A potential dating technique using 228Th/228Ra ratio for tracing the chronosequence of elemental concentrations in plants

We propose a radiometric method based on measurement of the radioactivity of the naturally occurring radionuclides 228Ra and 228Th and the derived 228Th/228Ra ratios in plant samples to estimate plant age and the corresponding nutritional conditions in a field-growing fern, Dicranopteris linearis. Plant age (tissue age) was associated with the 228Th/228Ra ratio in fronds, which implies the accumulation time of immobile elements in the plant tissue or the life span of the fronds. Results indicated that the accumulation of alkaline earth elements in D. linearis is relatively constant with increased age, while the K concentration is reversed with age because of translocation among plant tissues. Estimation of dating uncertainty based on measurement conditions revealed that the radiometric technique can be applied to trace chronosequential changes of elemental concentrations and environmental pollutants in plants with ages of less than 10–15 years.