J. Plasma Fusion Res. SERIES, Vol. 10 (2013)

Trapping of Tritium by Stainless Steel Exposed to Plasmas inExperimental Campaigns of LHD
M. Matsuyama1), S. Abe1), K. Nishimura2), Y. Ono3), Y. Oya4), K. Okuno4), T. Hino5) and A. Sagara2)* masao@ctg.u-toyama.ac.jp
1)

Hydrogen Isotope Research Center, Univ. of Toyama, Gofuku 3190, Toyama 930-8555, Japan
2)

3)

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan

Center for Research and Development in Natural Sciences, Univ. of Toyama, Gofuku 3190, Toyama 930-8555, Japan
4)

5)

Radiochemistry Research Laboratory, Shizuoka Univ., Shizuoka 422-8529, Japan
Laboratory of Plasma Physics and Engineering, Hokkaido Univ., Sapporo 060-8628, Japan(Received: 7 May 2012 / Accepted: 5 October 2012)

Retention behavior of tritium by stainless steel exposed to plasmas in the Large Helical Device (LHD) has beenstudied by E-ray-induced X-ray spectrometry (BIXS) and an imaging plate (IP) technique. Plasma-exposed stainlesssteel samples were prepared by exposing the small plates at the location of 6.5L in LHD. X-ray photoelectron
spectroscopy (XPS) was also applied to analyze deposition layers on the surface of a sample. XPS analyses showedthat the deposition layers contain B, C, O and Ti as well as constituent elements of stainless steel. Chemical form of
metallic elements was mainly oxides, but a part was metallic state. The plasma-exposed sample was exposed totritium gas along with a bare stainless steel plate for comparison. The BIXS and IP measurements showed that thetritium retention largely increased by plasma exposure and it strongly depended on sample temperatures during
vacuum heating and tritium exposure. In addition, it was seen from the IP images that non-uniform tritium
distribution on the surface was formed even tritium exposure at room temperature.
Keywords: tritium retention, plasma exposure, BIXS, imaging plate, plasma-facing materials
samples were fixed at four different locations, which are
1.5U, 5.5U, 6.5L and 9.5L in LHD [2], and those samples
were exposed to plasmas for one cycle in the 13th
experimental campaign. After plasma exposure, they
were applied to tritium exposure at 623 K for 4 hours
after heating in vacuum at 673K.
It was seen that all of the stainless steel samples werecovered with deposition layers, although their thickness
was different from each other. Tritium retention in eachsample was strongly dependent on the sample location [1].
In addition, significant non-uniform tritium distribution
appeared in the plasma-exposed surface of the 6.5L
sample, although other samples showed almost uniform
distribution. Therefore, the present study was focused on
the trapping behavior of tritium in the 6.5L sample.

1. Introduction

Reduction of tritium retention in the plasma-facing
materials (PFMs) and the structural materials of fusion
experimental device such as ITER is one of great
important issues from viewpoints of the safety andeconomy of tritium as well as the fuel particle balance inthe reactor core, since a huge amount of tritium is used in
the device. These materials are exposed to various energy
particles, and surfaces of them are modified. Deposition
layers are formed on the surfaces as a result of plasma
exposure. They will affect tritium retention. The tritium
retention strongly depends on surface states such as
chemical state and composition of constituent elements inthe deposition layers. Namely, it is important tounderstand the correlation between tritium retention andsurface states of deposition layers.
We have examined so far the trapping and release
behavior of tritium in the PFM’s of the Large Helical
Device (LHD) as an example of the effects of exposure toplasmas for tritium retention [1]. Stainless steel plate isused as a protection plate in LHD. Small stainless steel

2. Experimental

The samples used in this study are stainless steel type
316 (SS316), and size of the sample plates was 10×10mm and 0.5 mm in thickness. These sample plates were
finally electropolished, and they were fixed at four64©2013 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchM. Matsuyama et al., Trapping of Tritium by Stainless Steel Exposed to Plasmas in Experimental Campaigns of LHD

0.10

A

0.08

Sample: 6.5L(13 cycle)
Evacuation temp. : 296 K
Exposure temp. : 296 K
Exposure Time : 4 hrs
Tritium gas : 2.66 kPa

