Irradiated Crystals Research Articles

RaDMaX: a graphical program for the determination of strain and damage profiles in irradiated crystals

RaDMaX(radiation damage in materials analysed with X-ray diffraction) is a user-friendly graphical program that allows the determination of strain and damage depth profiles in ion-irradiated crystals. This task is achieved by fitting experimental X-ray diffraction data, recorded in symmetrical θ–2θ geometry, with a dynamical diffraction model parametrized with variable strain and damage profiles based onB-spline functions. The strain and damage profiles can be graphically manipulated so as to fit the calculated curve to the experimental data. Automatic fitting procedures (generalized simulated annealing and conventional least squares) are also implemented.RaDMaXis free and open source (CeCILL licence) and can be downloaded from http://aboulle.github.io/RaDMaX.

Lithium fluoride colour centres-based imaging detectors for proton beam characterization at high doses

Proton beams of 7 MeV energy, produced by a linear accelerator, were used to irradiate LiF crystals and thin films thermally evaporated on glass substrates in the dose range from 103 to 4 × 106 Gy, inducing the formation of stable photoluminescent colour centres (mainly F2 and F3+), emitting in the visible spectral range. Using a conventional fluorescence microscope, the transversal proton beam intensity was mapped by acquiring the photoluminescence image of the irradiated spots. Image analysis allowed measuring the integrated photoluminescence intensity as a function of the irradiation dose: a linear optical response was obtained up to different maximum dose values, after which a quenching was observed, depending on the nature of the samples (crystals or films). The colour centres formation was investigated by optical absorption spectroscopy at room temperature and the Principal Component Analysis was applied to the absorption spectra of irradiated LiF crystals. In samples irradiated at highest doses, it allowed clearly identifying the formation of more complex aggregate defects, which appears strictly related to the observed photoluminescence quenching effect.

Radiation damage caused by swift heavy ions in CaF2 single crystals

The radiation-induced optical absorption in a wide spectral region of 1.5–10 eV have been investigated in nominally pure CaF2 single crystals irradiated at 295 K with 0.23 GeV Xe132 or 2.38 GeV Bi209 ions (fluences of 1011−1014 ions/cm2) providing an extremely high density of electronic excitations. The stepwise annealing of the radiation-induced optical absorption have been analysed at the heating of irradiated crystals up to 1023 K and accompanying thermally stimulated luminescence has been detected at 300–750 K. The origin of several absorption bands (incl. vacuum ultraviolet region), the possible creation mechanisms of the corresponding radiation defects as well as the difference in radiation damage caused by Xe132 or Bi209 ions have been considered.

Luminescence of photochromic centers in calcium fluoride crystals doped with Lu3+ ions

We report data on the luminescence spectra associated with photochromic centers in X-ray irradiated calcium fluoride crystals doped with Lu ions. Irradiation in low energy photochromic centers absorption band excites emission, which can be identify with transitions into photochromic centers. Ab initio calculation of absorption spectrum of photochromic center agrees rather well with experimental data.

Temperature behavior of optical absorption bands in colored LiF crystals

We measured the optical absorption spectra of thermally treated, gamma irradiated LiF crystals, as a function of temperature in the range 16–300K. The temperature dependence of intensity, peak position and bandwidth of F and M absorption bands were obtained.

Characterisation of irradiation-induced defects in ZnO single crystals

Positron annihilation spectroscopy (PAS) combined with optical methods was employed for characterisation of defects in the hydrothermally grown ZnO single crystals irradiated by 167 MeV Xe26+ ions to fluences ranged from 3×1012 to 1×1014 cm-2. The positron lifetime (LT), Doppler broadening as well as slow-positron implantation spectroscopy (SPIS) techniques were involved. The ab-initio theoretical calculations were utilised for interpretation of LT results. The optical transmission and photoluminescence measurements were conducted, too. The virgin ZnO crystal exhibited a single component LT spectrum with a lifetime of 182 ps which is attributed to saturated positron trapping in Zn vacancies associated with hydrogen atoms unintentionally introduced into the crystal during the crystal growth. The Xe ion irradiated ZnO crystals have shown an additional component with a longer lifetime of ≈ 360 ps which comes from irradiation-induced larger defects equivalent in size to clusters of ≈10 to 12 vacancies. The concentrations of these clusters were estimated on the basis of combined LT and SPIS data. The PAS data were correlated with irradiation induced changes seen in the optical spectroscopy experiments.

