Irradiated NaCl Crystals Research Articles

Real-time observation of dynamic structure of liquid-vapor interface at nanometer resolution in electron irradiated sodium chloride crystals

The dynamics and structure of the liquid and vapor interface has remained elusive for decades due to the lack of an effective tool for directly visualization beyond micrometer resolution. Here, we designed a simple liquid-cell for encapsulating the liquid state of sodium for transmission electron microscopic (TEM) observation. The real-time dynamic structure of the liquid-vapor interface was imaged and videoed by TEM on the sample of electron irradiated sodium chloride (NaCl) crystals, a well-studied sample with low melting temperature and quantum super-shells of clusters. The nanometer resolution images exhibit the fine structures of the capillary waves, composed of first-time observed three zones of structures and features, i.e. flexible nanoscale fibers, nanoparticles/clusters, and a low-pressure area that sucks the nanoparticles from the liquid to the interface. Although the phenomenons were observed based on irradiated NaCl crystals, the similarities of the phenomenons to predictions suggest our real-time ovserved dynamic structure might be useful in validating long-debated theoretical models of the liquid-vapor interface, and enhancing our knowledge in understanding the non-equilibrium thermodynamics of the liquid-vapor interface to benefit future engineering designs in microfluidics.

Characterization of the size and orientation of Na andCl2 nanocrystals in electron irradiated NaCl crystals by means of synchrotron radiation

Samples of synthetic NaCl crystals have been exposed to doses of electron irradiation up to10−2 TGy (1 Trad) at about100 °C, and studiedsubsequently at T = 95 K by means of synchrotron radiation (SR). In addition to the earlier establishedKurdjumov–Sachs orientation relationship (K–S OR) for Na precipitates, thefollowing OR is revealed between solid chlorine and the host NaCl crystal system:, . The size and shape of the Cl2 precipitates has been studied as a function of the amount of radiation damage (i.e. the concentrations ofNa and Cl2).

Characterization of Na precipitates in electron irradiated NaCl crystals by wide angle X-ray scattering (WAXS)

Samples of synthetic NaCl crystals have been exposed to different doses of electron irradiation up to 1500 MGy (150 Grad) at elevated temperatures, and studied subsequently by X-ray diffraction. Our experimental results clearly show that there is a close correspondence between the geometrical properties (such as lattice distances and the crystal orientation) of the host crystal and the radiation-induced Na precipitates, which is referred to as the Kurdjumov–Sachs orientation relationship (K–S OR). The size of the precipitates has been estimated.

AFM of Metallic Nano-Particles and Nano-Structures in Heavily Irradiated NaCl

AFM investigations are reported for heavily, electron irradiated NaCl crystals in ultra high vacuum (UHV) in the non-contact mode with an UHV AFM/STM Omicron system. To avoid chemical reactions between the radiolytic Na and oxygen and water, the irradiated samples were cleaved and prepared for the experiments in UHV. At the surface of freshly cleaved samples, we have observed sodium nano-precipitates with shapes, which depend on the irradiation dose and the volume fraction of the radiolytic Na. It appears that the nano-struchires consist of (i) isolated nano-particles, (ii) more or less random aggregates of these particles, (iii) fractally shaped networks and (iv) “fabrics” consisting of bundles of Quasi-1D arrays forming polymeric networks of nano-particles. Almost independent of the concentration of the metallic Na in the samples the size of the individual nano-particles is in the range 1–3nm. Our new AFM results are fully in line with our CESR and previous Raman scattering results.

Effect of the void formation on the explosive fracture of electron irradiated NaCl crystals

Experimental and theoretical results are presented on formation of colloids, halogen bubbles and large vacancy voids in heavily irradiated NaCl crystals leading to their explosive decomposition into small pieces under further irradiation or subsequent heating. The dependence of the radiation stability of material with increasing irradiation dose on the void evolution is analyzed. It is shown that voids can grow very fast as compared to colloids and bubbles. For doses higher than 100 Grad, the void dimensions can exceed the mean distance, first, between bubbles and then between colloids resulting in their collisions with voids. Collisions with bubbles fill the voids with gas, and subsequent collisions with colloids (during further irradiation or heating) bring the halogen gas and metal to a back reaction inside the voids. Such a sudden release of stored energy can be shown to result in a temperature spike (above 104 K) and instantaneous gas pressure rise up to 1 GPa within the voids, which may transform voids into penny-shaped cracks along the cleavage planes of the matrix. A subsequent growth of the cracks results in fracture of the material. Dependence of the critical amount of stored energy required for the void–crack transition on the mean size of the voids is estimated and compared with experimental data.

