Pre-irradiated Samples Research Articles

Reactor annealing of pre-irradiated model materials

Experiments on annealing together with reactor irradiation of diamond and silicon carbide which have been pre-irradiated at low temperature are described. The results are compared with the data on annealing of the same pre-irradiated samples without irradiation – annealing in a furnace. It is shown that in a certain range of experimental conditions annealing with irradiation is more effective than thermal annealing alone. The lattice parameters of diamond and silicon carbide are restored more rapidly with such irradiation stimulated annealing than with simple annealing in a furnace at the same temperature and for the same time. The effect obtained depends on the intensity of the irradiation – the higher the intensity, the more quickly and completely the properties of the pre-irradiated samples are restored. Thus a paradoxical situation arises on some time segment of annealing with simultaneous irradiation where the concentration of defects actually decreases with increasing irradiation dose.

Method of nondestructive monitoring of fuel-element seal tightness

A method of monitoring the seal tightness of fuel elements is described. The method is based on determining leaks of gaseous fission products during annealing of preirradiated samples. The basic steps using this method are described and mathematical expressions for determining the constants of the activation model of the leakage of gaseous fission products, which is used for processing and analyzing experimental results, are presented. The measurements results obtained using the method develop are compared with the results obtained in reactor tests of spherical fuel elements. An example using the technique is described: simulators, for which the temperature dependence of 135 Xe leakage (to 1400 K) is obtained and a quantitative relation between the number of microfuel elements with damaged coatings and leakage of gaseous fuel products, are tested. It is found that technological contamination of graphite of the simulators by uranium is present.

Thermoluminescence and photoluminescence study of caso4: Dy nanophosphor for 6 mev energy electron dosimetry

Nanoparticles of CaSO 4 : Dy with size around 25 nm, were synthesized by the chemical co-precipitation method for the purpose of high energy electron dosimetry. The nanocrytstalline samples were irradiated with 6 MeV energy electrons having fluence varied from 3 × 10 14 to 2 × 10 15 e/cm 2 .The pre and post irradiated samples were characterized by the XRD, SEM, PL and TL techniques. The XRD spectra show the orthorhombic phase and do not change with the electron fluence. Moreover, the particle size found to be around 25 nm and marginally increased from 25 nm to 34 nm with the increase in the electron fluence. SEM image confirms the existence of the nanoparticle around 30 to 40 nm. In PL emission spectra, a shift towards lower wavelength has been observed with decrease in particle size from micrometer to nanometer. This mainly attributes to the extension in the band gap of Dy 3+ ions. The TL spectra exhibit four peaks at around 437,545,638, and 748 K respectively. The TL response curve shows that the peak intensity initially increased with electron fluence, and at a fluence of 9 × 10 14 e/cm 2 saturates then decreased with increase in the electron fluence. It is mainly due to the generation of different kinds of trapping centers. The present study indicates that the CaSO 4 : Dy phosphor can be used for the measurement of dose of 6 MeV energy electrons over a range varying from 1 kGy to 25 kGy.

Irradiation effects in CaF2: ZnO nanostructed crystals

Effects of β, X, and UV radiation were studied in CaF2: ZnO single crystals in which ZnO was embedded as nanoparticles. Absorption measurements of these crystals showed a steep increase below 250nm and a weak absorption peak at about 310nm. After prolonged β irradiation, additional absorption bands were recorded at 395 and 595nm. The irradiated samples showed during heating several thermoluminescence (TL) peaks. Samples which had been exposed to β-irradiation at RT and subsequently illuminated at LNT with 390nm light showed during re-heating to RT several TL peaks that are attributed to a process of photo-transferred TL (PTTL). Main photoluminescence (PL) emission bands were recorded at 320 and 340nm with excitation maxima near 250 and 300nm. These emission bands were also observed during X-irradiation as well as additional emission bands near 355 and 400nm. In pre-irradiated samples, a 320nm luminescence band could also be excited by 395nm light and is attributed to a process of photostimulation. The stimulation maxima of the OSL and PTTL in the 390nm region are apparently due to the observed absorption band at 395nm induced by the β-irradiation. The fact that some of the same emission bands appeared in the XL, PL, TL and OSL of this crystal indicates that the same luminescence centers are involved in these emissions.

