The Effect of Different Fill Gases on Bragg Curve Spectrometer Detectors.

A Bragg curve spectrometer was built and run using both isobutane and freon® independently as fill gases. Analysis of the signals produced by light fission fragments emitted from a Cf252 source allowed detailed comparison of the gases‟ characteristics when used in detector chambers. Isobutane was found to provide larger signal amplification, however this appeared to deteriorate with the age of the gas, with an observed loss of 0.824% (±0.049%) per hour. Freon® provided considerably faster signals however the rise time increased over time, at a rate of 0.967% (±0.106%).Attempts to determine the range of fission fragments did not agree with simulated predictions in the case of either gas. Furthermore the electron drift velocity shows a different trend against reduced electric field strength for the two gases. Signal amplitude losses were observed as the drift time increased as a result of recombination and addition effects. A combination coefficient was calculated for both gases and found to be 0.0831(±0.0069)μs-1 for isobutane and 0.3265(±0.0154)μs-1 for freon®. From this the mean electron „lifetime‟ was found to be 12.0(±1.0)μs for isobutane and 3.06(±0.14)μs for freon®. However below reduced field strengths of 0.658 Vcm-1mbar-1 isobutane was found to deviate from the expected exponential decay trend, possibly indicating the presence of a new recombination phenomena.