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Development of defect structures from displacement cascade damage in D-T neutron irradiated gold
410
Journal
DEVELOPMENT IN D-T
M. KIRITANI ’
OF DEFECT STRUCTURES
NEUTRON
IRRADIATED
‘, Y. SHIMOMURA
FROM DISPLACEMENT
2, N. YOSHIDA
Fucult), of Engineering,
Hokkardo
Unruersit~v, Suppom
060. Jupcm
Hiroshima
Unioersrt.~, HIgash
- Hiroshrmrr
for Applied
Mechanics,
Materials
1335tl.34 (lYX5) 410 414
CASCADE
DAMAGE
GOLD *
’ Fucu1t.v of Engineering, -’ Research Instrtute
of Nuclear
Kyushu
University.
j, K. KITAGAWA’
and T. YOSHIIE
’
742, Jrrpan
Kusugo
X16, Jopun
Pure gold is adopted as a suitable material for the exposure of important damage and defect processes induced by fusion neutron irradiation. Vacancy type unit defects, typically the stacking fault tetrahedra of l-2 nm, form groups of a size up to 20 nm containing up to 20 unit defects. reflecting the damage process in the presence of sub-cascades. The three dimensional configuration of sub-cascade damage is measured and illustrated. From the density of the sub-cascade groups, the neutron collision cross-section to create the observable defects is estimated to be 1.8 barn. The observed formation of vacancy clusters at low temperatures implies the existence of the dynamical effect of collisions in the point defect reactions. The mechanism of defect structure evolution at higher temperatures. one defect cluster from one neutron collision, is discussed and the importance of point defect cluster stability and the role of free insterstitials are emphasized.
1. Introduction
It is not intended to make the first wall of a fusion reactor gold plated, and the reason for the choice of pure gold as one of the most suitable materials in the present research on micro-structure evolution by D-T fusion neutron irradiation is as follows. In order to obtain an understanding of the complex point defect processes, one should obviously adopt materials whose point defect processes are better understood. Point defect processes in gold. especially those concerned with the clustering of defects, are the most well understood among materials; these inclucde the nucleation and growth of clustered defects of both vacancy [l] and institial [2] type, their thermal [3] and mechanical [4] stability, together with the basic properties of the point defects themselves. An understanding of the simplest material should be the first step in the steady progress of research in this field, though we realize that this understanding may not directly assist in the understanding of more complex practical materials.
The irradiation with 14 MeV D-T fusion neutrons was performed with the RTNS-II (rotaing target neutrons source at LLNL in US), with an irradiation intensity of about 10’” n/m2s at the strongest part of the specimen container. The irradiation up to 10” n/m2 was performed at 673 K, 473 K, 300 K and 20 K. The main purpose of the lowest temperature irradiation is in the cryo-transfer experiment and details are reported in a separate paper in these Proceedings [6].
3. Observed results, analyses and discussion 3.1.
Defects
developed
from
sub-cascade
damage
When the irradiation is performed at temperatures lower than the temperature above which the smallest nucleus of the stacking fault tetrahedra in this material
2. Experimental procedure All the specimens were prepared from 99.999% pure gold material for electron microscope observation prior to irradiation. Care was taken to have the variation of the specimen thickness appropriate for the observation of the defect structure development as a function of specimen foil thickness. The distinction between thin foil irradiation and bulk irradiation will be discussed in another paper in these Proceedings [5]. * Japan-USA
Fusion Cooperation Program on Collaboration in the RTNS-II Utilization sponsored by Monbusho (The Japanese Ministry of Education. Science and Culture).
0022-3115/85/$03.30
(North-Holland
0 Elsevier
Physics Publishing
Science Publishers Division)
B.V.
