The collection efficiency of Whatman 41 filter paper has been determined using submicron test aerosols of monodispersed polystyrene latex. Measurements w-ere made over a velocity range of 12-195 f.p.m., using aerosols with diametcrs of 0.088,0.188,0.264, 0.365 and 0.557 p. For sizes less than 0.557 ,LL, well-developed efficiency minima occur in the velocity range of 20-30 f.p.ni. In no case was the efficiency found to be below 70 per cent. At 195 f.p.m. the efficiency was essentially size-independent.

NOTICE "Thh report »at prepared it an jecounl a' »v.j\ iponiorcd by the United Suie* Gouromcnt. Neilrlcr Ihe Unlicd SMlet nor tlic United States Atomic Fnctty CotRsr.eui?:i. r-tr »ny of Unit employee*, nor any oflhcir contractor*. lupaiMraaurt. or HKOemployed, make* any warrinly, expeett or Implied,or Jerome* eny kpil liability ot «e*potwiblli;y foe Ittcareeuraey, ecmpleten.'** or urerulrw*! of Any tn'Termlkro. jppjratut, projut* or r/roccu citeloKd, or (eprCKt.li that ill uve would not In'rlfife privjuly uwned rt*hl*."

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During the period from March 1 to June 1, 1971, the Lawrence Livermore Laboratory made simultaneous measurements of environmental radiation background at 107 weather stations throughout the United States.Measurements were made using CaF":Dy thermoluminescent dosimeters (TLD-200).Freshly annealed dosimeters were mailed to the stations where they were exposed in the station's instrument shelter. At the end of the exposure period, the dosimeters were returned to Livermore for readout. Light output is proportional to the radiation dose received by the phosphor from the sum of terrestrial and cosmic sources. The cosmic component was estimated from the elevation and geomagnetic latitude of the station, and terrestrial radiation was obtained by difference.Median environmental radiation exposure rate (terrestrial + cosmic) was 9.4 uR/hr with a range from 3.7 to 19.9 pR/hr. The median terrestrial exposure rate was 5.5 pR/hr. Low backgrounds were found in the Hawaiian Islands, Northern Alaska, and Florida. High backgrounds in the Rocky Mountain Work perforated under the auspices of the U. S. Atomic Energy CoiKtission.

described herein are sample collection and analysis proceduros employed in p-ironmental monitoring at the Lawrence Livermore Laboratory. An inte al part of the quality assurance program developed £or environmental monI ring at Livermore, these procedures provide a basis for verifying that sarvp' nq and analytical activities are being performed as specified.