Infographics / Nuclear Medicine

99Mo/99mTc generator & transient equilibrium

Semi-logarithmic plot of activity versus time. The parent Mo-99 (66 hour half-life) falls slowly as a straight line. The daughter Tc-99m (6 hour half-life) grows in, peaking near 23 hours just above the parent. Because the parent half-life is only moderately longer, the daughter reaches transient equilibrium and thereafter falls with the parent's 66 hour half-life. Saline elution ("milking") at 24 and 48 hours removes the Tc-99m, dropping its activity to near zero, after which it re-accumulates back toward the equilibrium envelope.

Molybdenum-99 / technetium-99m generator: activity against time Semi-logarithmic plot of activity versus time. The parent Mo-99 (66 hour half-life) falls slowly as a straight line. The daughter Tc-99m (6 hour half-life) grows in, peaking near 23 hours just above the parent. Because the parent half-life is only moderately longer, the daughter reaches transient equilibrium and thereafter falls with the parent's 66 hour half-life. Saline elution ("milking") at 24 and 48 hours removes the Tc-99m, dropping its activity to near zero, after which it re-accumulates back toward the equilibrium envelope. Molybdenum-99 / technetium-99m generator — activity against time 10 20 50 100 200 activity (log scale, arbitrary units) 0 12 24 36 48 60 72 time / hours ⁹⁹Mo ⁹⁹ᵐTc grows in, peaks by ≈ 23 h elution elution re-accumulates after each elution transient equilibrium: ⁹⁹ᵐTc tracks ⁹⁹Mo (66 h T½) ⁹⁹ᵐTc daughter, T½ ≈ 6 h (eluted daily) ⁹⁹Mo parent, T½ ≈ 66 h envelope if never eluted saline elution (“milking”)
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