V.A. Skuratov

On the conflicting roles of ionizing radiation in ceramics

Abstract Ionizing radiation can produce competing effects in ceramic materials. It is well established that ionizing radiation can produce displacement damage via radiolysis in alkali halides and some other ceramics. At high stopping powers (electronic d E /d x >5–50 keV/nm, depending on the material), additional displacement damage via inelastic collision processes can also be created in the vicinity of the ion track (swift-heavy-ion displacement damage). On the other hand, ionizing radiation can promote the recovery of displacement damage in many ceramic insulators by enhancing the mobility of point defects (ionization-induced diffusion). Therefore, under different irradiation conditions (electronic stopping powers), ionizing radiation can lead to either a substantial enhancement or suppression of radiation resistance in ceramics. The microstructures of SiC, Al 2 O 3 , MgO, MgAl 2 O 4 , Si 3 N 4 and AlN were examined by transmission electron microscopy (TEM) following irradiation with ion beams ranging from 1 MeV H + to 710 MeV Bi + . The oxides and Si 3 N 4 were found to be susceptible to ionization-induced diffusion. In these materials, high fluxes of ionizing radiation produced coarsening of dislocation loops and cavities, and inhibited low-temperature amorphization. At high electronic stopping powers, displacement damage was produced in the ion tracks in the oxides and Si 3 N 4 that could not be attributed to normal elastic collision processes. The amorphous ion track diameter in Si 3 N 4 associated with 710 MeV Bi ion irradiation was 3.5 nm. AlN and SiC were resistant to swift-heavy-ion-track displacement damage up to electronic stopping powers of 34 keV/nm.

Redox response of actinide materials to highly ionizing radiation

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems. As advanced nuclear fuels and wasteforms are developed, fundamental understanding of the processes controlling radiation damage accumulation is necessary. Here we report oxidation state reduction of actinide and analogue elements caused by high-energy, heavy ion irradiation and demonstrate coupling of this redox behaviour with structural modifications. ThO2, in which thorium is stable only in a tetravalent state, exhibits damage accumulation processes distinct from those of multivalent cation compounds CeO2 (Ce(3+) and Ce(4+)) and UO3 (U(4+), U(5+) and U(6+)). The radiation tolerance of these materials depends on the efficiency of this redox reaction, such that damage can be inhibited by altering grain size and cation valence variability. Thus, the redox behaviour of actinide materials is important for the design of nuclear fuels and the prediction of their performance.

Swift heavy ion-induced modification of Al2O3 and MgO surfaces

Abstract Surface topography changes in single-crystal alumina and magnesium oxide samples irradiated with 245 MeV Kr and 128–710 MeV Bi ions have been studied by atomic force microscopy. The surface response consists of nanoscale hillock-like defects associated with single ion impact. These defects are observed on the surfaces of Al 2 O 3 and MgO targets at ionizing energy loss values of about 25 and 15.8 keV/nm, respectively, which is less than the expected threshold values of amorphous latent track formation in these materials. Corresponding electron diffraction and high-resolution transmission electron microscopy studies show no evidence of an amorphous core of the ion track in sapphire irradiated with Bi ions at surface electronic stopping power of 41 keV/nm. Possible mechanisms of hillocks formation, alternative to crystalline–amorphous phase transition are discussed.

Luminescence of aggregate centers in lithium fluoride irradiated with high energy heavy ions

Abstract Dose behavior of F 3 + and F 2 center luminescence intensity in lithium fluoride irradiated with 3–5 MeV/amu Ar, Kr, Xe and Bi ions has been studied by using ionoluminescence and photoluminescence methods. As was found, the ion fluence dependence of the F 3 + center luminescence intensity is characterized by a stage of fast rise followed by exponential decrease for both “in situ” and postradiation measurements. The ion fluence, corresponding to the maximal value of luminescence intensity is associated with the fluence value reached when individual tracks start to overlap. Ion track halo overlapping leads to complex defect creation and, probably, the appearance of mechanical stress, suppressing the radiative decay of the excited states of aggregate color centers in lithium fluoride. Track halo radii deduced from the luminescence data are close to those found from the optical absorption spectroscopy. No specific “track” effects have been registered in the luminescence of F 3 + and F 2 centers at high level of ionising energy loss, exceeding 10 keV/nm.

Luminescence studies on electron and structural states in dielectrics under irradiation

Abstract Spectra of radiation-induced luminescence (RIL) and photoluminescence (PL) of Al2O3 and BeAl2O4:Cr3− single crystals and BN ceramics have been obtained. In Al2O3 under 8 MeV proton irradiation, the recharging of defects causing RIL has been shown to occur in the track vicinity of 10−6 cm size. After neutron irradiation, an essentially non-equilibrium distribution of Cr3+ impurities over structurally distinguishable sites in the crystal lattice of BeAl2O4 was registered by PL spectroscopy. An effective temperature characterising this distribution under neutron irradiation exceeds the melting point of the material. The RIL and PL of BN were caused by colour centres on grain boundaries. Radiation-induced structural transformations in BN ceramics under neutron and 26.7 MeV Ne ion irradiation principally occur on the grain boundaries but not in the bulk of grains.

Atom "Pinhole Camera" with Nanometer Resolution

An atom “pinhole camera” with nanometer resolution has been experimentally implemented for the first time. Owing to the use of this camera, an array of ∼106 identical nanostructures of Cr atoms with a characteristic size of the nanostructure of less than 50 nm has been created on a glass surface. Nanostructures of arbitrary shapes have been created.

Luminescence characterization of radiation damage of α-Al2O3 under 1 MeV/amu ion irradiation

Abstract The damage dose, the irradiation temperature and exciting density effects on luminescence spectra of α-Al2O3 single crystals during B (13.6 MeV), Ne (26.7 MeV), Ar (46.3 MeV) and Kr (210 MeV) ion irradiation have been studied. It was shown that F/F+ band intensity ratio decreases with increasing electronic stopping power and energy losses of elastic collisions. Cathodoluminescence spectra registered from samples previously irradiated by heavy ions are characterized by the absence of F band emission.

Roscosmos facilities for SEE testing at U400M FLNR JINR cyclotron

Aim of this report is to describe the main features of the Russian Federal Space Agency (Roscosmos) facilities which has been developed recently and will develop next year for SEE testing of the electronic devices at U400M cyclotron in Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna. At present specialized ion beam line with energy of 3÷6 MeV/nucleon O, Ne, Ar, Fe, Kr, Xe, Bi ions covering the LET range 4.5–100 MeV/(mg/cm2) is available to users. The project of ion beam line with ion energy up to 40 MeV/nucleon is presented too.

Orbital quantization in a system of edge Dirac fermions in nanoperforated graphene

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level EF, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO2 substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of EF through an equidistant set of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.

IC-100 accelerator complex for scientific and applied research

Industrial production of nuclear filters has been implemented at the IC-100 cyclotron complex of the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. After the complete upgrade, the cyclotron was equipped with the superconducting ECR ion source and the system of external axial beam injection. The implantation complex was equipped with the special transportation channel with the beam scanning system and the setup for irradiation of polymer films. Intense beams of heavy ions Ne, Ar, Fe, Kr, Xe, I, and W with an energy of ∼1 MeV/nucleon were obtained. the properties of irradiated crystals were studied, different polymer films were irradiated, and several thousands of square meters of track membranes with pore densities varying in a wide range were produced. Other scientific and applied problems can be solved at the cyclotron complex.