0.06
0.04
0.02
0.00

0

1.0

2

4

6

Counting rate, N / counts min-1 ('E)-1

B

0.8

8

10

12

0.6
0.4

16

18

0.4

Ar

Ti

0.3

0.2

0.1

0.0

Cr
0

2

4

Fe

6

8

Energy of X-rays, E / keV

10

12

Sample: 6.5L(13 cycle)
Evacuation temp. : 673 K
Exposure temp.: 296 K
Exposure Time : 4 hrs
Tritium gas : 2.66 kPa

0.2
0.0

14

Energy of X-rays, E / keV

0

10

2

4

6

C

8

8

10

6
4

14

Ar

1.0

16

Cr
Mo

0.6

Ti

0.4

Cr

0.2
0.0

18

Fe

0.8

0

2

4

6

Fe Ni
8

Energy of X-rays, E / keV

10

12

Sample: 6.5L(13 cycle)
Evacuation temp. : 673 K
Exposure temp.: 623 K
Exposure Time : 4 hr
Tritium gas : 2.66 kPa

2
0

12

Energy of X-rays, E / keVCounting rate, N / counts min-1 ('E)-1

Counting rate, N / counts min-1 ('E)-1

Counting rate, N / counts min-1 ('E)-1

Counting rate, N / counts min-1 ('E)-1

different walls in LHD before beginning of the 13th
plasma campaign, which was conducted for 13 weeks
from October 2009. After plasma exposure, only 6.5L
sample was provided for surface analyses and tritium
exposure experiments in this study.
As a first step, the plasma-exposed surface wasobserved by a digital microscope. This sample was also
used to analyze chemical states of surface elements by
X-ray photoelectron spectroscopy (XPS). The XPS
analysis was performed on a Thermo Fisher Scientific
Model ESCLAB250Xi XPS system using Al(KD) X-rays
with an energy of 1486.6 eV.
Tritium exposure tests were conducted by thefollowing procedures. The 6.5L sample and a bare SS316
plate with the same size as a reference sample were set in
the tritium exposure device, and it was evacuated below
2x10-6 Pa at room temperature. The latter sample wasused for comparison. In order to examine the effects of
pre-heating in vacuum of the samples, at first, they were
exposed to tritium gas at room temperature. After
E-ray-induced X-ray spectrometry (BIXS) and imaging
plate (IP) measurements of them, as the second
examination, those samples were again set in the tritium
exposure device and then it was evacuated below 6x10-6
Pa at 673 K. After this evacuation, the samples were
exposed to tritium gas at room temperature for 4 hours.
Subsequently, as the third examination, the samples wererepeatedly set in the tritium exposure device, and thosewere heated at 673 K in vacuum and exposed to tritium
gas at 623 K for 4 hours. Total pressure and tritium
concentration of tritium gas used in this study were 2.66
kPa and 4.8%, respectively.
After each procedure of the tritium exposure, toestimate the amount and distribution of tritium retained insurface layers, both of 6.5L and bare SS316 sample were
contacted with an IP along with a set of standard tritium
sources, which were made of a polymer material labeledwith tritium. In this procedure, a thin poy-phenylenesurfide film (PPS: 1.2 Pm) was inserted between thesamples and IP to avoid contamination of the IP surface.
After exposure to IP for a given time, two-dimensional
mapping of E-ray dose was obtained by measuring theintensity of photo-stimulated luminescence with theimaging analyzer (Fujifilm FLA-7000). The spatial
resolution was 25×25 Pm. Some examples of tritium
measurements by a similar IP technique have been
recently reported by Hatano [3-4]. The BIXS was also
employed to evaluate the tritium retention in surface
layers and the tritium distribution in depth of a sample.
The details of BIXS are described elsewhere [5].

0

2

4

6

8

10

12

14

Energy of X-rays, E / keV

16

18

Fig. 1 X-ray spectra observed by BIXS for 6.5L sample.
Each of upper, middle and bottom figures was observed after
vacuum heating and tritium exposure under the following
conditions. (A) ; heated at 296 K and exposed at 296 K, (B);heated at 673 K and exposed at 296 K, and (C); heated at 673
K and exposed at 623 K. The dashed line in the figure (A)shows the background level of the present X-ray detector.

