RPI DOSIMETRY. Therefore the description of the work is grouped in two main areas:

Transcription

1 RPI DOSIMETRY Introduction The main objective of the RPI Dosimetry is the characterization of the radiation field of the facilities available in the reactor. Most of the use of the reactor centers in irradiation in experimental facilities located in the pool and in the use of neutron beams. At present, as is well known, such characterization, although essential and requiring detail, does not entail, in general, a very close follow up. This is not the case, for instance, for irradiations involving biological materials, that need radiation fields with adequate characteristics and a detailed dosimetry of the experiences. Work has been centered on facilities, aiming at implementation of the BNC technique, in particular of a beam tube for experimental work, and on the study of the best conditions for irradiation. Therefore the description of the work is grouped in two main areas: - DOSIMETRY OF RPI FACILITIES - DOSIMETRY FOR BNC Research Team Researchers 2* (2 PhD or equivalent) Technicians 1 Grantee (three months) 1 * With collaboration of Dra. Isabel F. Gonçalves and Dr. J. Salgado Publications: Journals 1 Proceedings 1 Conf. Commun.: 4 Internal Reports: 1 157

2 RPI Dosimetry Dosimetry of RPI Facilities Introduction As main objectives for the Dosimetry of RPI Facilities activities, the support to the reactor users and the implementation of dosimetry techniques, must be referred. It is also an important goal, the collaboration with universities so as to allow the familiarization of students with nuclear techniques. Related with the first of the above objectives, the dosimetric characterization of the reactor facilities as the thermal column and a beam tube, should be referred. Studies for the implementation of the Thermoluminescent Technique for gamma radiation measurement have been done. In what concerns training actions, it s worth referring collaboration in: Course for Reactor Operators; Experimental Class on Radiometric Methods for students of a Master degree in Analytical Chemistry from the University of Evora; Experimental Class on Radio-Chemistry Methods for students of the Chemical Engineering Course of Instituto Superior Técnico; Experimental work for a Master Thesis in Educational Sciences of Coimbra University. Current Work Preparation and quality control of 198 Au-sodium aurothiomalate. Evaluation of its potential value for rheumatoid arthritis imaging in rabbits Maria dos Anjos das Neves, Isabel C.Gonçalves, Luciana Patrício A study of feasibility of obtaining adequate 198 Au specific activities, by irradiation of sodium aurothiomalate, was performed. The chemical composition of the compound was tested by activation analysis, and the irradiation conditions were defined so as to obtain the required 198 Au specific activity. With an adequate combination of irradiation and delay times, it s possible to have an 24 Na insignificant contamination in the final product. Lyophilised samples were irradiated under optimized conditions and pharmaceutical formulations were performed as well as radiochemical quality control. These preparations were supplied to IBILI, for evaluation of its value as rheumatoid arthritis imaging in rabbits. 158

3 RPI Dosimetry Determination of thermal neutron flux profiles at the tangential tube of RPI using copper monitors Isabel C.Gonçalves, António Falcão Thermal neutron fluxes were determined with gold foils in positions along the axis of the tangential tube. Detailed profiles of the neutron fluxes along lines parallel to the face of the reactor were also obtained with copper wires and correlated with the absolute values of the fluxes measured with gold. Dosimetry for BNC Introduction The forseable importance of BNC has been recognized world wide, therefore it can be seen that activity in the area is being carried out in a large number of reactors or neutron sources. The work conducted in 1996 is a continuation of the one performed in the previous years which includes experimental activity involving the irradiation of biological materials and extends in the future aiming at patient treatment. The experimental work included the irradiation, and therefore the corresponding dosimetry of mouse and cells with thermal neutrons, for which an adaptation of the thermal column was done in 1995, aiming at improving the ratio th / D. The irradiation with thermal neutrons limits its use to thin samples. Therefore if a thick sample (like a tumor) is to be irradiated, more energetic neutrons are needed. That has led us to study the arrangements of a beam tube so that a neutron beam of thermal and epithermal neutrons (minimum of fast and gamma dose) could be used for experimental work. In this context the design of the arrangement to be performed has been made and the preparation of a safety analysis report has been done to assure, inter alia, that the insertion / removal of samples can be safely performed with the reactor running. With the ultimate objective identified above, activity has been initiated to study the filter arrangements for the thermal column of the RPI, so that the adequate neutrons beam will be available. The participation in projects aiming at standardizing the control conditions of BNCT irradiation facilities and some specific studies on boron carriers and melanoma, has been sought. 159

4 RPI Dosimetry The Boron Neutron Capture Therapy - BNCT. The development of the Ibero BNCT Group F.Mascarenhas 1, I.C.Gonçalves 2, A.Ramalho 2, J.Pertusa 3, M.J.Lorente 3, A.Irles 3, V.Alcober Coloma 3, V.Alcober Bosch 4, M.Castro 5, J.Toscano Rico 5 1 Radiotherapy Service of Santa Maria Hospital, Av. Prof. Egas Moniz Lisboa, Portugal 2 Nuclear and Technological Institute, E.N.10, 2685 Sacavém, Portugal 3 Biology Department of Valence University, C/Dr. Moliner, Burjassot, Spain 4 U.P.Madrid, Dep.Física Aplicada, Ciudad Universitaria,s/n Madrid, Spain 5 Experimental Clinical Pharmacology Centre of Faculty of Medicine of Lisbon, Av. Prof. Egas Moniz Lisboa, Portugal Abstract A description of the Boron Neutron Capture Therapy methodology, focused to its human therapy application, is presented. The work performed by the Ibero BNCT Group and the actions, planned for the near future, are refered. Acta Portuguesa de Radiologia (in press). Establishment of new irradiation facilities at the Portuguese Research Reactor I.F.Gonçalves 1, A.J.G.Ramalho 1, I.C.Gonçalves 1, J.F.Salgado 1, V.Alcober Bosch 2 1 ITN - Instituto Tecnológico e Nuclear, E.N.10, 2685 Sacavém, Portugal 2 U.P.Madrid, Dep.Física Aplicada, Ciudad Universitaria,s/n Madrid, Espanha Abstract A short review of the activities conducted at the RPI in the irradiation with thermal neutrons of bilogical materials loaded with boron, is made. Work performed to establish thermal and/or epithermal beams in one beam tube of the reactor is described. The results of MCNP calculations optimizing the materials arrangement seems to indicate that the replacement of the Be reflector by an aluminium block with the same thickness, would improve the intensity of the epithermal beam, with a degradation though of the thermal beam and of the D fast /n epi. This result will be further exploited in the current work aiming at the installation in the thermal column of the reactor of a BNCT irradiation facility. Communication to: Ninth International Symposium on Reactor Dosimetry, Praga,

