Radionuclides in the atmosphere are associated with nonradioactive air particulates and hence serve to trace the fluxes of air particulates to various surfaces. Natural and artificial radioactivities found in the atmosphere have been measured in vegetation for 10 years to elucidate some of the mechanisms of acquirement by forest trees of atmospheric particulates. Whole tree analysis, in conjunction with soil assay, has served to establish the fraction of the flux of radionuclides retained by above-ground tissues of a forest stand. Interpretation is facilitated because most radionuclides in the atmosphere are superficially acquired. Typically 5-20% of the total open field flux is retained by the forest canopy in a moderately rainy climate (120 cm/year). Short-lived daughters of radon give a dry deposition velocity of particulates in the Aitken size range of 0.03-0.05 cm/s, thus permitting an estimate of transient removal by forest canopies by dry deposition of this size fraction.Paper number 80C0916. 0148-0227/81/080C-0916501.00 lated near the tips of plants, where the maximum surface area offers the greatest opportunity for collection. Rain functions to add, to remove, and to transfer pollutants in the tree system.Whole tree analysis provides a method for estimating an average efficiency appropriate to a specified accumulation time for each radionuclide measured. However, we must distinguish between soil-derived and superficially deposited radionuclides. Morphological rather than physiological processes apparently are chiefly responsible for the distribution of most superficially deposited radionuclides in the tree. Nuclides we have found suitable for estimation of superficial efficiency are the rare earths 32.5 day •4•Ce, 285 day •44Ce, 4.93 year •SSEu. Other useful isotopes in the superficial class are 65 day 9SZr, 39.7 day •ø3Ru, 369 day •øSRu, and 2.7 year mSb. The foregoing are all products of nuclear fission, and they encompass a range of physical and chemical properties. Another important radionuclide that follows superficial behavior is 53.5 day ?Be. This isotope is of cosmogenic origin and represents one of the more promising tracers for future work in the absence of nuclear testing in the atmosphere. Long-lived fission product nuelides that simulate macronutrients, such as 30 year •37Cs and 29 year 9øSr have significant soil reservoirs and are found in forest trees largely as a consequence of uptake from the soil. With the exception of vøSr, all the above radionuclides are easily quantified via their gamma ray emissions. Other important gamma-emitting radioactive species encountered in our work include 310 day •4Mn, daughter products of •6Ra and •aSRa, and 4øK. The 10.6 h daughter of •2øRn is particularly useful for study,.ing dry deposition processes. METHODS Beginning in 1968 we have measured radionuclides and on occasion nonradioactive pollutants in vegetation taken from forested and cultivated settings. Sampling was conducted in Newton, Massachusetts, 10 km west of Boston; in Framingham, Massachuset...

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Concentrations of fission product radionuclides from v/ell spaced Chinese nuclear explosions in the megaton ranee have been measured in conifer and deciduous leaf trees in the New England area from 1968 to 1974. Stratospheric fission yield source strengths of these discrete events have been estimated by others. Radionuclide concentrations per unit area of leaf are obtained by high rcso.lution ganma ray spectroscopy of compressed pellets of leaf ash of oak, maple, white pine, gingko, beech, birch and selected additional species. Dividing by total source strengths one obtains the fractional source strength per unit area of leaf.-NOTICE-T h,s report was ^P-^," ^0'4"rn«°fN,X k r sponsored by the United States Gov ^^ ,". United States no. the "»'»*«' nor any of Comm.ss.on, nor any of the"^e p y emp ,oyees, .herr contractors subcont^or' ^ ^^ ^ would not infringe pr.vately owned r.ghts

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