3. Results and discussion

3.1 Tritium measurements by BIXS
Figure 1 shows the X-ray spectra observed by BIXS
measurements. All measurements by BIXS were carriedout under the argon atmosphere. Each X-ray spectrum
consists of characteristic X-ray peaks and a bremsstrahlung
X-ray peak. Number of characteristic X-ray peak observed
was dependent on conditions of the vacuum heating andexposure temperature. In the case that both temperatures

65M. Matsuyama et al., Trapping of Tritium by Stainless Steel Exposed to Plasmas in Experimental Campaigns of LHD

2

4

6

Length, L / mm

8

10

0.002
0.000

0

2

4

6

Length, L / mm

8

0.04
0.02
0.00

10

0

2

4

6

Length, L / mm

8

0.06
㻌

㻌

0.06

0.04
0.02
0.00

10

Sample: 6.5L(#12)(13 cycle)
Vac.: 673 K
Expos.: RT
Time: 4 hr

0.08

0

2

4

6

Length, L / mm

810Fig. 3 IP images and line analyses for bare SS316 and 6.5L
samples. Vacuum heating was 673 K and exposure
temperature was 296 K.

Fig. 2 IP images and line analyses for bare SS316 and 6.5L
samples. Both temperatures in vacuum heating and tritium
exposure were 296 K.

(bare SS316)

during vacuum heating and exposure processes were room
temperature as shown in Fig. 1 (A), only a single peak ofAr(KD) X-rays was observed. On the other hand, pluralcharacteristic X-ray peaks appeared as shown in Figs. 1 (B)and (C), when vacuum heating and/or exposure
temperature were raised. Those X-ray peaks were assigned
to Ti, Cr, Fe, Ni and Mo from energies of X-rays as shownin the inset of Figs. 1 (B) and (C). It is considered thatappearance of a rather large titanium peak in Fig. 1 (B) is
due to the use of a titanium sublimation pump as one of
vacuum pumps in LHD. It should be noted that intensity of
the Ti(KD) peak in Fig. 1 (B) is 5 times larger than that ofFe(KD) peak. Other characteristic peaks are due toconstituent elements deposited on the surface by sputteringof stainless steel walls with plasmas in LHD.
It is known that intensity of an Ar(KD) peakcorresponds to the amount of tritium retained in surface
layers of a sample because of a short escape depth of
E-rays [6]. Intensity of an Ar(KD) peaks in Figs. 1 (A), (B)and (C) was 0.13, 3.5 and 39 counts/min, respectively. The
amount of tritium retained in surface layers largely
increased with increasing temperatures of vacuum heating
and tritium exposure: namely, tritium activity increased 27
times by elevating the temperature of vacuum heating, andit increased about 300 times by elevating both temperaturesof vacuum heating and tritium exposure. The former
increase may be due to removal of impurities adsorbed on
the surface and diffusion of metallic species from bulk tothe surface since the tritium exposure temperature was thesame. On the other hand, it is expected that the latter
increase was caused by acceleration of tritium diffusion
into the deposited layers since the exposure temperature
increased.
In addition, the shape of the bremsstrahlung X-ray peakin Fig. 1 (C) was different from that in Figs. 1 (A) and (B).
Namely, the shape in Fig. 1 (C) was convex above 3.5 keV.

㻌

1.0

Intensity of PSL, I / hr-1

Plasma-exposed SS316 (6.5L)

0.8
0.6
0.4
0.2
0.0

㻌

1.0
Sample: SS316
Evacuation temp.: 673 K
Exposure temp. : 623 K
Exposure Time: 4 hr
Tritium gas: 2.66 kPa

0

2

4

6

Length, L / mm

810Sample: 6.5L(13 cycle)
Evacuation temp.: 673 K
Exposure temp. : 623 K
Exposure Time: 4 hr
Tritium gas: 2.66 kPa

0.8
0.6

㻌

0

0.004

0.08

Intensity of PSL, I / hr-1

0.002

0.006

㻌

0.10
Sample: SS316
Vac.: 673 K
Expos.: RT
Time: 4 hr

㻌

0.004

0.008

Plasma-exposed SS316 (6.5L)

㻌

0.10
Sample: 6.5L(#12)
13 cycle
Vac.: RT
Expos.: RT
Time: 4 hr

㻌

㻌

0.006

Intensity of PSL, I / hr-1

0.008

0.000

㻌

0.010
Sample: SS316
Vac.: RT
Expos.: RT
Time: 4 hr(bare SS316)

Intensity of PSL, I / hr

㻌

0.010

Intensity of PSL, I / hr-1

Plasma-exposed SS316 (6.5L)

Intensity of PSL, I / hr-1

(bare SS316)

0.4
0.2
0.0

0

2

4

6

Length, L / mm

810Fig. 4 IP images and line analyses for bare SS316 and 6.5L
samples. Vacuum heating was 673 K and exposure
temperature was 623 K.

