EPJ Web of Conferences 115, 03004 (2016)
DOI: 10.1051/epjconf/201611503004
© Owned by the authors, published by EDP Sciences, 2016
2nd Int. Workshop Irradiation of Nuclear Materials: Flux and Dose Effects
November 4-6, 2015, CEA – INSTN Cadarache, France
Positron Annihilation Spectroscopy to Characterize Irradiation Induced
Vacancy Type Defects in Materials for Nuclear Fission and Fusion
Marie-France BARTHE1
1
CEMHTI, CNRS, Université d’Orléans (Orléans, FRANCE)
In nuclear reactors, materials are submitted to irradiations and modification of their macroscopic
properties such as swelling or hardening is observed… It is of first importance to understand the
origin of these evolutions and how damage at the atomic scale such as vacancy and interstitials type
defects can interact with each other or with solutes and impurities to make the microstructure
evolved. So the properties of defects have to be determined.
Positron annihilation spectroscopy (PAS) is a well-established technique to characterize materials
[1]. Due to its positive charge, positron is sensitive to the local variations of the Coulomb potential in
solids. As the anti-particle of the electron, both particles can annihilate leading to the emission of
gamma rays with energy depending on the momentum of the electron positron annihilated pair. The
detection of these gamma rays arises original information on the defects because positron can be
trapped and annihilate in localized state such as vacancies. Two different and complementary
annihilation characteristics can be measured. Firstly Positron Annihilation Lifetime Spectrometer
(PALS) allows to measure the positron lifetime which depends on the local electron density at the
annihilation site. The second characteristic is the momentum distribution of the electron positron
annihilated pairs and is obtained by measuring the energy spectrum of the gamma annihilation rays
using a Doppler Broadening Spectrometer (DBS). Both characteristics give the signature of the
defects and allow determining some of their properties such as their nature, concentration, chemical
environment... By using slow positron accelerators which produce monokinetic positrons beams with
energy varying from 0.1 to 30 keV it is possible to study the depth profile of defects in thin layers from
0.1 to about 5 µm depending on the density of materials with a resolution of the order of 0.1xdepth.
22
Na source based beams [2] or user facilities taking advantages of high positrons flux available
around nuclear reactor (FRMII, Garching [3]) or LINAC( as in AIST in Japan [4]) are now available to
study defects in materials. PAS has numerous advantages among them, it is non-destructive and can
be used for conducting as well as insulating materials crystalline or amorphous. This technique is
especially useful to probe vacancy defects in metals for which it is one of the only direct
characterization. The annihilation characteristics can be predicted by first principle calculations and
these data when available can help to identify defects. Sensitive to the single vacancy, PAS can
allow to determine the size of the vacancy clusters up to a maximum of 1 nm approximately in the
concentration range from 1015 to a few 1018 cm-3.
In nuclear science this technique is very powerful to characterize not only damage induced by
irradiation but also to determine some fundamental properties of defects that are required for
modeling of the microstructural evolution of materials such as formation, migration, agglomeration,
interaction with solutes, impurities or transmutation products such as Helium or Hydrogen. PAS has
already demonstrated its major role in the study of vacancy defects and material related properties.
For example the results obtained by Vehanen et al [6] have had an outmost impact on the knowledge
of the role of carbon on vacancy behavior in Fe. They have demonstrated the trapping of vacancy in
Carbon Vacancy complexes and the non-localization of C atoms in the center of the vacancy. This
attractive interaction and localization has been confirmed by ab initio calculations [7]. It has also to be
underlined that positrons can be trapped in precipitates if its affinity for the material of precipitate is
higher than the one of the matrix. Nagai et al have demonstrated the complementarity of positron
techniques with Atomic Probe Tomography and have recently underlined the effects of matrix
damage probed by PAS on the hardening [5].
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
2nd Int. Workshop Irradiation of Nuclear Materials: Flux and Dose Effects
November 4-6, 2015, CEA – INSTN Cadarache, France
300
300
250
250
200
200
150
150
100
100
 45 MeV
50
e- 1 MeV
e- 2,5 MeV
Virgin
50
0
0
0
2x10
16
4x10
16
18
2x10
-2
4x10
18
6x10
18
Vacancy defects lifetime (ps)
Average lifetime (ps)
In this work we will report different results on the determination of the properties of vacancy defects in
W and UO2 using separate effects irradiation experiments coupled to PAS experimental
measurements and theoretical data. Recently the self-consistent two components Density Functional
Theory has been implemented in PAW approximation and has allowed circumcising the nature of the
detected vacancy defects in UO2 irradiated with electrons or alpha particles [8]. The comparison of
the experimental positron lifetime with calculated values show that the Schottky defects made of one
uranium vacancy associated to 2 oxygen vacancies seem to be the most detected defects. Due to its
properties tungsten has been chosen to cover part of the divertor in ITER and is envisaged for first
walls in next tokamak generation such as DEMO. In order to better understand its swelling and
embrittlement observed in special irradiation conditions, we use PAS to study the vacancy defects
properties in this material. We have first shown the migration and agglomeration of single vacancy in
the temperature range from 473 to 600K [9] and its interaction with helium [10]. More recently we
have observed the formation of vacancy clusters in self ion irradiated W and the effect of the
temperature on the size of these clusters. Today, the development of positron microbeams is very
promising. It has already allowed to show the creation of vacancies in region close to the fracture
zone of H charging stainless steel [11].
