Optical time projection chamber for imaging of two-proton decay of /sup 45/Fe nucleus

We present a design of the gaseous detector for 3-D measurement of the topology of a recently discovered radioactive decay of /sup 45/Fe nucleus which involves simultaneous emission of two protons from the ground state. Our apparatus, called optical time projection chamber, consists of several parallel wire-mesh electrodes inside a gaseous medium which form the conversion region and the multistage charge amplification structure. Selected gas mixture enables strong emission of UV photons during avalanche process. UV photons from charge avalanches are converted into visible light by means of a wavelength shifter foil. A CCD camera located outside the detection volume records 2-D image of the decay process. Drift time of primary ionisation charge towards the amplification stage provides the third coordinate. Correlation of 2-D image with drift-time structure allows 3-D reconstruction. We present results on: the light yield, the charge gain and the electron drift velocity for several gas mixtures consisting of: Ar, He, N/sub 2/ and triethylamine vapour. A feasibility of the event topology reconstruction and the energy measurement is addressed.