Project summary

   The project proposal IRCOAL refers to a change of irradiation metallic targets from gamma sources with iridium and cobalt made to SCN Pitesti, with targets from intermetallic compounds with aluminium. A very important element which needs to act on irradiation design is the factor of auto screening  to the neutrons and the obtaining of a distribution of the activity inside the produced source.

   This challenge may be realized by the creation of a new structure which includes around target atoms, other atoms whose nuclear reactions drive to the production of radioisotopes with a short time of life comparing with those of Ir and Co. One of this elements is Al. On this line, the bigger is the dispersion of target atoms in the irradiation chanel the less is the auto screening factor and practically the targets atoms find a bigger neutronic flux. Thus,  there may be obtained a preset activity for a standard source (50 Ci - gamagrafie, 2000 Ci - cobaltoterapie) in a shorter irradiation time. 

   Another important advantage is constituted by the target material economy. Intermetallic materials represent a material class which answer to this challenge by the realization of a imbedded network with activate material and aluminium.

   These materials have metallic and ceramic properties with metallic and covalence bond, function to the constituent and proportion of metals. They differ to the conventional metallic alloys by the fact that they have a big range of ordering of the crystal structure. There will be prepared  the  CoAl with  T_t= 1918K and IrAl with T_t=2393K compound; their structure is with B2 tipe (CsCl). They will be obtained in powdered state by the solid state reaction by the mechanical alloying. Modern  technology that needs last hour equipment, mechanical alloying was imposed as one of the main methods for the realization of intermetallic compounds. The irradiation targets will be obtained with dimensional tips of the old targets, by the pressing sintering processes. The targets will be covered with a thin nickel layer in order to assure the irradiation and manipulation protection.

   During the realization phases the obtained materials in various phases, will be characterized. The obtained powder will be characterized by the point of view of composition by XRD, morphologic by electronic microscopy (SEM) anf physically (determination of grading distribution and of bulk density). There will be investigated the properties for the obtaining of targets from the point of view of composition, morphologic, mechanic and physical properties. The targets from CoAl and IrAl will be irradiated in the TRIGA reactor and there will be analyzed the obtained result.

   The benefits brought from the change of metallic targets with intermetallic compounds targets refer to a shortening irradiation time to obtain a preset activities. In this idea the time of reactor’ function may be used efficiently, the dependence of stopped reactor times may be reduced and there will be assured a good and quick correlation with the beneficiary’s requirements. Also, there will be obtained an important reduction of materials costs, the iridium being a precious material and the cobalt a strategic material.

   The research consortium is interdisciplinary achieved with 4 partners with high scientific authority in the materials science and in the irradiation technology.  This experience is attested by the scientific books and papers, doctorate participations and nationals and Europeans research projects. The project will develop the material basis and the research competently of consortium, and offers the new research directions, the conditions of a connection to the priorities, objectives and activities of European research area.

  S/T current stage in the field, at national in international level, according to project theme. 

   SCN Pitesti fabricated iridium and cobalt gamma sources, products which were homologated. The metallic targets for this sources are made beginning from 1991. For the obtaining process of the Ir powder there were obtained BV-Nr.115704/2000. The sources made at SCN Pitesti are analogous with those made in the other country which are manufacturers of radioisotopes. The attempts to diminuate the factor of auto screening  of cobalt and especially  iridium gamma sources, had as scope. The optimization of the irradiation’ geometry of targets for the obtaining of a distribution with a good distribution of activities inside of produced source, or the variations of neutrons flux. (Attya A. Abou-Zaid, M. Nasr_, Annals of Nuclear Energy Volume 31, Issue 1, January 2004, Pages 87-96; V. A. Tarasov and Yu. G. Toporov Applied Radiation and Isotopes Volume 48, Issues 10-12, October-December 1997, Pages 1697-1701). Concerning the methods for the obtaining the mechanosynthesis of metallic, ceramics and composites materials, in the last ten years, they knew a special expansion, due to the possibility to develop a large spectrum of microstructure, from amorphous, nanocrystaline  and mesoscopique microstructure, to a polycrystalline structures in the hierarchic composites  ( L. M. Di, H. Bakker and F. R. de Boer  Condensed Matter, Volume 182, Issue 2, October 1992, Pages 91-98; A. Chiba, T. Ono, X. G. Li and S. Takahashi Intermetallics, Volume 6, Issue 1, 1998, Pages 35-42; D.L. Zhang, Progr. Mater. Sc., 49 (2004), 537).

 Contribution of the project to the development of the knowledge in the specific        field including the degree of novelty and complexity of the proposed solutions.