=310±10 ps
Fluence (cm )
Fig. 1 : Positron Lifetime in electron and alpha irradiated UO2 and positron isodensities in
Uranium vacancy and complexes with oxygen vacancy as calculated in self-consistent 2
components Density Fonctionnal Theory [8]
References
[1] M.-F. Barthe et al., Techniques de l’Ingénieur P3(P145) 2610 (2003).
[2 ] P Desgardin et al.,” Slow positron beam facility in Orleans”, Materials science Forum 363, 523
(2001).
[3] https://www.frm2.tum.de/en/the-neutron-source/secondary-sources-for-neutrons-and-positrons/
positron-source/
[4] https://unit.aist.go.jp/rima/xr-pos/group_detail/facilities/facilities.html
[5] A. Kuramoto et al., “Microstructural changes in a Russian-type reactor weld material after
neutron irradiation, post-irradiation annealing and re-irradiation studied by atom probe
tomography and positron annihilation spectroscopy”, Acta Materialia 61, 5236 (2013).
[6] A. Vehanen et al., “Vacancies and carbon impurities in α-Fe- electron irradiation”, Phys. Rev. B
25, 762, (1982).
[7] C. Barouh et al.,” Interaction between vacancies and interstitial solutes (C, N, and O) in α -Fe:
From electronic structure to thermodynamics”, Phys. Rev. B 90, 054112 (2014).
[8] J. Wiktor et al., “Coupled experimental and DFT plus U investigation of positron lifetimes in UO2”,
Phys. Rev. B 90, 184101 (2014).
[9] P. E. Lhuillier et al., “Positron annihilation studies on the nature and thermal behaviour of
irradiation induced defects in tungsten”, Physica Status Solidi C 6, 2329 (2009).
[10] P. E. Lhuillier et al., “Helium retention and early stages of helium-vacancy complexes formation
in low energy helium-implanted tungsten”, JNM 433, 305 (2013).
[11] N. Oshima et al., Rapid three-dimensional imaging of defect distributions using a high-intensity
positron microbeam”, Appl. Phys. Lett. 94, 194104 (2009).
2
Positron Annihilation Spectroscopy to Characterize
Irradiation Induced Vacancy Type Defects in Materials
for Nuclear Fission and Fusion
M-F. Barthe
CEMHTI, CNRS/Orléans University, 3A Rue de la Férollerie, 45071 Orléans, France
FRFCM
MF Barthe, MINOS, Cadarache, 4-6/11/2015
www.kit.edu
CEMHTI Facilities for the study of irradiation in Materials
Light ions : H+, D+, 
• Energy = 10 - 45 MeV
• Temperatures -120° to 1200°C DIAMANT
• Neutrons flux  a few 1011 neutron/cm2/s
Particles beams :
Irradiations, and chemical and
structural characterization
Cyclotron
RAMAN / Irradiation / HT
DIAMANT
Creep (PSI)
Radiolysis, corrosion
Feb. – Oct. 2014 :
Now running
Pelletron New
Positrons
Na22, Slow positron beam (0.5-25 keV)
• vacancy defects
Positron Lifetime Spectrum
511 keV
START
STOP
Sample
1,28 MeV
e+
ee+
511 keV
– Light ions : H+, D+, 3He, 
• Energies = 0.5 - 3 MeV
Temperatures -130°C to
1200°C
Positron Annihilation Spectroscopy
Positron e+ = antiparticule of electron (opposite charge, same mass)
Positron Annihilation Spectroscopy is based on 2 properties of positron
In dense solids annihilation leads to emission of 2  : E= 511 keV ± E
Trappping in vacancy defects
2/ Implantation, diffusion
3/ Trapping
e+
511 keVE
4/ Annihilation
keV-MeV
e-
1/ source
 ANNIHILATION
e+
Échantillon
Electronic Structure of solids
Probe for vacancy defects (negative or neutral) and free volumes
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Positron Source (1) : 22Na
22
Na : fast positrons
At CEMHTI
1.0
22
Emax
(β+
0.8
)=0.54 MeV
Stopping profile
T1/2 = 2.6 ans,
Na Source Positrons
3
Positrons Stopping Profile in W (density 19.3 g/cm )
0.6
70µm
0.4
0.2
0.0
0
20
40
60
80
100
Positron implantation depth [µm]
Thick samples
Slow positron beam:
monokinetic slow positrons (0.5-25 keV)
Positron implantation profile in W
Moderator
10-4 to 10-5
Surface
Energy
filter Acceleration
0-25keV
a.u.
