β decay is one of the most fundamental and thoroughly studied nuclear decay. Surprisingly, the β decay rate constants were found to have periodic time variability. However, others argued that there is no evidence for such cyclic deviation from the exponential first order kinetics decay law. Here we first propose that the β decay is a pseudo first order exchange reaction triggered by a tetraquark boson, and second develop a QCD gas theory assuming that the proposed tetraquark bosons fill space and form a reactive, polarizable, and compressible gas. In analogy to the atmospheric gas density, the proposed QCD gas density drops with elevation from the sun surface. Accordingly, we propose that the β decay rate variability is due to the pseudo first order exchange reaction kinetics and the QCD gas atmospheric density drop. Our main result is a formula for calculating the mass of the QCD gas based on the observed β decay rate variability.