Experimental Verification of the "Incoherent Scattering" Theory for the Transport of Resonance Radiation

The predictions of the incoherent scattering theory of the transport of resonance radiation developed by Holstein and by Biberman are shown to agree with laboratory measurements of the decay constants for the intensity of the mercury 2537 A resonance radiation following a period of optical excitation. Also, the relative importance of the diffusion of resonance atoms and the escape of resonance radiation as mechanisms for the destruction of mercury atoms in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ or resonance state are determined from measurements of decay constants as a function of mercury density and cell radius. The experimental results show that diffusion of the resonance atoms is negligible and that the predictions of imprisonment theory are confirmed to within 15%. The experiment sets an upper limit to the diffusion coefficient at unit gas density for atoms in the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of 5×${10}^{17}$ ${\mathrm{cm}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at 340°K, which is consistent with a value of 4×${10}^{16}$ ${\mathrm{cm}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ predicted using the frequency of excitation transfer collisions calculated by Holstein. The success of the theories based on completely incoherent scattering of resonance radiation points to the desirability of including this feature in the treatment of those astrophysical problems in which the spectral line shape is determined by Doppler broadening or by collision broadening.