In this post, we would like to introduce to you the photocathodes which are the source of the electrons in the LightHouse accelerator. The accelerator is designed and built by RI for our customer IRE and their SMART project (Source of MedicAl RadioisoTopes), which aims to demonstrate a sustainable method to produce 99Molybdenum (Mo-99), the world’s most used medical isotope and a unique tool in medical diagnostics.
At RI in Bergisch Gladbach we are currently setting up the beam test facility to demonstrate the feasibility of this electron accelerator. As electron source we use a photocathode, where a pulsed green laser beam (515nm, 40W) hits a carefully prepared bi-alkali antimonite film releasing pulses of electrons into the vacuum. Preparing such photocathodes is an art in itself, but thanks to the close collaboration with Cornell University and Helmholtz-Zentrum Berlin we have mastered the vacuum vapor deposition and learnt how to fabricate the photocathodes ourselves. The dedicated deposition system was designed in collaboration with CreaTec Fischer, a manufacturer of customized vacuum deposition systems. Already in our second attempt we achieved a quantum efficiency (QE) of >4%, enough to start operating the beam test facility.
The QE will be further optimized in the months to come, but we already look forward to the next step: Accelerating the electrons in the beam test facility once it is fully assembled.
The pictures show a polished metallic puck (top left) before vapor deposition, which is then coated with a black, light absorbing film (top right) and the ultra-high vacuum vapor deposition system in which the coating process takes place (bottom).