+
Positrons
(~ 3 eV)
0.7µm
Annihilation
+
e+
Source
22Na
e Energy
5 keV
10 keV
12 keV
15 keV
20 keV
25 keV
e
Sample bulk
0
100
200
300
400
500
600
700
Depth (nm)
Thin layers
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
4
800
Doppler broadening spectrometry
NaI
 511 keV
Sample
+
E = cPL/2
e
+
-
e
e
Ge
PL : e- e+ pair
momentum
 511 keV ±E
coïncidence
Annihilation line at 511 keV
Momentum distribution of
electron- positron annihilated pairs
counts
511 keV
0
ΔE # momentum
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Doppler broadening spectrometry
NaI
 511 keV
Sample
+
e
+
DE = cPL/2
-
e
e
Ge
PL : e- e+ pair
momentum
 511 keV ±E
coïncidence
Annihilation line at 511 keV
Momentum distribution of
electron- positron annihilated pairs
counts
511 keV
0
ΔE # momentum
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Momentum Distribution: Al
Comparison of theoretical and experimental annihilation probability densities
valence
electrons 3s
and 3p
dominate
Al
1s2
2s2p6
3s2p1
2p3/2
2p1/2
2s1/2
High momentum : core electrons
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Doppler broadening
Experimental Spectra in SiC
without vacancies
SL, WL
 Energy (keV)
504
506
508
510
512
514
516
518
Epitaxial layer 6H-SiC,
17
-3
(n = 10 cm , 4 µm)
Annihilation characteristics
in Lattice (without defects)
as-received
Count number
10000
1000
100
0
PL (103m0c)
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Doppler broadening
Experimental Spectra in SiC
with and without vacancies
SL, WL
 Energy (keV)
504
506
508
510
512
Epitaxial layer 6H-SiC,
17
-3
(n = 10 cm , 4 µm)
514
+
516
16
518
+
-2
H , 1µm, 4.10 H .cm
and 900°C annealed
as-received
Annihilation characteristics
in Lattice (without defects)
Count number
10000
1000
100
0
PL (103m0c)
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Doppler broadening
Experimental Spectra in SiC
with and without vacancies
SL, WL
 Energy (keV)
504
506
508
510
512
Epitaxial layer 6H-SiC,
17
-3
(n = 10 cm , 4 µm)
514
+
516
16
518
+
-2
H , 1µm, 4.10 H .cm
and 900°C annealed
as-received
Annihilation characteristics
in Lattice (without defects)
Count number
10000
Vacancies
W ,S
Valence
electrons
1000
Core electrons
100
0
PL (103m0c)
S = annihilation fraction of e- e+ with low
momentum,
S= AS/AT
W = annihilation fraction of e- e+ with high
momentum,
W= WL+WR= (AWL+AWR)/AT
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Doppler broadening
Experimental Spectra in SiC
with and without vacancies
SL, WL
 Energy (keV)
504
506
508
510
512
Epitaxial layer 6H-SiC,
17
-3
(n = 10 cm , 4 µm)
514
+
516
16
Annihilation characteristics
in Lattice (without defects)
518
+
-2
H , 1µm, 4.10 H .cm
and 900°C annealed
as-received
Count number
10000
Vacancies
W ,S
Valence
electrons
1000
Core electrons
100
0
PL (103m0c)
S/SL
S = annihilation fraction of e- e+ with low
momentum,
S= AS/AT
W = annihilation fraction of e- e+ with high
momentum,
W= WL+WR= (AWL+AWR)/AT
R: Slope
lattice
W/WL
VN : N
 S, R
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
,W
Positron Annihilation Lifetime Spectroscopy
Positron Lifetime
511 keV
START
Sample
STOP
+
e
+
e-
e
PALS with PLEPS
in Münich
511 keV
Positron lifetime
r0 : electron radius
c : light velocity
ne-* :Local electronic density
Lifetime spectrum
Fast -Fast
spectrometer
  (r02 cne* ) 1
S(t) = BG + R(t)O P(t)
P(t) : prob. for positron to annihilate at time t
P(t) = i Ii exp(- t/ i ),
with i Ii = 1
i = 1/ i : lifetime component i and its intensity Ii
2 lifetime components
at least 2 annihilation states
2 long component = vacancy defect
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Positron lifetime in W
Specific lifetime for
each type of defects
Theory (DFT) [1]
Vn = 440 ps
450
400
Lifetime (ps)
350

Lattice
300
250
V = 200 ps
200
150
= 108 ps
100
0
20
40
60
80
100
Number of vacancies
Lacunes VN :
N

[1] T. Troev, E. Popov, P. Staikov, N. Nankov, T. Yoshiie, NIMB 267, 3, 335

13
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Vacancy defects properties
Use separate effects experiments combining irradiations in
different conditions and PAS (and other techniques)
measurements and calculations to characterize vacancy
defects in materials:
 Nature
 Interactions with impurities …..
 Migration
In W and UO2
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Vacancy defects in W : Single vacancies
properties and V-clusters
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Dpa and He, H induced in material for fusion
 ITER, DEMO : steps in the development of fusion energy production
 Fusion reaction
2H
+ 3H  4He(3,5 MeV) + n (14.1 MeV)
 W divertor, first walls?
dpa : displacements per atom
Temp. 800- 1700°C
dpa, vacancies, interstitials …..
