99Mo recoil atoms yield in the 100Mo(p,x) reaction on cyclotron irradiation of Mo nanofilms

We study the possibility of increasing the specific activity of Mo-99 produced by irradiating molybdenum targets with the use of the Szilard-Chalmers effect. According to the Szilard-Chalmers effect, recoil atoms of the Mo-99 radionuclide can be produced in nuclear reactions and retained in surrounding buffer substance. The objective of our work is to measure the yield of recoil atoms in the buffer as a function of the molybdenum layer thickness. The yield of recoil Mo-99 atoms in the Mo-100(p,x)Mo-99 nuclear reaction as a function of metallic molybdenum nanolayer thickness has been measured. Measurements were carried out after irradiation of nanolayers in the U-150 cyclotron with 28-MeV protons. Nanolayers of molybdenum with thickness of 30 to 220 nm were produced by magnetron sputtering on sapphire plates. The yield of the mass of Mo-99 recoil atoms was found to be the highest with the molybdenum layer thickness of 80 +/- 5 nm. The enrichment factor (EF) has been defined as a ratio of the Mo-99 collector specific activity (SA) to the entire target SA before separation as EF = 1200 +/- 150. The specific activity of Mo-99 produced in the collector was estimated to be approximately equal to 25 Ci center dot g(-1).