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RADIOACTIVE_DECAY_REACTION

Specifies parameters for radioactive decay reaction. This reaction differs from the GENERAL_REACTION in that only one reactant species may be specified with a unit stoichiometry (i.e. the rate is always first order) and the reactant species is decayed in both the aqueous and sorbed phases.

Required Cards:

REACTION <string>

Reaction equation. Only one reactant species may be listed on the left side of the equation (i.e. or on the right side with a negative stoichiometry). The reactant’s stoichiometry is fixed at 1.0. The forward rate is applied to that one species as a first order rate constant. Multiple species are supported as daughter products on the right hand side and stoichiometries can be specified.

RATE_CONSTANT or HALF_LIFE (but not both):

RATE_CONSTANT <float> <optional units_string>

Rate constant for 1st-order decay reaction [1/sec, default units]. The rate constant may be calculated from -ln(0.5) / half-life. (default units [1/sec])

HALF_LIFE <float> <optional units_string>

Half life of species. (default units [sec])

Examples:

RADIOACTIVE_DECAY_REACTION
  REACTION Tracer <-> Tracer2
  RATE_CONSTANT 1.7584d-7 ! half life at 0.125 y
/

CHEMISTRY
  PRIMARY_SPECIES
    A(aq)
    B(aq)
    C(aq)
  /
  ...
  RADIOACTIVE_DECAY_REACTION
    REACTION A(aq) <-> B(aq)
    ! Calculating forward rate from half-life
    ! rate = -ln(0.5) / half-life [1/sec]
    RATE_CONSTANT 1.75836d-9  ! 1/s  half life = 12.5 yrs
  /
  RADIOACTIVE_DECAY_REACTION
    REACTION B(aq) <-> C(aq)
    RATE_CONSTANT 8.7918d-10  ! 1/s  half life = 25. yrs
  /
  RADIOACTIVE_DECAY_REACTION
    ! Note that C(aq) simply decays with no daughter products
    REACTION C(aq) <->
    HALF_LIFE 5. y
  /
  ...
/