PNNL

Abstract

Electron-beam induced damage of NaNO3 single crystal is examined using laser resonance enhanced multiphoton ionization detection of the neutral desorption products, post irradiation temperature programmed desorption (TPD), secondary electron emission microscopy (SEEM) and Auger electron spectroscopy (AES). The damage initially involves destruction of the nitrate group and production of O (3PJ) and NO (2II) fragments with non-thermal energy distributions. Specifically, the O (3PJ) J-state distribution measured at 100 eV incident electron energy is 5 : 1.5 : 0.25 for J = 2 : 1 :0, the NO (2II) vibrational state distribution is 1 : 0.56 : 0.35 : 0.40 : 0.23 for v = 0 :2 : 2 : 3 : 4, and the NO (2II 1/2,3/2) rotational distribution has a high population of the upper (2II 3/2) spin-orbit component. Thermalized NO, O2 and NO2 are also produced and released, though the latter is a minor product. Yields of thermalized NO and O2 exhibit similar temperature dependencies with activation energies of 0.010 +- 0.004 and 0.1 +- 0.03 eV. These values are close to well-known activation energies of NO2 creation in the NaNO3 crystals. We suggest that the formation and desorption of thermalized molecular products involve NO2 defect states and unimolecular dissociation of NO3 which is activated by lattice phonons and vibrons. A significant amount of O2 gas is also released in post-irradiation thermal cycling from 110-440 K with peaks at ~260 and ~340 K. We associate the post-irradiation TPD of O2 with reactions involving O atoms released during thermal decompositions of {NO2 ...O} and ONOO. The SEEM image shows damage features and the AES spectra indicate that the irradiated region is depleted in both nitrogen and oxygen relative to Na. The elemental composition shows Na2O as a final product of the NaNO3 radiation decomposition. The ESD cross section using 100 eV electrons is at least ~10 -16cm2.