Methods

Current standard practice in the calculation of alpha-ejection corrections for broken grains in (U-Th)/He apatite thermochronometry systematically overcorrects for helium loss. For individual grains, this can result in older ages by a few percent in most cases, and by as much as 12% depending on the aspect ratio of the broken grain. The overcorrection can significantly bias results for samples with few ideal grains. This work uses a synthetic dataset to demonstrate that a simple revision to the alpha-ejection correction can improve the accuracy and precision of the correction by several percent. Taking into account alpha-ejection, thermally-activated diffusion, and accumulation of radiation damage over a range of thermal histories, the corrected ages using the revised alpha-ejection correction deviates from the corrected age of an unbroken grain by 0.4% on average. Most importantly, the revised alpha-ejection correction does not introduce any significant systematic bias to the apparent ages from a sample.

**A revised FT correction for broken grains in (U-Th)/He apatite thermochronology**Current standard practice in the calculation of alpha-ejection corrections for broken grains in (U-Th)/He apatite thermochronometry systematically overcorrects for helium loss. For individual grains, this can result in older ages by a few percent in most cases, and by as much as 12% depending on the aspect ratio of the broken grain. The overcorrection can significantly bias results for samples with few ideal grains. This work uses a synthetic dataset to demonstrate that a simple revision to the alpha-ejection correction can improve the accuracy and precision of the correction by several percent. Taking into account alpha-ejection, thermally-activated diffusion, and accumulation of radiation damage over a range of thermal histories, the corrected ages using the revised alpha-ejection correction deviates from the corrected age of an unbroken grain by 0.4% on average. Most importantly, the revised alpha-ejection correction does not introduce any significant systematic bias to the apparent ages from a sample.