(n,p)
n 14.1 MeV
H, (n,α)
He
ITER Tokamak
He, H high flux
Low energy
Change the microstructure and chemical composition
Evolution of thermal, electrical, mechanical properties of materials
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Damage dose calculations in DEMO
Divertor
W = predominant recoil
W for FW or divertor
Damage dose max in 3 years = 12dpa
[He]max in 3 years = 20-30 appm
He/damage = 1.6-2.5 appm/dpa
• Large energy distribution (up to
300 keV) mean value at 3.3 keV
[1] M.R. Gilbert et al. / Journal of Nuclear Materials 442 (2013) S755–S760,
M.R. Gilbert et al. / Journal of Nuclear Materials 467 (2015) 121
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Macroscopic properties:Irradiations with neutrons
Pure W
Vacancy defects ?
W-Re 25%
 Formation de cavités
Swelling in W irradiated with
neutrons (E>0.1MeV), 5.5x1026n.m2
(9.5dpa) [1]
[1] J.Motolich et al., Scripta Metallurgica, 8 (1974) 837-842; [2] V. Barabash, G. Federici, M. Rödig, L.L. Snead, C.H. Wu, Journal of Nuclear
Materials, 283–287, Part 1 (2000) 138-146.
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Experimental approach
Virgin samples : thin foils (150µm), 7*7 mm2, annealed at 1600°C/1h/Vacuum
3
16
-2
He 800 keV 10 cm
0.70
Defects
0.12
0.10
0.60
He
0.50
25 keV positon
implantation profile
0.08
0.06
0.40
0.30
10-100 appm
0.04
0.20
0.02
0.10
0.00
0
250
500
750
1000
1250
0.00
1500
Depth (nm)
Study of defects in the
Track region with PAS
Fluence
1014
1015
1016
5×1016
Estimated Damage (dpa)[SRIM]
0 to 700 nm
2.5×10-4
2.5×10-3
0.025
0.13
PAS ; Positron Annihilation Spectroscopy
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
He (at%)
Implantation to induce defects
3He 800keV
Fluence de 1013 à 5.1016cm-2
Damage (dpa)
0.14
Implantation-induced defects
Virgin sample annealed 1600°C/1h/vacuum
800 keV implantation, Fluence from 1013 to 5x1016 cm-2 (VDG Orléans)
W
Positron Energy (keV)
0
One single type of defect V
5
10
15
20
25
0.055 0.060 0.065 0.070 0.075 0.080 0.085
0.42
0.42
0.41
0.41
S
0.40
Initial
State
0.39
0.39
0.38
0.38
0.37
0.37
0.085
Virgin sample
0.080
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.075
W
0.40
0.070
0.065
0.060
0.055
0
5
10
15
20
25
Positron Energy (keV)
A Debelle , MF Barthe et al., J. Nucl. Mat., 376 (2008) 216-221
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
S
3He
Single vacancy in W
One single type of defect
0.46
low momentum fraction S
Virgin sample : annealed 1500°C/1h/ArH2
3He 800 keV irradiation
Fluence from 1014 to 5x1016 cm-2
Virgin sample
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.44
0.42
0.40
Initial
State
0.38
Lattice
0.36
0.05
0.06
0.07
0.08
high momentum fraction W
[1] A Debelle , MF Barthe et al, JNM.376 (2008) 216; [2] T. Troev, E. Popov, et al, NIMB 267, (2009), 335; [3] P.E. Lhuillier, MF Barthe et al., PSS ,C6, (2009), 2329,
[4] C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans – MINOS 2015, Cadarache , France, 4-6/11/2015
P. 21
Single vacancy in W
One single type of defect
Positron Lifetime
In agreement with calculations
τ=200±0.4ps I=98±0. 2% , [3] VCalc=200ps [2]
τ
Single vacancy (V)
0.46
low momentum fraction S
Virgin sample : annealed 1500°C/1h/ArH2
3He 800 keV irradiation
Fluence from 1014 to 5x1016 cm-2
Virgin sample
0.44
SV, WV
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.42
0.40
Initial
State
0.38
Lattice
0.36
0.05
0.06
0.07
0.08
high momentum fraction W
[1] A Debelle , MF Barthe et al, JNM.376 (2008) 216; [2] T. Troev, E. Popov, et al, NIMB 267, (2009), 335; [3] P.E. Lhuillier, MF Barthe et al., PSS ,C6, (2009), 2329,
[4] C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans – MINOS 2015, Cadarache , France, 4-6/11/2015
P. 22
Single vacancy in W
Trapping in one trap = 2 annihilation states
• Lattice, SL and τL = 110ps
• Single Vacancy V, SV
Trapping KV
Delocalised
Positrons
λL
Localised Positrons
detrapping
δV  0
annihilation
0.46
low momentum fraction S
