In situ determination of radon concentration and total gamma radiation in Kastel Gomilica, Croatia

To determine current radiation background of the environment at the “Giricic” location in Kastel Gomilica, Croatia, in situ measurement of radon concentration (²²²Rn and ²²⁰Rn) in an open atmosphere on a ground level and at the height of 1.5 m has been made as well as total gamma radiation at the height of 1 m in an energy range of 15 keV to 2 MeV. The researched location was divided in three specific parts: (i) regulated area with the bottom ash and flying ash in the basis (“old” depot), (ii) unregulated area with waste materials, including bottom ash and flying ash, in the basis (“new” depot), (iii) uncontaminated area with no waste materials deposited on. Average radon concentration on a ground level was 213 Bq/m³ for the “old” depot, 214 Bq/m³ for the “new” depot and 59 Bq/m³ for the uncontaminated area and at the height of 1.5 m 20 Bq/m³ for the “old” depot, 34 Bq/m³ for the “new” depot and 26 Bq/m³ for the uncontaminated area. Average total gamma radiation values in selected energy range were 109.92 cps (counts per second) for the “old” depot, 357.76 cps for the “new” depot and 65.97 cps for the uncontaminated area. For selected radionuclides (²¹⁴Pb, ¹³⁷Cs, ²²⁸Ac, ^234mPa, ⁴⁰K and ²¹⁴Bi) average gamma radiation values at characteristic energies have been determined as well.     

Software for automatization of IEA-analysis of plasma-laser spectra

A software has been developed in order to automatize the ion energy analyzer (IEA) spectra analysis of laser-generated plasmas.A Nd:Yag laser operating at an intensity of the order of 10¹⁰ W/cm², 9 ns pulse width and energy of the order of 600 mJ, has been employed to irradiate different metallic targets (Al, Ti, W) and to produce plasma pulses. The ion emission from the plasma is monitored through an IEA instrument permitting time-of-flight (TOF) measurements to determine the ion energy distributions as a function of the charge state.The software program consists in two sections. The first one permits to identify the IEA ion peaks corresponding to different charge states as a function of the theoretical TOF values. The second section permits to plot the ion velocity and energy distributions as a function of the charge state. The obtained distributions are fitted using the “Coulomb-Boltzamnn shifted” function approach through the “Peakfit” code. The fit of the experimental data permits to estimate the equivalent plasma temperature and the average energy shift of the distributions as a function of the ion charge state.     

Development of function-graded proton exchange membrane for PEFC using heavy ion beam irradiation

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe⁵⁴⁺ ion beam with the energy of 6 MeV/u under a vacuum condition. The induced trapped radicals by the irradiation were measured by electron spin resonance (ESR) spectroscopy. Irradiated films were grafted with styrene monomer and then sulfonated. X-ray photo-electron spectroscopy (XPS) spectra showed that the densities of sulfonic acid groups were controlled for injection “Surface” and transmit “Back” sides of the fabricated PEM. The membrane electrode assembly (MEA) fabricated by the function-graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.     

Accelerator-based research activities at “Centro Nacional de Aceleradores”, Seville (Spain)

In February 1998, almost 10 years ago, the set-up of the first IBA (ion beam analysis) facility in Spain took place with the arrival of a 3 MV tandem accelerator [J. García-López, F.J. Ager, M. Barbadillo-Rank, F.J. Madrigal, M.A. Ontalba, M.A. Respaldiza, M.D. Ynsa, Nucl. Instr. and Meth. B 161-163 (2000) 1137]. Since then, an intensive research program using IBA techniques has been carried out. Subsequently, a cyclotron for 18 MeV protons has been also installed at the “Centro Nacional de Aceleradores” (CNA), devoted mainly to isotope production for PET (positron emission tomography) techniques, but possibly applied to material analysis and damage studies on a dedicated beam line. Moreover, a 1 MV tandem has been recently installed for AMS (accelerator mass spectrometry) ¹⁴C dating and environmental research with other isotopes.In the present paper we describe the new facilities and the developments of the 3 MV tandem beam lines occurred during the past years, as well as some examples of the most recent research activities in our Center in the fields of Material Science, Archaeometry, Biomedicine and Environment.     

