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Cross section measurements

Production of radionuclides
The radionuclides that are used for medical applications are generally produced artificially. They are obtained by sending projectiles on targets formed from stable elements in nature.
The choice of the projectile used depends on the decay mode of the radionuclide that is to be produced. For beta + emitting radionuclides, charged particles such as protons will be used, produced by an accelerator. For emitting radionuclides beta-, neutrons, produced in a reactor, are used. For alpha-emitting radionuclides, neutrons from reactors will also be used. Thus we see that accelerators and nuclear reactors are complementary with regard to the production of radionuclides.
The quantity of radionuclides produced during the irradiation of a target is proportional to the number of target nuclei and the flow of the projectile used. The coefficient of proportionality, which contains all the physics of the interaction, is called production cross section. It depends on the energy of the projectile.
To optimize the production of a radionuclide, we must determine the proper energy interval of our projectiles and take into account the fact that for a given projectile energy, several different nuclear reactions are possible. These other nuclear reactions will produce unwanted radioisotopes (contaminants) that must be removed later. It is therefore important during the optimization phase of irradiation parameters to see how we can avoid the production of these contaminants in order to simplify the subsequent work of radiochemical purification.
The production cross sections
This optimization work is done using the production cross sections of the different isotopes.
These cross sections are available, when they are known, in data bases (NNDC). For some reactions, cross sections are not known precisely and it is necessary to measure them again. To this end, a program of cross sections measurement is implemented at Arronax using the "stacked foils » technique.