Khoa Vật lý, Trường Đại học Khoa học Tự nhiên - Đại học Quốc gia Hà Nội

This paper presents a Monte-Carlo code to simulate the time sequences of the \(\beta\)-decay following implantation of a continuous radioactive ion beam in to a segmented silicon detector. We extended our simulation to the \(\beta\)-delayed neutron process. Ananalis is procedure, which has been developed to obtain simultaneously the \(\beta\)-decay half-life and the \(\beta\)-delayed multi-neutron emission probability, was verified by the simulation data.

Because strange quark produced copiously in pp collisions, strange hyperon production is one of the ideal tools to investigate the hadronization process and baryon transport theory. We are especially interested in the hyperon Ω production because this baryon contents only strange quark. Our new studies of the pure strange hyperon Ω produced in pp collision at s = 8 TeV are shown in this report. The following strategy is used to reconstruct the strange hyperon Ω. In the LHCb experiment, the hadrons p, π and K are identified by the RICH detector with PT threshold > 100 MeV. Only Lambda (from channel Λ → p + π) with PT > 500 MeV are chosen to combine with kaon daughter particle in order to reconstruct a strange hyperon Ω. The reconstructed particles are accepted as Ω candidates in the case it satisfies several criteria such as its invariance mass must be located within the window mas ± 50 MeV/c2 around the nominal value. More than 63 millions selected events are used for this analysis and about 8100 hyperon Ω candidates are reconstructed.

In this work, biomaterial based microlasers were successfully fabricated by a cost effective, simple and environmental friendly fabrication method. The as-fabricated microlasers were made of biocompatible material including ovalbumin doped Rhodamine B at low weight percentage. The lasers had solid-state spheres with various diameters ranging from 20 µm to over 100 µm. It was shown that inside the spherical cavity which supported whispering gallery mode, a lasing emission was generated with a low threshold of 17.5 µJ/mm2, and a high Q-factor of approximately 3000. The remarkable lasing properties of the dye doped ovalbumin microlasers are considered as important bases for their future biological and medical applications.

We have measured the excitation function for the production of 96Nb in proton induced reaction on natural zirconium in the energy range of 10.58 MeV to 43.61 MeV. The measurement was performed using a stacked-foil activation method combined with off-line γ-ray spectrometry. The stack containing Zr samples, Cu monitors, and several energy degraders was irradiated at the MC-50 Cyclotron of the Korea Institute of Radiological and Medical Sciences (KIRAM), Korea. The cross section of the natZr(p,x)96Nb reaction was extracted from the measured activity of reaction product using an HPGe γ-ray detector. The energy of the proton beam along the stacked foil was calculated using the code SRIM-2013. The proton beam flux was determined via the natCu(p,x)62Zn and natCu(p,x)65Zn monitoring reactions. The measured cross sections of the natZr(p,x)96Nb reaction as a function of the proton energy are compared with the literature data as well as with the theoretical predictions using the TALYS-1.95 nuclear model code and the TENDL-2019 nuclear data library.

Abstract: We will present main results of our recent investigations on the validity of the cosmic no-hair conjecture proposed by Hawking and his colleagues in some conformal-violating Maxwell models, in which a scalar field or its kinetic term is non-trivially coupled to the electromagnetic field. In particular, we will show that the studied models really admit the Bianchi type I metrics, which are homogeneous but anisotropic space time, as their stable cosmological solutions. Hence, these models turn out to be counterexamples to the cosmic no-hair conjecture. Keywords: Cosmic no-hair conjecture, cosmic inflation, Bianchi type I space time, Maxwell theory. References[1] A.H. Guth, Inflationary universe: A possible solution to the horizon and flatness problems, Phys. Rev. D 23 (1981) 347.[2] A.D. Linde, A new inflationary universe scenario: A possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems, Phys. Lett. 108B (1982) 389.[3] A.D. 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Magnetic properties of magnetic nanoparticles FePt prepared by sonochemistry were investigated. Upon annealing at temperature from 450ºC to 650ºC samples have ordered L10 structure and show hard magnetic properties. Influence of heat treatment conditions (annealing temperature, cooling rate) on the magnetic properties of the annealed samples has been studied.Keywords: FePt, nanoparticle, sonochemistry, magnetic properties.