Effect of dose rate, temperature and impurity content on the radiation damage in the electron irradiated NaCl crystals

The dependencies of void formation and radiolytic sodium accumulation on the irradiation dose, dose rate, temperature and impurity content are analyzed within a framework of a theoretical model, which is based on a new mechanism of dislocation climb. The mechanism involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of excess H centers at dislocation lines. Voids are shown to arise due to the reaction between F and VF centers at the surface of halogen bubbles. All reactions involved in the evolution of extended defects are controlled by the difference between the absorption of H centers and F centers. This difference is determined by the material specific parameters responsible for the bias factors of extended defects and by the mean concentration of point defects. The latter depends on the temperature and dose rate as described in the present paper. Impurities can facilitate or suppress radiation damage formation depending on their effect on the nucleation of extended defects under irradiation. This is demonstrated by comparing theoretical results obtained for dose dependence of colloid volume fraction at different dislocation densities with experimental data obtained in crystals doped with different impurities.

A Thin, Composite Sodium Chloride Dosimeter with Diffuse Reflected Light Spectrophotometric Read Out

Optical absorption by electrons trapped in natural anionic vacancies in NaCl has been used for the construction of a dosimeter for radiation processing. To meet the demands of electron beam processing, characterised by congestion of isodoses, the active part of the dosimeter, i.e., the microcrystals of NaCl are embedded in a 0.3 mm thick polyethylene film, in which doses from 10 MeV electrons do not exceed ±2% difference in extreme parts of the dosimeter body. The dosimetric film is opaque and the optical density at the wavelength λmax = 465 nm, i.e., the maximum absorption of the F band, is measured by diffuse reflected light spectrophotometry (DRS). The measurement is performed against the unirradiated film as reference, thus increasing the accuracy, by self-compensation of signals not belonging to the absorption of F-centres. The spectrum obtained in such a way is identical with that of F-centres in irradiated single NaCl crystals. The calibration curve of the height of the band is almost linear versus the dose in the range of several tens of kilograys. As ordinary grades of sodium chloride may be used, the dosimeter developed is cheap and enables to map the irradiation field in objects of complicated geometry.

Study of Sodium Colloids in Heavily Irradiated NaCl Crystals by Nuclear Magnetic Resonance

AbstractStrong irradiation of NaCl crystals results in a formation of sodium colloids which exhibit metallic properties. In consequence, besides the 23Na line of NaCl a second well‐separated 23Na line occurs in the NMR spectrum caused by the Knight shift of the conduction electrons. We present Knight shift and nuclear spin relaxation measurements performed on the “metallic” 23Na line in e–‐irradiated NaCl single‐crystals between about 4 and 390 K. Evaluation of the data leads to detailed information on the electronic properties, atomic self‐diffusion, and melting behavior of the colloids. The results are discussed in view of corresponding data obtained in bulk sodium.

Magnetoplastic effect in irradiated NaCl and LiF crystals

The effect of low x-ray irradiation doses (≈102 rad) on the magnetoplastic effect — the detachment of dislocations from paramagnetic centers under the action of an external magnetic field B — in alkali-halide crystals has been investigated. The measurements were performed on LiF crystals and three types of NaCl crystals, differing in impurity content. The dependence of the mean free path l of the dislocations on the rotational frequency ν of a sample in a magnetic field was especially sensitive to low irradiation doses. In unirradiated crystals this dependence is a single-step dependence and is characterized by a critical frequency νc ∝B2 above which the magnetoplastic effect is not observed. The frequency νc depends only on the type of paramagnetic centers, and not on their density. Even the lowest irradiation dose employed (<100 rad) leads to a sharp restructuring of the dependence l(ν), converting it into a two-step dependence (for edge dislocations) with an additional critical frequency νc2, that is insensitive to the irradiation dose, and that corresponds to the appearance of magnetically sensitive stoppers of a new type under irradiation. The initial critical frequency νc1, as a rule, also varies with the dose, reflecting the change in state of the impurity complexes (Ca in NaCl and Mg in LiF). Specifically, it is shown for NaCl(Ca) crystals that as the irradiation dose increases, the frequency νc1 increases, gradually approaching the value νc2, so that by the time the dose is ≈300 rad, the dependence l(ν) once again becomes a single-step dependence, dropping sharply only for ν⩾νc2. It is shown that the addition of a small number of Ni atoms to a NaCl crystal makes the Ca complexes radiation resistant, and the critical frequency νc1 corresponding to them initially equals νc2 for crystals with no Ni. The recombination kinetics of radiation defects in the case in which the samples are irradiated under a tungsten lamp was investigated. A possible physical model of the observed dependences is discussed.

Explosive Phenomena in Heavily Irradiated NaCl

In heavily irradiated NaCl crystals explosive phenomena can be initiated during irradiation or afterwards when samples are heated to temperatures between 100 and 250 degrees C. During irradiation of NaCl Na and Cl-2 precipitates and void structures are produced along with the accumulation of stored energy (maximum value today similar to 76 kJ/mol, or 18.5% of the enthalpy of formation of NaCl, -411.2 kJ/mol). It is proposed that the collapse of large voids initiate the explosive release of stored energy, giving rise to a localized hot spot and a thermal shock wave. We discuss the nature of these explosive phenomena and show that a basically stable insulating material, such as NaCl may become very unstable after subjecting them to high doses of ionizing radiation.

