Neutrino-recoil induced desorption

Nuclear decay induced 37Cl ion desorption from the electron capture decay 37Ar→37Cl+ν is reported for the first time. A mixture of one part 36Ar and ∼5x10-5 parts 37Ar (36/37Ar) is physisorbed on a gold-plated Si wafer kept at 16 K under ultrahigh vacuum conditions. The time of flight (TOF) of recoiled 37Cl ions is measured using coincidence techniques. The observed kinetic energy distribution of the 37Cl ions is approximately Gaussian in shape, with a maximum at ∼9.0 eV and a full width at half-maximum of ∼3 eV. Considering the binding energy of physisorbed 37Ar is ∼80 meV, the 9-eV peak energy compares well with that of the gas-phase value, where conservation of the energy and momentum fixes the kinetic energy of 37Cl ions at 9.54 eV. Using a combination of TOF and retarding field energy analysis, the charge states of detected ions for 1 ML (monolayer) of 36/37Ar are determined as 53%+1e, 21%+2e, and 26%+ne, where n≥3. The fraction of decaying 37Ar atoms which emerge from the surface as positive 37Cl ions is found to be 10%. Finally, a strong charge exchange reaction between a 37Cl ion and near-neighbor atoms causes a Coulomb explosion within the multilayers, increasing the kinetic energy of desorbing ions by as much as ∼7 eV