 The intention to intervene at atomic network level and to realize the activate element, with a great and very great absorbing cross-section of neutron, dispersion, such are the cobalt and respectively iridium, in the element with the absorbing cross-section of neutrons very small, such is aluminium, by the creation of a interpenetrate network of intermetalic compound is a premiere, contributing to a decrease of the factor of auto screening. Basically, the bigger is the dispersion of the target atoms in the irradiation channel the smaller is the factor of auto screening, and practically the target atoms look a much more flux of neutrons. In this way, may be obtained a preset activity for a standard source (50 Ci - gamagrafie, 2000 Ci - cobaltoterapie) in a short irradiation time. The intermetallic compounds answer to this challenge having the interpenetrating network, achieving the dilution of activate components. Their accomplishment in the form of irradiation targets needs the complex technological solution ; the obtaining by the solid state reaction of intermetallic compounds by mechanic alloying, the processing of resulted powders and the prove of the obtained characteristics by the complex analyze methods

   Detailed description of activities, coherent with the proposed objectives.

    - The activities for the production of irradiation targets from intermetallic compounds. The realization

of intermetallic compounds will be made in the powdered state, by solid phase reaction, by mechanical alloying. Modern technology which appeal equipments of the last hour, the mechanical alloying  imposed as a main method for the accomplishment of intermetallic compounds. The assessment of work conditions implicate the determination of the value of mixing time, work atmosphere, the ratio balls/material. The verification of these will be made by XRD on the tested material and the comparison with the calculated spectrums. The operation will be carried out at UT Cluj by specialists with experience in this domain and the relieve of CoAl, IrAl by XRD at UPIT-CCMA. The put in form and the realization of irradiation targets in the dimensional tips and the characteristics defined from the specifications of targets, including the realization of some devices such as dies and pins, drum for electrolytic plating etc, will be accomplish at SCN Pitesti, after the execution in front of the tests for the assessment of work conditions for sintering and patting with a nickel protection layer.

   -The activities for the characterization of obtained materials in all fabrication process phases

 The determination of obtained materials characteristics will be make in the inside of the research network prove his functionality. So the XRD analyze on the CoAl and IrAl in powdered state and after sinterization, will be effectuate at UPIT-CCMA. The morphological properties of the powder and sintered targets, the size and form of grains, the interface with nickel layer and the punctual analyses of composition, constituting a cross verification of XRD analysis, will be effectuate at UTCluj by electronic microscopy SEM and EDX. The physical  properties, the granulometric spectrum, the bulk density of powder and sintered targets, the size of Ni layer, the chemical and radiochemical purity, and the mechanic properties, the hardness and the compression resistance will be effectuated at SCN Pitesti.  

   - Irradiation tests of metallic compounds and postirradiation examination

The irradiation tests will be execute at SCN Pitesti in research reactor TRIGA. The documentary study and the demand neutron calculations will be realized at SCN Pitesti together with IFIN HH; will be determined by calculus of neutron activation the demand time of activation for the obtaining of preset specific activities; the values will be compared with those obtained for the metallic targets irradiation; the location of irradiation will be characterized from the point of view of neutron. After irradiation will be measured the activities of the targets will be compared with theoretical precognition. It will be analysed in the documentary study the way of irradiation source, including the target, at the end of life to the final storage. 

   -Dissemination of results, the integration in the European projects spooned in the frame of PC7.

The subject is developed at the chapter “Dissemination of results”

Expected S/T results for each proposed activity.

   The scientific results obtained on the route of the run activities of consortium IRCOAL will be presented in phase and annual rapports and will be materialized in documentary studies, calculus, technologies and materials characterizations.                                 

    -Documentary studies - Documentary study about the obtaining methods, the characteristics and

area of utilization of intermetallic compounds. The elaboration of technology’ model for the realization of CoAl, IrAl. The accomplishment  of realization variants of CoAl, IrAl; Documentary study – “End-life” of source, final storage

   - Bases of data – Theoretical base of data of crystal structures

   - Calculus The calculus of formation enthalpy of CoAl, IrAl; Demand activation neutron calculus for accomplished of preset activities.

   - Technologies – Technology for obtaining powdered CoAl, IrAl by mechanical alloying; technology for obtaining the irradiation targets CoAl, IrAl; technology for the plating of CoAl, IrAl targets with a nickel layer, technology for irradiation of  CoAl, IrAl targets.                           

   - Characterization of products – The characterization of powdered CoAl, IrAl : morphological

characterization – size of grains, form of grain by electronic microscopy SEM, compositional characterization – XRD analysis,  characterization of physical properties ; granulometric spectrum, bulk density, technologic properties – accomplishment of technologic conditions of work for putting in form; characterization of CoAl, IrAl: compositional characterization, XRD, EDX analysis, chemical and radiochemical purity, morphological characterization – grain size, physical properties – bulk density, thermic properties – determination of coefficient of thermic transfer, mechanical properties – hardness and compression resistance; characterization of  CoAl, IrAl targets plated with a Ni layer, an interface phenomenon by SEM; the characterization of  irradiated targets CoAl, IrAl determination of activity, radiochemical purity, post irradiation characterization macro and micro structure