The Variable Energy Positron Beam

Instrument: Medium Intensity Positron Beam: VEP and PADB

Location: Experimental hall, Reactor Institute Delft, Mekelweg 15, Delft (building #50)

Key words: Positron Annihilation, Doppler broadening, vacancy dopant complexes, voids, nano-precipitates, surfaces, interfaces and thin films

Measured quantity: one measures the annihilation (gamma) radiation of a positron-electron annihilation event (511 keV)

Main application: Determination of defect depth distributions and characterization of open volume defects in sub-surface regions, in thin films and at interfaces by means of Doppler Broadening and positron (back)diffusion measurements.

Instrument specification: Medium intensity variable energy positron beam (VEP) with one- and two-detector equipment for measuring Doppler Broadening of Annihilation Radiation (PADB)

Positron source:  22Na isotope (1 GBq), magnetostatic positron beam transport.
Positron beam intensity: 1 x 105 e+ s-1
Positron beam diameter at target:  ca. 8 mm  (preferred sample dimensions 10 x 10 x 1 mm^3)
Maximum positron energy : 30 keV 
one (or two)  high purity Ge solid-state detectors, energy resolution 1.8 keV at 1.33 MeV (60Co) 

Target chamber: 
equipped with a closed loop cryostat (20 – 300 K), high temperature heaters (up to 1700 K), a 4 point bending device.

Data analysis with VEPFIT