determined neutron capture yields of the 241Am. In order to obtain incident neutron energy
distribution, boron sample measurements were carried out. Data analysis is in progress.

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