Thermoluminescence of some [formula omitted] doped fluoride crystals

Irradiation effects and dosimetric properties have been studied for CaF 2 , KYF 4 and CsY 2 F 7 crystals doped with Pr 3 + . In particular, thermoluminescence (TL) excitation spectra have been measured in the 120–200 nm region and the CaF 2 : Pr 3 + and KYF 4 : Pr 3 + crystals show excitation maxima at 135 and 140 nm, respectively. Some of the main TL peaks appear after vacuum ultraviolet (VUV) irradiation at the same temperatures as after β irradiation, indicating that they are due to the same radiation-induced trapping levels. Optically stimulated luminescence (OSL) and phototransferred TL (PTTL) have also been recorded in pre-irradiated samples and stimulation spectra have been measured. The OSL emission spectra show some of the same bands as in the case of the XL and TL, indicating that they are due to the same luminescence centers. The TL sensitivity of CaF 2 : Pr 3 + is ∼ 5 times higher than that of TLD-100, and the TL sensitivity of KYF 4 : Pr 3 + is slightly higher than that of TLD-100, whereas the sensitivity of CsY 2 F 7 : Pr 3 + is much lower. The main TL peaks of KYF 4 : Pr 3 + and CaF 2 : Pr 3 + appear above 480 K and, accordingly, only low TL fading is expected during storage at RT. The dose dependence of the main TL peaks is nearly linear in a dose range up to about 2000 Gy.

Recent developments of CERN RD39 cryogenic tracking detectors collaboration: CERN RD39 Collaboration

CERN RD39 Collaboration is working on radiation hard cryogenic silicon detectors, for environments such as at the Super-LHC. A promising technique for the operation of low temperature detectors and diodes is the current injection of pre-irradiated samples (CID). A new setup, based on the Cryogenic Transient Current Technique (C-TCT), has been built to characterize Si samples (CCE). In addition, we report here some preliminary measurements for the evaluation of laser and plasma-cut sensors developed for edgeless detectors, for which the sensitive area should extend to a few μm from the physical border.

Tritium release from breeding blanket materials in high magnetic field

Under the operating conditions of a fusion reactor, the blanket materials: ceramic and Be pebbles will be at a high temperature (up to 1123 K), under action of intense radiation (up to 10 19 n m −2 s −1) and magnetic field (MF) up to 7–10 T. In order to introduce action of radiation and MF in post-irradiation investigations of the tritium release from the blanket materials, a special rig for thermo-annealing of pre-irradiated samples at a high temperature up to 1120 K under irradiation with fast electrons of 5 MeV and dose rate 14 MGy/h in MF up to 1.7 T was used for this study. A delay of the tritium release in MF of 2.4 T at thermo-annealing of the lithium orthosilicate Li 4SiO 4 pebbles (FZK) irradiated in the EXOTIC-8/8 experiment was observed. Chemical forms of the tritium localised in the pebbles and the tritium distribution were determined (up to 75%, in T +). The main form of the tritium localized in the beryllium pebbles irradiated in the BERYLLIUM experiment is T 2 (85–95%). A stimulating effect of a MF of 1.7 T on the tritium release from the Be pebbles at the annealing at 1120 K under the radiation was observed (up to 80%).

Interaction of alpha radiation with thermally-induced defects in silicon

The interaction of radiation-induced defects created by energetic alpha particles and thermally-induced defects in silicon has been studied using a Deep Level Transient Spectroscopy (DLTS) technique. Two thermally-induced defects at energy positions E c-0.48 eV and E c-0.25 eV and three radiation-induced defects E2, E3 and E5 have been observed. The concentration of both of the thermally-induced defects has been observed to increase on irradiation. It has been noted that production rates of the radiation-induced defects are suppressed in the presence of thermally-induced defects. A significant difference in annealing characteristics of thermally-induced defects in the presence of radiation-induced defects has been observed compared to the characteristics measured in pre-irradiated samples.

