The relative neutron yield of several targets of light elements exposed to monoenergetic ionized helium beams from the Argonne tandem accelerator was determined for alpha energies ranging from 4.8 to 8.8 Mev. Our ratio of the neutron yields for 5.3 Mev are in agreement with published data on thick target yields obtained with Po210 α particles. The average (α, n) yield per α particle of the natural radioactive series for some elements and for different soil compositions was calculated from our results assuming an (α, n) yield of 75 neutrons per 108 α particles of Po210 α for aluminum. If 3 ppm U238 and 11 ppm Th232 are assumed as representative of the earth's upper crust, a production rate of 6.7 ± 0.7 n/g/yr in sand and 13.5 ±1.3 n/g/yr in granite is obtained. Additional 1.4 n/g/yr will be generated because of the spontaneous fission of U238. As the production rate of neutrons through interactions of cosmic rays with the earth's surface at sea level is of the order of 800 n/g/yr, these (α, n) reactions cannot be of any significance to exposure rates of human populations. They may be of some interest to geologists, however, and may be the main contributors to neutron fluxes in tunnels, deep caves, or mines, where cosmic‐ray background is very low.

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Selective reflection from mercury and cadmium vapors in the neighborhood of the resonance lines was investigated quantitatively using incident light of continuous spectral distribution. For a given experimental arrangement the lowest vapor density (atoms per cubic centimeter) at which selective reflection could be detected at Hg 2537 Å, Cd 2288 Å, and Cd 3261 Å was inversely proportional to the oscillator strength (f-value) of the absorption line. Contours of the selective reflection of the Hg 2537 Å and Cd 2288 Å lines were obtained over a large range of vapor densities up to 80 × 1018 atoms per cc. At this density the cadmium reflection extended over several thousand cm.−1 compared to about a hundred cm.−1 for mercury. The general features of the reflection contours can be explained by the theory of reflection from an absorbing medium. Fitting a theoretical curve to the experimental reflection contour yields values of the oscillator strength and the damping constant. For Hg 2537 Å and Cd 2288 Å the f-values are 0.0268 and 1.40 respectively, in good agreement with those found by other methods. The damping constant, γ, varies as the square root of the number of atoms per cubic centimeter, indicating that the mechanism of selective reflection is not the same as that for absorption and emission. An empirical areal law for selective reflection confirms the relationship [Formula: see text]. A shift of the resonance frequency of the order of magnitude of the coupling shift calculated by Weisskopf was observed for Hg 2537 Å. Deviations from theory at both high and low pressures were observed for Cd 2288 Å. The low pressure deviation takes the form of a line of residual intensity at the resonance frequency, which may be due to a different kind of selective reflection.

AcknowledgmentsThe a u t h o r s wish to t h a n k M. tI. W h i t e h i l l for t a n t a l u m s p u t t e r i n g , K. L. B r o w n and E. E. P a c h e r for e l e c t r i c a l m e a s u r e m e n t s , and D. P. C a m e r o n for the e l e c t r o n m i c r o g r a p h s .ABSTRACT ZnS powder, irradiated in a high density thermal neutron flux, was p a r t l y converted to radioactive Zn-65, Zn-69, and S-35. These radioisotopes decay to Cu-65, Ga-69, and C1-35, respectively. One week after removal from the nuclear reactor the sample was fired at 900~ to anneal out radiation damage occurring in the reactor. The brightness and spectral distribution under 3650A excitation and the diffuse reflectance spectra of the annealed sample were monitored during a period of 600 days. The principal results are interpreted in terms of an increasing concentration of uncompensated copper centers produced by the decay of Zn-65.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-10 to IP

Radioactive mercury was used to determine whether there is any relationship between the depreciation of fluorescent lamps and the amount of mercury picked up on the lamp walls during lamp operation. It was found that early in lamp life there is no such relationship. However, after 1000-2000 hr, depending on the phosphor type, a relationship was established.