Unattached Fraction : The fraction of potential alpha energy of radon progeny that arises from atoms that are not attached to ambient aerosol particles
International Atomic Energy Agency IAEA, Department of Nuclear Safety and Security, IAEA Safety Glossary (Terminology Used In Nuclear Safety and Radiation Protection), IAEA, Vienna. Austria 2007. ISBN 92-0-100707-8, http://www-pub.iaea.org/MTCD/publications/PDF/Pub1 290_web.pdf, (Nucl Sfty and Rad Prot - Brit) {459}