BẢN TIN KHOA HỌC

Van Thang Nguyen, Nguyen Phong Thu Huynh, Cong Hao Le

Journal of Environmental Management 271 (2020) 111001

Abstract:

In topsoils, the activity concentrations of natural radionuclides (hereafter NRs) increase due to the addition of NRs from fertilizers, irrigation water, and air dust pollution. On the other hand, various physical-chemical and environmental processes such as radioactive decay, volatilization, leaching, erosion, and plant uptake were responsible for the decrease of the activity concentrations of NRs in the topsoils. In this study, behaviours of ⁴⁰K, ²¹⁰Pb, ²²⁶Ra, ²³⁸U, and ²³²Th in topsoils were modelled by the CEMC soil model and the HYDRUS-1D model. An exponential equation was proposed for estimating the accumulation rates of these radionuclides in the topsoils. Long-term accumulation of radionuclides was assessed for water spinach (Ipomoea Aquatica Forssk.) soil (here-after VES) and rice (Oryza sativa L.) soil (hereafter RIS). We found that the current agricultural practices caused the increase of ⁴⁰K activity concentration in the water spinach soil, and ⁴⁰K, ²¹⁰Pb, ²²⁶Ra, and ²³²Th activity concentrations in the rice soil. The accumulation rates of radionuclides were in the order ²³⁸U <²³²Th <²²⁶Ra <²¹⁰Pb <⁴⁰K. 25 years of cultivation with water spinach can increase/decrease +(165 +/- 6) Bq of ⁴⁰K, – (8.2 +/-0.7) Bq of ²¹⁰Pb, – (4.3 +/-0.2) Bq of ²²⁶Ra, – (7 0.3 +/-0.3) Bq of ²³⁸U, and – (1.8 +/-0.1) Bq of ²³²Th in 1 kg soil. For rice cultivation, these values are +(1004 +/-39), +(3.3 +/-0.2), +(3.0 +/-0.2), – (5.1 +/-0.3), (2.2 +/-0.1) Bq kg^-¹for ⁴⁰K, ²¹⁰Pb, ²²⁶Ra, ²³⁸U, and ²³²Th, respectively.

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A Treatment Planning Comparison between Intensity Modulated Proton Therapy (IMPT) and Volumetric Modulated Arc Therapy (VMAT) for prostate cancer

Thi Cam Thu Nguyen, Thanh Xuan Le

Sci. Tech. Dev. J.; 25(1):2297-2307

Abstract:

Introduction: We made a comparison between IMPT plans and VMAT plans for ten prostate cancer patients with the analysis of dosimetric quantities and EUD for both target volume and OARs.

Methods: Ten patients planned for VMAT were retrospectively replanned with scanned proton beams. Target and OARs were kept as originally delineated in photon plans with the assumption that the change in dose distribution is acceptable. The prescribed dose to the PTV is 74 Gy using an RBE of 1.1. The optimized VMAT plan of each case was normalized using the PTV coverage value obtained from the optimized IMPT plan. For the PTV and OARs, the dosimetric quantities were analyzed. Moreover, EUD with the exponential parameter a with a 95% confidence level was calculated for both the PTV and OARs.

Results: For the PTV, all the averaged dose metrics, including the mean dose, the median dose and the maximum dose, the HI and the EUD, in the IMPT plans were statistically (p0.05) better than those in the VMAT plans. The dose to the PTV from IMPT plans ranged from 69.14.7 to 79.01.1 Gy (RBE), while that from VMAT plans ranged from 68.0 2.8 to 81.6 1.3 Gy (RBE). The mean dose of 2.6 Gy (RBE) to the body from the IMPT plan was significantly (p=0.007) lower than the mean dose of 5.8 Gy (RBE) from the VMAT plans. For all OARs except for the rectum, in the low-to-medium dose region, the volumes receiving low doses in IMPT plans were statistically (p0.05) lower than those in VMAT plans. The IMPT plans show statistically (p0.05) superior dose sparing of the rectum and bladder in comparison to the VMAT plans at the Dmax, Dmean, and V30Gy indices and at all dosimetric indices.

Conclusions: The results show that the IMPT plans were statistically superior to the VMAT plans for both the PTV and OARs. IMPT plans produced a more homogeneous dose in the PTV. For OARs, the volumes receiving the low doses were statistically lower in IMPT plans than in VMAT plans.

