FACULTY OF PHYSICS & ENGINEERING PHYSICS

DEPARTMENT OF NUCLEAR PHYSICS - NUCLEAR ENGINEERING - MEDICAL PHYSICS

Onset of collectivity for argon isotopes close to $N = 32$

B. D. Linh et al.

Phys. Rev. C 109, 034312

Abstract:

The shell closure at $N = 32$ has been investigated by a first spectroscopy of the $N = 31$ nucleus $49 Ar$ at the Radioactive Isotope Beam Factory. Using the $50 Ar (p, p n)$ reaction channel in inverse kinematics, $50 Ar$ projectiles at 217 MeV/nucleon impinged on a 150 mm long liquid hydrogen target, part of the MINOS device. Prompt deexcitation $γ$ rays were measured with the NaI(Tl) array ${DALI 2}^{+}$ . Reaction products were analyzed with the SAMURAI spectrometer, which allowed the measurement of the momentum distributions and angular momentum transfer. Data were compared to state-of-the-art theoretical predictions, including shell-model, energy-density functional, and ab initio calculations. An onset of collectivity is suggested besides the spherical configuration typical of a closed shell nucleus, such as for $52 Ca$ .

On the Bohr-Sommerfeld quantization condition and assault frequency in a semiclassical model for α decay

Le Hoang Chien, Nguyen Tri Toan Phuc

Nuclear Physics A 1018 (2022) 122373

Abstract:

We study the impacts of the Bohr-Sommerfeld quantization condition and the assault frequency on the α decay half-life within the semiclassical model. The potential between the α particle and daughter nucleus is calculated by the double-folding model using the CDM3Y3 density-dependent nucleon-nucleon interaction with a finite-range exchange term. We show that the proper implementation of the Bohr-Sommerfeld condition leads to a considerable change of the calculated α decay half-life with certain forms of potential. We also propose an alternative treatment for the assault frequency based on the generalized oscillator potential. This description of assault frequency considerably improves the agreement between the calculated α decay half-lives and the experimental data.

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Nuclear rainbow of the symmetric nucleus-nucleus system: Interchange of the nearside and farside scattering

Nguyen Tri Toan Phuc, Nguyen Hoang Phuc, and Dao T. Khoa

Phys. Rev. C 109, 064606 – Published 4 June 2024

Abstract:

Extensive elastic scattering data measured at energies around 10 to 20 MeV/nucleon for some light identical systems, like ¹²C+¹²C and ¹⁶O+¹⁶O, were shown to exhibit the nuclear rainbow pattern of broad Airy oscillations of the elastic scattering cross section at medium and large angles. Because of the identity of the scattered projectile and recoiled target, the smooth rainbow pattern at angles around and beyond 𝜃_c.m.≈90^∘ is strongly deteriorated by the boson exchange in the ¹²C+¹²C and ¹⁶O+¹⁶O systems at low energies. The exchange symmetry of two identical nuclei implies the Mott interference of the direct and exchange scattering amplitudes, which destroys the nuclear rainbow pattern. The nuclear rainbow features in the elastic scattering of two identical nuclei have been discussed so far based on the nearside-farside (NF) decomposition of the scattering amplitude given by an optical model calculation neglecting the projectile-target exchange symmetry. Moreover, the NF decomposition method was developed in the 1970s by Fuller for nonidentical dinuclear systems only, and the details of how the exchange symmetry of an identical system affects the evolution of nuclear rainbow remain unexplored. For this purpose, the Fuller method is generalized in the present work for the elastic scattering of two identical (spin-zero) nuclei, with the projectile-target exchange symmetry taken explicitly into account. The results obtained for elastic ¹²C+¹²C and ¹⁶O+¹⁶O scattering at low energies show that the exchange symmetry results in a symmetric interchange of the nearside and farside scattering patterns at angles passing through 𝜃_c.m.=90^∘, which requires a more subtle interpretation of nuclear rainbow. We found further that a similar NF interchange also occurs in a nonidentical nucleus-nucleus system with the core-core symmetry at low energies, where the elastic cross section at backward angles is due mainly to the elastic transfer of cluster or nucleon between two identical cores. This interesting effect is illustrated in the elastic ¹⁶O+¹²C scattering at low energies where the elastic 𝛼 transfer between two ¹²C cores has been proven to enhance the elastic cross section at backward angles.

