Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) have conducted a study on preparation of low specific activity (LSA) ⁹⁹Mo/^99mTc generator, which has potential application prospect for the accelerator/reactor-based production of the medical isotope ⁹⁹Mo. 

^99mTc, produced from the decay of its parent radioisotope ⁹⁹Mo, is the most commonly used diagnostic medical radioisotope, comprising 80% of all diagnostic radionuclides. Annual worldwide demand for ⁹⁹Mo is estimated to be approximately 500 thousand Ci, which provides diagnoses for about 30 million people. However, in China, the clinical ⁹⁹Mo/^99mTc generators are totally dependent on imports at present. 

Currently, the production of ⁹⁹Mo (a high specific activity of 10⁴ Ci g^-1) is mainly generated from (n, f) reaction in reactor using highly enriched uranium-235 target. Nevertheless, most of nuclear reactors are confronted with many issues, such as security, technique, overhauling, which cannot satisfy with the growing demand for ⁹⁹Mo. Besides, the route of ⁹⁹Mo separation is complex and a great amount of high-level radioactive waste liquid is produced during the process, increasing the probability of nuclear proliferation risk. 

To make sure a reliable supply of ⁹⁹Mo, accelerator/reactor-based production of ⁹⁹Mo has been explored all over the world. Thus, it is of great importance to develop LSA ⁹⁹Mo/^99mTc generators using the column absorbents which has high absorption capacity for Mo ions, and achieve recycling of enriched Mo target. 

The researchers from the Nuclear Chemistry Group of IMP have carried out an investigation on the synthesis of hierarchically macro/mesoporous γ-Al₂O₃ (HMMA), which is applied in the preparation of LSA ⁹⁹Mo/^99mTc generator. 

Compared with the ordinary alumina (2-20 mg Mo per g of alumina), which is used for fission ⁹⁹Mo/^99mTc generator, HMMA exhibited high capacity to Mo ions with about 250 mg Mo per g of HMMA.  

Furthermore, a LSA ⁹⁹Mo generator prepared using HMMA as column matrix is capable of fine recovery of ^99mTc (89%) for a long time. ^99mTc product, which could be eluted from the generator with little volume, is of high radionuclidic and radiochemical purity, thus suitable for the labeling study. With the labeling efficiency and radiochemical purity both reaching more than 96%, ^99mTc product was used for preparation of radiopharmaceuticals. 

It is worth mentioning that a very efficient way to recycle ^100/98Mo with a high total recovery yield of about 95% was realized in the work. In addition, absorption mechanism results indicated that Mo ions reacts strongly with γ-Al₂O₃ and a hydroxyl on the surface of HMMA, simultaneously.  

According to the study, the preparation of HMMA is easy, efficient and economical, and is suited for large-scale fabrication of LSA ⁹⁹Mo/^99mTc generator. This study lays important foundation for the accelerator/reactors-based ⁹⁹Mo production. 

The study has been published in Applied Radiation and Isotopes and it was financially supported by the National Natural Science Foundation of China and competitive projects of the special fund for the guidance of the innovation and development of science and technology, Gansu Province.

The investigation on preparation of LSA ⁹⁹Mo/^99mTc generator. (Image by WANG Jieru and QIN Zhi)