Thin Layer Activation Research Articles

Experimental studies of the deuteron-induced activation cross-sections on natAg

Excitation functions were measured for the natAg(d,x) 105,106m,110mAg, natAg(d,x) 107,109Cd and 27Al(d,x) 24Na reactions by the stacked-foil activation technique and high-resolution gamma-spectroscopy over the energy range 0.44–40 MeV. The thick target integral yields were deduced using the measured cross-sections. No experimental data on the natAg+d process are available in the literature above 27 MeV. The nuclides 105Ag, 106mAg and 109Cd produced with deuteron induced activation of natural silver have suitable yields and decay characteristics important for thin layer activation (TLA) analysis. The cross-section for the production of 107Cd and 109Cd is significantly large. Therefore, the Ag+d process can be an efficient route for the production of isotope with a medium energy accelerator. The results of the model calculation using the TALYS code are not consistent with the present data. A large shift in the incident energy is found in TALYS calculations.

Thin layer activation of large areas for wear study

Thin layer activation (TLA) method is a versatile tool for activating thin surface layers (from several micrometers to millimeters range) in order to study the wear, corrosion or erosion processes of the activated parts without disassembling or stopping the running equipment in question. Mainly parts made of metals and alloys are suitable for direct activation, but by using secondary particle implantation other materials can also be measured in micrometer thick surface range [F. Ditrói, I. Mahunka, Nucl. Instrum. Meth. Phys. Res. B 113 (1996) 415; F. Ditrói, I. Mahunka, Wear 219 (1998) 78]. In most practical cases the activation of a point-like spot (several square millimeters) is enough to monitor the wear, corrosion or erosion, but by special problems relatively great surface of complicated spatial geometry should be activated uniformly. Two ways are available for fulfilling this task: (1) production of large area beam spot or scanning the beam over the surface in question from the accelerator side, or (2) a programmed 3D movement of the sample from the target side. Taking into account the large variability of tasks occurring in our practice, the latter method was chosen as routine solution in our cyclotron laboratory.

Optimization of n–i–p protocrystalline SiGe:H thin film solar cells for application in thin film multijunction solar cells

In developing n–i–p structured narrow band gap protocrystalline SiGe:H thin film solar cells, an S-shape was encountered in the cells’ current–voltage characteristics, which was not present in the curves of p–i–n cells that incorporated the same i-layer material. With the help of a carefully designed series of annealing experiments, the S-shape was found to consist of two barriers, one of which is located at the p/i interface while the other one is at the ITO/p front contact. Further investigations using thin layer Raman spectroscopy and activation energy measurements pointed out that the barriers are mainly due to a drifting of the μc-Si p-layer deposition from optimized conditions. By optimizing the p-layer deposition and with the use of post-deposition annealing of the entire cell structure, an efficiency of 8.7% was achieved for a 1.55eV band gap protocrystalline SiGe:H n–i–p cell on an Asahi U-type substrate coated with a Ag/ZnO back reflector.

A compact fretting device for testing of biomaterials by means of thin layer activation

Thin layer activation has been applied to measure fretting wear release of medical grade Ti–6Al–4V that was subjected to cyclic loading in order to simulate the application of the material in hip joint replacement. Material release rates in the order of magnitude of 10 −4 ng per simulated gait cycle have been determined. Thin layer activation allows defining an area of interest by local irradiation and avoids artefacts of fretting effects on specimen grips or elsewhere. The aim of the paper is to demonstrate the suitability of thin layer activation for quantitative measurements of very small material quantities released during fretting experiments. For the present experiments a piezoelectrically driven fretting device was constructed that is sufficiently small and easy to maintain in order to comply with space restrictions and the requirements of working in a radiation protected environment. The equipment and the applied radiotracer methodology are described. First results are presented that were obtained in two sets of experiments when semi-spherical samples were fretted against two groups of flat fatigue samples that were both machined form Ti–6Al–4V but exhibited a different surface finish. Both set of experiments where conducted under nominally identical mechanical parameters.

