実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF	 Experimental Report
課題番号 Project No.2012A0122

提出日 Date of Report
2013/10/15

装置責任者 Name of responsible person
Hideo Harada

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Measurement of Angular Distribution of Prompt Gamma-rays

BL04

from Radiative Capture Neutron Reactions

実施日 Date of Experiment

実験責任者名 Name of principal investigator2012/11/02-2012/11/08

Hirohiko Shimizu
所属 Affiliation
Nagoya University
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.
La metal.

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.

We placed a lanthanum foil at the normal sample position, which is located 21.5 m from the moderator surface,and acquired gamma-ray signals from the set of cluster germanium detectors. The amplitude of thegamma-ray signals from individual germanium crystals were recorded as a function of neutron time-of-flight.
The obtained time-of-flight spectrum is shown in Fig.1, in which the gamma-ray signals are histogramed as afunction of neutron time-of-flight. P-wave and s-wave resonances of 139La are observed at tof=1.8ms and18µs, which corresponds to the neutron energy of En=0.75 eV and En=72 eV. Random pulser signals with aconstant rate were merged into the data acquisition system for the correction of the deadtime of thegermanium detectors and the data acquisition system. The pulser signals had a constant amplitude beyond thepulse height region of physics signals and were unambiguously distinguished from physics signals. Figure 2
shows the observed rate, that was distorted from the constant rate due to the dead time of the detector anddata acquisition system. The dead time correction was applied so that the pulse signals have a constant rateover the neutron time-of-flight.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
0.018ms ⇄ En=72 eV (139La)

pulser countgamma-ray counttof=1.8ms ⇄ En=0.75 eV
p-wave 139La

calculated neutron flux [arbitrary unit]

0.9ms ⇄ En=3 eV (138La)

time from proton pulse [s]time from proton pulse [10ns]

time from proton pulse [10ns]

Fig.1 Raw time-of-flight spectrum

Fig.2 Pulser signal spectrum

Fig.3 Calculated intensity of incident neutrons

Ep+Γp Ep-Γp

gamma-ray countcorrected tof spectrum [arbitrary unit]Ep

out ofp-wave
resonance(s-wave)
Pulse Height [ADC ch. ~keV]time from proton pulse [10ns]

Fig.4 Corrected TOF spectrum

Fig.5 Gamma-ray spectrum

The corrected TOF spectrum with the dead correction and normalized by the incident neutron spectrum isshown in Fig.4. We observed no apparent p-wave contribution in the red region in the figure, which should haveno angular distribution. The detection efficiency and angular coverage of all germanium crystals will benormalized so that gamma-ray yields are isotropic in that region.
The integrated gamma-ray spectrum is shown in Fig.5. Three gamma-ray transitions are clearly identifiedin the figure. They are considered to be corresponding to the ground state 3- (green in the figure) , 5- and 4-.
We are converting the gamma-ray counts into the angular distribution

The A1 and A3 are dependent on the neutron energy as described in the proposal. Currently, the statisticalerror of these terms are approximately 0.01 and 0.015, respectively. Further analysis to identify the accuracyof correction and the systematic errors is in progress2