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Enumeration of Stereoisomers of Chiral and Achiral Derivatives of Monocyclic Cycloalkanes Having Heteromorphous Alkyl Substituents with Distinct Length <i>k</i>

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Computational Chemistry 2019年第3期7卷 72-93页

作者： Alphonse Emadak Ibrahim Mbouombouo Ndassa beauregard thomas makon Issofa Patouossa Robert Martin Nemba Laboratory of Applied Physical and Analytical Chemistry Department of Inorganic Chemistry Faculty of Sciences University of Yaounde 1 Yaounde Cameroon Laboratory of Chemistry Department of Chemistry High Teacher Training College University of Yaounde 1 Yaounde Cameroon

A combinatorial method based on the determination of the averaged weight of permutations controlling the chirality/achirality fittingness of 2n substitution sites of the monocyclic cycloalkane allows to obtain generalized functional equations for direct enumeration of enantiomers pairs and achiral skeletons of any derivatives of monocyclic cycloalkanes having heteromorphic alkyl substituents with the distinct length k with the empirical formula , wherein at least two alkyl groups??of the distinct size ?each. ?is the number of alkyl radicals ?of the system??verifying the relation . The integer sequences of enantiomer pairs and achiral skeletons are given for substituted derivatives of monocyclic cycloalkane for n = 3, 4 and k = 3, 4, 5. The composite stereoisomerism of this particular compound is also highlighted.

关键词： Enumeration Stereoisomer Chirality Achirality Monocyclic Cycloalkane Order of Alkyl Trees Polyalkylation

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Investigation of Gamma-Emitting Natural Radioactive Contents in Three Types of Vernonia Consumed in Cameroon

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World Journal of Nuclear Science and Technology 2011年第2期1卷 37-45页

作者： thomas B. makon Robert Martin Nemba Pascal Tchokossa Department of Physics Obafemi Awolowo University Ile-Ife Nigeria

The specific activity concentration and the derived Annual Effective Dose(AED) in three types of vernonia cultivated and consumed within and outside Cameroon were measured by means of a well-calibrated high-purity germanium detector. Vernonia samples were collected directly from the production farms, oven-dried to a constant mass, crushed, sieved and sealed for at least a month before analysis. The specific activity of 238U in the three types of vernonia ranged from 20 - 50 Bq kg-1 with an average of 42 ± 15 Bq kg-1, 232Th from 9 - 22 Bq kg-1 with an average of 17 ± 7 Bq kg-1 while 40K ranged from 115 - 460 Bq kg-1 with an average of 302 ± 36 Bq kg-1. The average AED for 40K, 238U and 232Th were 0.15, 0.92 and 0.92μSv y-1 respectively. 238U and 232Th show the same trends both for the regional distribution of the radioactivity content and the AED. The discrepancies in our data can be attributed to many factors such as geological formation, foliar deposition, type and age of the plant, etc. Although the results obtained represent only some fractions of the standard limit, but they are within some range obtained in other countries.

关键词： Radionuclides Specific Activity Dose Vernonia Gamma-Ray Cameroon

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Assessment of Radioactivity Contents and Associated Risks in Some Soil Used for Agriculture and Building Materials in Cameroon

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Journal of Environmental Protection 2012年第11期3卷 1571-1578页

作者： Pascal Tchokossa thomas B. makon Robert M. Nemba Department of Physics Obafemi Awolowo University Ile-Ife Nigeria Laboratory of Theoretical and Physical Chemistry Department of Inorganic Chemistry Faculty of Sciences University of Yaounde I Yaounde Cameroon

A survey of radioactivity content and associated radiological risks was carried out in various soils used for agriculture and building materials in Cameroon by means of a well-calibrated high-purity germanium detector. Soil samples were collected directly from the agricultural farms and the brick’s factories, air-dried at room temperature to a constant mass, crushed, sieved and sealed for at least one month before analysis. The specific activity of 238U ranged from 5.36 ± 0.39 to 51.28 ± 9.67 Bq﹒kg–1 with an average of 34.52 ± 7.18 Bq﹒kg–1;232Th from 4.03 ± 1.03 to 24.74 ± 3.10 Bq﹒kg–1 with an average of 16.67 ± 4.28 Bq﹒kg–1;40K ranged from 16.18 ± 3.11 to 467.40 ± 50.80 Bq﹒kg–1 with an average of 186.96 ± 16.21 Bq﹒kg–1;while that of the fallout 137Cs ranged from 0.00 to 4.79 ± 1.75 Bq﹒kg–1with an average of 2.32 ± 0.99 Bq kg–1;The mean result obtained for the Representative levels index (Iγ), the radium equivalent (Raeq), the total absorbed dose rate (ADR), the external hazard index (Hex), the internal hazard index (Hin) and the Ceasium intervention levels were 0.52, 72.75 Bq﹒kg–1, 33.73 nGy﹒h–1, 0.20 Bq﹒kg–1, 0.29 Bq﹒kg–1 and 0.0028 Bq﹒cm2 respectively. The discrepancies of our data can be attributed to several factors such as past nuclear disasters, geological formation, transport process, etc. Although our results are just some fractions of the international standard limit, but still within the same ranges when compared with those obtained elsewhere. This results also will serve as a baseline data for future investigations.

关键词： Radionuclides Radiological Hazards Soil Gamma Spectroscopy Cameroon

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