Collision cascade temperature

Interaction of a projectile with a solid has been considered in detail. It has been found that any collision cascade generated by a projectile can be characterized by the average kinetic energy of cascade atoms that represents an “instantaneous temperature” of the cascade during its very short lifetime (10⁻¹² s). We refer to this value as the “dynamic temperature” in order to emphasize the fact that cascade atoms are in a dynamic equilibrium and have a definite energy distribution. The dynamic temperature defines the electron distribution in the cascade area and, hence, the ionization probability of sputtered atoms. The energy distribution of cascade atoms and, as a consequence, the dynamic temperature can be found experimentally by measuring the energy distribution of sputtered atoms. The calculated dynamic temperature has been found to be in good agreement with the experimental data on ion formation in the case of cesium and oxygen ion sputtering of silicon. Based on the developed model we suggest an experimental technique for a radical improvement of the existing cascade sputtering models.     

RADI—A RF source size-scaling experiment towards the ITER neutral beam negative ion source

IPP Garching is currently developing a negative hydrogen ion RF source for the ITER neutral beam system. The source demonstrated already current densities in excess of the ITER requirements (>200 A/m² D⁻) at the required source pressure and electron/ion ratio, but with only small extraction area and limited pulse length. A new test facility (RADI) went recently into operation for the demonstration of the required (plasma) homogeneity of a large RF source and the modular driver concept.The source with the dimension of 0.8 m × 0.76 m has roughly the width and half the height of the ITER source; its modular driver concept will allow an easy extrapolation in only one direction to the full size ITER source. The RF power supply consists of two 180 kW, 1 MHz RF generators capable of 30 s pulses. A dummy grid matches the conductance of the ITER source. Full size extraction is presently not possible due to the lack of an insulator, a large size extraction system and a beam dump.The main parameters determining the performance of this “half-size” source are the negative ion and electron density in front of the grid as well as the homogeneity of their profiles across the grid. Those will be measured by optical emission and cavity ring down spectroscopy, by Langmuir probes and laser detachment. These methods have been calibrated to the extracted current densities achieved at the smaller source test facilities at IPP for similar source parameters. However, in order to get some information about the possible ion and electron currents, local single aperture extraction with a Faraday cup system is planned.     

X-ray production cross-sections measurements for high-energy alpha particle beams: New dedicated set-up and first results with aluminum

The “IPNAS” laboratory, in collaboration with the “Centre Européen d’Archéométrie” is partly focused on material analysis by means of IBA techniques: PIXE, PIGE and RBS. A new transport beam line has been developed at our CGR-520 MeV cyclotron to analyze Cultural Heritage objects using these techniques. This facility allows us to produce proton and alpha particle beams with energies up to 20 MeV. A vacuum chamber dedicated to X-ray production and Non-Rutherford cross-section measurements has been recently constructed. After determination of the chamber’s geometry for X-ray detection using thin foils of several elements (11 ? Z ? 82) and 3 MeV proton beams, the measurement of the X-ray production cross-sections in the 6-12 MeV energy range has started using alpha particle beams on light element targets. These experiments contribute to the filling a serious lack of experimental values for alpha particles of this particular energy range in databases. The recent decision to focus our work on the alpha particle interaction with light elements was taken because of the high interest of the low Z elements in the field of archaeometry.     

Si nanocrystals formation by a new ion implantation device

Metallic and non-metallic ion beams can be used to modify the properties of wafer surfaces if accelerated at moderate energies. We developed a new “implantation machine” able to generate ions and to accelerate them up to 80 kV. The ion generation is achieved by a laser-plasma source which creates plasma in expansion. The device consists of a KrF excimer laser and a generating vacuum chamber made of stainless steel. The laser energy was 45 mJ/pulse with a power density of 2.25 × 10⁸ W/cm². The target was kept to positive voltage to accelerate the produced ions. The ion dose was estimated by a fast polarised Faraday cup. This machine was utilised to try synthesizing silicon nanocrystals in SiO₂ matrix. Preliminary results of Si nanocrystals formation and the glancing-angle X-ray diffraction analyses are reported.     

