 Helium-3 relaxation time

A small abundance displacement from the helium-3 equilibrium abundance obeys $\dot{x}=-x/\tau$ to linear order. Rapid relaxation relative to background evolution allows the abundance to track its equilibrium. If the equilibrium drifts, the displacement equation also contains $-{\dot{n}}_{3e}$. In the pp-I limit the rate is $n_1\sqrt{2{\lambda }_{11}{\lambda }_{33}}$, so both production and destruction temperature dependences matter.