Fig. 3-13 Technetium-99m generator 99Mo is fixed on the alumina adsorbent. By the reduced pressure of the vial on the top of the generator a saline solution is passed through the adsorbent eluting 99mTc and collected in the vial. The newly developed zirconium polymer having a high adsorbability can be used instead of a conventional alumina adsorbent. The production of the generator is very easy and 99Mo produced by a (n, gamma) reaction without radioactive wastes can be used.

Fig. 3-14 Elution of 99mTc from newly developed generator After dissolution of natural molybdenum (MoO3) irradiated with neutrons, molybdenum-99 was adsorbed on the adsorbent from a generator, from which 99mTc was eluted by using a saline solution. Most of 99mTc could be obtained in the first few milliliters.

A radioisotope technetium-99m (99mTc) has been used widely for the examination and diagnosis of cancer. 99mTc is obtained as the radioactive decay product of molybdenum-99 (99Mo, half-life: 66 hours), which is produced by irradiating natural molybdenum or uranium with neutrons in nuclear reactors. As the half-life of 99mTc is short, 99Mo is made into a "Generator" from which 99mTc is separated and made into radio-pharmaceuticals at the medical site. The generator, shown in Fig. 3-13, consists of 99Mo adsorbed on an alumina adsorbent in a glass tube. 99mTc can be obtained by passing a physiological saline solution through the tube. Today 99Mo produced from uranium and having a very low ratio of 99Mo to non-radioactive molybdenum is used because of the poor adsorbability of alumina to molybdenum. The production of 99Mo from uranium has large difficulties such as the requirement of heavily shielded production facilities, the evolution of large quantities of radioactive wastes etc.. An epoch-making adsorbent for alumina has been developed. Zirconium chloride was allowed to react with an alcohol and treated thermally to form a novel high polymer zirconium compound. This compound adsorbs 99Mo 100 times as much as alumina does. Whereas the yield of 99mTc is larger than 80% (Fig. 3-14), the desorption of 99Mo is less than 0.1%. For the sake of such characteristics, this adsorbent can be used for the preparation of the generator by using 99Mo easily produced by irradiating natural molybdenum. Practical applications of the adsorbent are expected.

Reference M. Tanase et al., A new Tc-99m Generator using an Organic Polymer Adsorbent for (n, gamma) Mo-99, Appl. Radiat. Isot., in press.

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