A new slow pulsed positron beam, including a positron source, a moderator, a chopper, a prebuncher, a main-buncher and a sample chamber, etc, has been installed and tested. It is necessary to simulate the acceleration, transportation and space focusing of positrons to meet the needs of beam debugging and further positron annihilation experiments. The result from SIMION simulations shows that the radius of the focused positron beam is less than 5 mm, which is further confirmed in our practical debugging process.

This paper presents the positron study on carbon-Fe3O4 coaxial nanofibers, which is one kind of new promising functional materials. According to the positron annihilation lifetime spectra and the coincidence Doppler broadening spectra, we find in this material that positrons annihilate partly in monovacancies of Fe3O4, partly in microcavities of Fe3O4 and partly in shelled carbon nanotubes. We also estimate the annihilation proportion in each part, which reveals the nanofibers’ microstructure to a certain extent.

Simulation of time bunching for a pulsed positron beam * Gao Chuan-Bo() a) † , Xiong Tao() a) , Xi Chuan-Ying() b) , Weng Hui-Min() a) , Ye Bang-Jiao() a) , Han Rong-Dian() a) , and Zhou Xian-Yi() a)