Behaviour of simplified nuclear waste glasses under gold ions implantation: A microluminescence study

Simplified nuclear borosilicate glasses doped with rare-earth elements were irradiated by gold ions. Thanks to fluorescence line narrowing spectroscopy (selective excitated photoluminescence), two major Eu3+ sites distributions were identified in the case of pre-irradiated samples due to the splitting of the 5D0→7F1 transition triplet. Evolution of europium ion environments under irradiation in these glasses was studied by non-selective microluminescence at room temperature. As well, spectroscopic studies demonstrated strong broadening in the distribution of the rare-earth environment for increasing irradiation doses. Determination of the luminescence asymmetric ratio allowed us to conclude that the symmetry of the sites is lowered by high energy nuclear deposits. Environment modifications under irradiation are attributed to a site distribution enlargement within the same two site distributions, a silicate and a borate one, and to lower symmetry mean sites.

Radiation effects, energy storage and its release in solid rare gases

An irradiation of solid argon sample by electrons ionizes the Ar atoms, and part of the beam energy is stored in the solid mainly in the form of self-trapped Ar(2)(+) holes. The pre-irradiated samples are investigated by methods of the so called "activation spectroscopy". During their controlled warm-up three thermally stimulated effects are observed and, in our experiments, simultaneously monitored: a VUV emission resulting from neutralization of the Ar(2)(+) holes by electrons, an anomalous desorption of surface atoms, and an exoelectron emission. A comparison of experiments with linear and step-wise sample heating shows clearly that all three processes are intimately connected. The heating detraps electrons, which neutralize the Ar(2)(+) holes resulting in a bound-free emission of argon dimers, centered around 9.7 eV. The excess energy set free during this process may dislodge surface atoms leading to an anomalous, low temperature, pressure rise. Some of the electrons can also be directly extracted from the sample and detected as an exoelectron current. The experiments provide information about the depth of electron traps, and indicate that there is a nearly continuous distribution of trapping energies.

Effects of photostimulation in natural zircon

Abstract Effects of optical stimulation were studied in unirradiated as well as in X, β and VUV irradiated natural zircon crystals. Various optical and dosimetric properties were investigated and in particular thermoluminescence (TL) and optically stimulated thermoluminescence (OSTL or PTTL), as well as optically stimulated luminescence (OSL). After X or β irradiation at RT, main TL peaks appeared in the samples at about 354, 385 K and weaker ones at about 470, 520 and near 600 K. TL could also be excited by monochromatic VUV radiation. Results show that the same traps are responsible for the TL induced by VUV as by X or β irradiation. In pre-irradiated samples, a notable OSTL was recorded below RT as well as at about 420 K. The same emission bands appeared in the XL as in various TL and OSTL peaks, indicating the same luminescence centers are involved in these emissions. OSTL stimulation spectra showed maxima at 425 and 294 nm. Prolonged illumination with these wavelengths also caused a notable decrease in the OSTL; this bleaching effect is attributed to the depletion of the carriers from the trap responsible for the phototransfer. The TL sensitivity of the main TL peaks below 400 K was ∼ 1 10 of that of TLD-100, and that of the higher temperature TL peaks was even lower by 1–2 orders of magnitude. The TL peaks below 400 K are subject to fast thermal fading at RT. The application of the OSTL method may therefore be preferable to the regular TL method in these crystals.

Radiation hardness of silicon detectors based on pre-irradiated silicon

Radiation hardness of planar detectors processed from pre-irradiated and thermo-annealed n-type FZ silicon substrates, and standard FZ as a reference, was studied. The high purity n-Si wafers with carrier concentration 4.8×10 11 cm −3 were pre-irradiated in Kiev's nuclear research reactor by fast neutrons to fluence of about 10 16 neutrons/cm 2 and thermo-annealed at a temperature of about 850 °C. Silicon diodes were fabricated from standard and pre-irradiated silicon substrates by IRST (Italy). All diodes were subsequently irradiated by fast neutrons at Kiev and Ljubljana nuclear reactors. The dependence of the effective doping concentration as a function of fluence ( N eff =f( Φ)) was measured for reference and pre-irradiated diodes. Pre-irradiation of silicon improves the radiation hardness by decreasing the acceptor introduction rate ( β), thus mitigating the depletion voltage ( V dep) increase. In particular, β in reference samples is about 0.017 cm −1, and for pre-irradiated samples is about 0.008 cm −1. Therefore, the method of preliminary irradiation can be useful to increase the radiation hardness of silicon devices to be used as sensors or detectors in harsh radiation environments.