Fig. 1. Defects formed in gold by D-T fusion neutron tion at room temperature. 3.9~ 102’ n/m* at 300 K.
irradia-
M. Kiritani
et al. / Displacement
411
cascade damage
unstable (400 K [l]), the defect configurations clearly expose features of the displacement damage as-
become
sociated with sub-cascades. In fig. 1 irradiated at 300 K, the dot-like defects are not distributed homogeneously but appear in closely spaced groups. Some of the dot-like defects are identified as stacking fault tetrahedra from their shape as observed from several crystallographic directions. Smaller defects whose nature is difficult to identify from their shape are found to be similar to stacking fault tetrahedra by the 24 D stereo method [7]. A similar defect structure was observed at temperatures below 150 K in low temperature (20 K) irradiated gold [6]. Here, the important implication arising from the formation of such vacancy type defect clusters at temperatures at which isolated vacancies are immobile is the existence of a dynamical effect during and immediately after the collision process and/or the existence of vacancy mobility when the vacancy concentration is extremely high. An example of the population of grouped defects is illustrated in fig. 2. When the number of defect groups is multiplied by the number of unit defects belonging to each group. one finds that the groups contain much more than isolated defects and have 7 to 8 as the average number of defects in a group. The spatial extent of the defect group, referred to as the size of the group, though having a large scatter, increases in proportion to the square- to cube-root of the number of defects it contains as shown in fig. 3; this indicates that the average mutual separation between unit defects ranges from 3.5 to 7 nm when the distribution in the group is postulated to be isotropic. This distance can be used as a first approximation for the distance between the subcascade damage events. The last data presented in this section is the size distribution of unit defects shown in fig. 4. They are highly populated within a narrow range between 1 to 2 nm, showing the clusters to be of 10 to 40 vacancies if well developed stacking fault tetrahedra are postulated.
I;:!: . :.*
at
AU, 3.9x102’n/m2
,
I
15 20 IO Number of Defects in a Group
25
I
,
5
: l
I
Fig. 3. Size of defect groups plotted against the number of unit defects contained in the group.
3.1.
Analysis
and
discussion
of defect
yield
An estimate of the density of three dimensionally distributed defects can be accurately obtained by measuring the area1 density of defects as a function of specimen thickness; by this procedure the influence of the specimen surfaces, such as defect free layers along the surface, can also be eliminated. An example is given in fig. 5 for the irradiation at 300 K. and the estimated densities of unit defects and their groups are listed in table 1. The collision cross-section estimated from the density of defect groups and the given neutron fluence agree well with each other from 300 K and 20 K irradiation giving a figure of 1.8 barn. and should be regarded as the neutron collision cross-section to form observable defects. The estimated cross-section from the total density of individual defects also listed in table 1 is smaller for higher temperatures. and this indicates the decrease of the density of unit defects in a group at higher temperatures. though the number of groups is preserved. When the above value of the cross-section is compared with the theoretically estimated PKA energy spec-
50
3 yj
:
20
G 2 IO 2 0
I
loot-
B 2 40 t $j 30
I...
I
2
3 4
5
6
7 8
9 IO II
12 13 14 15 I6 17 18
Number of Defects in a Group Fig. 2. Population of defect cluster groups plotted against the number of unit defect clusters contained in the group.
Au, 3.9x102’n/m2
at 300K
P L
I
Size
of Defects
(nml
Fig. 4. Size distribution of unit de)fect clusters in gold irradiated at room temperature.
NT-
I
5 15-
Au, 3.4x102’n/m2
at 300K
.
0” e ;; 9 p io.L r” t F 0 2 5: $ b 2 f
i Oo
t
Defect Groups ,0---o--~
_o_
0-o-o
0_O-oIO
20
30
Specimen
Thickness
I 40
50
(nm)
Fig. 5. Thickness gradient plot of the measured areal number densities of unit small defects and their groups at room temper-
Fig. 6. Stereo-pair micrographs to disclose
ature.
configuration at 300 K.
trum by Logan and Russell [8], the apparent cut-off energy is estimated to be about 65 keV. Here, this energy should not be taken as a disinct cut-off energy, and an appreciable number of defect clusters should be understood to be produced by the transfer of smaller energy than this value, because there certainly exists a large probability of the self-annihilation within cascades as is discussed in another paper by one of the present authors [5]. When the number of observed defect groups consisting of more than 10 defect clusters is compared with the above theoretical energy spectrum, a PKA energy of about 1100 keV is required to produce a group of 10 sub-cascades.
damage ture.
