This processo of annealing of fission tracks has been well investigated in the laboratory and emperical relationships of annealing have a form like this� Time * e ^ Temperature. In other words, temperature is clearly the dominant term. For example, exposure at 400 degrees for 20 minutes will completely anneal tracks but at half that temperature (200�), it will take 15 years.
In other words, we can sense quick pulses of very high temperatures, or extremely long exposures of moderate temperatures.