Borg, Dana TamaraCurrently, there are few studies of post-detonation materials due to their extremely complex nature. The cesium isotopic composition of trinitite, the product of the first nuclear detonation, was determined using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) to evaluate the relationship between the time since the detonation of nuclear materials and their cumulative fission yields. The ratio of <super>137</super>Cs/<super>135</super>Cs in trinitite was found on average to be 0.31±0.06, with abundances of <super>137</super>Cs (t<sub>1/2</sub>=30.07a) and <super>135</super>Cs (t<sub>1/2</sub>=2.3x106a) equal to 21.8±0.6pg/g and 68±12pg/g, respectively. These values result in an under-calculation of the amount of time that has passed since detonation. It is recommended that an initial <super>137</super>Cs/<super>135</super>Cs ratio of 1.5±0.3 be used, instead of the proportion that they are produced during fission of 239Pu 0.87±0.02, due to the fractionation of <super>137</super>Cs and <super>135</super>Cs before their deposition in trinitite due to the approximately 200 times longer cumulative half-life of the precursors to <super>135</super>Cs.THE ISOTOPIC ABUNDANCE OF CESIUM IN TRINITITE: IMPLICATIONS FOR POST-DETONATION ANALYSIS OF NUCLEAR MATERIALSThesisGeochemistrycesiumnuclearradiogenictrinitite