@misc{indiciae4185ef70081e,
  title = {Natural gamma aeroradioactivity map of Puerto Rico},
  author = {J. A. MacKallor},
  year = {1965},
  doi = {10.3133/gp525},
  url = {https://pubs.usgs.gov/publication/gp525},
  note = {Source identifier: gp525}
}