3.3. The three dimensional structure of sub-cascade damage A careful observation as in fig. 6 by stereo-microscopy and its analysis reveal the three dimensional configuration of unit defects in defect groups. Examples of positions of defects are given in seven groups in fig. 7, shown as the projection on three orthogonal principal crystallographic planes, are the first successful measurement, though the configuration might be slightly modified from the original configuration of the sub-cascade
Table 1 Defect data and collision Irradiation temperature
cross-sections
Fluence (n/m*)
(KI 473
300 20
for three irradiation Number density of unit defects (m
12.0
x102’
3.9 x102’ 1.00x10*’
‘) All the data from the observation at room temperature. h) oD, apparent cross-section to form individual unit defects. ” a,;. cross-section of collision to form defect groups.
because
three dimenuonal damage. 3.9 x 10 J’ n/m’
they were observed
at room tempera-
3.4. Defects formed at high temperatures An example of well developed stacking fault tetrahedra formed by the irradiation at the elevated temperature of 473 K is shown in fig. 8. At first glance. they do not form groups as in the lower temperature irradiation. The density measured by the thickness gradient method is listed in table 1. The coincidence of the estimated cross-section of 1.8 barn with those estimated for the defect groups at lower temperatures is clearly showing that the stacking fault tetrahedra at this temperature each originate from one neutron collision and do not correspond to the unit defects in the defect groups as found at lower temperatures. The size of vacancy clustered defects at high temperature is found to be smaller in thicker specimens as shown in fig. 9. This size variation together with the difference of the defect configuration from that at lower temperatures stated above introduces an important feature concerning the stability of point defect clusters and the role of the free interstitial atoms.
temperatures
” h) OD (barn)
Number density of defect groups (mm’)
q; C) (barn)
1.8 6.3 14
(1.3X102’) 3.6x IO*’ 1.05 x 10 22
(1.8) 1.6 1.8
‘)
1.3x10*’ 1.4x1o*J 8.1 x lo=
of defects in sub-cascade
413
M. Kirirani et al. / Displacement cascade damage
~IOIOI
(100)
r
(001)
IO ii
.*
l
.
-.:L
--i-IO
5 DistonceCnm)
l
‘S
5 .
e rf
:
. 5
0
5
,” 2.0 e f t l.57 e Fl.O1 s ; 0.5 -
IO
.
[IO01
I_
IO :
%55
IO
5 r’ IO
.
. I--
15
-
&rooll
.
.
. (O’O)
R Cij o0
l.
A!__u_
.
IO
.
.
5
90
20
15
IO
5
.
l.
5
.
.
; . . .
i . .
I 20
l
:
i
.
i
‘E;;:
.
. .
I
Specimen
I 40
: .
l
: :
i
jLi
l
1
i
1
Thickness
I 60
1: I
I 80
.
(nm)
IO
.
IO
20 I
:
8
Fig. 9. Variation of vacancy clustered defect size with the specimen thickness in an elevated temperature irradiated gold. 1.2~ 1O22 n/m2 at 473 K.
.
15
:
. . 5
0
.
.
l
The nucleus of a stacking fault tetrahedron is known to become unstable above 400 K [l], and vacancies in a sub-cascade which could not form such clusters should be dispersed throughout the volume of the sub-cascade groups. Cooperating with other vacancies from other sub-cascades to form a highly concentrated vacancy region, they then condense to form a single large stacking fault tetraheron. This process needs more vacancy jumps, and thus gives more chance for interstitials to destroy more vacancies, especially in the thicker foils in which interstitials will have longer life before disappearing at the specimen surfaces. Although the result is not presented here, no variation of the defect size with specimen thickness was detected at the lower temperatures, strongly suggesting the short reaction time for the formation of defect clusters; extremely short by the dynamical process during and/or immediately after the displacement of atoms initiated by neutron collision.
