Irradiation-induced Transformations Research Articles

Spectroscopic features of dissolved iodine in pristine and gamma-irradiated nitric acid solutions

While iodine speciation is important for a wide range of nuclear safety activities, understanding the mechanisms of the transformations of iodine between chemical forms and the sensitivity of these transitions to solution conditions and exposure to radiation remains an active area of research. This work curates spectroscopic data from several experimental techniques and establishes their sensitivity and limitations in detecting changes in iodine speciation in both neutral and acidic regimes. The techniques include Raman spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, 127I nuclear magnetic resonance (NMR) spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy. Analysis of these data indicates that these commonly accessible spectroscopies often have dynamic ranges of measurable concentrations that do not always overlap between all techniques. The experimental techniques are disparately sensitive to iodide (I−), molecular iodine (I2), triiodide (I3−) iodate (IO3−), and periodate (IO4−) species. Raman, FTIR, and NMR spectra were subsequentially analyzed using two-dimensional correlation analyses to generate high-resolution autocorrelation spectra. The use of these spectroscopies is then extended to tracking acidification-induced and gamma irradiation-induced transformations of dissolved sodium iodide in deionized water and concentrated nitric acid. Both dissolution into nitric acid and irradiation with a gamma source are demonstrated to perturb the iodine speciation promoting their assembly into I2 and/or I3−. While I2 and I3− species are undetectable with FTIR spectroscopy and 127I NMR spectroscopy, the species can be detected with UV–Vis spectroscopy, and in some instances, I3− can be detected with Raman spectroscopy in the low wavenumber region. Ultimately, the results of this work provide a path to designing optimal combinations of techniques to detect forms of iodine across a wide range of concentrations and conditions.

Electron beam irradiation-induced transformations in the electrical properties of 4’-octyl-4-cyanobiphenyl (8CB)

Changes in the dielectric and thermodynamical properties of electron beam-irradiated 4′-octyl-4-cyanobiphenyl (8CB) were studied. Irradiation-induced changes in the phase transition temperature, dielectric anisotropy, relaxation frequency and activation energy of an observed non-collective relaxation mode corresponding to molecular rotation about the short axis were determined in both nematic and smectic Ad phases. In the nematic phase, dielectric anisotropy increased for a small dose but decreased for a relatively high dose, whereas the relaxation frequency increased due to the irradiation. The pure and irradiated samples were characterised by UV–visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography, gas chromatography coupled with mass spectroscopy and pulse radiolysis. The observed changes in the dielectric parameters are related to the detachment of the CN group from some of the 8CB molecules due to the electron beam irradiation.

Irradiation-induced phase transformation in undeformed and deformed NiTi shape memory thin films by high-energy ion beams

Irradiation-induced transformations in sputter-deposited Ti-rich NiTi thin films have been investigated with special attention given to the effects of prior deformation on the response of martensite phase. Irradiation at low fluence was carried out at room temperature with Au ions at 350 MeV, such that the projected ion range greatly exceeded the film thickness and lattice damage was attributable mainly to electronic stopping effects (43 keV nm−1). Ion-beam modified microstructures were investigated using transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry. Amorphous tracks were observed in both Ti2Ni precipitates and martensite. The track diameter and the amount of amorphization were larger in the pre-deformed sample as compared to the undeformed sample. In both cases the displacive transformation temperatures and transformation enthalpies were depressed by irradiation, but to a greater degree in the pre-deformed material. Similarly, the extent of austenitic and R-phase regions observed to surround individual ion tracks was substantially greater for the pre-deformed films. These observations are discussed in terms of differences between the deformed and undeformed cases with respect to microstructure.

A viable way to tailor carbon nanomaterials by irradiation-induced transformations

Since the discovery of carbon nanotubes (CNT), transmission electron microscopy (TEM) has been the most important tool in their investigation. It is possible to use electron irradiation in a TEM to construct a single-walled carbon nanotube (SWCNT) from an amorphous carbon film. Here we show that such a synthesis method creates a large number of carbon ad-atoms, which after some critical amount of radiation act to restore the system by reconstructing the carbon film. The behavior of the ad-atoms can be controlled by adjusting the current density in the microscope, suggesting that carbon nanomaterials can be tailored by electron irradiation.