Non-destructive evaluation of thickness of material plates through Compton back-scattering technique using Si(Li) detector

Huynh Dinh Chuong, Nguyen Duy Thong, Vo Hoang Nguyen, Le Hoang Minh, Nguyen Thi Truc Linh, Phan Long Ho, Tran Thien Thanh, Chau Van Tao

Radiation Physics and Chemistry (2022), 109978

Abstract:

This study aims to develop the system for the non-destructive evaluation of the thickness of material plates based on the Compton back-scattering technique using a Si(Li) detector and ²⁴¹Am radioactive sources. The calibration curve is constructed based on the areas under the Compton scattering peak obtained from the measurements of reference samples. This calibration curve is used to determine the saturation thickness, the maximum measurable thickness (MMT) with the desired accuracy, and the unknown thickness of a sample. To validate the reliability of the system, we have performed thickness measurements for seventeen aluminum samples with different thicknesses in the range of 4.40–21.07 mm. The samples are measured seven times, except for two samples with thicknesses of 11.52 mm and 14.98 mm up to twenty times. The Pearson's correlation coefficient between the reference and measured thicknesses presented a strong positive correlation. The average relative deviation between the reference and measured thicknesses is less than 1%.

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NGHIÊN CỨU PHƯƠNG PHÁP ĐÁNH GIÁ HOẠT ĐỘ RADON TRONG NHÀ SỬ DỤNG HỆ PHỔ KẾ GAMMA

Lê Quang Vương, Nguyễn Huỳnh Khánh Duyên, Huỳnh Đình Chương, Hoàng Đức Tâm, Trần Thiện Thanh, Châu Văn Tạo

TẠP CHÍ KHOA HỌC TRƯỜNG ĐẠI HỌC SƯ PHẠM TP HỒ CHÍ MINH, Tập 20, Số 12 (2023): 2081-2094

TÓM TẮT

Theo Tổ chức Y tế thế giới (WHO), khí radon trong nhà là một trong những nguyên nhân gây ung thư phổi và cần được giám sát. Trong nghiên cứu này, chúng tôi trình bày một phương pháp đánh giá hoạt độ radon (²²²Rn) trong nhà dựa trên phép đo phổ gamma của đồng vị ²¹⁴Bi, là sản phẩm phân rã của ²²²Rn trong chuỗi ²³⁸U. Đầu tiên, hoạt độ ²²²Rn trong năm căn phòng có kích thước khác nhau được đo bằng hệ thiết bị RAD7. Tiếp theo, hoạt độ ²¹⁴Bi được xác định bằng hệ phổ kế gamma sử dụng đầu dò NaI(Tl) kết hợp với mô phỏng MCNP6. Hàm làm khớp tuyến tính thể hiện mối tương quan tốt giữa kết quả hoạt độ ²¹⁴Bi và ²²²Rn (R² = 0,998). Phương pháp này có thể cho kết quả dự đoán nhanh chóng hoạt độ ²²²Rn trong nhà, hỗ trợ điều tra giám sát các khu vực có hàm lượng ²²²Rn bất thường.

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Natural Radionuclides in Rice Soils in the Mekong Delta Region, Vietnam: Health Risk, Transfer to Rice, and Long-Term Accumulation in Topsoil

Van Thang Nguyen, Binh An Le, Nguyen Phong Thu Huynh & Cong Hao Le

Water, Air, & Soil Pollution volume 232, Article number: 354 (2021)

Abstract:

In the world, many studies have focused on the natural radioactivity in agricultural soils and food crops and the transfers of radionuclides between two components. However, the influence of long-term agricultural practices on the activity concentrations of radionuclides in the soils remains unclear. On the other hand, the soil-to-plant transfer factors of radionuclides for a specific plant type are different between the regions of the world. In this study, activity concentrations of natural radionuclides in 16 rice and corresponding soil samples in the Mekong Delta region of Vietnam were measured by a gamma spectrometer with a high purity germanium detector. The accumulation rates of radionuclides were predicted by using a model based on the balance between input and output rates of radionuclides in the topsoil. Based on the analysis of radionuclides in soil and rice samples, the average values of TF estimated for ⁴⁰ K, ²²⁶Ra, ²³²Th, and ²³⁸U were 4.2 ± 0.5 × 10⁻², 3.2 ± 0.6 × 10⁻², 4.6 ± 1.1 × 10⁻³, and 1.9 ± 0.4 × 10⁻², respectively. For long-term assessment, the annual rates 39 ± 2 Bq kg⁻¹ year⁻¹, 26.8 ± 2 mBq kg⁻¹ year⁻¹, − 418 ± 34 mBq kg⁻¹ year⁻¹, and − 358 ± 30 mBq kg⁻¹ year⁻¹ were estimated for ⁴⁰ K, ²²⁶Ra, ²³²Th, and ²³⁸U, respectively. From the results of this study, it is evident that irrigation system is the main factor that caused accumulations of radionuclides in the soil. Water leaching and rice uptake were two processes that were responsible for the rejection of radionuclides from the soil. The accumulation rates of radionuclides are therefore controlled by changing the cultivation conditions.

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