We are developing new gamma-radiation detectors that are based on the formation of fluorescent silver nanoclusters. Our approach is to use reverse micelles (RMs) that contain aqueous solutions of silver ions. Upon exposure to gamma-irradiation, the water molecules undergo scission, yielding solvated electrons, hydroxyl radicals, and hydrogen atoms. This process causes rapid reduction of the silver ions to silver atoms that aggregate into nanoclusters that are often fluorescent. The size of the clusters is constrained by the RM walls which is important because larger clusters are generally not fluorescent.
It is envisioned that the RMs could be suspended in a transparent resin that can be applied to walls, floors, the insides of shipping containers, etc. and allowed to dry. Periodic testing for fluorescence will reveal if gamma radiation was once present. In this manner the RMs may be useful in efforts to detect or track fissile materials and their by-products.
To date, we have shown that fluorescent silver nanoclusters can indeed be formed in block copolymer-based RMs by gamma irradiation sources in the dose range 50 Gy – 1000 Gy. The chemical process used for reverse micelle formation was very simple to perform. They have dimensions of ~50-120 nm, as measured by dynamic light scattering methods, and were readily suspended in an organic solvent (toluene). The nanocluster fluorescence within the reverse micelles was easily measured using a fluorometer. As the radiation dosage was increased, the fluorescence increased in a linear relationship. We also found that the introduction of free-radical scavengers into the reverse micelles caused the fluorescence levels to increase by a factor of at least two.