This indicates the diffusion of tritium into the bulk as wellas adsorption on the surface. It can be seen, therefore, thatthe amount of tritium retained in surface layers is strongly
affected by both of vacuum heating and exposure
conditions even though the surface is covered with thedeposited layers.
3.2 Measurements of surface tritium distribution by IP
techniqueSurface tritium distribution was measured by an IP
technique. To determine tritium activity in surface layers,
seven standard polymer plates labeled with a given
concentration of tritium were used. Main deposition of thesurface of plasma-exposed sample was carbon describedlater and its thickness was thinner than about 1Pm.
Therefore, escape depth of E-rays in the sample wasassumed to be almost same as the standard samples. Figure
2 shows the observed IP image (upper) and the result of66

Intensity, I / arb. units

M. Matsuyama et al., Trapping of Tritium by Stainless Steel Exposed to Plasmas in Experimental Campaigns of LHD

21 nm
Fe(2p)

O(1s)Intensity, I / arb. units

1000

Fe(2p)C(1s)
Cr(2p)Mo(3p)

800

600

400

Fe(3p)

200

Binding energy, EB / eV0Fig. 5 An example of XPS spectra observed by wide scan.

[B]

[A]

center A

O(1s)
Cr(2p)

10 nm

C(1s)
Mo(3d)
B(1s)w/o etching

red
21 nm

B

10 nm

w/o etching

1000

800

600

400

200

Binding energy, EB / eV0Fig. 7 Changes in XPS spectra for two spots with depth.

This is clearly shown by the result of line analysis. Tritium
activity in the green region was 4.06 GBq/m2, which isabout twice of the average concentration. These indicatethat high tritium retention appears even though exposure
temperature is low, when the sample was pre-heated in
vacuum at high temperature. It is considered, therefore,that the large increase in tritium retention is due to thechange in adsorption properties of deposition layers byvacuum heating as mentioned above.
Further examination for the vacuum heating effects was
carried out: namely, both samples were simultaneously
exposed to tritium gas at 623 K after vacuum heating at
673 K. The results are shown in Fig. 4. Tritium retention insurface layers of the 6.5L sample was estimated to be 56.0
GBq/m2 as an average. This activity was 437 times larger
than that observed in Fig. 2, and it was close to the result
observed by BIXS. On the other hand, tritium retention ofbare SS316 was 3.23 GBq/m2. Tritium retention of the
6.5L sample was about 17 times larger than that of bare
SS316 sample. Furthermore, remarkably non-uniform
tritium distribution appeared clearly in the left side of 6.5L
sample and the tritium activity in the yellow region was ashigh as119 GBq/m2.

Fig. 6 Photograph of the sample surface and the analyzed
spots by XPS.

line analysis (lower) at the red broken line in the image,where both the vacuum heating and exposure temperatures
were room temperature. In comparison, similar
measurements for a bare stainless steel that is not exposed
to any plasma are also shown. Image of tritium distribution
measured by IP technique is represented by a color
measure. Red color shows the highest activity, while blue
color does the lowest activity. Namely, tritium activity
decreases relatively with the following color change: red,
yellow, green and blue. Surface tritium activity of the 6.5L
sample was estimated to be 128 MBq/m2, while that ofbare SS316 was 16 MBq/m2. Difference in tritium activity
was as large as 8 times. It is clear that such a large
difference in tritium retention is due to the plasma
exposure.
To examine the effects of vacuum heating, exposure totritium gas was carried out at room temperature after
vacuum heating at 673 K. After this, surface tritium
distribution was similarly measured by IP technique. The
results are shown in Fig. 3. Tritium retention in surface
layers of the 6.5L sample was estimated to be 1.97 GBq/m2
as an average, while that of bare SS316 sample was 0.16
GBq/m2. The difference in tritium retention of both
samples became larger by increasing in temperature of
vacuum heating. In addition to this, high retention area
appears in the left side of the 6.5L sample as green color.

