Nuclear recoil separation in the photonuclear production of auger electron emitter Germanium-71 for high specific activity medical isotope production

Introduction The purity of a radionuclide is a crucial factor in the feasibility of medical isotope production methods. One measurement of purity is the ratio of the radionuclide of interest to all isotopes of the same element, or the specific activity. When the specific activity is too low, a sample can be unusable in medical applications due to inefficient radiolabeling with the intended radionuclide. A promising group of medical isotopes often produced with low specific activity are Auger electron (AE) emitting radionuclides. These radionuclides are often produced by irradiating a target material of the same element as the AE-emitting radionuclide of interest. Following such production methods, time-consuming and expensive mass separations would be needed to isotopically purify low specific activity products. Methods In this work, a new method of in-beam separation that relied on nuclear recoil and ultra-thin target foils was used to produce and separate AE-emitting germanium-71 (71Ge) from a natural germanium (natGe) target. Scientists at Idaho National Laboratory and Idaho State University have conducted photonuclear irradiation at the Idaho Accelerator Center to test this separation method by measuring the separation yield for 71Ge from natural Ge foils and to compare the measured separation yield to predictions from a nuclear recoil model. Results and Discussion With this targetry approach, a nuclear recoil efficiency of 0.13(4)% was measured for 71Ge from natural Ge foils. A comparable result of 0.23% was predicted for the recoil efficiency using analytical equations to describe the kinetics of the recoil effect. This work showed that the separation method is feasible, but due to low yields, further targetry development is necessary. Additionally, the modeling method can be used to guide future targetry development and experimental planning.