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

提出日 Date of Report
2014/7/04

課題番号 Project No.

装置責任者 Name of responsible person

2013B0235

Hideo Harada

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Measurement of neutron capture by Be-9 up to 1 keV

ANNRI / BL-04

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Hiroyuki Makii

2014 3/5-7

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.
In this experiment, we used a following sample.
Name of sample chemical formula from shape

Quantity

Beryllium

20 mg

Be

solid

We also used B and C samples to estimate the neutron flux and to identify the background events,respectively.

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.

The experiment has been carried out with use of the ANNRI installed at beam line BL-04. The Ge
spectrometer consists of two cluster Ge detectors surrounded by BGO anti-Compton shields set at theneutron flight length position of L = 21.5 m was used to detect the -rays from the samples. A Be sample witha diameter of 5 mm and a thickness of 0.8 mm were located in the beam duct made of aluminum. The purposeof this study was to deduce the excitation function of 9Be(n,)10Be reaction and the -ray branching ratio oftransitions from a neutron capture state to low-lying states in 10Be in the energy region of En = 1.4 meV – 1.0
keV using time-of-flight (TOF) technique. Because of small cross section was expected for the 9Be(n,)10Be
reaction, particular attention should be given to identify the background due to neutron scattered by thesample. For this purpose, a C sample and an empty case were irradiated in the same arrangement. Here,neutron flux was obtained by 10B(n, )7Li reaction by using a B sample since the cross section of this reaction
is well known. Measuring time, total dose of protons for each sample are summarized in Table 1. Proton beam
power in this study was 300 kW.
Due to the simple structure of the nuclear levels of 10Be, the 9Be(n,)10Be cross section can be obtained12. 実験方法及び結果（つづき） Experimental method and results (continued)
Table 1: Measurement time and total dose of proton beam.
sampleMeasuring time [hours]

Proton dose (1019 protons)

Be

20.1

3.25

C

10.1

1.03

Empty

8.2

1.46

B

4.8

0.87

by summing the partial cross sections. Here the neutron capture in
9Be is expected to proceed through direct radiative transitions to theground (J = 0+), 1st excited (2+), and 2nd excited (2+) states in 10Be as
shown in Figure 1. In this study, we will deduce the partial crosssections and -ray branching ratio from the intensities of 6.81 MeV,
3.44 MeV, and 0.85 MeV -ray peaks due to the direct neutron capture
into the ground, 1st excited, and 2nd excited states in

10Be,respectively. Figure 2 shows -ray spectra for the Be sample [(a), (c),and (e)] and the C sample [(b), (d), (f)] obtained by gating the neutronenergy regions of 20 ≤ En ≤ 80 meV [(a) and (b)], 80 ≤ En ≤ 120
meV [(c) and (d)], and 500 ≤ En ≤ 1500 meV [(e) and (f)]. Here, theFigure 1. Level scheme of 10Be.

spectra obtained with the C sample contained the background events

due to the neutrons scattered from the sample. In the spectra of the Be sample, we clearly see the 6.81 MeV
peaks. On the other hand, in the spectra of the C sample, we did not observe any -ray peaks in the 6.81 MeVpeak region, although the strong background peak at 6.86 MeV due to 207Pb(n,)208Pb reaction is seen in thespectra of each sample. From Fig. 2, we found that the background due to neutrons would not provide any
problems to yield estimation of the 6.81 MeV peak. The study of the background event due to neutrons forother -ray peaks and the analysis to determine the absolute partial cross section values are now in progress.
800Counts / keV

600
400(a)

6.86
100

6.70

6.86(c)6.81150

6.81

6.70

100

5060(b)200100
6700

6800

6900

-ray energy (keV)

60(d)

40

40

20200

6.70

6.86
6.81

50200300(e)

6700

6800

6900

-ray energy (keV)

0(f)

6700

6800

6900

-ray energy (keV)

Figure 2. -ray spectra taken by the Ge spectrometer with the Be sample [(a), (c), and (e)] and the C sample[(b), (d), and (f)]. These spectra were obtained by gating the neutron energy regions of 20 ≤ En ≤ 80 meV [(a)and (b)], 80 ≤ En ≤ 120 meV [(c) and (d)], and 500 ≤ En ≤ 1500 meV [(e) and (f)]. Here 6.81 MeV -ray peakis due to the 9Be(n,)10Be reaction. On the other hand, 6.86 MeV one is due to the 207Pb(n,)208Pb reaction.
2