Cross-section transmission electron microscopy of the ion implantation damage in annealed diamond

It has formerly been shown that low-damage levels, produced during the implantation doping of diamond as a semiconductor, anneal easily while high levels “graphitize” (above about 5.2 × 10¹⁵ ions/cm²). The difference in the defect types and their profiles, in the two cases, has never been directly observed. We have succeeded in using cross-section transmission electron microscopy to do so. The experiments were difficult because the specimens must be polished to ∼40 μm thickness, then implanted on edge and annealed, before final ion beam thinning to electron transparency. The low-damage micrographs reveal some deeply penetrating dislocations, whose existence had been predicted in earlier work.     

Rayleigh to Compton ratio with monochromatic radiation from an X-ray tube (preliminary results)

Results on the Rayleigh to Compton ratio (R/C) for elements and compounds with low atomic number (5 ? Z ? 12) are presented. These materials are difficult to identify and characterize with other radiological techniques because of their very close linear attenuation coefficients. A transportable setup for R/C measurements was assembled and tested. This comprises an X-ray tube, in which the output radiation is partially “converted” to monochromatic radiation emitted by a secondary target. The experimental results are compared with theory, determined through coherent and incoherent scattering cross sections.     

Plasma grid design for optimized filter field configuration for the NBI test facility ELISE

Maintenance-free RF sources for negative hydrogen ions with moderate extraction areas (100-200 cm²) have been successfully developed in the last years at IPP Garching in the test facilities BATMAN and MANITU. A facility with larger extraction area (1000 cm²), ELISE, is being designed with a “half-size” ITER-like extraction system, pulsed ion acceleration up to 60 kV for 10 s and plasma generation up to 1 h. Due to the large size of the source, the magnetic filter field (FF) cannot be produced solely by permanent magnets. Therefore, an additional magnetic field produced by current flowing through the plasma grid (PG current) is required. The filter field homogeneity and the interaction with the electron suppression magnetic field have been studied in detail by finite element method (FEM) during the ELISE design phase. Significant improvements regarding the field homogeneity have been introduced compared to the ITER reference design. Also, for the same PG current a 50% higher field in front of the grid has been achieved by optimizing the plasma grid geometry. Hollow spaces have been introduced in the plasma grid for a more homogeneous PG current distribution. The introduction of hollow spaces also allows the insertion of permanent magnets in the plasma grid.     

Determination of the activity coefficient of Am in liquid Al by electrochemical methods

The activity coefficient of americium in liquid aluminium has been determined by electrochemical methods. To the author’s knowledge, this is the first time this value is published in the open literature. For radiation safety reasons only 100 mg of this highly radioactive element were permitted to be manipulated inside the glove-box. Hence an “ad hoc” experimental set-up, which allows working with small amounts of solvent, has been designed. The Am(III) solution has been prepared by direct AmO₂ dissolution into CaCl₂-NaCl; the conversion into its chloride form has been achieved by carbochlorination (Cl₂ + C) at 600 °C. Cyclic voltammetry technique, performed in the obtained CaCl₂-NaCl-AmCl₃ solution, has allowed a first estimation for the logarithm of the activity coefficient, being equal to logγ_Am(Al)=-6.7±1 at 700 °C.     

Polymer processing by a low energy ion accelerator

Ion implantation is a process in which ions are accelerated toward a substrate at energies high enough to bury them just below the surface substrate in order to modify the surface characteristics. Laser-produced plasma is a very suitable and low cost technique in the production of ion sources. In this work, a laser ion source is developed by a UV pulsed laser of about 10⁸ W/cm² power density, employing a C target and a post ion acceleration of 40 kV to increase the ion energy. In this work, we implanted C ions on ultra-high-molecular-weight-polyethylene (UHMWPE) and low-density polyethylene (LDPE). We present the preliminary results of surface property modifications for both samples. In particular, we have studied the modifications of the surface micro-hardness of the polymers by applying the “scratch test” method as well as the hydrophilicity modifications by the contact angle measurements.     

