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
2/4/2010

課題番号 Project No.

装置責任者 Name of responsible person

2009B0031

Fujio Maekawa

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Experimental study on a calibration method of devices for

NOBORU BL 10

neutrons from thermal to several 100 MeV using a spallation

実施日 Date of Experimentneutron source

1-2/2/2010, 24 h

実験責任者名 Name of principal investigator
Tetsuro Matsumoto
所属 Affiliation
National Institute of Advanced Industrial Science and Technology
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.
No use.

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.

1. Introduction
In the present experimental theme, we have developed neutron measurement devices that can be used in ahigh flux neutron field with a spallation neutron source. Characteristics of the devices are evaluated using theNOBORU facility.
The devices will be applied for the study on single-event phenomenon of a semiconductor and epi-thermal
neutron calibration of radiation protection devices. Experimental hours were 24 hours.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
2. Experiment
2.1 Detector
For the purposes, we must prepare detection devises that can be used in a high flux neutron field. We prepareda Bonner sphere spectrometer in this proposal research.
The Bonner sphere spectrometer is composed of neutron moderators and a spherical 3He proportionalcounter (CENTRONICS SP9 gas pressure 0.2 atm) . We used 6 kinds of moderator for the Bonner sphere
spectrometer as shown in table 1. We prepared the Bonner sphere with the lead to be high sensitive to highenergy neutrons as shown in figure 1.
2.2 Experimental setup
Experiment systems are shown in figure 2. A rotary collimator was inserted in the beam course in order toreduce neutron flux. Moreover, we adopted the low pressure (0.2 atm) 3He proportional counter to performmeasurements in the high flux neutron field. However, pulse height spectra observed with the Bonner sphere
spectrometer was distorted by the gamma flash from the neutron source. Therefore, we set the lead blocks
between the beam shutter and the spectrometer to shield the gamma flash as shown in figure 2.
An incident neutron beam had a spatial distribution because a rotary collimator was inserted in the beamcourse in the present experiment. We assumed a neutron beam with a 50 mm diameter and a uniform
distribution at first. The response function of the spectrometer was derived using the MCNPX monte-carlocode (Nuclear data file is JENDL-High Energy file [1]) under this condition. The response function is shown infigure 3.
Neutron spectra were derived by means of an unfolding method using the response function and observedcounts. We used MAXED and GRAVEL codes included UMG3.3 package [2] as an unfolding program. The
GRAVEL is modified SAND-II code. Figure 4 shows the neutron spectra. On the other hand, under theexperiment systems the neutron spectra were guessed by the MCNPX simulation. The calculated spectra arealso shown in figure 4. There is a discrepancy between the two spectra. In figure 4, above 1MeV experimental
results are lager than calculated ones. We think because we did not consider a neutron leakage caused by asmall gap between lead blocks in our calculation.
In this data analysis, we used an assumption for beam condition. Therefore, these are preliminary results.
The response function will be derived under more detail condition in future. We will extract more precise
information from the measurement data.
References[1] Nuclear data center of JAEA: http://wwwndc.tokai-sc.jaea.go.jp/index.html[2] M. Reginatto, et al.: Nucl. Instr. Methods A476, 242 (2002).

2Table 1. Moderators used in the Bonner sphere spectrometer

diametermaterial

3polyethylene

4polyethylene

5polyethylene

6polyethylene

10polyethylene

357p

3"

polyethylene,

5"

lead,

7"

polyethylene

100
Sensitivity(cm2)

357p

10-1

10-2 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2
10 10 10 10 10 10 10 10 10 10 10
Neutron Energy(MeV)

Figure 1. Detection efficiency curve of the Bonner sphere (moderator type of 357p)

Type1

NeutronType2NeutronbPbP5mm

Figure 2. Experimental setup

2Efficiency(cm )

10-1
10-2
10-3
3"
4"
5"
6"
10"
357p

10-4

10-5 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2
10 10 10 10 10 10 10 10 10 10 10 10
Neutron EnergY(MeV)

Figure3. Response function of the Bonner sphere spectrometer

10-11

n/cm /lethargy/proton

10-12
10-13

2

10-14
10-15
10-16

calculated result
experimental result(MAXED)
experimental result(GRAVEL)

10-17 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3
10 10 10 10 10 10 10 10 10 10 10 10 10
Neutron Energy(MeV)

Figure4. Experimental results