Sputtering of Molybdenum thick films for cyclotron targets to produce Technetium-99m – Master Thesis Sara Cisternino

Author: Sara Cisternino ; Type of thesis: Master thesis

99mTc is the principal radioisotope used in medical diagnostics worldwide. Its 6-hour physical half-life and the 140 keV photopeak makes it ideally suited to medical imaging using conventional gamma cameras. 99mTc is derived from its parent element 99Mo that is derived almost exclusively from the fission of uranium-235 targets (using primarily highly-enriched uranium) irradiated in a small number of old-aged research nuclear reactors.
A global shortage of 99Mo exposed vulnerabilities in the supply chain of medical radioisotopes, therefore, individual countries and companies are exploring options for a future supply of medical radioisotopes. Cyclotron-based production of 99mTc starting from 100Mo by 100Mo(p,2n)99mTc reaction has been developed and evaluated at National Institute of Nuclear Physics – Legnaro National Laboratory (LNL-INFN); however some issues must be resolved. Among them innovative target development, because different requirements should be considered:

  • target strength;
  • ability to achieve desired thickness of target material;
  • adherence of target material to baking;
  • chemical resistance of backing;
  • thermal performance at desired current.

Target design strategies, which have been identified in literature, include evaporation, e-beam melting, rolling of thick/self-supported targets, sintering, and electrodeposition. However, they are not performing good enough from the heat conduction point of view. In fact, the resulting targets have high oxidation level and low density, and the deposition technique does not allow to control the thickness and to deposit onto specific substrates .
The purpose of this thesis is the development of an innovative target based on the deposition of the target material, specifically Mo, by magnetron sputtering technique in order to provide high density, thick, uniform and adherent film onto chemically inert backing, as sapphire.
After the sputtering parameter optimization, thick ( ̴ 100 μm) Mo films have been obtained and neither stress nor delamination have been observed.
Successful irradiations were carried out with 16 MeV cyclotron in Sant’Orsola Hospital, in Bologna, with different current beams. In fact, the system has performed at a current of more than 20 μA.