Mixing of Cr and Si atoms induced by noble gas ions irradiation of Cr/Si bilayers

Cr/Si bilayers were irradiated at room temperature with 120 keV Ar, 140 keV Kr and 350 keV Xe ions to fluences ranging from 10¹⁵ to 2 × 10¹⁶ ions/cm². The thickness of Cr layer evaporated on Si substrate was about 400 Å. Rutherford backscattering spectrometry (RBS) was used to investigate the atomic mixing induced at the Cr-Si interface as function of the incident ion mass and fluence. We observed that for the samples irradiated with Ar ions, RBS yields from both Cr layer and Si substrate are the same as before the irradiation. There is no mixing of Cr and Si atoms, even at the fluence of 2 × 10¹⁶ ions/cm². For the samples irradiated with Kr ions, a slight broadening of the Cr and Si interfacial edges was produced from the fluence of 5 × 10¹⁵ ions/cm². The broadening of the Cr and Si interfacial edges is more pronounced with Xe ions particularly to the fluence of 10¹⁶ ions/cm². The interface broadening was found to depend linearly on the ion fluence and suggests that the mixing is like a diffusion controlled process. The experimental mixing rates were determined and compared with values predicted by ballistic and thermal spike models. Our experimental data were well reproduced by the thermal spikes model.     

Assessment of DNA damage of Lewis lung carcinoma cells irradiated by carbon ions and X-rays using alkaline comet assay

DNA damage and cell reproductive death determined by alkaline comet and clonogenic survival assays were examined in Lewis lung carcinoma cells after exposure to 89.63 MeV/u carbon ion and 6 MV X-ray irradiations, respectively. Based on the survival data, Lewis lung carcinoma cells were verified to be more radiosensitive to the carbon ion beam than to the X-ray irradiation. The relative biological effectiveness (RBE) value, which was up to 1.77 at 10% survival level, showed that the DNA damage induced by the high-LET carbon ion beam was more remarkable than that induced by the low-LET X-ray irradiation. The dose response curves of “Tail DNA (%)” (TD) and “Olive tail moment” (OTM) for the carbon ion irradiation showed saturation beyond about 8 Gy. This behavior was not found in the X-ray curves. Additionally, the carbon ion beam produced a lower survival fraction at 2 Gy (SF2) value and a higher initial Olive tail moment 2 Gy (OTM2) than those for the X-ray irradiation. These results suggest that carbon ion beams having high-LET values produced more severe cell reproductive death and DNA damage in Lewis lung carcinoma cells in comparison with X-rays and comet assay might be an effective predictive test even combining with clonogenic assay to assess cellular radiosensitivity.     

Dynamic observations of heavy-ion damage in Fe and Fe-Cr alloys

We give an overview and summary of recent in-situ heavy-ion irradiation experiments on Fe and Fe-Cr alloys carried out on the Argonne IVEM Facility at irradiation temperatures up to 500 °C. Several new and unexpected observations were made. At low doses the contrast of new irradiation-induced dislocation loops sometimes developed over time intervals as long as 0.2 s, many orders of magnitude longer than expected for a process of cascade collapse. In addition at temperatures ?300 °C, “hopping” of 1/2<1 1 1> loops was induced by the ion or electron beams, especially in UHP Fe. At high doses complex microstructures developed in all materials, involving the formation of large interstitial loops. At 300 °C and RT these loops had Burgers vectors of type b = 1/2<1 1 1> and large shear components. At 500 °C only edge loops with b = <1 0 0> were produced.     

Ion energy dependence of interface parameters of ion beam sputter deposited W/Si interfaces

W thin films and W/Si/W tri-layer samples have been deposited on c-Si substrates in a home-made ion beam sputtering system at 1.5 × 10⁻³ Torr Ar working pressure, 10 mA grid current and at different Ar⁺ ion energies between 600 and 1200 eV. Grazing incidence X-ray reflectivity (GIXR) measurements in specular and diffused (detector scan) geometry have been carried out on the above samples. The measured GIXR spectra were fitted with theoretically simulated spectra and the different interface parameters viz., interface width, interface roughness and interface diffusion have been estimated for both Si-on-W and W-on-Si interfaces in the above samples. The variation of the above interface parameters as a function of ion energy used for W sputtering has been studied.     