.
l.
l . 0.. .
l
*5 1’
&ie-
oh-G 5
. .
l
.
IO 15
r-
l
.
Fig. 7. Measured configuration of defects in seven sub-cascade groups, illustrated as the projection principal crystallographic planes.
onto
three
orthogonal
Acknowledgements
The authors would like to express their sincere thanks to the organizers of the present program, Professors K. Kawamura, K. Sumita and S. Ishino. Their encouragement is greatly appreciated. The authors are grateful to Drs C.M. Logan and H. Heikkenen of LLNL for their great help in the D-T neutron irradiation procedure. They are also grateful to the Oarai Branch for JMTR Utilization of Tohoku University for facilitating the post-irradiation examination.
References
Fig. 8. Defects formed in gold by D-T neutron irradiation an elevated temperature. 1.2 x lo** n/m* at 473 K.
at
[l] A. Yoshinaka, Y. Shimomura, M. Kiritani and S. Yoshida, J. Sci. Hirosjima Univ., Ser. A-II 31 (1967) 55. [2] N. Yoshida and M. Kiritani, J. Phys. Sot. Japan 35 (1973) 1418.
[3] Y. Shimomura, M. Kiritani, A. Yoshinaka and S. Yoshida. Proc. Sixth Int. Congress for Electron Microscopy. Kyoto. 1966. p. 349. [4] S. Yoshida, M. Kiritani, Y. Deguchi and N. Kamigaki, Trans. Japan Inst. Metals 9 (1968) 83. [5] M. Kiritani. these Proceedings.
[6] Y. Shimomura, M. Guinan and M. Kiritanl, thcw I’r~)cccb ings. [7] J.B. Mitchell and W.L. Bell, Acta Met. 24 (1976) 147. [8] C.M. Logan and E.W. Russell. UCRC-52093 (1976) llntc of California.
Journal
DEVELOPMENT IN D-T
M. KIRITANI ’
OF DEFECT STRUCTURES
NEUTRON
IRRADIATED
‘, Y. SHIMOMURA
FROM DISPLACEMENT
2, N. YOSHIDA
Fucult), of Engineering,
Hokkardo
Unruersit~v, Suppom
060. Jupcm
Hiroshima
Unioersrt.~, HIgash
- Hiroshrmrr
for Applied
Mechanics,
Materials
1335tl.34 (lYX5) 410 414
CASCADE
DAMAGE
GOLD *
’ Fucu1t.v of Engineering, -’ Research Instrtute
of Nuclear
Kyushu
University.
j, K. KITAGAWA’
and T. YOSHIIE
’
742, Jrrpan
Kusugo
X16, Jopun
Pure gold is adopted as a suitable material for the exposure of important damage and defect processes induced by fusion neutron irradiation. Vacancy type unit defects, typically the stacking fault tetrahedra of l-2 nm, form groups of a size up to 20 nm containing up to 20 unit defects. reflecting the damage process in the presence of sub-cascades. The three dimensional configuration of sub-cascade damage is measured and illustrated. From the density of the sub-cascade groups, the neutron collision cross-section to create the observable defects is estimated to be 1.8 barn. The observed formation of vacancy clusters at low temperatures implies the existence of the dynamical effect of collisions in the point defect reactions. The mechanism of defect structure evolution at higher temperatures. one defect cluster from one neutron collision, is discussed and the importance of point defect cluster stability and the role of free insterstitials are emphasized.
