A funny mistake by ICR and example of poor scholarship

I have to wonder if Humphreys' extrapolation of the diffusion rate due to concentration gradient across the zircon crystal boundary is valid.It seems to me that the decreasing rate of diffusion of radiogenic (or primordial) helium from zircon with a decrease in temperature is a consequence of thermodynamics. As the temperature of the crystal and helium decrease the fraction of helium atoms with sufficient kinetic energy to overcome the "barrier" of the zircon crystal boundary decreases. At or below the closure temperature effectively no helium atoms have enough kinetic energy to escape.Humphreys then seems to argue that if more radiogenic helium atoms are created then the increasing concentration will eventually cause the helium atoms to start leaking out again (reopening). But, is such a concept only applicable to a permeable or semipermeable barrier? If a radiogenic helium atom is created with insufficient kinetic energy to escape the crystal boundary immediately, how would that atom or another helium atom gain enough kinetic energy to escape irrespective of how many helium atoms are trapped in the zircon crystal?So, if the confined atoms do not have sufficient energy to cross a semipermeable barrier, does this mean that the bariier is now impermeable? Is Humphreys simply applying Flick's Law to the wrong situation?

Chris, it appears that Humphreys postualtes a "reopening" of zircon crystals to helium diffusion some time after closure temperature is reached.Is it accurate to say that the term closure temperature is the temperature at which the rate of diffusion is equal to the rate of production by radioactive decay?You imply that there is a temperature at which diffusion becomes negligible, presumably at a lower temperature than the diffusion rate. What term could be used to identify this temperature?Humphreys asserts that the accumulation of radiogenic helium in the crystals would eventually cause the helium to "reopen". Is there any evidence that this occurs after crystals have cooled to the temperature at which diffusion becomes negligible?Could it be that Humphreys is using the confusion of the term "closure temperature" to model a process which happens just below the closure temperature of zircon but which does not occur when the zircon cools further to a temperature at whcih diffusion becomes negligible?