In situ and postradiation analysis of mechanical stress in alumina under swift heavy ion irradiation V.A.Skuratov 1, G.Bujnarowski 1,2, Yu.S.Kovalev 1, K.Havancsak 3 J.Stano 4, S.I.Tyutyunnikov 1 1 Joint Institute for Nuclear Research, Dubna, Russia 2 Institute of Physics, Opole University, Poland 3 Eötvös University, Budapest, Hungary 4 BIONT, a.s., Bratislava, Slovakia

Outline Introduction Real time examination of mechanical stress in Al 2 O 3 under swift heavy ion irradiation Residual stress depth profiles in alumina irradiated with high energy heavy ions Summary

Main questions addressed to real time measurements:  Radiation damage and stress accumulation processes before and after ion track region overlapping  Variation in the stress state under ion irradiation characterized by specific ionizing energy losses higher and lower than the threshold of radiation damage formation via electronic excitations. Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy The knowledge about of high energy heavy ion-induced stress is of considerable practical value in view of simulation of fission product impact in radiation resistant oxides and ceramics, considered as candidate materials for nuclear waste management

High-resolution lattice image of  -Al 2 O 3 irradiated with 710 MeV Bi ions The average TEM track diameter is ~3 to 4 nm. V.A. Skuratov, S.J. Zinkle, A.E. Efimov, K. Havancsák. Nucl. Instr. Meth. B203(2003), Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy

at S e =41 keV/nm TEM micrograph of  -A 2 O 3 target irradiated at S e =41 keV/nm to a fluence of 7  cm -2 The presence of numerous subgrains suggests that considerable internal stresses were induced by the Bi ion irradiation Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy

The mean positron lifetime in Al 2 O 3 as a function of Kr ion fluence. The figure shows different stages of point defect accumulation Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy

Experimental set-up for ion-beam-induced luminescence measurements on IC-100 FLNR JINR cyclotron

Basis of the piezospectroscopic effect – the applied stress strains the lattice and alters the energy of transitions between electronic states  =  ij ×  ij  ij – piezospectroscopic coefficients Typical piezospectroscopic probes: Cr 3+ in Al 2 O 3 Eu 3+, Nd 3+ in silica glasses Sm 3+ in borosilicate glasses STRESS IN Al 2 O 3 :Cr UNDER SWIFT HEAVY ION IRRADIATION

Ion type and energy, MeV Т, К , cm -2 s -1 P, W cm - 2 Ar +16, × Kr +26, (I) 300 (II) 6.3× Bi +51, × Ion irradiation parameters  =  (  ) +  (T) +  (n Cr ) the hydrostatic stress component  h = (  11 +  22 +  33 )/3   2 /7.61  h (GPa),  (cm -1 ) STRESS IN Al 2 O 3 :Cr UNDER SWIFT HEAVY ION IRRADIATION

Dose dependence of the R-lines spectra under 167 MeV Xe ion irradiation. Ion beam incidence angle is 30 o. T=80 K. STRESS IN Al 2 O 3 :Cr UNDER SWIFT HEAVY ION IRRADIATION

The R-lines spectra measured during Kr, Xe and Bi tilted ion bombardment as a function of ion fluence. Spectra are normalized on maximum of the R 1 -line intensity The threshold of damage formation through dense ionization is about 20 keV/nm. B. Canut et al. Phys. Rev. B 51 (1995) MeV Bi Se=41 keV/nm 167 MeV Xe Se=24.7 keV/nm 107 MeV Kr Se=16.4 keV/nm ! No stress relaxation occurs if S e less than threshold value of damage formation via electronic excitation

Dose dependence of the difference between current and first registered R 1 -line spectrum during 167 MeV Xe ion irradiation STRESS IN Al 2 O 3 :Cr UNDER SWIFT HEAVY ION IRRADIATION

Dose variation of the R-lines spectra under 167 MeV Xe and 107 MeV Kr ion irradiation at normal ion beam incidence each Cr 3+ ion acts as an independent strain sensor The splitting of the R-lines directly indicates on the presence of differently stressed regions in the irradiating ruby specimen The stresses are compressive in basal plane of the sample and tensile in perpendicular direction

Confocal microscope LASER CONFOCAL SCANNING MICROSCOPY (LCSM) STUDY OF RESIDUAL STRESS PROFILES IN Al 2 O 3 :Cr AFTER SWIFT HEAVY ION IRRADIATION Conventional optical microscope LCSM Solar TII

n Cr (z) In-depth resolution of LCSM technique Luminescence intensity of R 1 -line as a function of depth measured in virgin ruby specimen.  z =  1.75  m

Depth-resolved R-lines photoluminescence spectra measured using LCSM technique (postradiation examination ) 240 MeV Kr, 300 K, ion fluence cm -2 virgin

Photoluminescence R-lines spectra registered in virgin and 710 MeV Bi ion irradiated ruby specimens

Stress tensor components and ionizing energy loss profiles in ruby The signs of the stress tensor components indicate that stresses are compressive in basal plane of the sample and tensile in perpendicular direction

4.12 µm Xe J.H. O'Connell, E.J. Olivier Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa Ion irradiation in the track overlapping regime leads to amorphization of A 2 O 3 :Cr crystals with XTEM micrograph of A 2 O 3 :Cr single crystal irradiated with E=167 MeV Xe ions.  t=2.9  cm -2, T=80 K, ion beam incidence angle 30 o, R p  5 µm

300 nm 150 nm with Microstructure of the end-of-range area in A 2 O 3 :Cr single crystal irradiated with E=167 MeV Xe ions.  t=4  cm -2, ion beam incidence angle 30 o, R p  5 µm Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa J.H. O'Connell, E.J. Olivier

Depth-resolved R-lines photoluminescence spectra measured on 167 MeV Xe ion irradiated specimen

Summary Piezospectroscopic method was explored for monitoring of the build up and accumulation of mechanical stresses in alumina irradiated with high energy heavy ions. Both in situ ionoluminescence and postradiation depth-resolved photoluminescence measurements reveal high level compressive stresses in Al 2 O 3 :Cr crystals ascribed to radiation damage formed due to dense ionization effects. It was shown that stress accumulation proceeds in several stages if the electron stopping power exceeds the threshold of radiation damage formation via electronic excitations. It is suggested that ion track region overlapping may stimulate the stress relaxation processes.