Ecological dosimetry: radiation levels influenced by plant growth.

The feasibility of using lithium-7-fluoride thermoluminescent dosimeters under field conditions for natural radiation at levels of 5 milliroentgens is demonstrated. Radiation dosages in tree trunks increased threefold from winter to spring and summer. This increase is attributed to the gamma radiation field resulting from relatively high levels of potassium-40 and other radionuclides present in the foliage and branches during the growing season.