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A simple approach for developing model OF Si(Li) detector in Monte Carlo simulation

Huynh Dinh Chuong, Nguyen Thi Truc Linh, Le Thi Ngoc Trang, Vo Hoang Nguyen, Le Hoang Minh , Chau Thanh Tai, Tran Thien Thanh

Abstract

In this paper, a simple approach for developing the model of a Si(Li) detector in Monte Carlo simulations is presented and validated. Experimental measurements using “point-like” standard radioactive sources including ¹³³Ba, ¹³⁷Cs, ¹⁵²Eu, ¹⁵⁴Eu, ²⁴¹Am were performed for both configurations with and without collimator, respectively. The MCNP6 code was used for Monte Carlo simulation of photon transport inside the models constructed similar to these configurations. Firstly, an initial model of the Si(Li) detector was constructed based on the manufacturer's specifications, but the simulated efficiency shows a very high discrepancy from the experiment. Then, the critical geometric parameters of the model of Si(Li) detector were improved step-by-step to achieve the optimized model. For the optimized model, a good agreement was obtained between the experimental and simulated results. The relative deviations of experimental and simulated efficiencies are less than 4% with energies in the range of 12–60 keV for both configurations.

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Huynh Dinh Chuong, Le Thi Ngoc Trang, Vo Hoang Nguyen, Tran Thien Thanh

Applied Radiation and Isotopes, Available online 10 April 2020, 109179

Abstract:

In present work, the validity of the virtual point detector (VPD) model for the NaI(Tl) detectors is studied and confirmed in the photon energy range of 60-1408 keV. The full energy peak efficiency (FEPE) of two NaI(Tl) detectors, which have scintillation crystal dimensions of 5.08×5.08 cm and 7.62×7.62 cm respectively, is measured for “point-like” radioactive sources on the symmetry axis with source-to-detector distances in the range of 2-40 cm. It is found that the VPD model is valid to fit too well to the experimental FEPE for the two surveyed NaI(Tl) detectors. The dependence of the VPD position on the incident photon energy for the NaI(Tl) detectors with different scintillation crystal dimensions is shown based on experimental data. A semi-empirical equation involving incident photon energy and source-to-detector distance is proposed to calculate the FEPE for the NaI(Tl) detectors. The calculated results for the two surveyed NaI(Tl) detectors by this equation are in a good agreement with experimental results for photon energies in the range of 344-1408 keV. However, the difference between experimental and calculated results is quite significant for source-to-detector close geometries for photon energies lower than 344 keV.

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Huynh Dinh Chuong, Le Thi Ngoc Trang, Hoang Duc Tam, Vo Hoang Nguyen, Tran Thien Thanh

NDT & E International Available online 4 May 2020, 102281

Abstract:

This study proposes a new approach to determine the thickness of the material plate. This approach uses Monte Carlo simulation to construct the calibration curve of the ratio R versus the thickness of the material plate (R is the ratio of area under a scattering peak for a given thickness to that for a saturation thickness). Using this calibration curve, the unknown thickness of a material plate is determined by experimentally measuring the ratio R. To validate the proposed approach, we performed 39 measurements for 13 aluminum samples with thicknesses in the range of 7.00 mm–35.20 mm. The results showed that except for two measurements with relative deviations of 5.45% and 6.17%, the relative deviation for the remaining measurements is less than 5%. Besides, the method for estimating the maximum measurable thickness with the desired deviation was presented, which shows good agreement between theoretical calculation and experimental value. The obtained results are the basis for completing the thickness measurement system using semi-empirical methods in further studies.

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A Geant4 procedure for precise simulation of PGNAA prompt gamma‑ray spectrum in a wide energy range up to 8 MeV

Thanh Tai Chau, Ngoc Son Pham, Thien Thanh Tran, Cong Phat Vo, Van Tao Chau

Journal of Radioanalytical and Nuclear Chemistry

Abstract:

In reality, after subtracting the beam background from the prompt g-ray spectrum induced by the irradiated sample with the same time measurement, it still exists the remaining g-ray background induced by the nuclei capturing the thermal neutrons scattered by the sample. This makes it difficult to validate the accuracy of the PGNAA detector response between the simulation and the experiment in the wide energy range. In this study, a simple method to construct the remaining g-ray background in the simulation prompt g-ray spectrum of ³⁵Cl(n,g)³⁶Cl reaction is proposed. Then the simulation prompt g-ray spectrum with the remaining g-ray background is compared to the experimental spectrum to validate the simulation PGNAA detector response in the energy range from 0.1 MeV to about 9 MeV.

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