Method for measuring the exhalation of radon from building materials

The health hazards associated with radon, a naturally occurring radioactive gas, may be significantly greater in buildings where ventilation is restricted. Since building materials such as concrete, gypsum, brick, and wood are potential sources of radon, it is important that their radon emanation rate be determined. A rapid and accurate method is presented for determining the radon emanation rate per mass from building materials by determining simply the radon exhalation rate per unit mass. A small sample of the material is sealed in a container from one to three days. The emanated radon is then collected on glass wool cooled to liquid-nitrogen temperature and subsequently transferred to a scintillation flask where the ..cap alpha..-activity is counted. The reproducibility errors of the measurements are on the order of 5%

Strain enhanced electron spin polarization observed in photoemision from InGaAs

Electron spin polarization in excess of 70% has been observed in photoemission from a 0.1 {mu}m-thick epitaxial layer of In{sub x}Ga{sub 1-x}As with x {approx} 0.13 grown on a GaAs substrate. Under these conditions, the epitaxial layer is expected to be highly strained by the 0.9% lattice mismatch, as confirmed by X-ray diffractometer measurements of the lattice parameter. The electron polarization and the quantum efficiency have been measured as a function of the excitation photon energy from 1.25 to 2.0 eV. A significant enhancement of the electron polarization occurs in the vicinity of 1.33 eV where the expected strain-induced level splitting permits optical excitation of a single band transition. Measurements made on a control sample of 1.14 {mu}m thickness, significantly larger than the critical thickness for pseudomorphic strain, show no polarization enhancement. These measurements represent the first observation of strain-enhanced electron spin polarization for photoemitted electrons. 7 refs., 3 figs