Ion-beam irradiation

Ion-beam irradiation, even at a small dose, alters the microstructure of the surface layer of the polymer, and high fluence of irradiation results in a large number of small-size microvoids in the surface. 

Xu and Coleman [76] modified the 6FDA-pMDA (polyimide) films by irradiating ion beam and studied the structure and morphology by AFM. The AFM images data indicated that free-standing polyimide films had deep surface valleys which could extend to a depth of several micrometers. 

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Thermal decomposition of palladium acetate, either by laser irradiation or conventional means, leads to complete volatilization of the organic components. The purity of the ion beam-irradiated samples is significantly improved by heating the samples in hydrogen at 300 °C after removal of unirradiated palladium acetate. 

Ion Beams. Several investigations have been made on the effects of ion beam irradiation on simple chemical systems. Polymers have also been irradiated with ion beams as an extension of studies on the ion implantation of other materials. To date, most of these studies have been concerned with gross effects, sometimes through to carbonisation (70) but here is a field which could have an industrial potential. 

In addition to the above-mentioned features, the ion beam irradiation has functions of implantation of different atoms in the irradiated medium and of the nuclear transmutation of the irradiated medium atoms. So far, the underlying physics and the subsequent relaxation processes in the interaction between ion beams and matter have been extensively studied not only for purely scientific interests but also for practical purposes, such that a series of international conferences on these topics have been held on a worldwide scale [2]. 

Table 1 Ion Beam Irradiation Parameters and Their Related Ion Beam Technologies...

Simulation of the neutron-induced damages using triple ion beams is schematically shown in Fig. 7. A proton and a helium ion are provided by the ion implanter and the single-ended accelerator, respectively. Heavy ions, such as iron or silicon, accelerated by the tandem accelerator, are injected into the target simultaneously. For example, the SiC/SiC composite was tested under triple ion beam irradiation consisting of a 380-keV proton, a 1.2-MeV helium ion, and a 7.8-MeV Si " ion. The triple irradiation system is equipped with an energy degrader and a beam scanner for uniform three-dimensional (3-D) irradiation. 

Figure 7 Schematic drawing of the damage in reactor materials induced by neutrons, and its simulation by the triple-ion-beam irradiation.

Artificial satellites, which are now used for communication, broadcast, weather forecast, etc., are equipped with a variety of semiconductor devices, which are often exposed to the high levels of radiation found in space. Such energetic particles, called cosmic rays, cause the degradation and malfunction of semiconductor devices, which lowers both the mission lifetime and reliability of satellites. Using ion beam irradiation facilities at TIARA, which have been uniquely adapted for simulating the radiation environment of space, we have... 

Using the triple-ion beam irradiation apparatus, the microstructural evolution of austenitic stainless steel, which is considered as a structural material for water-cooled fusion reactors... 

The 355 nm emission is sharp and intense at the start of irradiation, and the intensity decreases with prolonged irradiation time. The 440 nm emission is weak and broad, and the intensity does not change with the irradiation time. Emission spectra of PMPrS obtained at ion fluences of 0.15,0.76, and 1.53 p,C/cm2 shows emission bands at 350 nm and 440 nm. The decrease in the intensity of the main peak indicates that main chain scission (photolysis) occurs under ion beam irradiation. Intense and sharp emission at 340 nm and weak broad emission at 440 nm for PDHS at 354 K are observed at the beginning of the irradiation and decrease on further irradiation. At 313 K and 270 K, sharp intense main emissions at 385 nm are seen. The 340 nm and 385 nm emission bands are assigned to a - a fluorescence. Experimental results have shown the presence of a phase transition at 313 K for PDHS.102,103 Below 313 K, the backbone conformation of PDHS is trans-planar, and above the solid-solid phase change temperature, a disordered conformation is seen. Fluorescent a -a transitions occur at 355 nm for PMPS, 350 nm for PMPrS, and 385 nm and 340 nm for PDHS. Emissions around 440 nm are observed at all temperatures examined and are assigned to defect and network structures induced by ion beams. 

Some new trends can be recognized in the points such as the interaction of short-lived active species in some spatial distributions measured by spin echo and pulse radiolysis methods. The application of polymers for drug-delivery systems is here discussed with reference to low temperature radiation polymerization techniques. Ion beam irradiation of polymers is also reviewed for which further research is becoming important and attractive for so-called LET effects and high density excitation problems. In the applied fields the durable polymers used in strong and dense irradiation environments at extremely low temperature are here surveyed in connection with their use in nuclear fusion facilities. 

