実験報告書様式（プロジェクト利用）

MLF Experimental Report

提出日 Date of report

25/Jul/2013

実験課題番号 Project No.

装置責任者 Name of responsible person

2012P0601

Kenichi Oikawa

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Development of fundamental techniques for pulsed neutron

BL10

imaging

利用期間 Dates of experiments

実験責任者名 Name of principal investigator

13/May/2012 – 16/May/2012

Yoshiaki Kiyanagi

1/Jun/2012 – 3/Jun/2012

所属 Affiliation

11/Jun/2012

Hokkaido University

25/Jun/2012 – 28/Jun/2012
5/Dec./2012 – 6/Dec./2012
14/Dec./2012 – 17/Dec./2012
17/Jan./2013 – 19/Jan./2013
17/Mar./2013 – 19/Mar./2013

１．研究成果概要（試料の名称、組成、物理的・化学的性状を明記するとともに、実験方法、利用の結果得られた主なデータ、考察、結論、図表等を記述してください。
Outline of experimental results (experimental method and results should be reported including sample
information such as composition, physical and/or chemical characteristics.
Ⅰ.Bragg edge imaging
I.1 Transmission experiment on high temperature alloys(1) Sample: Inconel(2) Experimental procedure and results
High temperature alloys (HTA) need superior ability of creep strength, resistivity for thermal cycle fatigue andhot gas corrosion. So far, optimization of the properties has been achieved by the improvement of the properties of
initial component adjustment. But the desired properties are sometimes disappeared by the effect, such as age
precipitation or subsequent welding. Therefore, we apply the neutron transmission spectroscopy technique to themicrostructure investigation of HTA which has the controlled grain boundary for the improvement of engineering
properties. The aim of the study is the analysis of the change in crystal microstructure by the friction stir welding(FSW) of Inconel 600 alloy.
The measurements were performed with the 256ch Li glass detector set on the 14 m position at BL10. The alloy
samples were installed to its front. The source power of the MLF was around 220 kW. We chose the rotarycollimator size small and the beam was narrowed down to 50 mm × 50 mm by the B4C slit at the beam tube exit.
Fig. 1 shows the imaging results of FSW samples. These are obtained by visualizing the value obtained by the
integration of the transmission between the first and the second Bragg-edge wavelength. They are adjusted for
friction stir position to come to the right at 25 mm position on the vertical axis. The order of the samples, FSM4,
FSM6 and FSM8, are corresponded from lowest rotational speed of the friction stir. From the figure we canrecognize the transmission intensity is lower particularly for FSM4 and FSM8 compared with FSM6. There is a1

１．研究成果概要（つづき） Outline of experimental results (continued).
possibility that certain change in micro structure, such as the change of the crystallite size, is generated in them.
However, comparing the shapes of the transmission spectra of these samples, significant changes have not been
observed. This means that the strong texture is not formed in the process.

Fig. 1 Transmission images for the friction stir welding (FSW) samples of Inconel 600 alloy.
The red triangles indicate the welding point, respectively.
I.2 Demonstration experiment on axisymmetric strain tomography by Bragg-edge neutron transmission
spectroscopy with the tensor CT method(1) Sample: VAMAS cylinder (neutron strain-stress analysis international standard material, Aluminum, Bulk, 5
cm diameter×5 cm height)(2) Experimental procedure and results
In this experiment, we tried to quantitatively reconstruct two-dimensional cross-sectional image ofaxisymmetric strain distribution in the VAMAS cylinder (neutron strain-stress analysis international standard
material, Aluminum, Bulk, 5 cm diameter×5 cm height) by using the pulsed neutron transmission spectroscopic
imaging technique. Before the experiment, we developed a new CT reconstruction method, a tensor CT method.
Strain tomography is quite difficult in principle. This is because the traditional CT reconstruction can deal with
only “scalar” quantity although strain is “tensor”. Therefore, we developed such a new CT reconstruction method,and evaluated the validity of the method by simulation calculation studies.
We performed the pulsed neutron transmission spectroscopic imaging experiment at BL10 “NOBORU” at MLF
J-PARC. The beam line conditions were w/o frame overlap chopper, w/o filters, w/o B4C slits, and w/ rotarycollimator “small”. The neutron TOF imaging detector was the GEM detector. The sample was the VAMAS
neutron strain-stress analysis international standard Al cylinder. We tried to quantitatively reconstruct both theradial strain and the hoop strain of the VAMAS sample experimentally. Fig. 2 shows an example of measured
Bragg-edge neutron transmission spectrum at one pixel. Aluminum Bragg edges are clearly observed. After then,we extracted d-spacing projection data, and reconstructed CT images on each strain component by the tensor CT
method. Fig. 3 shows the reconstruction results. The CT image reconstruction of the hoop strain compact was