1. Introduction
It is not intended to make the first wall of a fusion reactor gold plated, and the reason for the choice of pure gold as one of the most suitable materials in the present research on micro-structure evolution by D-T fusion neutron irradiation is as follows. In order to obtain an understanding of the complex point defect processes, one should obviously adopt materials whose point defect processes are better understood. Point defect processes in gold. especially those concerned with the clustering of defects, are the most well understood among materials; these inclucde the nucleation and growth of clustered defects of both vacancy [l] and institial [2] type, their thermal [3] and mechanical [4] stability, together with the basic properties of the point defects themselves. An understanding of the simplest material should be the first step in the steady progress of research in this field, though we realize that this understanding may not directly assist in the understanding of more complex practical materials.
The irradiation with 14 MeV D-T fusion neutrons was performed with the RTNS-II (rotaing target neutrons source at LLNL in US), with an irradiation intensity of about 10’” n/m2s at the strongest part of the specimen container. The irradiation up to 10” n/m2 was performed at 673 K, 473 K, 300 K and 20 K. The main purpose of the lowest temperature irradiation is in the cryo-transfer experiment and details are reported in a separate paper in these Proceedings [6].
3. Observed results, analyses and discussion 3.1.
Defects
developed
from
sub-cascade
damage
When the irradiation is performed at temperatures lower than the temperature above which the smallest nucleus of the stacking fault tetrahedra in this material
2. Experimental procedure All the specimens were prepared from 99.999% pure gold material for electron microscope observation prior to irradiation. Care was taken to have the variation of the specimen thickness appropriate for the observation of the defect structure development as a function of specimen foil thickness. The distinction between thin foil irradiation and bulk irradiation will be discussed in another paper in these Proceedings [5]. * Japan-USA
Fusion Cooperation Program on Collaboration in the RTNS-II Utilization sponsored by Monbusho (The Japanese Ministry of Education. Science and Culture).
0022-3115/85/$03.30
(North-Holland
0 Elsevier
Physics Publishing
Science Publishers Division)
B.V.
Fig. 1. Defects formed in gold by D-T fusion neutron tion at room temperature. 3.9~ 102’ n/m* at 300 K.
irradia-
M. Kiritani
et al. / Displacement
411
cascade damage
unstable (400 K [l]), the defect configurations clearly expose features of the displacement damage as-
become
sociated with sub-cascades. In fig. 1 irradiated at 300 K, the dot-like defects are not distributed homogeneously but appear in closely spaced groups. Some of the dot-like defects are identified as stacking fault tetrahedra from their shape as observed from several crystallographic directions. Smaller defects whose nature is difficult to identify from their shape are found to be similar to stacking fault tetrahedra by the 24 D stereo method [7]. A similar defect structure was observed at temperatures below 150 K in low temperature (20 K) irradiated gold [6]. Here, the important implication arising from the formation of such vacancy type defect clusters at temperatures at which isolated vacancies are immobile is the existence of a dynamical effect during and immediately after the collision process and/or the existence of vacancy mobility when the vacancy concentration is extremely high. An example of the population of grouped defects is illustrated in fig. 2. When the number of defect groups is multiplied by the number of unit defects belonging to each group. one finds that the groups contain much more than isolated defects and have 7 to 8 as the average number of defects in a group. The spatial extent of the defect group, referred to as the size of the group, though having a large scatter, increases in proportion to the square- to cube-root of the number of defects it contains as shown in fig. 3; this indicates that the average mutual separation between unit defects ranges from 3.5 to 7 nm when the distribution in the group is postulated to be isotropic. This distance can be used as a first approximation for the distance between the subcascade damage events. The last data presented in this section is the size distribution of unit defects shown in fig. 4. They are highly populated within a narrow range between 1 to 2 nm, showing the clusters to be of 10 to 40 vacancies if well developed stacking fault tetrahedra are postulated.
I;:!: . :.*
at
AU, 3.9x102’n/m2
,
I
15 20 IO Number of Defects in a Group
25
I
,
5
: l
I
Fig. 3. Size of defect groups plotted against the number of unit defects contained in the group.
3.1.
