Separation of positron beam-induced charges in polyethylene by external electric fields

We show the results of positron beam Doppler broadening measurements on low-density polyethylene under external electric fields. It is found that long-term measurements with a moderate beam intensity of approximately 10 5 e +/s result in the accumulation and separation of charges in the polymer. These effects are found to affect the S and W Doppler parameters and thus should be taken into account for a correct interpretation of the experimental data.