Signals
As mentioned before, HERON makes use of real-time detection via the elastic scattering reaction
of low energy neutrinos produced in the p–p and 7Be solar fusion reactions. The neutrino leaves the scene—quietly—after scattering, but the recoil electron is left there to generate all kinds of detectable signals.
A charged particle, in this case the e-, moving in the liquid with evergy above 100 eV loses its energy principally by ionizing helium atoms (24.6 eV) and generating secondary electrons. If a secondary electron has sufficient kinetic energy, it can again lose energy through excitation or ionization. The recoil electron may travel up to a few millimeters before its energy falls below 20 eV, the threshold to further excite atoms; and elastic scattering off atoms becomes the only route for its energy loss. All the energy losses eventually turn into signals we can detect:
energy distribution diagram- Recombination of ions and electrons occurs. An excited helium atom can combine with a normal atom to form a He2* dimer; these excited states then can produce radiation, i.e. scintillation, during their transition down.
- The recoil energy of helium atoms imparted by scattering electrons is transformed into elementary excitations in the liquid. If the 3He impurity in the liquid is sufficiently low, phonons and rotons can propagate meters without decay. When a phonon or roton reaches the liquid surface, quantum evaporation may occur.
- There still is the original recoil electron. Exhausted of energy and unable to recombine with a helium ion, it will eventually form an electron bubble. With appropriate electric field, this electron bubble can be drifted to the surface, pulled out of the liquid, and accelerated into a waiting detector.