Activation cross-sections on cadmium: Proton induced nuclear reactions up to 80 MeV

Cross-sections of proton induced nuclear reactions on natural cadmium were measured up to 80 MeV using the standard stacked foil irradiation technique and high resolution gamma-ray spectroscopy. Experimental cross-sections and derived integral yields are reported for the natCd(p,xn) 107g,108m,108g,109g,110m,110g,111g,112m,113m,114m,115m,116m1In, natCd(p,x) 107,109,111m,115gCd and natCd(p,x) 104g,105g,106m,110m,111g,113gAg reactions. Earlier experimental data measured on natural cadmium were found only for 109,110,111,113,114In in the literature. The experimental data are analyzed and compared to the results of the theoretical model code ALICE-IPPE. Applications of the new cross-sections for data validation, medical radioisotope production, thin layer activation and dose calculation are discussed.

Electrochemical release testing of nickel–titanium orthodontic wires in artificial saliva using thin layer activation

Alloys based on Ni–Ti intermetallics generally exhibit special shape memory and pseudoelastic properties, which make them desirable for use in the dental field as orthodontic wires. The possibility of nickel release from these materials is of high concern, because the allergenicity of this element. The aim of this study was to test pseudoelastic Ni–Ti wires in simulated physiological conditions, investigating the combined effect of strain and fluoridated media: the wires were examined both under strained (5% tensile strain) and unstrained conditions, in fluoridated artificial saliva at 37 °C. Real time electrochemical nickel release testing was performed using a novel application of a radiotracer based method, thin layer activation (TLA). TLA was validated, in unstrained conditions, against adsorptive stripping voltammetry methodology. Control tests were also performed in non-fluoridated artificial saliva. From our research it transpired that the corrosion behaviour of Ni–Ti alloy is highly affected by the fluoride content, showing a release of 4.79 ± 0.10 μg/cm 2/day, but, differently from other biomaterials, it does not seem to be affected by elastic tensile strain. The application of the TLA method in the biomedical field appears a suitable technique to monitor in real time the corrosion behaviour of biomedical devices.

Experimental studies on excitation functions of the proton-induced activation reactions on yttrium

Proton-induced activation cross-sections were measured for the 89Y(p,x) 89,88,86Zr, 89Y(p,x) 88,87,87m,86Y, 89Y(p,x) 85,83,82Sr and 89Y(p,x) 84,83Rb reactions by a stacked foil technique in the energy range 15–80 MeV which was covered by two separate measurements for 15–50 and 32–80 MeV energy range with 50 and 80 MeV incident protons. The differences between the results of two irradiations were found within 6% in the overlapping energy regions. The production yields for the long-lived products like 88Zr, and 88Y are significantly larger than that of natMo+p, natNb+p and natZr+p processes. The productions of the medical isotopes, 85Sr and 83Sr are also effective by Y+p process using an 80 MeV beam. Thick target integral yields were also deduced using the measured cross-sections. The 87Y, 88Y, 88Zr and 89Zr radionuclides have suitable yields and decay characteristics important for thin-layer activation (TLA) analysis.

Wear evaluation of a cross-linked medical grade polyethylene by ultra thin layer activation compared to gravimetry

Most of today’s artificial joints rely on an articulating couple consisting of a CoCrMo alloy and a medical grade polyethylene. The wear of the polyethylene component is the major cause for long-term failure of these prostheses since the wear debris leads to adverse biological reactions. The polyethylene wear is usually measured by gravimetric methods, which are limited due to a low sensitivity and accuracy. To demonstrate the reliability of ultra thin layer activation (UTLA) as an alternative technique, wear tests on a cross-linked ultra-high-molecular weight polyethylene (XLPE) sliding against CoCrMo were performed on a wear tester featuring multi-directional sliding motion. The amount of polyethylene wear was evaluated by both UTLA and gravimetry. The particular TLA method used in this work employed the implantation of 7Be radioactive recoils into the polyethylene surface by means of a light mass particle beam. The results indicate that apart from its relatively high sensitivity, UTLA also offers the possibility for on-line measurements of polyethylene wear. This makes it a viable and complementary technique in wear test studies for medical implant purposes especially for those involving wear resistant materials and for rapid wear screening.

