The natural radionuclide content of mineral phosphate fertilizers has been determined gammaspectrometrically. The investigations comprised ca. 70% of the mineral phosphate fertilizers authorized and used in the Federal Republic of Germany (FRG). At maximum, we found specific activities of 62 nCi Unat/kg, 23 nCi 226Ra/kg, 1.6 nCi Thnat/kg and 262 nCi 40K/kg. The mean values, weighted by the percentual agricultural consumption of the main phosphate fertilizer groups in 1973/74 and related to the phosphate content, amounted to 58, 40, 2, and 584 nCi/kg P2O5 for Unat, 226Ra, Thnat, and 40K respectively. This resulted in an annual distribution due to phosphate fertilizing of about 3.9 muCi Unat, 2.7 muCi 226Ra, 0.1 muCi Thnat, and 39.9 muCi 40K per ha of arable or pasture land in 1973/74 on the average. From these values the air dose rates over agricultural areas have been estimated under extreme conservative assumptions resulting in an additional external exposure of members of the population of 0.02 mrd/a on the average and 0.4 mrd/a in the region of highest phosphate fertilizing intensity. If it is assumed that radium contained in phosphate fertilizers were completely accumulated in the soils during the last 80 years, this value would be raised to 0.3 mrd/a on the average. The occupational external radiation exposure due to natural radionuclides contained in phosphate fertilizers was estimated to be 0.1 mrd/a on the average and 2.3 mrd/a at maximum for persons working in agriculture. These estimates show that natural radionuclides in phosphate fertilizers contribute but very little to the mean terrestrial radiation exposure of the population which is 50 to 55 mrd/a in Germany. Only for the small group of persons working in fertilizer production plants or storehouses a significant increase of the external radiation exposure has to be expected which could reach a doubling of the mean natural exposure value.
We have performed calculations of the field dependent excitonic absorption spectra of semiconductor superlattices in a model which is capable of fully taking into account the Coulomb interaction and both bound and continuum excitonic states. Results are obtained for the complete range of fields from the Franz-Keldysh to the Wannier-Stark regime. The lineshapes of the excitonic spectra are shown to resemble the derivative of the corresponding single particle spectra with respect to the wavelength. In addition characteristic excitonic features have been found, which also have been observed in photocurrent spectra
In this investigation the occupational exposure of single persons due to the gamma radiation of the natural radionuclides in rock phosphates and phosphate fertilizers and their contribution to the population dose in the FRG has been determined. The exposure rates in the working fields production, transport, loading and storage or rock phosphates and phosphate fertilizers and due to their application in agriculture have been measured by means of scintillation dose rate meters or LiF-thermoluminescence dosemeters or have been estimated from specific activities. Mean additional exposure rates of 2--26 muR/h, with local maximum values up to 190 muR/h, were observed. From these values, together with statistical data for the number of occupied persons and annual working times in the various working fields, the mean and maximum annual dose of individuals and the contribution to the mean population dose have been estimated. The results show that a maximum annual dose to individuals from 0.4 mrem/y (agriculture) up to 45 mrem/y (production plants or storehouses) can occur. The corresponding mean annual doses are 0.05--20 mrem/y. The contribution of the occupational radiation exposure due to rock phosphates and phosphate fertilizers to the mean population dose is 174 man . rem/y related to whole body. To this, fertilizer production contributes 40 man . rem/y, transport and loading 45 man . rem/y, agricultural storehouses 31 man . rem/y, and agriculture 58 man . rem/y. Altogether, this investigation shows that an occupational radiation exposure of individuals may occur which corresponds to the mean terrestrial radiation exposure in the FRG. The contribution of the occupational collective doses due to phosphates to the population dose, however, is negligibly small.
A method of determining the uranium content of environmental samples by gamma spectroscopy of the 1.0015 MeV gamma radiation of the 234Pam (beta-) 234U leads to 234U daughter decay is described. The detection limit is 1 nCi/kg sample. The transition probability has been determined to be 0.87 +/- 0.03%.
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