An apparatus for producing a radionuclide includes a target chamber including a beam strike region for containing a liquid and a condenser region for containing a vapor. A particle beam source is operatively aligned with the beam strike region, and a lower liquid conduit communicates with the beam strike region. The condenser region is disposed above the beam strike region in fluid communication therewith for receiving heat energy from the beam strike region and transferring condensate to the beam strike region. The lower liquid conduit transfers liquid to and from the beam strike region. In operation, the target chamber acts as a thermosyphon that is self-regulating in response to heat energy deposited by the particle beam source. A portion of the liquid expands into the lower liquid conduit prior to boiling. After boiling begins, a vapor void is created above the liquid and an evaporation/condensation cycle is established, with additional liquid being displaced into the lower liquid conduit.