  We present a multi-scale formalism that accounts for the formation of
nano-scale bubbles/cavities owing to a burst of water molecules after the
passage of high energy charged particles that leads to the formation of hot
non-ionizing excitations or thermal spikes (TS). We demonstrate the coexistence
of a rapidly growing condensed state of water and a hot spot that forms a
stable state of diluted water at high temperatures and pressures, possibly at a
supercritical phase. Depending on the temperature of TS, the thin shell of a
highly dense state of water grows by three to five times the speed of sound in
water, forming a thin layer of shock wave (SW) buffer, wrapping around the
nano-scale cylindrical symmetric cavity. The stability of the cavity, as a
result of the incompressibility of water at ambient conditions and the surface
tension, allows the transition of supersonic SW to a subsonic contact
discontinuity and dissipation to thermo-acoustic sound waves. We further study
the mergers of nanobubbles that lead to fountain-like or jet-flow structures at
the collision interface. We introduce a time delay in the nucleation of
nano-bubbles, a novel mechanism, responsible for the growth and stability of
much larger or even micro-bubbles, possibly relevant to FLASH ultra-high dose
rate (UHDR). The current study is potentially significant at FLASH-UHDRs. Our
analysis predicts the black-body radiation from the transient supercritical
state of water localized in nano-cavities wrapping around the track of charged
particles can be manifested in the (indirect) water luminescence spectrum.
