Physics of Radiation InteractionS with Matter and Applications
The activities are divided into three axes for the first two, the group's involvement is paramount. The third is transdisciplinary activity involving different skills laboratory and the Ecole des Mines de Nantes. All these activities are carried out with strong support from technical services of SUBATECH laboratory.
1. DEVELOPMENT AND OPTIMIZATION OF PRODUCTION OF RADIOACTIVE ISOTOPES
Our involvement in the production of radioactive isotopes for medical applications is related to the installation of a high energy (70 MeV) and high intensity (2 * 350 µA) cyclotron in Nantes, ARRONAX. It began by participating in a focus group on the production of innovative β + emitters for medical imaging in oncology. In partnership with physicians and researchers at INSERM U892, a list of isotopes that can be produced at ARRONAX and consistent with medical needs has been established. It served as the basis for establishing the priority list of radionuclides to be delivered by ARRONAX. This list includes isotopes for vectorized internal therapy such as β-emitters (Cu-67, SC-47) and α (At-211), generators for imaging by positron emission tomography (PET) Sr-82/Rb-82, Ge-68/Ga-68 and PET emitters to enable dosimetry before vectorized internal radiotherapy (Cu-64, SC-44). This priority list is deliberately reduced and will be called upon to extend progressively according to the needs of the community. In parallel, in order to optimize the production of radionuclides, a computer code for production calculations from the experimental cross sections that can get in the database was developed. Indeed, the determination of irradiation parameters for optimizing the production of isotopes has to be based on a good knowledge of reaction cross sections. In some cases, these data are incomplete or unclear what led us to develop the ability to make ourselves some of these measures. For this, we use the method of "Stacked-Foils". The principle is to irradiate a plurality of thin sheets of known thickness with a flux of projectiles fixed at a given energy, and then to measure the activities of all the isotopes in each sheet. We can then go back to the values of the cross sections investigated. Three irradiation tests at 35 MeV, 45 MeV and 61 MeV have been carried out on sheets of natural Titanium and Nickel. The values of cross sections of 24 different reactions were obtained during these irradiations. The measured values are in good agreement with existing data. A device for irradiation of 10 sheets simultaneously is in the final stages of completion and will be tested in September 2010 ARRONAX (PhD E. Garrido). We also use Monte Carlo computational tools MCNPX and Geant4 to perform the estimation of the inventory of radioactive species produced during irradiation. This allows us to anticipate the constraints on extraction and chemical separation of our targets and to estimate the expected dose rates. The cyclotron ARRONAX was put into operation in March 2010. Ten irradiation tests were performed with low activity for the development of production. For this, it is interesting to not use the shuttle ARRONAX that results in shielded enclosures. So we built an easy sytem "ad-hoc" enabling irradiation of any kind of target (powder, sheet) in the room AX. This device will also be used to achieve the first irradiation tests on Rb metal for the production of Sr-82 in the context of collaboration with INR Troitsk (Russia). Moreover this device irradiation, other developments are underway:
- To optimize the production of certain radioactive elements, it is necessary to use beams whose energy is not available directly at Arronax. This is the case, for example, for the production of At-211 that requires a particle beam of 28 MeV α with energy spread less than 1 MeV and for producing Cu-64 (proton beam of about 12 MeV). For this, an energy degrader was developed at SUBATECH. This device is capable of supporting a high flux of particles (40μA protons and 70μA α). The chosen solution includes two removable devices mounted in the same enclosure. This choice comes from the strong constraints related to the degradation of a α beam: poor control of energy production lead to Polonium 210 presence in our production of At-211, via the decay of At-210. The device placed on the beam lines upstream the irradiation stations is controlled from the control room of the cyclotron. An energy calibration of degraders has to be made using an experience of elastic scattering, which is being developed. The installation of degraders should be finalized by the end of 2010.
- Productions at mean intensity (100μA protons) should be performed using the shuttles provided by IBA (the manufacturer of the accelerator). These shuttles designed for electrodeposited targets have been modified in order to receive capsules containing the target material such as the RbCl for the production of Sr-82. This system will allow the irradiation of several targets carefully chosen and placed one behind the other. A first prototype has been built and tested in spring 2010. Changes appeared necessary, especially related to the constraint of assembly and disassembly in hot cell using manipulators. In parallel with this, a set of specialized tools to facilitate ths work is being designed and implemented . The system should be operational by fall 2010.
- The target manufacturing is also within the scope of the group. For their production, we use all available techniques: vacuum evaporation, electroplating, using compacted powder, foils, ... The choice of technique depends on the characteristics of the target material and irradiation conditions. In all cases, it is necessary to have a very precise control of the final surface to ensure perfect grip and better cooling of targets. For the production of copper-64, we introduced the nickel-64 plating on Gold media (regular irradiations since 2 years of our targets at CEMHTI Orleans). For the production of astatine-211, we have implemented the technique of vacuum deposition of Bi on a support AIN. For the production of strontium-82, we are currently using compacted RbCl targets that are then encapsulated.
Besides the use of charged particles as a projectile, many radioactive isotopes can be produced advantageously using neutrons. This requires the use of nuclear reactors which are rare and / or inaccessible. Through the use of very intense proton beams, it becomes possible to generate high-flux neutron interaction on heavy targets. The addition of the target of suitable materials (moderator and reflector) optimizes the flow and energy of these neutrons for specific applications such as neutron capture in the resonances range. This is the principle of "Adiabatic Resonance Crossing" proposed by C. Rubbia in 1998 which the AAA company has the license. As part of OSEO-FUI, a consortium was set up around the company to design and install such a device "neutron activator" on ARRONAX (Theranean project). The objective of this project is the development and preclinical validation of a methodology for therapy of solid tumors with submicron particles loaded with lanthanide oxides (holmium or lutetium) beta and gamma emitters. These particles, prepared under radiopharmaceutical conditions without radioactivity, are then activated using the neutrons generated by the activator. The activator being developed will leverage the available high energy (70 MeV) and high intensity (350μA) proton beam available at ARRONAX. As part of this collaboration, AAA handles the target and us the rest of the activator and its mounting. Simulation work is underway to assess the radiation constraints related to the use of the activator and maintenance.