Lyoluminescence of luminol in aqueous alkaline metal hydroxides

The lyoluminescence emission spectra of luminol, induced by γ-irradiated NaCl in aqueous alkaline earth metal hydroxides, are recorded. Continuous emission bands are observed in the visible region from 390 to 535 nm. These emission bands on resolution showed two peaks at 430 and 460 nm, respectively in all hydroxides. An additional band of 490 appears in the case of calcium hydroxide. The colour centres released during disintegration of irradiated NaCl crystals in aqueous solution react with luminol to produce various excited molecular species, which are responsible for observed lyoluminescence of luminol.

Efficiency of transfer of stored energy from gamma-irradiated NaCl in aqueous ammonium nitrate solution

The reduction of nitrate to nitrite is studied by the transfer of energy stored in γ-irradiated NaCl crystals to aqueous ammonium nitrate solution. The G(NO 2 −) values are evaluated under varying conditions of energy transfer from γ-irradiated NaCl crystals. Similarly, the G(NO 2 −) value for direct radiolysis of 0.1 M aqueous ammonium nitrate solution is determined. The efficiency of energy transfer is the ratio of the G-values of the two pathways. The efficiency is 60% at low doses. It is explained on the basis of two processes. The first process depends upon the extent to which the energy can be stored in irradiated NaCl crystals, while the second process of energy transfer is governed by various parameters which limit the yield of nitrite.

Bleaching of color centers in NaCl crystals with laser pulses

Abstract Bleaching of F centers in gamma irradiated NaCl crystals at room temperature and elevated temperatures using laser pulses from pulsed laser systems is studied in this paper. The rate of decay of F centers is monitored and the decay constants are evaluated. A comparison on the decay kinetics is made for CW and pulsed bleaching with a He-Cd laser. F center to C center conversions using a thermo-optic scheme are carried out with nanosecond dye laser pulses in gamma irradiated NaCl crystals.

Photonic information storage in NaCl crystals via F→C conversion

Transformation of F centres in irradiated NaCl crystals to colloidal (or C) centres by a thermo-optic process is employed to write information into the crystals using a HeCd laser. Hurter-Driffield curves of the storage are constructed and optimum parameters for writing are determined.

Lyoluminescence induced by gamma-irradiated NaCl in aqueous acridine orange solution

The emission spectrum of lyoluminescence of acridine orange was recorded on a Fuess spectrograph. A continuous emission band was observed from 500 to 640 nm. On resolution, it showed two-banded emission with peaks at 565 and 603 nm respectively. The colour centers released during dissolution of irradiated NaCl crystals in aqueous acridine orange solution react to produce excited dimer and trimer species of acridine orange. It is suggested that these excited species are responsible for the observed lyoluminescence emission spectrum of acridine orange.

Lyoluminescence of luminol in aqueous ammonia

The emission spectrum of lyoluminescence of luminol in aqueous ammonia was recorded on a Fuess spectrograph. A continuous emission band from 370 to 600 nm, on resolution, showed three-banded emission with peaks at 413, 463 and 545 nm. The resolved fluorescence spectrum of luminol in ammonia showed two peaks, at 407 and 446 nm. The fluorescence lifetime of luminol in aqueous ammonia solution is 0.7 ns. The lyoluminescence emission bands are explained on the basis of the reactions of colour centres with luminol during the dissolution of irradiated NaCl crystals in an aqueous ammoniated solution of luminol.

Reduction of nitrate during release of stored energy from γ-irradiated NaCl crystals in aqueous NaNO3 solution

Reduction of nitrate to nitrite takes place when the stored energy in the form of colour centres is released during dissolution of γ-irradiated NaCl crystals in aqueous sodium nitrate solution. Various parameters like dose, amount, storage time and particle size of irradiated NaCl salt which control the yield of nitrite have been studied. Similarly, the effect of concentration of NaNO3 and the role of precipitation on the yields of nitrite in aqueous TlNO3 and AgNO3 have been investigated. The energy transfer parameter has been determined as the ratio of G/NO 2 − / obtained by the addition of irradiated NaCl to that of direct γ-radiolysis. The data permit the evaluation of the concentration of colour centres in the irradiated NaCl crystals on the basis of the mechanism of reduction of nitrate.

Influence of High AC Electric Field on Dielectric Properties of Quenched and X-Ray Irradiated NaCl and KCl Single Crystals

Mesures de la constante dielectrique, des pertes dielectriques et de la conductivite electrique, dans le domaine des frequences 10 2 a 10 7 Hz, entre 30° et 400°C; mise en evidence d'une modification importante des proprietes dielectriques sous l'effet d'une trempe (de 700°C a l'ambiance) suivie d'une irradiation RX, puis d'application d'un champ de 10 kV/cm

Infrared Properties of Doped and Irradiated NaCl Crystals

Infrared Properties of Doped and Irradiated NaCl Crystals

Diffraction efficiency of holograms recorded with radiation from an He-Ne laser in irradiated NaCl crystals

Diffraction efficiency of holograms recorded with radiation from an He-Ne laser in irradiated NaCl crystals