BẢN TIN KHOA HỌC

Study of nonlocality effects in direct capture reactions with Lagrange-mesh R-matrix method

Nguyen Hoang Phuc, Nguyen Tri Toan Phuc, Do Cong Cuong

International Journal of Modern Physics EVol. 30, No. 09, 2150079 (2021)

Abstract:

We apply the Lagrange-mesh 𝑅-matrix method to calculate the 𝑆-factor for the ¹³C(𝑝,𝛾)¹⁴N and ¹⁶O(𝑝,𝛾)¹⁷F direct radiative capture reactions. By comparing the astrophysical 𝑆-factors calculated with nonlocal and local potentials, we investigate the nonlocality effects coming from the nuclear potentials in the direct capture reactions. Our calculations are in good agreement with the experimental data and indicate a nonnegligible difference in the results of local and nonlocal potentials. The use of small diffuseness narrow potentials also provides a remarkably good fit in the case with multiple broad resonances. Our findings suggest that the nonlocal potential improves the calculated results although the difference between the local and nonlocal potentials is smaller than uncertainties from other sources. We propose the nonlocality potential should be used in the potential model calculation of future astrophysics rates evaluation.

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Tran ThienThanh, Le Hoang Minh, Nguyen Quoc Bao Cuong, Huynh Dinh Chuong,Nguyen Duy Thong, Vo Hoang Nguyen, Phan Long Ho, Chau Thanh Tai, Chau Van Tao

NIM A Available online 23 April 2020, 163995

Abstract:

Experimental data of Rayleigh to Compton scattering ratios depending on the effective atomic number of the fifteen powder samples in the range 10 < Z < 30 obtained at an energy of 59.54 keV using six well-known methods are presented in this article. In this study, a Si(Li) detector is placed at a scattering angle of 150 degrees to detect emitting signals from the interaction of incident gamma rays and powder samples. A new fitting procedure with the least squares method was used to fit the Compton peak using a Voigt function and the Rayleigh peak using a Gaussian function by Root software. The ten calibrating samples provided results that were in good agreement with the fitting procedure for all methods using linear functions. The estimated values of the Rayleigh to Compton scattering ratio using the effective atomic numbers were compared to the theoretical calculation. Furthermore, the best solution for the interpolated effective atomic number of the six methods was found and confirmed with the maximum relative deviation lower than 4% for five analysed samples.

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Phan Long Ho, Le Dinh Hung, Vu Tuan Minh, Dang Van Chinh, Tran Thien Thanh & Chau Van Tao

Scientific Reports Volume 10, Article number: 4299 (2020)

Abstract:

This paper presents information on the gross alpha and gross beta activity concentrations of two hundred twenty-six groundwater samples collected by gas ow proportional counters in southern Vietnam. The gross alpha results in the water samples ranged from 0.024 to 0.748 Bq L−1 with a mean of 0.183 ± 0.034 Bq L−1, and the gross beta results in the water samples ranged from 0.027–0.632 Bq L−1 with a mean of 0.152 ± 0.015 Bq L−1. The values obtained in this work were compared with those previously published for various regions or countries. Next, untreated and treated groundwater samples were analyzed to assess their in uences on the treatment process. The results showed that there
were di erences in the minimum detection concentrations and the mean activity values between the untreated and treated groundwater samples (The p-value of the mean comparison tests is signi cant with p < 0.05). In both sample groups, there was a strong positive correlation of the gross alpha versus the gross beta results (r > 0.6). This means that among the radionuclides, the major sources of beta radiation are uranium and thorium decay series radionuclides. Finally, the annual e ective dose for adults (>17 years) was calculated based on the assumption that major radionuclides have the highest e ective dose conversion factors. In general, the results for Pb-210, Ra-226, and Ra-228 were observed to be lower than the recommended reference values established by the World Health organization and the International Atomic Energy Agency, except for the value of Po-210.

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Simultaneous correction of the coincidence summing and self‑absorption for radioactivity measurement in solid samples by MCNP‑CP code

Le Quang Vuong, Tran Thien Thanh, Phan Long Ho, Le Cong Hao, Chau Van Tao

Journal of Radioanalytical and Nuclear Chemistry

Abstract:

The present work of this study involves an advanced analytical procedure that allows direct and fast determining the specific activity of ²³⁸U and ²³⁵U using the gamma-rays of 63.3 keV and 185.7 keV after subtraction of the contribution of overlapping peaks. This procedure also included MCNP-CP code in order to calculate the coincidence summing and the self-absorption correction factor. Validation of the developed procedure was confirmed by the IAEA proficiency test to calculate the activities of radionuclides in various types of samples such as rich thorium, secular equilibrium, and disequilibrium of uranium. The final scores were received “acceptable” for all radionuclides.

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Simulation dataset of thermal and epithermal neutron self-shielding correction factors for 186W(n, γ )187W reaction rate experiments using tungsten foil targets

Trinh T. Tu Anh, Pham N. Son, Chau T. Tai, Truong P. Dung, Trinh V. Cuong, Phan B. Quoc Hieu, Cao D. Vu

Data in Brief 52 (2024) 109937

Abstract:

In the experiments of neutron interaction with research samples, the incident neutron energy spectrum, distribution inside the irradiating sample volume, is affected by the unexpected neutron self-shielding effects. The nature of these effects is due to the formation and thickness of the irradiating sample, which significantly causes neutron self-absorption and multiple scattering inside the sample volume. The datasets presented in this article showed the thermal (G_th) and epithermal (G_epi) neutron self-shielding correction factors for the ¹⁸⁶W(n,γ)¹⁸⁷W neutron capture reaction rate in irradiating tungsten (W) foil samples with different thicknesses. The simulations were performed for three models of surface neutron source's geometries and relative orientations of the irradiating foil samples of isotropic cylinder surface neutron source with foil sample along to the center line, isotropic cylinder neutron source with foil sample flat to the center line, and isotropic spherical neutron source with foil sample placed at the center point. The range of sample thicknesses was from 10 µm to 2.5 mm. The uncertainties for each data point are also reported in the data table, making it more convenient for reuse in related experiments or evaluations.

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Sensitivity of secondary particle emission to hadronic physics models in GATE/Geant4 proton therapy simulations at 100 MeV

Pham Thi Cam Lai, Nguyen Tri Toan Phuc, Vo Hong Hai

Science & Technology Development Journal 2023, 26(3):2930-2936

Abstract:

Introduction: Proton therapy simulations rely on Monte Carlo techniques, such as the GATE code based on the Geant4 toolkit, to predict dose distribution and secondary particle production. The accuracy of these simulations is heavily influenced by the chosen physics models.

Methods: In this study, we analyzed three Geant4 hadronic physics models, BIC, BERT, and INCL++, by calculating the angular and energy distributions of secondary neutrons and gamma particles. We conducted GATE/Geant4 simulations on a water phantom irradiated with a 100 MeV proton beam.

Results: Our investigation revealed notable differences in the angular and energy distributions of emitted particles among the three models.

Conclusion: This study emphasizes the necessity of carefully selecting a hadronic physics model for GATE/Geant4 simulations in proton therapy.

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