In situ TEM study of irradiation-induced transformation in TiNi shape memory alloys

ABSTRACTTiNi shape memory alloy (SMA) has potential applications for nuclear reactors and its phase stability under irradiation is becoming an important topic. Some irradiation-induced diffusion-dependent phase transformations, such as amorphization, have been reported before. In the present work, the behavior of diffusion-independent phase transformation in TiNi SMA was studied by electron irradiation at room temperature. The effect of irradiation on the martensitic transformation of TiNi shape memory alloys was studied by Transmission Electron Microscopy (TEM) with in-situ observation and differential scanning calorimeter (DSC). The results of TEM and DSC measurements show that the microstructure of samples is R phase at room temperature. Electron irradiations were carried out using several different TEM with accelerating voltage of 200 kV, 300 kV, 400 kV and 1000 kV. Also the accelerating voltage in the same TEM was changed to investigate the critical voltage for the effect of irradiation on phase transformation. It was found that a phase transformation occurred under electron irradiation above 320 kV, but never appeared at 300 kV or lower accelerating voltage. Such phase transformation took place in a few seconds of irradiation and was independent of atom diffusion. The mechanism of Electron-irradiation-induced the martensitic transformation due to displacements of atoms from their lattice sites produced by the accelerated electrons.

Self-diffusion and solute diffusion in alloys under irradiation: Influence of ballistic jumps

We have studied the influence of ballistic jumps on thermal and total diffusion of solvent and solute atoms in dilute fcc alloys under irradiation. For the diffusion components that result from vacancy migration, we introduce generalized five-frequency models, and show that ballistic jumps produce decorrelation effects that have a moderate impact on self-diffusion but that can enhance or suppress solute diffusion by several orders of magnitude. These could lead to new irradiation-induced transformations, especially in the case of subthreshold irradiation conditions. We also show that the mutual influence of thermal and ballistic jumps results in a nonadditivity of partial diffusion coefficients: the total diffusion coefficient under irradiation may be less than the sum of the thermal and ballistic diffusion coefficients. These predictions are confirmed by kinetic Monte Carlo simulations. Finally, it is shown that the method introduced here can be extended to take into account the effect of ballistic jumps on the diffusion of dumbbell interstitials in dilute alloys.

Stability of metallic CsCl-structured alloys under ion irradiation

The ion irradiation stability of the CsCl phases CoAl, IrAl, SiRu, and AuZn has been investigated. Thin-film (∼500-Å-thick) transmission electron microscopy samples were irradiated with Xe to a maximum dose of 4×1015 ions/cm2 at room temperature. Irradiation-induced transformations in the compound samples were examined by transmission electron diffraction. The alloys CoAl, IrAl, and AuZn remained crystalline while SiRu became amorphous. Analysis of our findings and other previously reported experimental results indicate that CsCl compound stability under ion irradiation is strongly correlated with atomic mobilities.

Electron Irradiation-Induced Transformations in Alloys and Ceramics

Revue par microscopie electronique a haute tension des changements structuraux tels que precipitation, decomposition spinodale, amorphisation cristallisation dans differents alliages (NiTi, CuBe, FeMo) et ceramiques (SiC, Si 3 N 4 , TaC)

Photochemical studies. Photofragmentation of substituted 1,2-dihydrophthalic anhydrides

The irradiation-induced transformations of 4,5-diphenyl-1,2-dihydrophthalic anhydride as well as those of the 3,6-dimethyl-4,5-diphenyl and 3,4,5,6-tetraphenyl derivatives are elaborated. All undergo photofragmentation, viz., CO + CO/sub 2/ ejection to give aromatic hydrocarbons, while only 4,5-diphenyl-1,2-dihydrophthalic anhydride also closes electrocyclically to the bicyclo(2.2.0)hex-5-ene product. The quantum yields for fragmentation are indicative in this respect. The rearrangement accompanying the fragmentation of 3,4,5,6-tetraphenyl to give 1,2,3,5-tetraphenylbenzene was shown to occur via a triplet excited state, populated by benzene sensitization.

Synthesis and photochemistry of 2,3,8,9-tetrahydroindenone-1

The novel β,γ,δ,ε-unsaturated ketone ( 2 ) was prepared and all its photoproducts were identified, following wavelength dependent, irradiation-induced transformations.

ChemInform Abstract: PHOTOCHEMISTRY OF 1,2‐DIHYDROPHTHALIMIDE

AbstractDas durch Belichtung von (I) zugängliche Dihydrophthalimid (II) ergibt bei der Belichtung in Acetonitril die Verbindung (III)‐(VII).

Photochemistry of 1,2-dihydrophthalimide

The title compound undergoes irradiation-induced transformations, the most interesting being fragmentations to benzene and benzamide, and rearrangements including degenerate 1,5-acyl shifts and 1,2-acyl shifts with cyclopropane ring closure; a mechanism is proposed, following product isolation and deuterium labelling studies.