Tran Thien Thanh

This paper presents a gamma-ray transmission method for the non-destructive determination of concrete bulk density. The experimental setup comprises a 137Cs source, a NaI(Tl) detector, and lead collimators arranged in a narrow-beam transmission geometry. An MCNP model was developed to closely replicate the measurement configuration and was subsequently used to generate pulse-height spectra for elemental and concrete specimens covering densities of 2.10 – 8.96 g.cm-3 and thicknesses of 1 – 15 cm. From each spectrum, the net area of the 661.7 keV peak was extracted, and the attenuation indicator R was defined as the ratio of the peak areas recorded with and without the specimen. The simulations were benchmarked against measurements for aluminum and copper reference specimens at different thicknesses, showing good agreement in spectral response and relative deviations between simulated and experimental R values below 0.8%. Using the simulated R dataset, a linear calibration curve was established, enabling concrete bulk density to be determined without prior knowledge of the elemental composition. The method was applied to 22 concrete specimens fabricated with different aggregate systems, including ordinary concretes and concretes incorporating heavyweight additives (e.g., barite, Bi2O3, Fe2O3, and steel chips). These specimens covered densities of 2.2 – 2.6 g.cm-3 and thicknesses of 3 – 15 cm. Each specimen was measured at nine locations to assess spatial variability, and the weighted mean was taken as the representative bulk density. The resulting densities agree well with reference values obtained from mass-to-volume measurements, with relative deviations not exceeding 3.74% for all specimens. A coverage-probability–based statistical framework, augmented by additional sampling, was introduced to assess and improve measurement reliability when structural heterogeneity produces spatial variations in the inferred density. These preliminary results demonstrate that the proposed method is reliable and well suited for rapid concrete quality control.

Purpose: This study aims to validate HDR brachytherapy dosimetry for cervical cancer patients utilizing the egs_brachy Monte Carlo (MC) simulation. Methods: Three cervical cancer patients treated with ¹⁹² Ir HDR brachytherapy were included. Dose distributions were calculated by the Oncentra Brachy v4 treatment planning system (TPS) based on AAPM TG‐43. The newly developed eb_gui, an egs_brachy graphical user interface for MC simulations, was applied in recalculating dose distributions for 12 fractions using digital imaging and communications in medicine‐radiotherapy (DICOM‐RT) anatomical information. Comparisons were made for clinical target volume (CTV), bladder, and rectum using dose–volume histograms (DVH) and clinically relevant plan quality indices. Results: TPS‐calculated doses were greater than those obtained from MC simulations. For the CTV, the median percentage differences were 7.9% (Q1: 6.4%, Q3: 9.8%; range: 0.4%–10.4%) for D ₉₀ . For the bladder, the median percentage differences were 0.7% (Q1: 0.4%, Q3: 2.3%; range: −9.4–5.4%) for D _2cc . For the rectum, the median percentage differences were 3.6% (Q1: 2.8%, Q3: 5.6%; range: 0.9%–6.4%) for D _2cc . Conclusion: CTV and critical organ doses calculated by the TPS were consistently greater than those obtained from MC simulations. This suggests that the TPS may overestimate dose distributions, especially in heterogeneous regions like the pelvis. These results emphasize the need for continued validation of TPS algorithms in HDR brachytherapy for cervical cancer.

Aside from the natural background ionizing radiation that humans are constantly exposed to, there is a significant risk of elevated radiation levels from building materials with enhanced radioactivity. Given the time individuals spend indoors, this study is crucial in assessing the external radiation dose from commonly used construction materials. A room model with dimensions 5  4  2.8 m and walls 20 cm thick was developed to simulate radiation doses from materials such as cement, brick, sand, and rock collected from suppliers in Ho Chi Minh City, Vietnam. Absorbed dose rates from radionuclides, specifically ²³⁸U, ²³²Th, and ⁴⁰K, were calculated using the Monte Carlo N-Particle Transport code (MCNP6), with phantom water used to represent the dose absorption medium. The results indicate that the external radiation doses ranged from 0.11 – 0.64 mSv/y for sand, 0.47 – 0.79 mSv/y for cement, 1.07 – 1.58 mSv/y and 1.00 mSv/y for brick and rock, respectively. While most measured doses were below the reference value, specific brick samples exceeded these thresholds. In addition, a comparative analysis was conducted using the RESRAD-BUILD code, with dosimetric data derived from the ICRP 38 library. The comparison between MCNP6 and RESRADBUILD results showed a good agreement with relative deviations of less than 12%, underscoring the accuracy and reliability of the model. These findings suggest that the proposed methodology provides a reliable and efficient approach for quantifying external radiation doses from building materials, thus contributing to improved radiation safety assessments in indoor environments.

This paper presents findings on groundwater physiochemical composition and radioactivity levels in households in Bac Lieu province, Vietnam. Through discriminant analysis, it was observed that groundwater quality exhibits spatial variations corresponding to saline intrusion zones. The paired-samples T-tests revealed significantly different ratios of Ra-224, Ra-226, and Ra-228 isotopes between Na–Cl and Ca–Na–HCO₃ water types. All three water types had a ratio of Ra-226/Ra-228 of approximately one, indicating the presence of groundwater aquifers beneath the crust and fluvial marine sediment. Furthermore, strong associations between sulfate and calcium suggest that CO₂ enrichment in groundwater aquifers indicates anoxic aquatic environments. Twenty-five of the thirty-three evaluated samples exceeded the national technical regulations for domestic water quality with parameters such as chloride, sulfate, sodium, gross alpha, or total dissolved solids. Fifteen samples exceeded gross alpha's allowable contamination threshold of 0.1 Bq/L. The combination of Ra-226 and Ra-228 did not surpass the U.S. Environmental Protection Agency's recommended limit of 0.185 Bq/L. However, nineteen samples exhibited annual committed effective doses of radium isotopes for infants that exceeded the WHO recommendation of 0.1 mSv/year.