Virgin sample : annealed 1500°C/1h/ArH2
3He 800 keV irradiation
Fluence from 1014 to 5x1016 cm-2
Single vacancy (V)
Virgin sample
0.44
SV, WV
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.42
CV 
0.40
0.38
Initial
State
Lattice
0.36
0.05
0.06
0.07
0.08
high momentum fraction W
λV
annihilation
Trapping rate, KV= CV.µV
µV trapping specific coefficient,
µV=4 ± 2 ×1014 s-1[1]
, Snorm=S/SL
[1] PE Lhuillier Thesis CEMHTI 2010,
MF Barthe CEMHTI - CNRS – Orléans – MINOS 2015, Cadarache , France, 4-6/11/2015
P. 23
800 keV 3He irradiated W
PAS
Trapping in one trap = 2 annihilation states
• Lattice, SL and τL = 110ps
• Single Vacancy V, SV
Trapping KV
Delocalised
Positrons
λL
annihilation
Localised Positrons
detrapping
δV  0
λV
annihilation
Trapping rate, KV= CV.µV
µV trapping specific coefficient,
µV=4 ± 2 ×1014 s-1[1]
, Snorm=S/SL
[1] PE Lhuillier Thesis CEMHTI 2010, [2] A De Backer, C Becquart, C. Domain, MF Barthe, JNM 429 (2012) 78–91, [3] C.Becquart,et al JNM 403,
Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 24
800 keV 3He irradiated W
LAKIMOCA (C. Domain EdF) [3]
PAS
Recombination
Emission
Implanted
He
+
Interstitial Traps
loop
PBC
or
surface
200nm
dislocation Emission
cascade
Vacancy
cluster
Interstitial
Marlowe
cluster
Annihilation
+
Mixed He vacancy cluster
He cluster
Migration
[1] PE Lhuillier Thesis CEMHTI 2010, [2] A De Backer, C Becquart, C. Domain, MF Barthe, JNM 429 (2012) 78–91, [3]
C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 25
800 keV 3He irradiated W
PAS
LAKIMOCA (C. Domain EdF) [3]
Recombination
Emission
Implanted
He
+
Traps
Interstitial
loop
PBC
or
surface
dislocation
Emission
cascade
Vacancy
cluster
Interstitial
cluster
Annihilation
Marlowe
+
200nm
Mixed He vacancy cluster
He cluster
Migration
[1] PE Lhuillier Thesis CEMHTI 2010, [2] A De Backer, C Becquart, C. Domain, MF Barthe, JNM 429 (2012) 78–91, [3]
C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 26
800 keV 3He irradiated W
LAKIMOCA (C. Domain EdF) [3]
Species
Em (eV)
mono-SIA (1I)
0.013
mono-v (1v)
1.66
PAS
[1] PE Lhuillier Thesis CEMHTI 2010, [2] A De Backer, C Becquart, C. Domain, MF Barthe, JNM 429 (2012) 78–91, [3]
C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 27
Single vacancy/ V-clusters in W
Low momentum fraction S
One single type of defect
Single vacancy (V)
0.48
0.46
Annealing
3
He 800 keV (25 keV)
16
-2
5x10 cm
0.46
low momentum fraction S
Virgin sample : annealed 1500°C/1h/ArH2
3He 800 keV irradiation
Fluence from 1014 to 5x1016 cm-2
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.44
0.42
SV, WV
0.40
Initial
State
0.38
Lattice
0.36
0.05
0.44
300 K
473 K
623 K
873 K
1173 K
1273 K
1473 K
Virgin sample
0.06
0.07
0.08
high momentum fraction W
0.42
0.40
0.38
200 400 600 800 1000 1200 1400 1600
Temperature (K)
[1] A Debelle , MF Barthe et al, JNM.376 (2008) 216; [2] T. Troev, E. Popov, et al, NIMB 267, (2009), 335; [3] P.E. Lhuillier, MF Barthe et al., PSS ,C6, (2009), 2329,
[4] C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans – MINOS 2015, Cadarache , France, 4-6/11/2015
P. 28
Single vacancy/ V-clusters in W
Low momentum fraction S
One single type of defect
Single vacancy (V)
0.48
Annealing
0.46
3
He 800 keV (25 keV)
16
-2
5x10 cm
0.46
low momentum fraction S
Virgin sample : annealed 1500°C/1h/ArH2
3He 800 keV irradiation
Fluence from 1014 to 5x1016 cm-2
300 K
473 K
623 K
873 K
1173 K
1273 K
1473 K
Virgin sample
Implantation fluence
13
-2
10 cm
14
-2
10 cm
15
-2
10 cm
16
-2
5´10 cm
0.44
0.42
SV, WV
0.40
Initial
State
0.38
Lattice
0.36
0.05
0.44
0.06
0.07
0.08
high momentum fraction W
At 873K Positron Annihilation Lifetime
Spectrometry with PLEPS [3]
0.42
0.40
Mean
lifetime
0.38
200 400 600 800 1000 1200 1400 1600
Temperature (K)
V migration, 473-623K
Em(V) = 1.66 eV [4]
V-clusters
VN with N>30 [2]
1st component
2nd component
τm (ps)
τ1 (ps)
I1 (%)
τ2 (ps)
I2 (%)
331
176
54
458
45
