Châu Thành Tài, Võ Công Phát, Phạm Ngọc Sơn, Trần Thiện Thanh Châu Văn Tạo
Tạp chí Khoa học Trường Đại học Cần Thơ Tập 56,Số chuyên đề:Khoa học tự nhiên (2020)(1):127-133
Tóm tắt:
Trong công trình này, chương trình mô phỏng Geant 4 và MCNP-CP được sử dụng để mô hình hóa hệ phổ kế triệt Compton tại Viện Nghiên cứu hạt nhân Đà Lạt. Hệ phổ kế bao gồm 12 tinh thể nhấp nháy Bisthmuth Germanate (BGO) đặt xung quanh HPGe được sử dụng để giảm phông từ tán xạ Compton. Kết quả mô phỏng cho thấy có sự phù hợp tốt của hàm đáp ứng của nguồn phóng xạ dạng điểm đối với các đồng vị Na-22, Co-60 và Cs-137. Hơn nữa, hiệu suất đỉnh năng lượng toàn phần được so sánh giữa hai chương trình với độ sai biệt dưới 1%. Nghiên cứu này là kết quả ban đầu trong việc tối ưu hóa cấu hình của hệ đo và so sánh với kết quả thực nghiệm trong tương lai.
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Mean-field description of heavy-ion scattering at low energies and fusion
Dao T. Khoa, Le Hoang Chien, Do Cong Cuong, Nguyen Hoang Phuc
Abstract:
The nuclear mean-field potential built up during the 12C + 12C and 16O + 16O collisions at low energies relevant for the carbon- and oxygen-burning processes is constructed within the double-folding model (DFM) using the realistic ground-state densities of 12C and 16O, and CDM3Yn density-dependent nucleon–nucleon (NN) inter- action. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model (OM) analysis of the elastic 12 C + 12 C and 16 O + 16O scattering data at energies below 10 MeV/nucleon. These OM results provide a consistently good description of the elastic angular distributions and 90 excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the 12C + 12C and 16O + 16O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the 12C + 12C and 16O + 16O fusions very well over a wide range of energies.
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Manifestation of the divergence between antisymmetrized-moleculardynamics and container pictures of 9Be via 9Be(p, pn)8Be knockout reaction
Nguyen Tri Toan Phuc, Mengjiao Lyu, Yohei Chiba, Kazuyuki Ogata
Physics Letters B 819 (2021) 136466
Abstract:
We propose a new approach to probe the spatial extension of the valence neutron orbital in the 9Be nucleus via the 9Be(p,pn)8Be knockout reaction. This property of the nuclear molecular orbital has not been established in previous experimental studies and divergence exists between the theoretical descriptions of 9Be from different perspectives, i.e., the antisymmetrized molecular dynamics and the container pictures of cluster dynamics. These pictures are represented by two different well-proven microscopic models, the antisymmetrized molecular dynamics (AMD) and Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave functions. The corresponding reduced width amplitudes (RWAs) in the 8Be+n channel are extracted from both the AMD and THSR wave functions, and they are found to describe drastically different valence-nucleon motion, which shows the theoretical ambiguity in describing the π-orbitals in 9Be. Using the RWAs as input, the physical observables of the 9Be(p,pn)8Be knockout reaction are predicted by the distorted-wave impulse approximation (DWIA) framework. The magnitudes of the triple-differential cross sections (TDX) are found to be highly sensitive to the RWA input. It is concluded that the 9Be(p,pn)8Be knockout reaction could provide a feasible probing for the subtle differences between several structure models manifesting through the spatial extension of the π-orbital in the 9Be nucleus.
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Van Thang Nguyen, Nguyen Phong Thu Huynh , Ngoc Ba Vu, Cong Hao Le
Agricultural Water Management 243 (2021) 106453
Abstract:
Groundwater and inorganic fertilizers are regularly applied to agricultural soils, but their 226Ra content is potentially hazardous to human health and the environment. Due to irrigation and fertilization processes, 226Ra can accumulate in topsoils, and might also leach to subsoils, groundwater, and surface water. However, there are few studies on the accumulation of radium in the agricultural soils due to irrigation with groundwater. In this work, we analysed the radium content in 60 groundwater samples collected from a coastal area of Phu Yen Province, Vietnam where groundwater is regularly used for irrigation practices. Long-term accumulation of 226Ra in agricultural topsoils due to irrigation with groundwater was modelled for rice, maize, potato, and tomato top- soils. The fate of 226Ra in the topsoil (0–20 cm) was studied by using the Canadian Environmental Modelling Centre (CEMC) soil model and the HYDRUS-1D model. We found that the total inputs of 226Ra were 0.83, 2.45, 0.24, and 0.57 Bq m−2 d−1 for rice, maize, potato, and tomato soils, respectively. The total removals were 0.145, 0.236, 0.272, and 0.125 Bq m−2 d-1 found in rice, maize, potato, and tomato soils, respectively. A simple formula was developed to calculate the accumulation rate of 226Ra in the topsoil. Using this model we predict that the activity concentration of 226Ra will increase in rice, maize, and tomato soil, but will remain almost unchanged in potato soils. The accumulation rates 226Ra were 224, 791, and 115 Bq m−2 y−1. After 25 years of agricultural practices, the total activity values of 226Ra that accumulate in rice, maize, and tomato soils can reach 5147, 17278, and 2711 Bq m−2, respectively. We found the good agreements in the results based on two models. The irrigation practices with groundwater samples contribute 96.7, 79.5, and 79.8 % of 226Ra to the accumulation rates of 226Ra in rice, maize, and tomato soils, respectively.
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Levels of 226Ra in some paddy soils in the Mekong Delta region (Vietnam): current status and long-term assessment
Van Thang Nguyen, Binh An Le, Nguyen Phong Thu Huynh & Cong Hao Le
Journal of Radioanalytical and Nuclear Chemistry (2021)
Abstract:
226Ra levels in rice, soil, fertilizers, and water samples were analysed in 16 paddy fields in the Mekong Delta region. Levels of this radionuclide in the rice ecosystems caused radiation doses below the limits due to radionuclides in foodstuffs recommended by ICRP. Long-term change of 226Ra in the soil was predicted by a combination of experimental and modelling methods based on balance between its input and loss rates in topsoil. Similar results were found based on different mathematical models. The long-term increase of 226Ra found in the topsoil has not significantly changed since it has been studied ten years ago.
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Van Thang Nguyen, Nguyen Phong Thu Huynh, Cong Hao Le
Environmental Science and Pollution Research (2020)
Abstract:
Groundwater is a major source of drinking water and agricultural water in some regions of the world. However, it contains a high level of 226Ra that is potentially hazardous to human health and the environment. Normally, the activity concentration of 226Ra in groundwater is determined to assess the quality of groundwater that can be used as drinking water. There are few studies on the accumulation of 226Ra in the agricultural soil due to irrigation with groundwater. In this study, levels of 226Ra were determined on over 60 groundwater samples collected from the public water supply wells in Phu Yen province, Vietnam. Besides assessment of the health risks to population due to drinking groundwater samples, the impact of groundwater irrigation to the maize field in the study area was studied. For this purpose, two chemical fate models were applied and the comparison of their results was performed. Based on the model assessments, we predicted that the present agricultural practices increased the 226Ra activity concentration in the maize soil, and the level of 226Ra activity concentration in the topsoil can exceed the recommended level at 11.4 years of the present agricultural practices on the maize soil.
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