Activation cross-sections of long-lived products of proton-induced nuclear reactions on zinc

In the frame of a systematic study of excitation functions induced by medium energy protons, the activation cross-sections on natural zinc were investigated for different applications. Excitation functions for production of 66,67Ga, 62,65,69mZn, 64Cu, 57Ni, 55,56,57,58Co and 52,54Mn radioisotopes were measured by the stacked foil technique in the energy range of 26–67MeV. Results were compared with the earlier reported experimental data and theoretical calculations based on the ALICE-IPPE code. Experimental data are presented for the first time for most of the products in the investigated energy range. Applications of the measured data for validating the cross-sections on highly enriched isotopic Zn targets and for thin layer activation method are discussed.

Atmospheric corrosion evaluation of galvanised steel by thin layer activation

The release of certain metals, such as zinc, from outdoor constructions due to atmospheric corrosion is of some concern. For risk assessments the evaluation of the amount of released metal is of importance. Various methods can be used to study the release of metals. These include those using radiotracers, such as thin layer activation (TLA). To verify the reliability of TLA with respect to conventional techniques in the evaluation of atmospheric corrosion, galvanised steel was exposed to a mild marine environment. The amount of zinc in the corrosion products, released through artificial leaching, at different time intervals was evaluated by TLA and atomic absorption spectroscopy (AAS). A good correlation between the results was found indicating the feasibility of TLA for these release studies.

Corrosion monitoring of different steels by thin layer activation

For corrosion monitoring, the behavior of various steels (Sanicro 28, AISI 316 L, SAF 2507) and a carbon steel were investigated by thin layer activation (TLA) in acid solutions containing chloride. A loop system with a sample holder as well as a temperature and a flow control device were used in laboratory tests. Experimental parameters like fluid temperature, H2SO4 concentration and running time were selected as a function of the specific material under investigation. The congruence of TLA results was verified by comparison with mass loss data, obtained by gravimetry.

Excitation functions of deuteron induced nuclear reactions on natural zinc up to 50 MeV

Excitation functions were measured for production of 66,67Ga, 62,65,69mZn, 61,64,67Cu and 58Co radioisotopes in deuteron induced reactions on natural Zn up to 50 MeV by activation using stacked foil techniques. Detailed compilations were made of the earlier reported experimental cross-section and integral yield data. They are compared with the new values and theoretical calculations. The use of the measured formation cross-section for production of practically important radioisotopes of gallium and copper is discussed as well as the application of cross-section data of 65Zn in the field of wear monitoring by the thin layer activation method.

Excitation functions for production of radioisotopes of niobium, zirconium and yttrium by irradiation of zirconium with deuterons

Excitation functions of deuteron-induced reactions on natural zirconium were re-measured up to 50 MeV for the natZr(d,x) 90,91m,92m,95,96Nb, natZr(d,x) 88,89,95,97Zr and natZr(d,x) 86,87,88Y reactions. A physically accurate activation method on stacks of natural zirconium foils was used. The results were critically compared with a detailed compilation of earlier reported experimental data and with theoretical calculations. In the overlapping energy regions mainly acceptable agreement was found or our data complete the database where contradictory or scarce data were available. The possible alternative uses in medically relevant radionuclide production as well as applications in thin layer activation and dosimetry are discussed.

Quality control by autoradiography for the thin layer activation technique

In measurements of wearing and corrosion based on the thin layer activation technique; a part is locally activated by charged particles and placed in its working context and wear/corrosion is calculated precisely and continuously by measuring the removed activity. It is essential in the method to know the exact position of the activated zone because the wearing ratio may vary up to 50% for a shift of only 2 mm. So we do need a control procedure after irradiation. Our quality control system of irradiated parts is based on autoradiography. The films are chosen according to the type of emission of the source: high resolution films as Structurix D4 are used with beta sources whereas pure gamma sources need more sensitive films as Structurix D7 with lead filters. The finite range of the rays generates blur which can be partly corrected by digitizing and deconvoluting the image using IRIS software. The exposure time is empirically determined for each radioisotope and linked to the activity, in order to optimise contrast and resolution. The position control is mainly based on a system of detailed marks and cuts made under inactinic light; we can obtain a basic precision of approximately one tenth of millimetre. Routine applications of this control methodology confirm its simplicity, precision, speed and its relative low cost.