2

１．研究成果概要（つづき） Outline of experimental results (continued).
successfully carried out, but that of the radial strain one was evaluated as almost homogeneous distribution. It was
found that the tensor CT method was not perfect, in particular, on the radial strain component. Therefore, we are
improving the tensor CT algorithm.

Neutron transmission

90%

80%
70%
60%

50%
40%
30%

0

10000
20000
Neutron flight time / μs

30000

Fig. 2 Example of measured Bragg-edge neutron transmission spectrum of the VAMAS sample.

Fig. 3 Reconstructed CT images of (upper left) radial d-spacing and (upper right) hoop one, and comparison withtheoretical and reconstructed values of (bottom left) radial strain and (bottom right) hoop one.

3

１．研究成果概要（つづき） Outline of experimental results (continued).
Ⅱ. Resonance imaging
II.1 Development of a quantitative element amount analysis(1) Samples：
Ta, Au, Cu（for pulse function measurement）
Ta（for nuclide density quantitative evaluation）(2) Experimental procedure and results：
The observed resonance peaks are expressed by convolution of the intrinsic resonance, the emission time
distribution of neutrons emitted from a moderator and the time structure of the proton accelerator. Therefore, toperform the quantitative resonance peak analysis, the emission time distribution must be reproduced at arbitrary
neutron energy by synthetic functions.
We have carried out neutron resonance absorption spectroscopy (N-RAS) experiments to measure the emission
time distribution of the epithermal neutron at BL10. The emission time distribution of BL10 can be expressed by
the Cole-Windsor function at arbitrary energy. We measured prompt gamma ray spectra of tantalum, gold andcopper and then obtained the parameters of the function by fitting the observed resonance spectra.
Fig. 4 shows the observed resonance spectrum for the 262.4 eV resonance peak of gold. The blue line represents
fitting line expressed by the convolution of intrinsic resonance, Cole-Windsor function and time structure of the
proton accelerator. The effect of dual bunch structure appeared in the observed spectra and it is well fitted bysynthetic function.
Fig. 5 shows the energy dependence of the parameters relating to the pulse width of the Cole-Windsor function.
The broken lines represent the simulation results and the dots represent the experimental results obtained by fitting
to the resonance spectra. The tendency of energy dependence of the parameters obtained in experiments almost
corresponds to that of simulation. We succeeded to deduce the parameters of the emission time distribution at
BL10.
5.0x10

-2

Exp.
Fit

 (Simulation)
Exp. (Cu)Exp. (Au)Exp. (Ta) (Simulation)
Exp. (Cu)Exp. (Au)Exp. (Ta)

1.5

4.0
3.5
3.0

 / usGamma ray counts / a.u.

4.5

2.5

1.0

2.0
0.5

1.5
1.0
0.5

0.0

57.0

57.5

58.0

58.5

59.0

1

TOF / us

10

100

1000

10000

Energy / eV

Fig. 4 The observed resonance spectrum for

Fig. 5 The energy dependence of the parameters262.4 eV resonance peak of gold.

related pulse width of the Cole-Windsor function.

