1.1.1 Solid irradiation method

In the conventional solid irradiation method, solid targets including natural molybdenum such as MoO3 pellets are irradiated with neutrons in a testing reactor, and 99Mo is produced by the 98Mo (n, у) 99Mo reaction. The post-irradiation process is only dissolution of the irradiated solid targets with an alkaline solution, and only a small amount of radioactive waste is generated in the process compared with the (n, f) method. The 99Mo production cost of this method or the (n, y) method is only 0.83 US$/37 GBq (Boyd, 1997).

However, the (n, у) method has the disadvantage of producing 99Mo with a low-level specific activity of 37-74 GBq/ g-Mo and therefore the method has not had practical application in earnest. In order to utilize 99Mo with the low-level specific activity, a high — performance adsorbent for (n, y) 99Mo is needed. The Japan Atomic Energy Research Institute (the present organization: JAEA) and KAKEN Inc. had developed the high — performance molybdenum adsorbent of Poly-Zirconium Compound (PZC) in 1995 (Hasegawa et al., 1996) and improved PZC (Hasegawa et al., 1999), and then the practical application of the (n, y) method is just in sight. The molybdenum adsorbent performance of PZC is over 100 times compared with the conventional molybdenum adsorbent of alumina.