Analysis
and
discussion
of defect
yield
An estimate of the density of three dimensionally distributed defects can be accurately obtained by measuring the area1 density of defects as a function of specimen thickness; by this procedure the influence of the specimen surfaces, such as defect free layers along the surface, can also be eliminated. An example is given in fig. 5 for the irradiation at 300 K. and the estimated densities of unit defects and their groups are listed in table 1. The collision cross-section estimated from the density of defect groups and the given neutron fluence agree well with each other from 300 K and 20 K irradiation giving a figure of 1.8 barn. and should be regarded as the neutron collision cross-section to form observable defects. The estimated cross-section from the total density of individual defects also listed in table 1 is smaller for higher temperatures. and this indicates the decrease of the density of unit defects in a group at higher temperatures. though the number of groups is preserved. When the above value of the cross-section is compared with the theoretically estimated PKA energy spec-
50
3 yj
:
20
G 2 IO 2 0
I
loot-
B 2 40 t $j 30
I...
I
2
3 4
5
6
7 8
9 IO II
12 13 14 15 I6 17 18
Number of Defects in a Group Fig. 2. Population of defect cluster groups plotted against the number of unit defect clusters contained in the group.
Au, 3.9x102’n/m2
at 300K
P L
I
Size
of Defects
(nml
Fig. 4. Size distribution of unit de)fect clusters in gold irradiated at room temperature.
NT-
I
5 15-
Au, 3.4x102’n/m2
at 300K
.
0” e ;; 9 p io.L r” t F 0 2 5: $ b 2 f
i Oo
t
Defect Groups ,0---o--~
_o_
0-o-o
0_O-oIO
20
30
Specimen
Thickness
I 40
50
(nm)
Fig. 5. Thickness gradient plot of the measured areal number densities of unit small defects and their groups at room temper-
Fig. 6. Stereo-pair micrographs to disclose
ature.
configuration at 300 K.
trum by Logan and Russell [8], the apparent cut-off energy is estimated to be about 65 keV. Here, this energy should not be taken as a disinct cut-off energy, and an appreciable number of defect clusters should be understood to be produced by the transfer of smaller energy than this value, because there certainly exists a large probability of the self-annihilation within cascades as is discussed in another paper by one of the present authors [5]. When the number of observed defect groups consisting of more than 10 defect clusters is compared with the above theoretical energy spectrum, a PKA energy of about 1100 keV is required to produce a group of 10 sub-cascades.
damage ture.
3.3. The three dimensional structure of sub-cascade damage A careful observation as in fig. 6 by stereo-microscopy and its analysis reveal the three dimensional configuration of unit defects in defect groups. Examples of positions of defects are given in seven groups in fig. 7, shown as the projection on three orthogonal principal crystallographic planes, are the first successful measurement, though the configuration might be slightly modified from the original configuration of the sub-cascade
Table 1 Defect data and collision Irradiation temperature
cross-sections
Fluence (n/m*)
(KI 473
300 20
for three irradiation Number density of unit defects (m
12.0
x102’
3.9 x102’ 1.00x10*’
‘) All the data from the observation at room temperature. h) oD, apparent cross-section to form individual unit defects. ” a,;. cross-section of collision to form defect groups.
because
three dimenuonal damage. 3.9 x 10 J’ n/m’
they were observed
at room tempera-
3.4. Defects formed at high temperatures An example of well developed stacking fault tetrahedra formed by the irradiation at the elevated temperature of 473 K is shown in fig. 8. At first glance. they do not form groups as in the lower temperature irradiation. The density measured by the thickness gradient method is listed in table 1. The coincidence of the estimated cross-section of 1.8 barn with those estimated for the defect groups at lower temperatures is clearly showing that the stacking fault tetrahedra at this temperature each originate from one neutron collision and do not correspond to the unit defects in the defect groups as found at lower temperatures. The size of vacancy clustered defects at high temperature is found to be smaller in thicker specimens as shown in fig. 9. This size variation together with the difference of the defect configuration from that at lower temperatures stated above introduces an important feature concerning the stability of point defect clusters and the role of the free interstitial atoms.
temperatures
” h) OD (barn)
Number density of defect groups (mm’)
q; C) (barn)
1.8 6.3 14
(1.3X102’) 3.6x IO*’ 1.05 x 10 22
(1.8) 1.6 1.8
‘)
1.3x10*’ 1.4x1o*J 8.1 x lo=
of defects in sub-cascade
413
M. Kirirani et al. / Displacement cascade damage
~IOIOI
(100)
r
(001)
IO ii
.*
l
.
