Development of a geogenic radon hazard index—concept, history, experiences, Bossew, P., Cinelli Giorgia, Ciotoli G., Crowley Q.G., de Cort M., Medina J.E., Gruber V., Petermann E., and Tollefsen T. , International Journal of Environmental Research and Public Health, Volume 17, Number 11, p.1-24, (2020)