2. DEVELOPMENT OF NON-DESTRUCTIVE METHODS OF MATERIAL INVESTIGATIONS
The second group's main activity is the study and use of radiation to probe (analyze, characterize, control) materials. These probes and methods are essentially "nuclear" and "optical".
PIXE (Proton Induced X-ray Emission) uses a beam of protons to perform quantitative analysis of multielement nondestructively. They are based on the X-ray emission induced by the interaction of protons in matter. The X-ray energy is characteristic of the atom which has been energized. The large production cross section of X-rays gives to their use the characteristics of a fast and very sensitive method. Many device exist in France and throughout the world using low-energy protons (a few MeV). On ARRONAX, given the available beam energies, we can work to 30 MeV and beyond. This offers the possibility of using X-ray K-type with large energies and they are emitted in abundance for heavy nuclei (rare earths and beyond). The high energy beam can work "in the air" (not vacuum) thus facilitating the implementation especially for bulky or fragile specimen. The high energy beam and rays of type K allow to explore beyond the surface of the object. In addition, the use of X-ray K, more energetic than the type L, also allows easierv analysis of data (less overlap of peaks). However, the main disadvantage of the use of high-energy protons is the activation they generate in the sample. This can be limited by using low beam intensities and the choice of energy to limit the production of long-lived elements (a sample we spent for testing came back at the background noise after 15 days and can again be handled without special precautions). Finally, this disadvantage can be an advantage in some cases. Indeed, the nuclear reactions generate a stream of gamma "prompts" and/or activation gamma that can be used in the analyzes to provide additional significant information (see PIGE). Thus, in the interaction of protons with copper X-ray emission from 8 keV is rapidly attenuated limiting the exploration to the first 30 microns. By using 67 keV "prompts" gamma emitted by Ni-61 created during irradiation, it is possible to "track" the copper to several hundred microns deep. The first measurements made in May and June 2010 are promising: with a proton beam intensity of about 20 nA, we obtained sensitivities of the order of a few tens of ppm with a device whose shielding was not optimum.
The laboratory SUBATECH, through the PRISMA group is a founding member of the "Pôle de Compétence Évaluation et Contrôle Non Destructifs en Pays de la Loire" (ECDN-PDL) whose purpose is to amplify the existing academic collaborations, to create new ones and to foster a coordinate emergence of this activity at the regional level. Within this framework, we launched in collaboration with the "Laboratoire Central de Ponts et Chaussées" (LCPC) a research program around the non-destructive evaluation of the density of civil engineering materials by coupling RX and radar techniques as an alternative to gamma-densitometric measure techniques used routinely today.
We are also one of the four 'academic' partners of Technocampus of EMC ², technological research center dedicated to compisite innovation and industry. Our main activity is the design of a multimodal platform Non Destructive Testing, grouping, combining and merging various techniques and methods. This action is supported by the research program "Matériaux : caractérisation, procédés, contrôle" - Contrat de Projets État Région des Pays de la Loire (CPER 2007-2013). One goal is to find alternatives to the use of conventional ultrasound (U.S.) technics not well adapted to large objects and requiring the use of a coupling, usually water, to the acoustic wave propagation between the transmitter (receiver) and the part to be inspected. In particular, we designed a bank of active infrared thermography in which the thermal excitation is provided by high power "flashbulbs" ; recording of the sequence of the evolution of the surface temperature and the associated image processing allows us visualize defects or discontinuities present in the material ; work remains to be done on the processing algorithm for improving the spatial resolution, size and depth of "default" (of the order of mm).
As part of the regional project thermoplastic welding (MP16T5), we fully designed the CND multi sensor device online which equiped the welding heads and also the associated software. This device has to host on board three devices: ultrasonic sensor (U.S.) with coupling water box, laser profilometer and infrared thermal camera. The results suggest that our thermal acquisition is expected to replace the usual U.S. controls and avoid the use of water (coupling) during the welding operation.
Finally, the ultrasonic laser laser technique (LUIS, then LUCIE) is one of the innovative lines of research the CND Technocampus EMC ², we are conducting it in collaboration with AIRBUS and EADS IW. We bring our expertise in the context of optical characterization methods and numerical simulations. In this technique, heating caused by laser shock (power) will cause the propagation of a wave in the material, which will be reflected / disturbed by interface / defects encountered: measurement, by optical interferometry, of the deformation of the surface will allow to detect these (possible) defects. In the upstream phase of the project we are working on both simulations of wave and heat propagation in the material and optical characterization of surfaces to determine the conditions of use (reflectivity, angle of incidence ).
3. DEVELOPMENT OF ELECTROLOCALISATION SENSORS FOR ROBOTICS
In the RAAMO project (ANR Robotics), we support the Institute of Communication Research and Cybernetics of Nantes (IRCCYN), project holder, in the development of an electrolocalisation sensor for a "eel" robot : detection and recognition of underwater objects at short and medium range, through the distortion of electric field lines generated by a multipole electrokinetics. This work is conducted in collaboration with a SUBATECH research group in theoritical physics for modeling aspects. Besides the development of the sensor itself, the PRISMA group has actively participated in the design and construction of the demonstration bench and of the prototype.