Investigation of thermally stimulated properties of SHI beam irradiated polycarbonate/polystyrene double layered samples

The double layered samples of polycarbonate/polystyrene (PC/PS) have been prepared by solvent casting method and irradiated with 55 MeV C⁵⁺ beam at different ion fluences range from 1 × 10¹¹ to 1 × 10¹³ ion/cm². The effect of swift heavy ion (SHI) beam in interfacial phenomena, phase change, dielectric relaxation, degradation temperature, stability, charge storage and transport mechanism of PC/PS pristine and irradiated double layered samples have been investigated by thermally stimulated discharge current (TSDC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). TSDC show α, β-relaxation peaks shifted to the lower temperatures side with increase of fluence. The activation energy and relaxation time decrease, while the depolarization current and charge released increase with increase in the ion fluences. DSC curve show the glass transition temperature (T_g) and heat capacity decreases with increase in the ion fluences. The TGA characteristics represent the thermal stability, which is found to be decreased with increase in the ion fluences.     

Lateral straggling and its influence on lateral diffusion in implantation with a focused ion beam

Parallel stripes of nanostructures on an n-type Si substrate have been fabricated by implanting 30 keV Ga⁺ ions from a focused ion beam (FIB) source at three different fluences: 1 × 10¹⁵, 2 × 10¹⁵ and 5 × 10¹⁵ ions/cm². Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) measurements were carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 × 100 nm², appear as bright regions in the PEEM image. Line scans of the intensities from PEEM images were recorded along and across these stripes. Intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ∼10⁻¹⁵ m²/s. No significant dependence of diffusion coefficient on ion fluence was observed in the fluence range investigated here. Radiation enhanced diffusion has been discussed in the light of the associated defect distribution due to lateral straggling of the implanted ions.     

Failure characteristics of cladding tubes under RIA conditions

In the frame of actions for improving the safety of its nuclear power plants, Electricité de France needs to build the mechanical criteria ensuring the clad integrity for several operating conditions.This paper presents analytical mechanical models used to derive failure criteria for reactivity insertion accidents (RIA) and interpretation of the CABRI REP-Na experimental tests.Building analytical criteria requires an experimental database. Mechanical tests performed on non-irradiated and irradiated cladding tubes have been provided from French and international programmes (PROMETRA, EPRI, …). These tests consist of tube burst and axial tension, and ring tension. Several strain biaxiality ratios are thus available: pure circumferential tension (from ring tension), pure axial tension (from tube axial tension), and plane strain conditions (from tube burst tests). Several strain rates, temperatures, irradiation conditions are also available.The major feature of our study has been to make it possible that these several thermomechanical conditions be representative of “standard” RIA loading conditions.To this aim, we have derived some biaxiality and strain rate corrections to be applied to the results of experimental tests, in such a way that they could be representative of RIA biaxiality conditions (which are assumed to be strain equibiaxiality), and also representative of RIA strain rate conditions (which are assumed to be 5 s⁻¹).The corrections that we derive are based on the fracture properties of hydrided zirconium alloys (especially in terms of anisotropy), and also on an assumed form of the material constitutive equations.Each test of the “homogenized” database has thus been used to calculate a strain energy density, representative of its fracture (the strain energy density is defined as the integral of the stress times strain rate states, over the duration of the mechanical test). The SED values are plotted against the sample's oxide thickness, and a lower bound limit can be established, with respect to oxide thickness.In order to address the problem of representativeness of the laboratory database, an experimental set-up has been developed that aims at characterizing the failure behavior of cladding tubes under RIA conditions. The developed experimental set-up is based on electromagnetic forming.The development of the test and in particular of the die is delicate but leads to repeatable results with a controlled strain biaxiality ratio higher than those obtained through conventional tests such as ring tests or PSU ring tests. The use of electromagnetic forming process allows testing the specimen with very high strain rates. For the next test series other zircaloy alloys at the reception state and in hydrided conditions will be tested in order to look at hydrides influence on fracture strains.A first finite element simulation of the test was engaged. The simulation and the experimental results are in quite good agreement. In future, the consistency of the previously developed analytical mechanical criterion with the electromagnetic forming experimental results will be verified.