Excitation functions of heavy ion induced nuclear reactions between 16O ion beam and natural copper: Measurements, analysis and its applicability in TLA study

Experimental cross sections of a number of reaction channels of 16O ion induced reactions on natural copper target have been determined at different energies in the range of 50–110 MeV of 16O projectile by stacked foil activation technique. The cross sections have been compared with theoretical calculations using the computer code ALICE-91. The experimental values compared reasonably well with the corresponding theoretical estimates. The results indicate no significant role of incomplete fusion process in the 16O induced reactions on natural copper in the energy range of ⩽7 MeV/nucleon. As heavy ion beam produces an extremely narrow layer of activities in the surface of a material, these reactions could be useful for thin layer activation (TLA) study. The purpose of this work is to apply heavy ion activation in TLA technique for the study of surface wear with increased sensitivity.

Measurement and evaluation of the excitation functions for alpha particle induced nuclear reactions on niobium

Alpha particle induced nuclear reactions were investigated with the stacked foil activation technique on natural niobium targets up to 43 MeV. Excitation functions were measured for the production of 96mgTc, 95mTc, 95gTc, 94gTc, 95mgNb and 92mNb. Cumulative cross-sections, thick target yields and activation functions were deduced and compared with available literature data. Applications of the excitation functions in the field of thin layer activation techniques and beam monitoring are also discussed.

New data and evaluation of 3He-induced nuclear reactions on Cu

Excitation functions of natCu( 3He, x) 66Ga, natCu( 3He, x) 67Ga, natCu( 3He, x) 63Zn and natCu( 3He, x) 65Zn nuclear reactions were measured up to 36 MeV using stacked foil irradiation arrangement and activation technique. The results were compared with compiled literature data. The status of the experimental database was investigated with the goal to produce recommended values for different applications. The application of the deduced data in the field of beam monitoring and thin layer activation is discussed.

Electrochemical release testing of a stainless steel in a glucose solution using thin layer activation

The contamination of consumer products, e.g. food, during production, storage and/or transport, due to release of chemicals caused by contact with technical components is of some concern. Various methods can be used to study the release of these chemicals. These include those using radiotracers, such as thin layer activation (TLA). A dedicated facility combining TLA with electrochemical tests is presented. Its use is illustrated with Ni and Cr release during electrochemical testing of 316L stainless steel in a glucose solution. TLA offers various advantages, which include area selectivity, high sensitivity, and the possibility for in situ and on-line monitoring of elements. Due to the complementarity of TLA with the conventional electrochemical methods it contributes to a better understanding of the underlying release processes. Additionally, the usefulness of TLA to develop more reliable test methodology is indicated.

The use of thin layer activation in high-temperature cyclic oxidation studies

Thin layer activation (TLA) has been applied to a study of the high-temperature cyclic oxidation behaviour of pure and yttrium-implanted chromium, taking advantage of the high area selectivity of the technique. On pure chromium, two different sample areas, i.e. corners and the central part of a large surface area, were selected for activation. Due to this area selectivity, it was possible to distinguish the spallation behaviour of the oxide scale formed on flat from that formed on highly curved surfaces. In particular, the TLA data showed that the oxide scale formed during high-temperature cyclic oxidation near corners and edges was more prone to cracking and spallation. In the case of yttrium-implanted specimens, activation was performed only at the centre of the implanted zone, avoiding the distorting effect of the non-implanted parts of the sample. The area selectivity of TLA made it possible to study more accurately the beneficial effect of ion implantation on the cyclic oxidation behaviour than by conventional thermogravimetry. Due to the complementary character of TLA with respect to the conventional thermogravimetry, a more complete and better understanding of the cyclic oxidation performance of materials can be obtained.

The application of thin layer activation for on-line erosion monitoring

The washout of volcanic ash into the feedwater of a hydroelectric power station resulted in enhanced erosion of generator components. The damage prompted two novel applications of the thin layer activation (TLA) technique. TLA was used to select more resistant materials, and also as the basis of an automated, on-line alarm system to warn station operators on the likelihood of further damage. The latter application demonstrated that plant protection against irregular events is practical using TLA.