| Soils and tobacco were sampled together according to soil parent materials, soil types and cultivation practices. The a and p radioactivities in the samples were determined by LS-6500 liquid scintillation counter following digestion. And the actives of 60Co, 137Cs, 40K, 238U, 232Th, and 226Ra in soil samples were detected by low background y spectrometer. The measurements of radionuclides and activities were performed similarly in phosphorus, potassium and complex fertilizers. Moreover, the effects of phosphorus fertilizers on radionuclides and activities in tobacco were studied in a field experiment.Following are the results obtained:1. The concentrations of radionuclides in soils followed the role of 40K> 238U> 232Th> 226Ra>'37Cs. The means of 40K, 238U, 232Th, 226Ra and l37Cs are .549.14Bq/Kg, 77.77Bq/Kg, 56.43Bq/Kg, 48.64Bq/Kg and 3.64Bq/Kg, respectively. They fluctuated from 151Bq/Kg to 1170Bq/Kg (*%.), 13.8Bq/Kg to 281Bq/Kg (238U), 12.3Bq/Kg to 164Bq/Kg (232Th), 10.2Bq/Kg to 159Bq/Kg (226Ra) and 0.488Bq/Kg to 8.72Bq/Kg (I37Cs). The contents of ^Co were lower than the limit of detector. Furthermore, radionoclides varied in soils and highest concentrations of l37Cs, 40K, 226Ra and 238U and 232Th were found in the soils in Dali, Yuxi, Honghe and Lincang regions, respectively.2. Great changes of radionuclides were detected in soils and most of them came from, parent materials and fertilizers. The main reason for the variations could be explained by different parent materials, complicate landform, radionuclides absorption by plants, fertilization and cultivation practices.3. 40K and 238U accumulated, while 226Ra and 232Th depleted in soils. The accumulation and depletion were related to the nuclides in fertilizers, abilities of nuclides absorption by plants, physical and chemical properties of nuclides and soils such as pH and so on.4. The averages of a and P radioactivities were 548.03Bq/Kg and 654.49Bq/Kgrespectively, which varied from 248.74Bq/Kg to 1047.74Bq/Kg (a) and from 244.60Bq/Kg to 2082.70Bq/Kg (p). It is noticed a radioactivities were less than P radioactivities in soils except those in Yuxi area.5. The concentrations of 137Cs,226Ra, B2Th and238U were highest in red soils, while highest 40K and |3-radioactivity were observed in purplish ones and a in paddy soils.6. The conctents of I37Cs and a-radioactivities in tobacco growing soils were lower than Sichuan and Shanghai, respectively, in contrast to p-radioactivities, which was lower than both Sichuan and Shanghai. Moreover the average concentrations of 226Ra, 2j2Th and 238U were higher than those of our country, China, except K, which was relatively low. It is noticed that 238U was higher than those in any other areas in China. These contents of radionuclides in Yunnan were also higher than the volumes in typical areas.7. In regards to the concentrations of 137Cs in measured fertilizers, they followed the order of rare - organic fertilizer>composite fertilizers>phosphorus fertilizers> potassium fertilizers, but no remarkable differences of 137Cs were detected among these fertilizrs.The concentration of 40K were in order of potassium fertilizers?composite fertilizers and phosphorus fertilizers?rare - organic fertilizer, indicating the greate influences of 40K in potassium fertilizers on soil 40K.The measurement showed the higher contents of 226Ra and 2;>8U in phosphrous fertilizers than those in rare - organic fertilizer and in composite fertilizers and than those in potassium fertilizers once more. The concentrations of 226Ra in phosphate fertilizers were much higher than those in soils, enve though they were lower than the national regulation standards, showing that the two radionuclides in soils mainly could come from phophrous fertilizers in the case of large amount of phosphate supplied in tobacco production.The concentrations of Th were lowest in fertilizers compared to any other radionuclides. 232Th in rare - organic fertilizer was the highest in the fertilizers detected. |
PDF Full Text Request