Radiation damage and electron lifetime measurements for liquid ionization chambers

Abstract

Ionization chambers filled with liquids at room temperature have begun to be implemented in high-energy physics for total-ionization calorimeters and offer potential applications in medical physics for dosimetry and imaging of radiotherapy beams. One liquid that is commonly used is 2,2,4,4 tetramethyl pentane (TMP). When suitably purified, the lifetime of electrons in this liquid can be on the order of microseconds, and the mobility is high enough to allow the rapid collection of charge when desirable. In all of these applications, the susceptibility of the liquid to radiation damage is an important question. We present results of studies of radiation damage in TMP and the effect of doses of ~6000 Gy on the electron lifetime and on the output per unit dose. Our experience in purifying the TMP to optimize the electron lifetime is also described.