[1] A Debelle , MF Barthe et al, JNM.376 (2008) 216; [2] T. Troev, E. Popov, et al, NIMB 267, (2009), 335; [3] P.E. Lhuillier, MF Barthe et al., PSS ,C6, (2009), 2329,
[4] C.Becquart,et al JNM 403, Issues 1-3, 2010, 75-88
MF Barthe CEMHTI - CNRS – Orléans – MINOS 2015, Cadarache , France, 4-6/11/2015
P. 29
Vacancy defects in self ions irradiated W :
Positron annihilation spectroscopy
Transmission electron microscopy
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Experimental details : irradiations with W ions
Japet 2 MV
2 MV
ARAMIS
Yvette 2.5 MV
190kV
IRMA
Épiméthée 3 MV
Saclay
Japet
Yvette
200 kV
TEM
Orsay
Épiméthée
Experiments done at JANNuS (Joint Accelerators for Nanoscience and Nuclear Simulation), France
Irradiation W 20 MeV in bulk : postmortem characterizations
Irradiation W 1.2 MeV in thin foils: in
situ and post- mortem characterizations
PAS, TEM
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
High momentum Fraction W
Low momentum Fraction S
20 MeV W irradiation: low dpa
Mean positron implantation depth (nm)
249
354
153
24
77
0
0.44
0.44
0.42
0.42
0.40
0.40
Latice
Single vacancy
0.38
0.05
0.08
0.06
0.07
0.38
0.08
High momentum Fraction W
0.42
0.07
20 MeV W implanted W
0.025 dpa
1 dpa
12 dpa
0.06
0.05
virgin
0
5
10
15
Energy (keV)
20
25
Latice
Single vacancy
0.060
0.40
0.065
High momentum Fraction W
V-clusters (small 3D V-cluster+ V-loops ) are created even at low dpa
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Ex situ TEM observation : post-mortem
W irradiated 1.2 MeV W ions at 0.017 dpa at RT
Loops
Image 1 : over focused image, cavities appear black
surrounded by a white halo
20
Counts
15
Image 2 : under focused image, cavities appear
white surrounded by a black halo
Diam. = 0.6 ± 0.1 nm for visible V clusters
C > 4.2 ± 1.2 x 1023 V-clusters.m-3
Smaller V-clusters can not be excluded
10
5
0
0.5
1.0
1.5
2.0
2.5
Observed V-clusters size (nm)
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
33
High momentum Fraction W
Low momentum Fraction S
20 MeV W irradiation: effect of dpa
Mean positron implantation depth (nm)
249
354
153
24
77
0
0.44
0.44
0.42
0.42
Vn
0.40
0.40
Latice
Single vacancy
0.38
0.05
0.08
0.06
0.07
0.38
0.08
High momentum Fraction W
0.07
20 MeV W implanted W
0.025 dpa
1 dpa
12 dpa
0.06
0.05
virgin
0
5
10
15
Energy (keV)
20
25
V-clusters (small 3D V-cluster+ V-loops ) are created even at low dpa
Size and/or concentration of vacancy clusters increases with dpa
Saturation from 1 dpa
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Annealing in vacuum : effect of dpa
Low momentum Fraction S
0.51
0.51
Lattice
Single vacancy (V)
0.48
0.45
0.45
0.42
V
W 20MeV (0.025 dpa*)
W 20MeV (1 dpa*)
W 20MeV (12 dpa*)
0.39
0.36
0.48
300
450
600
750
Temperature (K)
0.42
0.39
900
0.04
0.06
0.08
High momentum Fraction W
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
0.36
Annealing in vacuum : effect of dpa
3He
0.48
Low momentum fraction S
Low momentum Fraction S
0.51
0.45
0.42
W 20MeV (0.025 dpa*)
W 20MeV (1 dpa*)
W 20MeV (12 dpa*)
0.39
0.36
300
450
600
750
Temperature (K)
800 keV irradiations
Lattice
Single
(V)
He vacancy
800 keV (25 keV)
0.48
3
16
-2
5x10 cm
0.46
0.44
0.48
0.45
0.42
0.40
V
0.38
200 400 600 800 1000 1200 1400 1600
Temperature (K)
900
0.51
V migration, ∼ 573K
0.06
E0.04
m(V) = 1.66 eV [4]
0.08
High momentum Fraction W
0.42
0.39
0.36
∀dpa clustering occurs in the same temperature range as for single vacancies
mainly due to V migration and agglomeration on small clusters
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Vacancy defects in UO2 :
MF Barthe, CEMHTI CNRS Orléans, MINOS , Cadarache 4-6/11/2015
Experiments : Indirect detection of defects in UO2
XRD, lattice parameter changes, [1,2,3 ]
[2]
[1]
[3]
RBS/C in Xe and He implanted UO2 [4]
dpa
Thermal properties in (U,Pu)O2 samples, [5]
[1] J.H.Davies et al, JNM 41 (1971), 143., [2] Weber W.J, JNM 114 (1983), 213 [3] N.Nakae, JNM 80 (1979), 314-322 , [4] F. Garrido et al.