4

１． 研究成果概要（つづき） Outline of experimental results (continued).
The neutron resonance absorption spectra contain the information of the atomic density and its motion. We canestimate the information quantitatively by analysis of the resonance peaks using the fitting code taking into
account the pulse function. Therefore, we have implemented the pulse function in the resonance shape analysis
code REFIT [1] to analyze the resonance peaks.
We have carried out the N-RAS experiments at BL10 to measure the transmission spectra of tantalum sample(the atomic density: 5.48×10-5 atoms/barn). In this experiment, we used the GEM detector, and then analyzed theobserved resonance dips to estimate the atomic density of the sample using by the revised REFIT code.
Fig. 6 shows the dips caused by tantalum 4.28 eV resonance and that of 10.36 eV resonance. The blue lines
represent the fitting line calculated by the code and the green dots represent the difference between the measured
data and fitting. The atomic density estimated by the fitting is 5.25×10-5 atoms/barn within an error of ± 0.24%. It
is deduced that the reason of under estimation of atomic density is caused by background arise from scatteredneutron and gamma ray from the sample.
1.00

Transmission

0.90
0.80
0.70
Exp.
Fit
Diff.

0.60
0.50
0.10
0.05
0.00
-0.05
-0.10
470

Difference

Difference

Transmission

1.00

480

490

500

510

520

530

0.95
0.90
0.85
0.80
0.10
0.05
0.00
-0.05
-0.10
310

Exp.
Fit
Diff.

315

320

TOF / us

325

330

335

340

TOF / usFig. 6 The dips caused by tantalum 4.28 eV resonance (left) and 10.36 eV resonance (right).
[1] P. Schillebeeckx, et al., Nucl. Data Sheets, 113, 3054-3100 (2012).
II.2 Element imaging using energy selective transmission(1) Samples: Step-edge sample made by Fe, Cu, polyethylene and Pb in metal form.
(2) Experimental procedure and results
In this study, we aimed to construct a system for neutron energy-resolved computed tomography imaging, using
a high-speed video camera system and an industrial camera system.
1. High-speed video camera system:
1-1.ExperimentFig. 7 shows the schematic view of the experiment at BL10. The system consists of a neutron converter made of
Li/ZnS (NR), lens, image intensifier (I.I.), a high-speed video camera and control-PC. An experiment was
performed with use of the high-speed camera with 4k frame/sec (dT=250sec) and the images were obtained at 45
steps of every 4 degree. The system was installed at 13.7m from neutron target.

5

１．研究成果概要（つづき） Outline of experimental results (continued).

Fig. 8 shows step edge samples made of Fe, Cu, Pb, and polyethylene(indicated as “poly” in this manuscript) and their size in unit of mm.
1-2. Result
Using transmission ratio images obtained by every 4 degrees step, theFig. 7 Schematic view of theexperimental systemenergy-resolved three-dimensional (3D) images were calculated by filtered backprojection (FBP) method. Fig. 9 shows the calculated 3D images as volume
rendering at neutron energy (En) of 4 eV and 5 meV. Comparison between thetwo images, the Pb was disappeared according to transmission ratio values.
This result suggested that the system could visualize material alternatively bychoosing neutron energy. In addition, with use of the energy dependence ofeach CT values, it is possible to emphasize the selected materials, even if

Fig. 8 Step edge sample size

materials such as Cu and Fe have similar energy dependence of CT values.

(mm)
Cross sectional
image

The CT values on Fe and Cu derived from 3D images
were shown in Fig. 10. The colored lines indicate the CT
values obtained at several positions on samples.

Cross sectional image
Poly.