In ion-beam irradiated polystyrene, some kinds of reactive intermediates are produced. The excimer, which is one of the reactive intermediates, emits intense fluorescence. Thus, we measured the time profiles of the excimer fluorescence (328.5 nm) from ion irradiated polystyrene thin films. One of the results is shown in Fig. 6a and b for irradiation with 0.6 MeV He+ (several hundred pA beam current). In Fig. 6a, the irradiation time dependence of the excimer fluorescence intensity is shown. In Fig. 6b, the time profile (I) was recorded with an irradiation time of 0 s-139 s (low dose-time profile), and (II) in the irradiation time of 1839 s- 3839 s (high dose-time profile). The following experimental results were obtained. 

Rutherford Backscattering Spectroscopy (RBS) is an established technique for analysis of inorganic materials. Recently, several applications of RBS on polymer films have been reported however, the effect of ion beams on these surfaces has not been well documented. RBS has been used to determine fluorine distribution in polymers. Since ion beam irradiation of polymers can induce chemical changes, instrumental parameters need to be optimized to minimize damage. 

Instrumental Techniques. Ion beam irradiation of samples was performed by focusing 2.1 MeV He2+ ions, using an Ionex Tandetron accelerator, to a spot size of approximately 4 mm2. Ion beam currents were held constant at 10 nA. Radiation effects were determined by varying the total charge on the sample between 0 and 20 pC. RBS spectra were collected with the samples at an angle of 45° with respect to the incident beam additional instrumental details can be found elsewhere (20). Spectral simulations were performed using the RUMP method designed by Doolittle (21). 

X-ray photoelectron spectroscopy (XPS) was used to analyze polymer surfaces before and after ion beam irradiation. Data were collected with a Surface Science SSX-100 spectrometer using A1 Ka x-rays in the high resolution mode with x-rays focused to a spot size... 

Information on the chemical changes, resulting from ion beam irradiation, can be identified from spectrum 4. The broad signal at about 1720 cm-1 is attributed to C=0 and to C=CF type bonds (25). 

Corbel C, Sattonnay G, Lucchini JF, Ardois C, Barthe MF, Huet F, Dehaudt P, Hickel B, Jegou C. (2001) Increase of the uranium release at an UOj/HjO interface under He ion beam irradiation. Nuclear Instruments and Methods in Physics Research B179(2) 225-229. 

Remita H, Lampre I, Mostafavi M, Balanzat E, Bouffard S. (2005) Comparative study of metal clusters induced in aqueous solutions by gamma-rays, electron or C6h- ion beam irradiation. Rad Phys Chem 72(5) 575-586. 

Chennamsetty R, Escobar 1, Xu XL. (2006) Characterization of commercial water treatment membranes modified via ion beam irradiation. Desalination 188(1-3) 203-212. 

In a continuing study of ion-beam irradiation of hydrated DNA, both oxygen and argon ion-beams were used to investigate the radical yields and composition of the stabilized radical cohort in hydrated DNA at 77 K. For the argon ion-beam irradiated experiments, computer analysis of the DNA composite ESR spectra allowed quantification of the yields of G, T , C(N3)H and a mix of neutral (presumed) sugar radicals Qualitatively it is evident that XS ... 

Table 2. Yields of radicals in argon ion-beam irradiated and 7-irradiated hydrated DNA. ...

The relatively low overall yields of radicals were attributed to the high recombination rate of closely spaced base ion radicals in the densely ionized track core. The proximity of these radicals coupled with Coulomb attractions facilitates fast core ion radical-ion radical recombination. However, neutral sugar radicals in the core are not affected by Coulomb attractions, thus they do not recombine as readily. Therefore, most of the neutral sugar radicals stabilized at 77 K are presumed to form in the core. On the other hand, most of the base radicals that are stabilized at 77 K are assumed to form in the isolated, low LET-like spurs formed by delta-rays. The similarity in the behavior of the base radicals in argon ion-beam irradiated samples and in y irradiated samples lends support to this picture.In this model C(N3)H is in equilibrium with C and is found to act as an ion-radical. 

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