CaLIPSO: TMBi properties for particles detection

Trimethyl bismuth (TMBi) is a "heavy" organometallic liquid: 82% by weight of Bismuth. TMBi is a transparent and dielectric liquid that efficiently converts through the photo-electric effect photons of energies below 1 MeV. Charge and light produced in the liquid are both detected in a CaLIPSO detector. This paper focuses on the measurement of the TMBi physical properties relevant for particles detection. We measured the TMBi transmission curve, the TMBi refraction index versus wavelength, the light production yield. In addition we present preliminary measurements on ionization. These are however sufficient to demonstrate the mobility of charges in TMBi. A first measurement of the free ion yield of the TMBi normalized to the well known free ion yield of the TMSi indicates that both liquids have similar ionization yields. The purification of the TMBi is still ongoing; electron lifetime in the TMBi is estimated by using the ionization yields together with an equation based on Onsager's theory.