Charge transport in liquid tetramethylsilane (TMS) at low and high electric fields

Abstract

Organo-liquids have never been satisfactory as di-electrics in radiation dosimeters operated as pulse detectors in the ionisation chamber and proportional counter modes. In an attempt to assess the key factors involved, ionisation chambers filled with liquid tetramethylsilane (TMS) have been used to measure the dark and ionisation currents. The results in general are consistent with previous work in revealing the existence of spurious charges, indicating the need for ultra-high purity of the di-electric; the importance of the electrode surface quality and the `bubble' phenomenon. A method has been devised to enable separation of the spurious and true contributions to the dark and ionisation currents by using electrodes with different gap separations. Electro-hysteresis was observed and attributed to the formation and decay of `bubbles'. For diagnostic purposes, a method using the W value was devised to discern the presence of spurious charges in the observed net ionisation current. An ionisation plateau, of slope∼5% kV/cm, was observed for electric fields in the range 1–25 kV/cm, before the onset of intrinsic charge multiplication extending to 200 kV/cm.