Fission Track Dating of Archaeological Materials from Japan

Abstract

THE method of dating by fission tracks¹ has been used by several workers to date rock minerals and baked relics². The method depends on the spontaneous fission of ²³⁸U atoms in mineral or glass taking place at a constant rate, and leaving fission tracks. Once formed, the fission tracks disappear if the material is heated above a critical temperature. The fission track age, T (yr), can be represented by the following equation³ where ρ_s is the fossil fission track density (cm⁻²), ρ_i is the induced track density by bombardment with thermal neutrons (cm⁻²), λ, is the total decay constant for uranium (yr⁻¹), λ_f is the fission decay constant for ²³⁸U (we use 6.85 × 10⁻¹⁷ yr⁻¹ (ref. 4), Φ is the thermal neutron dose (cm⁻²), σ is the thermal neutron cross section for fission ²³⁵U (cm⁻²), η) is the isotope ratio ²³⁵U/²³⁸U, and R_s and R_t are the mean values of the etchable length of the fragments produced by a spontaneous fission and that produced by the induced fission (cm).