Description and Analysis of an Accelerator-Based Production Method of the Brachytherapy Source ¹⁴⁵Sm

An accelerator-based ¹⁴⁵Sm production method is described. A target of a natural samarium compound, for example, Sm₂O₃, is bombarded with protons in the 70-MeV energy range. The resulting nuclear reactions produce ¹⁴⁵Eu as well as other europium isotopes that are chemically separated from the samarium target. If this separation is performed more than 15 min following the irradiation, then only ¹⁴⁵Eu and europium isotopes with half-lives longer than the halflife of ¹⁴⁵Eu remain in the europium fraction. Following the first separation, the separated europium undergoes radioactive decay until most of the ¹⁴⁵Eu in the europium fraction has decayed into ¹⁴⁵Sm. Then, a second chemical separation is performed in which the ¹⁴⁵Sm is removed from the long-lived europium radioactivities that accompanied the ¹⁴⁵Eu in the first separation. The result of the two chemical separations is a high-specific-activity ¹⁴⁵Sm product with contaminations from europium radioactivities that depend on the efficiencies of the separations and the time of their performance. The ¹⁴⁵Sm yield and purity for this production method for a high-current accelerator are compared with the yield and purity of ¹⁴⁵Sm from a reactor-based production method for a high-flux reactor. The yield of ¹⁴⁵Sm/day for the accelerator-based production method exceeds the yield per day for the reactor-based production method for reactor targets less than ∼1 g. For modest ratios of europium-to-samarium separation efficiencies for the first separation (∼10), the specific activity of the accelerator-produced ¹⁴⁵Sm exceeds the specific activity of the reactor-produced ¹⁴⁵Sm for reactor irradiation times <2 days. However, the activity of the ¹⁴⁵Sm contaminants is larger for the accelerator-produced ¹⁴⁵Sm than for the reactor-produced ¹⁴⁵Sm, unless the ratio of europiumto-samarium separation efficiencies for the second separation is greater than ∼5000.