5 RPI Dosimetry Utilization of RPI in BNCT Work I.C.Gonçalves, A.Ramalho Abstract The work performed in the area of BNC, by using RPI facilities, and the future developments expected for this field of work, are described. Communication to: 7 th Annual Meeting of the European Atomic Energy Society Research Reactors Operators Group, Lisboa, Boron Neutron Capture Therapy - Perspectives of utilization of RPI I.C.Gonçalves, A.J.G.Ramalho, I.F.Gonçalves, J.F.Salgado Abstract A review of the BNCT fundaments and a perspective of the development of this technique around the world, including its application in human therapy, were given. The activity developed by the Ibero BNCT Group, (that includes teams from ITN, Valence University, Polytechnic University of Madrid, Faculty of Medicine of the University of Lisbon and Santa Maria Hospital) was described. Communication to: FÍSICA th National Conference of Physics, Faro, Portugal, Sept Installation of a new irradiation tube at the RPI aiming at performing studies in the area of BNCT I.C.Gonçalves, A.J.G.Ramalho, I.F.Gonçalves, J.F.Salgado This work is essentially the one presented at the Ninth International Symposium on Reactor Dosimetry. Communication to: FÍSICA th National Conference of Physics, Faro, Portugal, Sept

6 RPI Dosimetry Optimization of the radiation field of the vertical access of the thermal column of RPI for experiences with biological samples I.C.Gonçalves, A.J.G.Ramalho The irradiation of biological samples in the neutron field of a reactor requires the maximization of the ratio of the intensities of the neutron to gamma components of the field. The results of measurements of the neutron flux and gamma dose rate performed in the thermal column of the RPI for various thickness of lead filters are presented. The experiments led to the removal of a few graphite blocks and to the installation of a lead shield 8cm thick, in the available irradiation space as the most suitable arrangement for the envisaged work. In the irradiation space the thermal neutron flux decreases with the distance to the reactor core face at an approximate rate of 2.5%/cm from 6.3 to n.cm -2.s -1. Along the lines parallel to the core face, the neutron flux is constant within 3%. The Cd ratio is of the order of 250 and the superimposed gamma field has an intensity of 50cGy. Irradiations of some biological materials were performed and the respective dosimetric control showed a reasonable good reprodutibility of the irradiation conditions. ITN Report Current Work Preparation of a beam tube for multiple applications A.J.G.Ramalho, I.C.Gonçalves, I.F.Gonçalves, J.F.Salgado The extraction of a neutron beam from the RPI, whose size and energy can be selected, is described. The beam will have the epithermal and thermal components enhanced with respect to the fast neutron and gamma components and will have the options of 5 and 2 cm diameter. The neutron spectrum and intensity of the beam were optimized with help of the Monte Carlo MCNP code. The external shielding is being designed to allow for changes of samples with the reactor in operation and to permit multiple use, including PGNAA. The PGNAA work will be initially centered in Boron analysis and therefore the cavity where the samples will be positioned is lithium lined and designed to have small Boron contamination. 162

7 RPI Dosimetry Use of the thermal column of the Portuguese Research Reactor (RPI) for BNC Therapy I.F.Gonçalves, I.C.Gonçalves, A.J.G.Ramalho, J.F.Salgado The Portuguese Research Reactor (RPI) is a small reactor provided with a thermal column. Around the thermal column there is still free space that can be used to isolate an area sufficient to install a BNCT facility without interfering with the present work in other areas. With this background it has been thought to use the thermal column for BNC Therapy. Preliminary indications show that it will be possible to have a location with sufficient intensity for that effect. To further study this problem calculations with the MCNP code are beeing made to determine the exit points of the beam and to optimize the filter materials and assure that adequate conditions can be created. Producing an optimized epithermal neutron beam in the Portuguese Research Reactor (RPI) I.F.Gonçalves, I.C.Gonçalves, A.J.Ramalho, J.F.Salgado The RPI is a 1 MW swimming pool research reactor in which we are seeking to improve the use of the available beam ports. Recent work 1 in producing an epithermal neutron beam has showed that it could be advisable to replace the Be reflector of the RPI by an Al block. To further evaluate the safety problems involved, in particular the effect on the critically of the reactor, calculations are beeing performed using the MCNP code to determine the effect on k eff of the reflector substitution and to conclude about the input neutron spectra to the beam tubes. 1 Establishment of new irradiation facilities at the Portuguese Research Reactor, I.F.Gonçalves, A.J.G.Ramalho, V.Alcober Bosch, I.C.Gonçalves, J.F.Salgado, 9 th Symposium on Reactor Dosimetry, Sept. 2-6,Prague, Czech Republic,

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