NIM B 266 (2008) 2842–2847, [5] D. Staicu, T. Wiss et al. JNM 397 (2010) 8–18
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 38
Experiments : Indirect detection of defects in UO2
XRD, lattice parameter changes, [1,2,3 ]
[2]
[1]
[3]
RBS/C
in Xe
and He imlanted
UO2 [4]defects
Indirect
information
about primary
No direct observation of vacancy defects
dpa
Thermal properties in (U,Pu)O2 samples, [5]
[1] J.H.Davies et al, JNM 41 (1971), 143., [2] Weber W.J, JNM 114 (1983), 213 [3] N.Nakae, JNM 80 (1979), 314-322 , [4] F. Garrido et al.
NIM B 266 (2008) 2842–2847, [5] D. Staicu, T. Wiss et al. JNM 397 (2010) 8–18
MF Barthe CEMHTI - CNRS – Orléans –MoD PMI2015, Marseille , France, 25-27/05/2015
P. 39
U
O
60 µm
Fluorine structure
Vacancy defects in irradiated UO2
 (fast) Positron Lifetime,
 Self-consistent Two Component DFT calculations of
positron lifetime
Positron Lifetime Spectrum
511 keV
START
STOP
1,28 MeV
Sample
e+
e+
e511 keV
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
PALS in UPuO2 [1]
DEN/DTCD/SECM/LMPA CEA Marcoule
[1] D. Roudil, M F Barthe et al. / Journal of Nuclear Materials 420 (2012) 63–68
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Vacancy defects in UO2
300
300
250
250
200
200
170 ps
150
150
100
100
 45 MeV
50
e- 1 MeV
e- 2,5 MeV
Virgin
50
0
0
0
2x10
16
4x10
16
18
2x10
-2
4x10
18
6x10
18
Vacancy defects lifetime (ps)
Average lifetime (ps)
Irradiations  45 MeV (2x10-4 dpa), 1 MeV and 2.5 MeV electrons
Positron Annihilation Spectroscopy (Fast Positrons), 300K Lifetime
V = 3074 ps
No vacancy defects are detected for
1 MeV e- irradiation
Vacancy defects detected
if 2.5MeV e- irradiation
Fluence (cm )
Open symbols : average lifetime
Full symbols : Second lifetime component
M F Barthe, et al Phys. Stat. Solidi C 4 3627-3632
2007
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Vacancy defects in UO2
300
-3
displaced atoms concentration (cm )
300
Average lifetime (ps)
8x10
19
200
6x10
19
150
19
4x10
100
Displacements induced in UO2
250
with electrons
programme S mott
200
170 ps
O Displacement
250
 45 MeV
5019
2x10
Virgin
U (Ed=40 eV[1,2])
150
100
O+U Displacements
e- 1 MeV
e- 2,5 MeV
50
O (Ed=20 eV[2])
0
0
0
0 02x1016 14x1016 2
18
3 2x104
4x10
5
18
18
6 6x10
Vacancy defects lifetime (ps)
Irradiations  45 MeV, 1 MeV and 2.5 MeV electrons
Positron Annihilation Spectroscopy (Fast Positrons), 300K Lifetime
-2
IncidentFluence
Energy of(cm
electrons
(MeV)
)
Open symbols : average lifetime
Full symbols : Second lifetime component
[1] J.Soullard, JNM 135 (1985) 190-196.;[2] C. Meis, A. Chartier JNM 341 (2005) 25
V = 3074 ps
No vacancy defects are detected for
1 MeV e- irradiation
Vacancy defects detected
if 2.5MeV e- irradiation
Displacement of U if E(e-)>2 MeV
VU, or complexes VU 2VO
M F Barthe, et al Phys. Stat. Solidi C 4 3627-3632 2007
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Fully self-consistent 2 components DFT calculations
Calculations in the ABINIT code (Two Components DFT) [1]
LDA SiC
*
GGA+U UO2
Self consistent scheme PSN2 with
gradient correction GC for the
enhancement factor g
*Defects were fully relaxed
Relaxation of defects due to positron
localization = iterations
DEN/DEC/SESC/LLCC
[1] J Wiktor, PhD thesis, University of Marseille, oct 2015, [2] M. J. Puska, A. P. Seitsonen, and R. M. Nieminen, Phys. Rev. B
52, 10947 (1995).
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Positron lifetime calculations in UO2
Calculations in the ABINIT code (Two Components DFT) [1]
Self consistent scheme PSN2 with gradient correction GC for the enhancement factor g
DFT(GGA, PBE)+U formalism3 to treat the 5f electrons
Defects were fully relaxed
Exp ~170 ps
Reduction of the lifetime with increase of the charge
Due to relaxation for VU
4- :+10% outward
0: +13% outward
Schottky defects
DEN/DEC/SESC/LLCC
1 J Wiktor, M. Bertolus, G. Jomard, MF Barthe et al, Phys Rev B 90, 184101 (2014)
2 M. J. Puska, A. P. Seitsonen, and R. M. Nieminen, Phys. Rev. B 52, 10947
(1995). 3 S. Dudarev, D. Manh, and A. Sutton, Philos. Mag. Part B 75, 613 (1997).