Low symmetry configurations of vacancy-oxygen complexes in irradiated silicon

Two new electron paramagnetic resonance (EPR) spectra, labeled KU2 and KU3, emerge as a result of annealing of γ-ray irradiated silicon crystals in the temperature range 360–560 °C. The EPR intensities of KU2 and KU3 increase in the upper range of the annealing temperature where the EPR peaks of the vacancy-oxygen complex (A-center) diminish. The angular dependence study shows that the EPR spectra of KU2 and KU3 resemble that of SL1, the excited triplet (spin S = 1) state of A-centers, but with slightly different g and D-tensors representing lowering in symmetries. Microscopic lattice distortions caused by capturing of extra interstitial oxygen atoms by the A-centers are proposed to be the source of lowering of the symmetries associated with KU2 and KU3.

Luminescence and EPR spectroscopy of neutron-irradiated single crystals of magnesium aluminium spinel

Neutron irradiated single crystals of stoichiometric MgAl2O4 and MgAl2O4:Mn2+ (0.15 wt. %) were studied using the methods of luminescence spectroscopy and versions of electron paramagnetic resonance. In stoichiometric MgAl2O4:Mn2+ single crystals, the transition of a part of manganese impurity ions from tetrahedral to octahedral coordination, caused by irradiation with fast fission neutrons, is detected using photoluminescence spectra. This fact confirms the partial inversion of a normal spinel due to neutron-irradiation. Using pulse EPR technique it is shown that an electron in the field of oxygen vacancy (i.e. from neutron-irradiation induced F+ centres, which are spatially separated from each other) is in hyperfine interaction only with neighbouring 27Al nuclei with nuclear spin 5/2.

EPR investigation of gamma irradiated single crystal guaifenesin: A combined experimental and computational study

Abstract Gamma irradiated single crystal of Guaifenesin (Glyceryl Guaiacolate), an important expectorant drug, were investigated with Electron Paramagnetic Resonance (EPR) spectroscopy between 123 and 333 K temperature at different orientations in the magnetic field. Considering the chemical structure and the experimental spectra of the gamma irradiated single crystal of guaifenesin sample, we assumed that alkoxy or alkyl-type paramagnetic species may be produced by irradiation. Depending on this assumption, eight possible alkoxy and alkyl-type radicals were modeled and EPR parameters of these modeled radicals were calculated using the B3LYP/6-311++G(d,p)-level of density functional theory (DFT). Theoretically calculated values of alkyl-type modeled radical(R3) are in good agreement with experimentally determined EPR parameters of single crystal. Furthermore, simulation spectra which are obtained by using the theoretical initial values are well matched with the experimental spectra. It was determined that a stable C α • H 2 α C β H β C γ H 2 γ (R3) alkyl radical was produced in the host crystal as a result of gamma irradiation.

Defect-induced photoluminescence of strontium titanate and its modulation by electrostatic gating

The photoluminescence (PL) spectra of ${\mathrm{Ar}}^{+}$-ion irradiated single crystals of ${\mathrm{SrTiO}}_{3}$ (STO) excited by the 325 nm line of a He-Cd laser are compared with those of pristine crystals, epitaxial films, and amorphous layers of STO at several temperatures down to 20 K. The 550 eV ${\mathrm{Ar}}^{+}$-beam irradiation activates three distinctly visible PL peaks: blue ($\ensuremath{\sim}430$ nm), green ($\ensuremath{\sim}550$ nm), and infrared ($\ensuremath{\sim}820$ nm) at room temperature, making the photoluminescence multicolored. The abrupt changes in PL properties below $\ensuremath{\approx}100$ K are discussed in relation with the antiferrodistortive structural phase transition in ${\mathrm{SrTiO}}_{3}$ from cubic to tetragonal symmetry, which makes it a direct bandgap semiconductor. The photoluminescence spectra are also tuned by an electrostatic gate field in a field-effect transistor geometry. At 20 K, we observed a maximum increase of $\ensuremath{\sim}20%$ in PL intensity under back gating of ${\mathrm{SrTiO}}_{3}$.

