Thermal Neutron Reactor-Produced Radioisotopes

Radioisotopes used in Nuclear Medicine are almost all synthetic. For thermal neutron reactor-produced radioisotopes, reactor is source of thermal neutrons. An (n,gamma) reaction occurs. Net effect: increase of A number by 1 and no change in Z number. Same element is therefore present. Example: ⁹⁸Mo (n,gamma) ⁹⁹Mo

Reactor yield dependent upon:

• neutron flux in reactor (n/sec/cm²)
• nuclear capture cross section
• number of target atoms
• decay of product after it is formed
• length of irradiation
• isotope enrichment of target

The product of an (n,gamma) reaction or other reaction may be described in terms of specific activity, i.e., radioactivity per unit mass of the element present. Examples: µCi/mg, dpm/mM, Ci/uM, kci/mole. Various separation techniques are available to separate product from target. Requirement: chemical forms of element in target and product must be different to effect separation.