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

課題番号 Project No.

装置責任者 Name of responsible person

2012A0142

Hideo Harada

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

62

Ni(n, γ) reaction measurement

BL4

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Mariko Segawa

2012/05/20 10:00-2012/5/25 9:00

所属 Affiliation
Japan Atomic Energy Agency
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.
The high purity sample (96 % enriched in 62Ni) of powder form and 197Au (metal sheet) were used.

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.

Introduction: The construction of stellar models of nucleosynthetic yields of massive stars of various
metallicities is quite im portant for finally constructing models for the chemical evolution of galaxies. Although
the calculated nucleosynthetic yields of most isotopes from A = 16 to A = 90 are in good agreement with thesolar abundances, the isotope 62Ni is overproduced. The origin of the overproduction is considered to be due toresidual uncertainties in the stellar models and/or in the nuclear physics inputs used for the calculation of thenucleosynthetic yields of massive stars. Previously, the MACS at 30 keV was derived as being 37.0 ± 3.2 mbarn, about 3 times larger than the value used for the nucleosynthetic yield estimate of massive stars. Here, inorder to derive the MACS, we have to know the cross sections below 5.5 keV. Thus, we need to know thecontribution of the s-wave resonance at Er=4.54 keV precisely, since its contribution to MACS of 62Ni could besignificant.
Aim: In the present study, we aimed to obtain the pulse-height spectrum for 62Ni(n,γ) reaction with good signal
to noise ratio below 5.5 keV and drive the absolute neutron capture cross section for 62Ni(n,γ) reaction, using
Ge-detector system and NaI detector system, respectively.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Experiments:(1) The pulse-height spectrum for 62Ni(n,γ) reaction taken by Ge-detectors and the resonance at 4.5keV
The pulse-height spectrum for 62Ni(n,γ) reaction was obtained with good signal to noise ratio below 5.5 keV.
Fig.1shows the TOF spectrum for 62Ni(n,γ) reaction obtained by Ge-detectors at ANNRI of BL04. The resonanceclearly seen at the black arrow corresponds to Er= 4.5 keV. We put the gates (gate1 and gate2) on resonance andoff-resonance regions on the Fig.1 indicated as blue and green lines. Fig.2 shows the γ-ray spectrum for the gate1
and gate2 of the TOF spectrum. The γ-ray peaks at Eγ= 6836keV was the γ-ray emitted from the captured state of63

Ni to that of ground state. We could obtain the sharp peak on the resonance energy region at Er = 4.5 keV.

Now, we estimate net γ-ray yields on careful analytical evaluation in order to obtain the capture cross
gate1
gate2

104

10105

c.s g.sE=6838keV

Count/100ns

103Count/2keV

Er = 4.5 keV104

103

5Count/2keVsection.

gate101000

gate2
2000

3000

4000

102
6000
6500
-ray Energy [keV]

103

102

TOF [100 ns/ch]
Fig.1 TOF spectrum for 62Ni(n, γ) reaction obtained byGe-detector.

101

02000

4000

6000

-ray Energy [keV]

8000

Fig.2 Pulse-height spectrum for 62Ni(n, γ)(2) The capture cross section for 62Ni(n,γ) reaction usingreaction obtained by Ge-detector.

by NaI detector system. However, in the neutron energy higher than a few
keV, the background neutron scattered by the collimator, which was placed
between Ge-detectors and the NaI detector system, was found to be severe
background. Because such scattered neutron could enter the NaI detector,
the γ-ray from 127I(n, γ) reaction were observed in the TOF spectrum takenby the NaI detector. Since the γ-ray energy of 62Ni(n, γ) and 127I(n,127

As our original plan, the absolute capture cross section would have obtainedI(n,) Peak Counts/ Pulse

NaI-detectorγ)reaction are very close, it was difficult to distinguish the true γ-ray of6221.6
1.2
0.8

0.4

010203040

Polyethlene thickness [cm]Ni(n, γ) reaction. Hence, in the beam time, the basic background study

was performed in order to reduce the scattered neutron. The thickness of theborated polyethylene shield set between the collimator and NaI detector wereincreased from 0 to 45 cm, and background γ-ray owing to 127I(n, γ) reaction

Fig.3 Polyethylene thickness
and background count rate

was studied as shown in Fig. 3. Owing to the result and other results taken by the developing group, the collimatorand neutron shield for NaI-detector has been improved.
2