Kinetics of NO and NO2Evolution from Illuminated Frozen Nitrate Solutions

The release of NO and NO2 from frozen aqueous NaNO3 irradiated at 313 nm was studied using time-resolved spectroscopic techniques. The kinetic behavior of NO and NO2 signals during on-and-off illumination cycles confirms that NO2 is a primary photoproduct evolving from the outermost ice layers and reveals that NO is a secondary species generated deeper in the ice, whence it eventually emerges due to its inertness and larger diffusivity. NO is shown to be more weakly held than NO2 by ice in thermal desorption experiments on preirradiated samples. The partial control of gaseous emissions by mass transfer, and hence by the morphology and metamorphisms of polycrystalline ice, is established by (1) the nonmonotonic temperature dependence of NO and NO2 signals upon stepwise warming under continuous illumination, (2) the fact that the NO, NO2 or NOx (NOx identical with NO + NO2) amounts released in bright thermograms performed under various heating ramps fail to scale with photon dose, due to irreversible losses in the adsorbed state. Because present NO/NO2 ratios are up to 10-fold smaller than those determined over sunlit snowpacks, we infer that the immediate precursors to NO mostly absorb at lambda > lambda(max) (NO3-) approximately 302 nm.

Effects of heat treatment on trapping and release of tritium from He pre-irradiated tungsten

The effects of heating on retention of tritium implanted into tungsten pre-irradiated with helium have been examined by β-ray-induced X-ray spectrometry (BIXS), which gives information about changes in the amount and depth profile of tritium retained on/in materials. Tritium implantation and isochronal heating of the helium pre-irradiated and un-irradiated tungsten samples were repeated as a series of experiments, and changes in the X-ray spectra were measured in each heating cycle. Quite different decreasing behavior between Ar(Kα) and W(Mα) X-ray intensities for both samples was observed in the heating process, and it was seen that the majority of tritium implanted into the helium pre-irradiation sample was trapped by the radiation defects rather than in helium bubbles.

Charge-carrier dynamics and trap generation in nativeSi/SiO2interfaces probed by optical second-harmonic generation

Employing femtosecond laser pulses [1.59 eV, $(80\ifmmode\pm\else\textpm\fi{}5)\mathrm{fs},$ 80 MHz], we perform time-dependent second-harmonic (SH) measurements to probe the dynamics of charge-carrier transfer processes across native ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ interfaces in a new peak intensity regime up to $100{\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}.$ The SH signal increases steadily during irradiation up to $45{\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$ laser peak intensity, but changes its temporal evolution above $45{\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}:$ as a different phenomenon, the SH signal surpasses a maximum, decreases slowly, and appears to approach a steady state level. We assign this observed signal decrease to the light induced injection of holes into the ${\mathrm{SiO}}_{2}$ thin layers involving a four-photon process, which opposes the electron contributions (three-photon process). Furthermore, we investigate the SH signal development after irradiation interrupts and find that preirradiated samples show a drastically accelerated SH response. Both, the electron and the hole injection processes appear to be about two orders of magnitude faster in preirradiated than in ``virgin'' samples. We assign this acceleration to the laser induced generation of permanent defects, which affect electron as well as hole trapping in the ${\mathrm{SiO}}_{2}$ layers. In addition the SH signal amplitude is shown to be a function of the dark period duration, and the typical time constant for the depopulation of hole trap sites under dark conditions has been extracted and amounts to $(110\ifmmode\pm\else\textpm\fi{}15)\mathrm{s}.$ We present an empirical model involving four exponential functions, taking into account the electron and hole contributions to the time-dependent SH response. This model fully reproduces the recorded experimental data. It supports our interpretation of opposing three- and four-photon processes being involved in electron and hole injection, respectively. Finally, we employ SH imaging in comparison with scanning electron microscopy to visualize sample areas with laser defects.