Poly.
Pb

Pb

Although about 30% deviation between each data-set
Cu

exists, the energy dependence of Fe and Cu CT values
was marginally agreed with each other. Thus, with use of

Cu

Fe

Fe

the energy dependence, we could obtain the material
emphasized CT images. The left CT image of Fig. 11
emphasized Fe, subtracting from the CT values at 5 meVFig. 9 Reconstructed 3D image by FBP method

to that of at En= 4 meV. The right CT image emphasized

Left; En=4eV(T=0.5 ms), Right;4 meV (T=15 ms)
0.05

0.05

technique has the possibility to visualize material
alternatively by choosing neutron energy and emphasize

0.045

0.045

CT ValuemeV to that of at 4eV. The results showed that thisCu(mid)Fe(mid)CT Valuepolyethylene, subtracting from the CT values at En= 4

0.04

0.04

0.035

0.035
0.03

0.03

materials with use of the energy dependence of CT

0.025

0.025

values.

0.02

0.02

0

10

20

30

0

10

20

30

TOF [ms]
TOF [ms]
Fig. 10CT values on CT images of Fe(left) and Cu(right)

Fig. 11 Fe(Left) and polyethylene(right) emphasized 3D images

6

１．研究成果概要（つづき） Outline of experimental results (continued).
2. Industrial camera system
2-1. Experiment

The system consists of a NR, lens, I.I., an industrial camera and control-PC. An
experiment was recorded by 25 frame/sec and the images were obtained at 36
steps of every 5 degree. Cylindrical metal foil sample made of Au, Ta and In wereused as shown in Fig. 12. Neutron energy was selected at En=4.9, 4.0, 1.3 eVadjusted for Au, Ta and In resonance energy.
2-2. Result
Fig. 13 shows the CT

Fig.12 Sample (): thickness in mm

En=4.9 eV
Au
Au

En=4.0 eV
Au

En=1.3 eV
TaIn

image calculated by FBP
method. They are clearlyseen the cylindrical structure of theFig. 13 Reconstructed 3D image at Au(4.9 eV), Ta(4.0 eV) and In(1.3 eV)

metal foil samples at resonance neutron

neutron resonance energy.

energy. The detail is under study.
III. Detector development
III.1 scintillation type detector(1) Samples
1) ASTM sensitivity indicator, (Aluminum, Lead, Acrylic resin)2) A spatial resolution indicator, (Gadolinium, Acrylic resin)3) BEFs (Brightness Enhancement Films), (Acrylic resin)(2) Experimental procedure
The pulsed-neutron imaging system consists of LiF/ZnS(Ag) scintillator and a high-speed video camera . An
image intensifier was combined with the video camera, amplifying the visible light emitted from the scintillator.
Samples were attached on back side of the scintillator, and transmitted neutron images were taken by the camera
system.
BEFs have been used as materials for flat panel displays. Their prismatic structure focuses light toward theviewer and controls the angle of light exiting from a backlight source. Thus BEFs were attacehed on front(light-emitting) side of the scintillator and the brightness of obtained image was evaluated.
(3) Experimental results
The camera system is essentially high-resolution imaging device. The video camera has 1k x 1k pixel resolution.
High-spatial-resolution imaging experiment was carried out. The sample is a newly developed line and spaceresolution indicator. The schematic of the indicator and the obtained image were shown in Fig. 14.
The result of spatial resolution measurement shows that the camera system has nearly 30 µm resolution that is assame as the camera pixel size.
The brightness of the fluorescence with BEFs was increased by approximately 2.5 to 3 times that of thebrightness without a BEF. This technique is very promising not only for conventional neutron imaging but also fortime-resolved neutron imaging.
7１．研究成果概要（つづき） Outline of experimental results (continued).

