Molybdenum-99 production via lead and bismuth moderators and milli-structure-$^{98}$Mo samples by indirect production technique using Monte Carlo method

We describe the design of a neutron activator that contains a beryllium target, a lead/bismuth moderator, graphite/$\rm PbF_{2}$ reflectors, and a boron absorber. Production of the $^{99}$Mo isotope using millimeter-sized $^{98}{\rm Mo}$ samples located in various regions of the activator was simulated using the MCNPX code. If the $^{98}{\rm Mo}$ samples are placed in the reflector region, the yield increases due to a larger flux of epithermal neutrons.