Effects of Additives, Photodegradation, and Water-tree Degradation on the Photoluminescence in Polyethylene and Polypropylene

Photoluminescence (PL) spectra induced by irradiation of ultraviolet photons are compared among low-density polyethylene (LDPE), crosslinked polyethylene (XLPE), and polypropylene (PP). Three PL bands appear around 4.2, 3.6, and 3.1 eV in LDPE and XLPE, while similar three PL bands are observed at similar energies in PP. The PL spectra and their decay profiles are independent of the presence of additives and are also independent of whether the samples were crosslinked or not. These results indicate that neither the additives nor the crosslinking has any significant effects on the respective three PLs in PE and PP. When the sample was pre-irradiated by the ultraviolet photons under different atmospheres (air, O2, and vacuum), all the PL intensities decrease with the progress of the pre-irradiation regardless of whether the sample is PE or PP. Therefore, all the PLs are considered to result from impurities. In all the pre-irradiated samples, a new PL band appears at 2.9 eV, of which intensity is stronger when the oxygen partial pressure during the pre-irradiation was lower. This PL is considered to be due to photo-induced conjugated double bonds. It has also been confirmed that water-tree degradation in LDPE or in XLPE does not contribute to PL.

Effect of high-energy radiation and alkali treatment on the properties of cellulose

The effect of the treatment with NaOH or tetramethyl ammonium hydroxide solutions on preirradiated cotton-cellulose was investigated. Both the radiation and the treatment with alkali solutions caused loss of weight in cellulose; however, there was a synergism, a high weight loss was observed during alkali treatment of preirradiated samples. The radiation caused scissions of the cellulose chains and during the treatment with aqueous alkaline solutions some smaller fragments dissolved, resulting in a strong absorbance of the solutions with maximum at around 268 nm. It was attributed to the absorbance of aldehyde/keto groups.

Enhancement of bulk nucleation in a-Si 1− xGe x on SiO 2 for low-temperature solid-phase crystallization

Nucleation phenomena in a-Si 1− x Ge x films on SiO 2 were examined in order to achieve low-temperature solid-phase crystallization. First, film thickness dependence of nucleation was investigated. The nucleation frequency per unit area increased with increasing film thickness, which was attributed to that bulk nucleation was dominant compared with interface or surface nucleation. Next, in order to enhance bulk nucleation in thin films, effects of the initial amorphicity modulation induced by Ar + irradiation (25 keV, 1×10 16 cm −2) before annealing were investigated. The incubation time for nucleation in pre-irradiated samples during subsequent annealing at 600 °C was significantly decreased to 1/20 of that without pre-irradiation, which was tentatively assigned to enhancement of atomic arrangement induced by densification of a-Si 1− x Ge x films. It is expected that optimization of the irradiation conditions will realize low-temperature (<500 °C) formation of poly-Si 1− x Ge x films on SiO 2.

Tunneling effect in electron-stimulated desorption of Li + from LiF/Si [formula omitted

It is shown that the kinetic-energy distributions of 6Li + and 7Li + ions desorbed during electron irradiation from the system LiF/Si(1 0 0) exhibit fine structures. Their character suggests that they correspond to Li + ions emitted according to the wave packet squeezing desorption model. This observation enables us to determine the final repulsion potential active in the Li + desorption process. The oscillatory-structure onsets show that these potentials have the potential-energy barrier of a height of about 1.4 eV for the virgin LiF samples and of about 2.8 eV for LiF preirradiated with a dose of 50 μC/mm 2. For preirradiated samples the oscillatory structures are less pronounced, but for such samples relatively strong and very narrow peaks located at 2.12 eV for 6Li + and at 2.03 eV for 7Li +, respectively, can be detected. These peaks are interpreted as ions trapped in the temporary bound-states located above the vacuum level of the sample. Due to a relatively high transmission coefficient the ions can tunnel trough the temporary existing potential barrier. The lifetime of the potential barrier estimated from the peak energy width and the Heisenberg uncertainty principle is about 7 fs. Some other aspects of the dynamic lattice distortion are also discussed.

Can a thin film to be pinned at the surface by hollows?

Glass slices with a low roughness (∼0.2 nm) irradiated with swift heavy ions were studied by atomic force microscopy (AFM). Ion impacts are materialized by the formation of hollow structures having a maximal depth of ∼3 nm. In order to investigate the role played by such modifications on the surface properties, thin gold films of ∼2 nm thickness were deposited on both virgin and pre-irradiated samples. After annealing at 150 °C, a red shift is observed in the optical absorption of virgin samples indicating a gold cluster formation, whereas no significant modifications were observed in samples pre-irradiated with energetic Kr ions. By combining AFM observations with optical absorption spectroscopy we discuss in this paper the role played by topographic modifications on both the surface diffusion and the film wetting phenomena.