Fig. 14. Neutron image and schematic of spatial resolution indicator
III. 2 GEM type detector(1) Sample: Fe(2) Experimental procedure and results
We are developing a GEM type neutron detector especially for the energy-selective neutron radiography. One of
key issues of this kind of detectors is how to readout two-dimensional position for one hit point. In the principle, apulsed GEM signal can be read out using a simple double side readout strip pattern. But, we had not succeeded inthis method for several years due to charge up on the front surface of the insulator. In order to avoid the charge up,
the high resistive sheet was set on the front surface of the readout pattern. Then, the AC signal can penetrate thehigh resistive sheet and also the insulator of the readout pattern. The DC real charge can move to ground throughthe resistive sheet. Fig. 15 shows a correlation diagram between of the pulse heights for front and rear strips usinga Fe-55 radiation source. The same amount of charge can be clearly induced for both strips. A test using theneutron beam at BL10 was performed. The 2D image could be obtained.
Two demonstrations for the energy-selective neutron radiography using GEM detector were performed. One isthat the maximum event taking rate improved to 1.6MHz. It is the highest value for this kind of detectors. The
second one is that a Fe absorption resonance peak (27.7keV) and corresponded two-dimensional image could beobserved. It is higher energy resonance than before and even higher resonance can be seen.
8１．研究成果概要（つづき） Outline of experimental results (continued).

Fig. 15 A correlation diagram between the ADC counts
for front and rear strips using the simple double side readout
pattern with the high resistive sheet.
III. 3 Camera type detector(1) Samples: Pb, Fe, Cu(2) Experimental procedure and results
The ideal device for the technique is a time-of-flight detector with the high spatial resolution ability. One kind of
the 2-dimensional position sensitive detectors has been developed as the counting type one, but it has still
problems in its spatial resolution, counting rate and so on. The other candidate is photon converting type, which isassembled with the neutron to photon converting device and the photon imaging device. The detector is expectedto accept the high counting rate in keeping with the high spatial resolution. The high counting rate in the intense
neutron facilities is a serious problem for the transmission experiment. We are constructing the C-MOS camera
type imaging device with the neutron image intensifier to avoid the difficulty of the counting rate. The detector
was assembled with a high speed camera for the time sliced imaging and a vacuum tube type neutron image
intensifier. There is the advantage in the neutron-photon converting that the camera can be expected higher spatial
resolution than usual counters. But the huge amount of TOF image data should be transferred and recorded in thedevice, and we need development for the system integration. In this presentation we introduce the developed highspeed camera device.
The neutron image intensifier (II) is a vacuum tube type with Gd2O5 neutron converting screen. The coming
neutron was converted to the electrons in the input screen in front of the II, and then the electrons were accelerated
and converged in the II. The electrons hit the II output screen and made an image. The image was reflected by amirror behind II and taken by the high speed camera through a lens. The camera was controlled by the accelerator
trigger signal, and took the time sliced image series of one neutron pulse. The images are transferred to therecording system.
The high speed camera used was the CMOS type, Mikrotron MC1362, having 1280 x 1024 pixels. The
associating TOF integrated recording system was developed. The system can record the each time channel image
with integrating the same time channel continuously. The recording data lengths for each time are set up as same9

１．研究成果概要（つづき） Outline of experimental results (continued).
like 32 bit/pixel. Under the camera bright depth (8 byte), the possible recording time becomes 180 hours for 25 Hz
repetition. That can be considered as enough time for the huge neutron facility. This recording system has thefollowing advantage of the data capacity, that is, the file size is always constant.
Using the obtained TOF image series we analyzed the brightness variation spectra versus neutron flight time.
Fig. 16 shows an example of TOF image series. The obtained spectra were varied correspond to the neutron
spectrum, and could assign the transmitted sample specimen. Fig. 17 shows the brightness transmission spectrum
and the Bragg edge feature is shown on the spectrum This result means that the developed system could be usefulfor the spectroscopic neutron imaging.

Fig. 16 TOF image series obtained by the neutron image intensifier system.
The time channel width was 0.2 ms.

(a) Brightness spectra(b) Transmission spectrum

Fig. 17 Obtained brightness spectra from the TOF image series (a).
(b) is calculated transmission spectrum using (a)10