Fission track dating of obsidians

Charged particles create their tracks in most dielectric solids. These tracks can be viewed under optical microscope after proper chemical etching. Tracks of uranium fission fragments in obsidians also can be viewed after etching by HF solution and used for age dating. In the paper, dating formula and experimental procedures for fission track dating are introduced. And spontaneous and induced fission tracks by thermal neutrons are counted under optical microscope (magnification of 400x). Measured fission track ages of obsidian samples, OM No. 147 and HM No. 40 are 8.86 x 105y and 7.67 x 105y, respectively. (Author)