Enhancement of critical current density and mechanism of vortex pinning in H+-irradiated FeSe single crystal

We report a comprehensive study of the effect of H+ irradiation on the critical current density Jc and vortex pinning in an FeSe single crystal. The value of Jc for FeSe is enhanced by more than a factor of 2 after 3-MeV H+ irradiation, which is explained by the introduction of point pinning centers. Vortex creep rates are found to be strongly suppressed after irradiation. Detailed analyses of the pinning energy based on collective-creep-theory and an extended Maley’s method show that the H+ irradiation enhances the value of Jc before the flux creep and also reduces the size of the flux bundle, which suppresses the field dependence of Jc owing to vortex motion.

The high-dose and high-temperature monitors of reactor irradiation based on insulators

Radiation-induced changes of the structure and properties have been investigated for oxide and nitride materials, and the use of high-temperature insulators as temperature/dose monitors for in-reactor irradiation of materials test assemblies has been validated.It has been experimentally shown that the use of Al2O3 single crystals and BN ceramics provides means of monitoring the temperature of irradiation from 370 to 1900 K. The temperature is derived from measurements of the optical absorption or X-ray diffraction line shifts after post-radiation annealing of the monitors. We discuss the applicability of (a) the optical absorption and F-center luminescence spectroscopies of irradiated Al2O3 single crystals for gamma dose evaluation and (b) the isotopic analysis of irradiated BN ceramics for neutron dose evaluation.

Rate of F center formation in sapphire under low-energy low-fluence Ar+ irradiation

Ionoluminescence, optical absorption spectroscopy and Rutherford backscattering spectrometry channelling (RBS-C) have been used to study the rate of F center formation with fluence in 170keV Ar+ irradiated single crystals of α-Al2O3 (sapphire) at room temperature. Implantation fluences range between 1013cm−2 and 5×1014cm−2. F center density (NF) has been found to display an initial rapid linear increase with Ar+ fluence followed by saturation to a maximum value of 1.74×1015cm−2. Experimental results show a 1–1 correlation between radiation damage in the oxygen sublattice and F center density. This suggest F center kinetics in sapphire under low-energy low-fluence Ar irradiation is a direct consequence of dynamic competition between oxygen defect creation and recombination. An attempt has also been made to extend this discussion to F center kinetics in sapphire under swift heavy ion irradiation.

Two-dimensional periodic arrangement of one-dimensional polymerized C60 evidenced by high-resolution cryo-transmission electron microscopy

We have observed an electron-beam (EB) irradiated C60 single crystal (SC) film, using high-resolution cryo-transmission electron microscopy (cryo-HRTEM) measured at a low temperature of 80 K, and obtained the lattice images of one-dimensional (1D) C60 polymer. The intermolecular distance between adjacent C60 molecules of the 1D polymer was obtained to be 0.92 nm, which is in good agreement with the previous result of 0.93 nm estimated from the electron diffraction (ED) patterns obtained at room temperature. Although the previous work indicated that the 1D C60 polymer is explained by a mixture of body-centered orthorhombic (BCO) and hexagonal-closed pack (HCP) models, the present cryo-HRTEM images and their fast Fourier-transformed patterns clearly exclude the BCO model, and demonstrate that the 1D C60 polymer structure can be explained only by the HCP-monoclinic model.

EPR study of gamma irradiated DL-methionine sulfone single crystals

Electron paramagnetic resonance (EPR) study of gamma irradiated dl-2-amino-4-(Methylsulfonyl) butyric acid (dl-methionine sulfone, hereafter dl-ABA) single crystals and powder was performed at room temperature. It has been found that this compound indicates the existence of C.O2− and N.H2 radicals after γ-irradiation. While g and hyperfine splitting values for the N.H2 radical were observed, for the C.O2− radical, only the g factor was measured. The EPR spectra have shown that N.H2 radical has two groups each having two distinct sites and C.O2− radical has one site. The principal g and hyperfine values for all sites were analyzed.

