Recent progress at the slow positron and neutron beam facilities at AIST

Date

Nov 28, 2024

Time

3:00 PM - 4:00 PM

Speaker

Dr. Brian E. O‘Rourke(NMIJ, AIST), Tsukuba, Japan

Language

en

Main Topic

Physik

Host

Andreas Wagner

Description

The slow positron facility at AIST has been developing positron lifetime measurement systems using a slow positron beam and conducting materials characterization using these systems. A positron probe micro-analyzer has been developed and used for defect and pore characterizations, local analysis, and operand measurements of various advanced materials. The measurement systems at the facility are open to the public under the Advanced Research Infrastructure for Materials and Nanotechnology (ARIM) project in Japan. In the past few years, we have been upgrading the positron beamlines and maximizing the performance of the facility. Positrons are generated using a dedicated electron accelerator which irradiates a Ta converter with a high-energy electron beam (energy: 40 MeV, power: several hundred W, repetition rate: 50 Hz, pulse width: 2 μs). The intensity of the generated slow positron beam is up to 2 ×10^7 e+/s. The beamline is equipped with a Positron Annihilation Lifetime Spectrometer (PALS) and a Positron Probe MicroAnalyzer(PPMA). Both instruments are designed to inject positrons vertically downwards into a sample, allowing not only for thin film samples but also for samples such as powders and liquids. In addition, the beamline has been extended to accommodate new experiments, and two ports have been added. One of the new ports is a positron trap system, which is used to generate a nanosecond pulsed beam by accumulating and pulsing positrons. This beam is used for plasma experiments with high-density positrons and synchronization experiments withnanosecondlasers. In addition to the slow positron facility, we have also recently developed an accelerator-based neutron source. Like the positron facility, neutrons are generated by irradiating a high energy electron beam on a water-cooled Ta target. Neutrons are moderated by solid-methane moderators cooled to 20 K. The neutron facility is now being used to perform various material characterization including Bragg-edge spectroscopy and transmissionradiography.

Last modified: Nov 28, 2024, 7:37:40 AM