Electro-purification studies and first measurement of relative permittivity of TMBi

Abstract

A new type of detector for positron-emission tomography (PET) has been proposed recently, using a heavy organo-metallic liquid — TriMethyl Bismuth (TMBi) — as target material. TMBi is a transparent liquid with the high Z element Bismuth contributing 82% of its mass. 511keV annihilation photons are converted efficiently into photo-electrons within the detector material producing both Cherenkov light and free charge carriers in the liquid. While the optical component enables a fast timing, a charge readout using a segmented anode can provide an accurate position reconstruction and energy determination. The charge measurement requires a high level of purification, as any electronegative contaminants cause signal degradation. In addition to the purity requirements, the reactive nature of TMBi poses many challenges that need to be met until a fully functioning detector for PET applications can be realized. The paper presents an experimental setup that aims to remove electronegative impurities by electrostatic filtering and to characterise the properties of TMBi, e.g. the relative permittivity, for its application as a detector medium for charge read out.