-.:L
--i-IO
5 DistonceCnm)
l
‘S
5 .
e rf
:
. 5
0
5
,” 2.0 e f t l.57 e Fl.O1 s ; 0.5 -
IO
.
[IO01
I_
IO :
%55
IO
5 r’ IO
.
. I--
15
-
&rooll
.
.
. (O’O)
R Cij o0
l.
A!__u_
.
IO
.
.
5
90
20
15
IO
5
.
l.
5
.
.
; . . .
i . .
I 20
l
:
i
.
i
‘E;;:
.
. .
I
Specimen
I 40
: .
l
: :
i
jLi
l
1
i
1
Thickness
I 60
1: I
I 80
.
(nm)
IO
.
IO
20 I
:
8
Fig. 9. Variation of vacancy clustered defect size with the specimen thickness in an elevated temperature irradiated gold. 1.2~ 1O22 n/m2 at 473 K.
.
15
:
. . 5
0
.
.
l
The nucleus of a stacking fault tetrahedron is known to become unstable above 400 K [l], and vacancies in a sub-cascade which could not form such clusters should be dispersed throughout the volume of the sub-cascade groups. Cooperating with other vacancies from other sub-cascades to form a highly concentrated vacancy region, they then condense to form a single large stacking fault tetraheron. This process needs more vacancy jumps, and thus gives more chance for interstitials to destroy more vacancies, especially in the thicker foils in which interstitials will have longer life before disappearing at the specimen surfaces. Although the result is not presented here, no variation of the defect size with specimen thickness was detected at the lower temperatures, strongly suggesting the short reaction time for the formation of defect clusters; extremely short by the dynamical process during and/or immediately after the displacement of atoms initiated by neutron collision.
.
l.
l . 0.. .
l
*5 1’
&ie-
oh-G 5
. .
l
.
IO 15
r-
l
.
Fig. 7. Measured configuration of defects in seven sub-cascade groups, illustrated as the projection principal crystallographic planes.
onto
three
orthogonal
Acknowledgements
The authors would like to express their sincere thanks to the organizers of the present program, Professors K. Kawamura, K. Sumita and S. Ishino. Their encouragement is greatly appreciated. The authors are grateful to Drs C.M. Logan and H. Heikkenen of LLNL for their great help in the D-T neutron irradiation procedure. They are also grateful to the Oarai Branch for JMTR Utilization of Tohoku University for facilitating the post-irradiation examination.
References
Fig. 8. Defects formed in gold by D-T neutron irradiation an elevated temperature. 1.2 x lo** n/m* at 473 K.
at
[l] A. Yoshinaka, Y. Shimomura, M. Kiritani and S. Yoshida, J. Sci. Hirosjima Univ., Ser. A-II 31 (1967) 55. [2] N. Yoshida and M. Kiritani, J. Phys. Sot. Japan 35 (1973) 1418.
[3] Y. Shimomura, M. Kiritani, A. Yoshinaka and S. Yoshida. Proc. Sixth Int. Congress for Electron Microscopy. Kyoto. 1966. p. 349. [4] S. Yoshida, M. Kiritani, Y. Deguchi and N. Kamigaki, Trans. Japan Inst. Metals 9 (1968) 83. [5] M. Kiritani. these Proceedings.
[6] Y. Shimomura, M. Guinan and M. Kiritanl, thcw I’r~)cccb ings. [7] J.B. Mitchell and W.L. Bell, Acta Met. 24 (1976) 147. [8] C.M. Logan and E.W. Russell. UCRC-52093 (1976) llntc of California.