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Identification of vacancy defects in UO2 irr
Exp .
Long lifetime ~310±10 ps
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
3 traps model
UO (set G, sintered polished and annealed
1700°C/24h/ArH ) irr alpha 45 MeV 2x1016 cm-2
; mesure sous vide en fonction de2la température
Measurement
in ultra
a function
of temperature
WHM
libre, 3 comp. source (230ps,
20% ; vacuum
450ps, 1.4% ; as
1500ps,
0.03%)
Long component
2 (ps)
Average lifetime
av
(ps)
2
rH2 Ga17/Al9/Ga59
irr alpha 45 MeV 2e16 cm
250
-2
Experimental data
Model with 3 Traps : negative ions IN, V1-, et V2
-
3 traps (IN, V1, V2 ) model
240
230
τIN=170 ps and τV-= τV2 =310 ps
220
210
200
330
>30 times more neutral
vacancies than negatively
charged ones
Cv2(cm-3)
µv1
6,50E+19 1,00E+15
320
310
Cv-(cm-3)
µ0 r
µ0 2
Er(eV)
Vr(s-1)
2.0E+18 3,40E+16 4,00E+16 1,00E-02 1,00E+11
300
290
Short lcomponent
1 (ps)
Long component
Intensity I2 (%)
280
60
CIN(cm-3)
µ0(IN)
EIN(eV)
1,00E+19 4,20E+16 3,00E-01
50
40
High binding energy
at Rydberg state of negative ions
30
20
10
190
short lifetime is constant
Trapping saturation
180
170
160
0
50
100
150
200
250
300
Temperature (K)
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Calculated formation energies
Formation energies of defects in stoichiometric UO2 [1]
In the undoped UO2 VO
should
be
positive,
hence not detected by
PAS
VU and VU+VO defects
should be negative,
while the VU+2VO should
be neutral.
DEN/DEC/SESC/LLCC
Close to stoechiometry , IO2-,VO2+ , VU4- DFT LDA+U [2]
[1] 1 J Wiktor, M. Bertolus, G. Jomard, MF Barthe et al, Phys Rev B 90, 184101 (2014), [2] J P Crocombette Phys Rev B 85,
144101 (2012)
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Identification of vacancy defects in UO2 irr
VU and VU-VO are negatively charged
close to the middle of the bandgap in
close stoechiometric UO2
Exp .
Long lifetime ~310±10 ps
Vacancy defects
2VU is 8- close to the middle of the
bandgap in close stoechiometric UO2
We propose
Neutral vacancy defects which are preponderant = Schottky defects
Negatively charged vacancy defects = a mixing of (VU-VO)2-, (2VU-2VO)4DEN/DEC/SESC/LLCC
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Conclusions
Positron annihilation spectroscopy
• Vacancy defects properties (nature, migration, agglomeration…) concentration
• From single vacancy to V-clusters
• Thin layers (damage region with HI) / thick samples (electron or high energy LI)
• DFT Calculations of annihilation characteristics
• Complementarity of Lifetime and Doppler
• Complementarity with TEM
In tungsten
• Light ions : single vacancies
 from T in the range 473-623K: migration and clustering
• Heavy ions
 at RT or lower temperature
 low dpa : V-clusters (3D small voids +V-loops ) + single vacancies
 high dpa : V-clusters with larger size + single vacancies
>423K clustering due to migration of single vacancies and
with V-loops as precurssors?
• He Plasma
nV-mHe complexes close to the surface
In UO2
• Identification of the dominant vacancy defect detected : Schottky defect VU+2VO
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
Thank to
 All collaborators
M SIDIBE, CEMHTI CNRS
PE LHUILLIER, CEMHTI CNRS
H LABRIM, CEMHTI CNRS
P DESGARDIN, CEMHTI CNRS
C. GENEVOIS-MAZELLIER, CEMHTI CNRS
E. AUTISSIER, CEMHTI CNRS
T SAUVAGE, CEMHTI CNRS
B DECAMPS, CSNSM CNRS
R SCHAUBLIN, ETHZ
A DE BACKER, UMET
C BECQUART, UMET
P TROCELLIER, CEA/SRMP
Y SERRUYS, CEA/SRMPS
J. WIKTOR, CEA/SESC/LLCC
M BERTOLUS, CEA/SESC/LLCC
G CARLOT, CEA/SESC/LLCC
M FREYSS, CEA/SESC/LLCC
P GARCIA, CEA/SESC/LLCC
G JOMARD, CEA/SESC/LLCC
S ESNOUF, LSI
D ROUDIL, CEA/SECM/LMPA
C VALOT, CEA/SESC/LLCC
F VELLA, CEA/SECM/LMPA
 Accelerators teams Jannus (Orsay and Saclay), LSI, CEMHTI
Thank You for your kind attention
MF Barthe, CEMHTI CNRS, Orléans, MINOS, Cadarache, 4-6/11/2015
51