A sensitive cloud chamber without radioactive sources
  We present a sensitive diffusion cloud chamber which does not require any radioactive sources. A major difference from a commonly used chamber is use of a heat sink as its bottom plate. A result of a performance test of the chamber is given. 
Syoji Zeze, Akio Itoh, Ayu Oyama and Haruka Takahashi
physics.pop-ph physics.ed-ph