Feature of secondary ion emission at various temperature of irradiated copper single crystal

The difference between the forms and positions of the maximum of the energy spectrum of secondary 63Cu+ ions emitted from the (100) face of a Cu single crystal in close-packed directions and between them at different target temperatures is revealed. For a sample at room temperature, it is established that the most probable ion energy Emax and the width h of the energy spectra at half-height increase with the polar emission angle, θ, measured from the normal to the surface. The opposite tendency, namely, a decrease in Emax with increasing θ, is obtained for ions emitted from a single crystal heated to several hundred degrees Celsius. Based on modern models of secondary ion emission, the observed regularities, which must be taken into account in the theoretical description of the process and in the practical application of secondary ions in mass spectroscopy, are discussed.

Radiation dosimetry using decreasing TL intensity in a few variety of silicate crystals

This study shows that there are some ionic crystals which after irradiation with high gamma dose Dm and subsequent irradiation with low doses ranging up to 500Gy present a decreasing TL intensity as dose increases. This interesting feature can be used as a calibration curve in radiation dosimetry. Such behavior can be found in green quartz, three varieties of beryl and pink tourmaline. In all these silicate crystals it can be shown that irradiation with increasing γ-dose there is a dose Dm for which the TL intensity is maximum. Of course, Dm varies depending on the crystal and irradiated crystal with the dose Dm is stable. If one of these crystals is taken and irradiated with doses from low values up to 400–500Gy, a curve of decreasing TL intensity is obtained; such a curve can be used as a calibration curve.

Effect of gamma ray irradiation on sodium borate single crystals

Abstract In this work, the effects of 5 kGy, 10 kGy and 20 kGy doses of gamma ray irradiation on sodium borate, Na 2 [B 4 O 5 (OH) 4 ]·(H 2 O) 8 single crystals have been studied. Initially these crystals were grown by solution growth technique and identified as monoclinic using X-ray diffraction analysis. X-ray rocking curves confirm the formation of crystalline defects due to gamma rays in sodium borate single crystals. The electron paramagnetic resonance spectra have been recorded to identify the radicals created due to gamma ray irradiation in sodium borate single crystals. The thermoluminescence glow curves due to the defects created by gamma rays in this crystal have been observed and their kinetic parameters were calculated using Chen's peak shape method. The optical absorption increases and photoluminescence spectral intensity decreases for 5 kGy and 20 kGy doses gamma ray irradiated crystals compared to pristine and 10 kGy dose irradiated one. The effect of various doses of gamma rays on vibrational modes of the sodium borate single crystals was studied using FT-Raman and ATR-FTIR spectral analysis. The dielectric permittivity, conductance and dielectric loss versus frequency graphs of these crystals have been analyzed to know the effect of gamma ray irradiation on these parameters.

Laser induced modification of the thermo-optical properties of Nd:YAG crystal determined by thermal lens technique

A Nd:YAG single crystal thin disc sample was irradiated by 200 pulses of 193 nm wavelength ArF laser at 35 mJ cm−2 laser fluence and 50 Hz repetition rate. The UV–Vis-NIR spectrum of the sample showed that the transmission has increased and the crystal quality has improved after the irradiation. A time-resolved mode mismatch dual beam thermal lens setup was used to determine thermo-optical properties of the Nd:YAG crystal before and after the irradiation. The results of the thermal lens (TL) experiment showed the thermal diffusion coefficient has been increased from 0.0459 to 0.0612 cm2 s−1. In addition, TL signal values of the irradiated crystal were obtained less than half of the TL signal values of un-irradiated crystal. The results show that low dose ArF laser irradiation improves thermo-optical properties of the Nd:YAG laser crystal.

Photoluminescence Spectra of CdTe Single Crystals Subjected to Nanosecond Laser Irradiation

Low temperature photoluminescence (PL) of high-resistivity detector-grade Cl-compensated CdTe semiconductor crystals subjected to irradiation with nanosecond (τ = 7 ns) laser pulses of the second harmonic (λ = 532 nm) of a YAG:Nd laser is studied. Irradiation of CdTe crystals within the certain range of laser pulse energy densities results in a relative decrease in the emission intensity in both the deep energy level and edge regions and an increase in the exciton band intensity in the PL spectra. The evolution of the PL spectra depending on laser energy density, excitation level and temperature under excitation are analyzed. Laser-stimulated transformation of the point defect structure of the CdTe surface region and mechanisms of laser-induced defect formation are discussed. The optimal regimes of laser processing have been obtained which result in the minimum ratio of the defect and exciton bands that is an evidence of an increase in the structural perfection of the irradiated crystals.