3.3 XPS analyses of the plasma-exposed surface
In order to examine causes of non-uniformity in thetritium distribution on the deposition layers of the 6.5L
sample, the plasma-exposed surface and its depth profile
was analyzed by XPS without any heating treatment.
Figure 5 shows an example of XPS spectra observed by67

M. Matsuyama et al., Trapping of Tritium by Stainless Steel Exposed to Plasmas in Experimental Campaigns of LHD

Fe(2p)

Fe(2p3/2)

A

Cr(2p)

Cr(2p3/2)

Cr(2p1/2)

Fe(2p1/2)A

Ti(2p)21 nm

A

Ti(2p3/2)

21 nm

w/o etching

B
21 nm

10 nm

w/o etching

B
21 nm

Intensity, I / arb. units

Intensity, I / arb. units

10 nm

㻌

Intensity, I / arb. units

21 nm

10 nm

10 nm
w/o etching

590

585

580

575

570

Binding energy, EB / eV

Fig. 8 Changes in Fe(2p) peak withdepth.

Fig. 9 Changes in Cr(2p) peak withdepth.
(-CH2-)
Carbide A

21 nm

475

Intensity, I / arb. units

10 nm

w/o etching

B
21 nm

470

465

460

455

450

Binding energy, EB / eV

Fig. 10 Changes in Ti(2p) peak withdepth.
(OH-)(O2-)

O(1s)

21 nm

Intnsity, I / arb. unitsB

w/o etching

Binding energy, E / eVC(1s)w/o etching

10 nm

w/o etching

740 735 730 725 720 715 710 705 700

10 nm

A

21 nm
10 nm
w/o etching

B

21 nm

10 nm

10 nm
w/o etching

w/o etching

295

290

285

545

280

Binding energy, EB / eV
Fig. 11 Changes in C(1s) peak withdepth.

540

535

530

Binding energy, EB / eV

525

Fig. 12 Changes in O(1s) peak with depth.

two analyzed spots of the deposition layers were measured
with etching by argon. The results are shown in Fig. 7.
Etching rate by argon ions was assumed to be 1.0 nm/s,
which was obtained from the sputtering of Ta2O5 by argon.
Difference in peak intensity was observed between two
spots: namely, intensity of a carbon peak in the spot [B]was less than that in the spot [A], while that of oxygen was
contrarily larger. It should be noted that intensities ofmetallic Fe, Cr and Mo peaks in spot [B] is larger thanthose in spot [A], although oxygen peak in spot [B] is more
intense than that in spot [A]. Such a remarkable difference
in both measurement spots was observed for the
as-received surface only, and it became small with depth.

wide scan from 0 to 1200 eV. The analyzed spot wasalmost center of the sample surface. As clearly seen fromthe spectrum, major elements on the surface are carbon andoxygen. In addition to these elements, small amount ofelements such as iron, chromium and molybdenum also
deposited on the surface. However, titanium was scarcely
deposited in surface layers.
Depth profiles of two spots on the sample surface, [A]and [B], were measured as an example. Location of two
spots is shown in Fig. 6. The former spot was the center ofthe surface, while the latter one is the region of left side,which corresponds to the region in which much tritium wasretained as shown in Fig. 4. Changes in XPS spectra for68

M. Matsuyama et al., Trapping of Tritium by Stainless Steel Exposed to Plasmas in Experimental Campaigns of LHD

that in point [A] as is shown in Figs. 3 and 4. It isconsidered, therefore, that the amount of carbon on thesurface of deposition layers is one of key factors for tritium
retention.
Figure 12 shows the changes in O(1s) peak with depth.
At least, the peak of O(1s) consists of two kinds of oxygen
species: O2- (530.1 eV) and OH- (531.5 eV) [11].
Assignment of these peaks coincides with that of oxide
peaks of iron and chromium observed in Figs. 8 and 9.
There are not large differences in a chemical state ofoxygen for both analyzed spots.

