Heures thésardes: Radioactive isotopes produced for medical applications: setting up an accurate measurement method for production cross section

Etienne NIGRON

Subatech (groupe Prisma)

jeudi 12 avril 2018

The nuclear medicine is a medical specialty that employs radionuclides for diagnosis or therapy. Several modalities are operated in diagnosis (PET/SPECT, Positron Emission Tomography/Single Photon Emission Computed Tomography) which takes advantage of the photon emissions occurring during the decay of the radionuclide. In therapy, strongly interacting particles obtained through radioactive decays are used such as alpha particles, beta or Auger electrons. They are mostly coupled to a vector for targeted therapy. The trend followed by nuclear medicine is to become more and more personalized to each patient. To reach that goal, a wide variety of radionuclides (different decay particles, different half-lives, different chemical properties) must be available to meet the patient’s need. Their production is achieved using reactor or accelerator and has to be well controlled. The aim of this PhD thesis is to study the production means of radionuclides having an interest for medicine using a cyclotron. To do that, a good knowledge of the radionuclide production cross section is required.

In collaboration with the GIP ARRONAX[1] which possesses a multi-particle high energy cyclotron, the project is to get an accurate measurement of production cross sections for a wide variety of radionuclides but also explore alternative production route and assess the final product quality. To measure cross sections, the “stacked-foils” technique is used. Among the information requires for a precise measurement, the flux of the incident particle is the more important one. The data about the particle flux of the beam can be evaluated using a monitor reaction with a well-known cross section whose values are recommended by the International Atomic Energy Agency (IAEA). The uncertainty (around 10%) associated to the monitor cross section values results in a high uncertainty on the measured ones. Another method is to measure the amount of charges crossing the stack allowing to reduce the uncertainty on the measured cross section (expected uncertainties are of the order of a few percent). In order to use this technique, a new experimental cross section measurement device has been set up and is being tested in well-known conditions. The results obtained show that the new device works well and the results are in good agreement with the IAEA recommended cross section values and other available data in the literature. This satisfying results show that this device can be used to measure cross sections with a reduced uncertainty and it will allow completing production cross section database for radionuclides of interest.