The disintegration rates of 98Mo (isotopic ratio: 24.138%) and 99Mo are shown as following equations:

( + ф—99 ) N99 + ф(Г98^98

The solutions of the equations (1) and (2) are as follows:

N 98 (t) = N 98(0)exp (_—t)

N99 (t) = . ф( 98———— ) N98(0) texp(- Ф-98t) — exp{- ( + —99 )t} ] (4)

Л+Ф (99 — 98 )

where N98 and N99 are the atom number densities of 98Mo and 99Mo (n/cm3), t is time (s), ф is neutron flux (n/(cm2-s)), o98 and o99 are the capture cross section of 98Mo and 99Mo (cm2), and X is the decay constant of 99Mo (1/s). When the neutron flux, the capture cross section, the decay constant and the time are given for the equations (3) and (4), 99Mo generation rate per unit volume can be calculated depending on the time.

The specific activity of the generated 99Mo is calculated from the following equation:

_ dN99 = Wx4.17x 1023 (5)

— dt ~ AT

where W is the mass of 99Mo (g), A is the atomic mass number of 99Mo, and T is the half-life of 99Mo (s).