Determination of half-value layer.

@article{Trout1960DeterminationOH,
  title={Determination of half-value layer.},
  author={E D Trout and J. Patrick Kelley and Allison Lucas},
  journal={The American journal of roentgenology, radium therapy, and nuclear medicine},
  year={1960},
  volume={84},
  pages={729-40}
}