Figs. 8 to 12 show the spectra observed by narrow scanof each element for two spots of [A] and [B]. The observed
spectra for iron are illustrated in Fig. 8. It is seen frombinding energy that chemical forms of iron consist of
metallic iron (707.1 eV (2p3/2) and 720.1 eV (2p1/2)) andthe mixed oxides of FeO, Fe2O3 and FeO(OH) (710.1 eV(2p3/2) and 723.2 eV(2p1/2)) [7]. Peak of oxide assigned to
the latter species shifted to the lower binding energy sidewith depth. This indicates that decrease in the amounts of
FeO(OH) and Fe2O3 is larger than that of FeO with depth.
Great difference in two analyzed spots is the fraction of
metallic iron as mentioned above. Metallic iron, which is
known as one of catalysts available for the adsorption ofhydrogen, will contribute to the adsorption of tritium [8].
In addition, existence of iron carbide was also suggested
from a C(1s) spectrum as described later.
The observed spectra for chromium are illustrated inFig. 9. It was seen that chemical forms of chromium aremetallic chromium (574.1 eV (2p3/2) and 583.6 eV (2p1/2))
and its oxides such as Cr2O3 and CrO(OH) (576.6 eV(2p3/2) and 586.2 eV (2p1/2)), although intensities of thesepeaks are fairly weaker than that of iron peaks. Fraction of
metallic chromium increased with the increase in depth.
This is a similar tendency to the changes in a peak intensityof iron.
The observed spectra for titanium are illustrated in Fig.
10. Only a weak peak appeared in the spectra. It was seenthat a chemical form of titanium is TiO2 (458.5eV (2p3/2)),
but metallic titanium (453.8 eV (2p3/2) can not be foundwithin a depth of 21 nm. However, an intense X-ray peakof titanium appeared as is shown in Fig. 1 (B), where thesample was heated at 673 K in vacuum and exposed totritium gas at 296 K. It is considered that titanium atoms
diffuse from bulk to the surface by vacuum heating, andtritium concentration near titanium atoms becomes high byannealing at high temperature in vacuum. Further
investigations by XPS are required about the diffusion oftitanium after vacuum heating at 673 K.
As is shown in Fig. 5, most of the surface was covered
with carbon and oxygen atoms. Figure 11 shows thechanges in C(1s) peak with depth. Two peaks apparently
appeared in each spot. The peak of 283.2 eV was assigned
to iron carbide [9], which may not contribute to the tritium
adsorption. The higher energy peak (284.9 eV for the spot[A], 284.5 eV for the spot [B]) consists of plural peaks, andthey were assigned to chemical forms such as graphite/aromatics and (-CH2-) [10]. There was a large difference inthe as-received surface: namely, carbon content in the spot
[A] is appreciably larger than that in the spot [B], andcarbon species in the spot [B] consist of chemical forms ofgraphite, (-CH2-) and carbide, although the content andchemical form of carbon in bulk is similar to each other.
Tritium retention in point [B] was several times larger than

4. Summary

Tritium retention behavior on the surface of a stainlesssteel plate, which was previously exposed to plasmas at thelocation of 6.5L in the Large Helical Device (LHD) during
one cycle, has been studied. To clarify the effects of plasma
exposure, the plasma-exposed sample along with a baresample were exposed to tritium gas under the given
temperature conditions. Three different temperature
conditions of the vacuum heating and tritium exposure
were applied to these samples.
It was seen from the BIXS and IP measurements thatthe amount of tritium retained in the plasma-exposed
surface was larger than that in the bare surface irrespectiveof temperature conditions and it remarkably increased inincreasing temperatures of vacuum heating and tritium
exposure. Large heating effects for tritium retention
appeared in the plasma-exposed sample than the baresample of stainless steel. Furthermore, significantly intense
X-ray peak of titanium was observed by vacuum heating at
673 K, although it did not appear at 296 K.
Non-uniformity of tritium distribution on theplasma-exposed surface was confirmed by the images of IP
irrespective of temperatures of the vacuum heating andtritium exposure. XPS analyses of the as-received surfaceof the 6.5L sample indicated the existence of metallic
chromium and iron, although the surface was exposed toambient atmosphere after exposure to plasmas. It isconsidered, therefore, metallic species in the depositedlayers are responsible for the non-uniformity of tritium
distribution. This will be clarified by further XPS analysesof the sample processed at high temperatures.

Acknowledgement

This work was supported by the Collaboration
Research Program of the National Institute for Fusion
Science (NIFS10KUHR001).

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70