Abstract: Along with the development of urban and modern life, Hanoi Capital has been constructing more and more sky buildings, big bridges and huge underground constructions. According to historical studies, Hanoi is a region located on the weak soil ground which has a rather thick sedimentary layer, complicated geology structure and shallow ground water aged in the Holocene and Pleistocene. Hanoi city is cut through by a Red River fault which has been considered to be a strong active fault zone. As a consequence, it is able to cause earthquakes with magnitude M = 6.1 corresponding to the 7th ground vibration level in intensity. In order to predict the casualty of this severe earthquake being able to happen, it is surely essential to assess both seismic site response and geological conditions in Hanoi. In the paper, we will analyze the soil ground data and borehole data obtained in this region to find the specific geological factors which are put into the DeepSoil Program to evaluate local site effects.

This paper presents some numerical simulation results on the influence of local site conditions on earthquake ground motions in Hanoi. Numerical simulation method through DEEPSOIL program was used in the study. Geological data of 600 groundwater survey and engineering geology boreholes in Hanoi as well as the acceleration records of Imperial Valley earthquake in 1979 with magnitude M = 6.5, hypocenter of 26.5 km, and PGA of 0.169 g were chosen as input data for the research. By analyzing geological conditions, tectonics, seismic characteristics of different soil types in Hanoi, a geological cross-section cutting through different engineering geology in Hanoi areas have been constructed. Numerical simulations of site effect at typical locations along the cross-section show: (i) The geological conditions on the surface of Hanoi clearly influence the earthquake ground motion, this is confirmed by the increase in the amplitude of the horizontal component of ground acceleration and the change of the strong vibrations from short to longer period. These effects obey a general rule, they become stronger when moving on the cross-section from west to east, corresponding to an increase in the thickness of the weak sedimentary layers covering the hard rock; and (ii) However, at the place where the weak and soft soil layer appear (LK50 borehole), despite of the vibrations that are still converted from short to longer periods, the amplitude of the PGA is strongly attenuated at the surface layer.

In this research, the dependence of the velocities and the absorption coefficients of ultrasonic waves propagated in 1018 low carbon steel on temperature range from 0 oC to 50 oC was investigated. The coefficients of the temperature dependence of the ultrasonic longitudinal wave and ultrasonic shear wave were estimated to be -0.8 m/s.oC and -0.44m/s.oC, respectively. The acoustic impedances of this carbon steel were also investigated and effected much by temperature. Simultaneous, the effect of temperature on the acoustic impedances and ultrasonic attenuations of the motor oil was also determined. As the results, reflection and transmission coefficients at the interface between the carbon steel and motor oil were estimated. It is concluded that the ultrasonic attenuation of the motor oil is one of the main reasons for the behavior of the ultrasonic absorption coefficients propagated in the steel sample.Keywords: Ultrasonic, Nondestructive Testing, Reflection and Transmission coefficients, Longitudinal Wave, Shear Wave, Ultrasonic Velocity, Low carbon steel, Ultrasonic Attenuation, Reflection and Transmission Coefficients, Pulse-echo Technique

Bài báo này nghiên cứu ảnh hưởng của nhiệt độ nung đến cấu trúc tinh thể, nhiệt độ tới hạn (Tc) và độ dẫn điện thừa của hệ thống Bi-Pb-Sr-Ca-Cu-O (BPSCCO). Các mẫu BPSCCO khối được chế tạo bằng phương pháp phản ứng trạng thái rắn. Bốn nhiệt độ khác nhau 835 °C, 840 °C, 845 °C, và 850 °C được áp dụng để nung bốn mẫu khác nhau. Cấu trúc tinh thể của các mẫu đã được điều tra thông qua các phép đo nhiễu xạ tia X (XRD) và kính hiển vi điện tử quét (SEM). Tính siêu dẫn của các mẫu được phân tích dựa trên phép đo điện trở phụ thuộc nhiệt độ. Kết quả thực nghiệm cho thấy sự tồn tại của cả hai pha Bi-2223 và Bi-2212 trong tất cả các mẫu. Về mặt định lượng, tỷ lệ thể tích của pha Bi-2223 được phát hiện là tăng từ 53.56% lên 75.97%, và kích thước hạt trung bình của pha Bi-2223 được quan sát là mở rộng từ 57.95 nm lên 86.50 nm khi nhiệt độ nung tăng từ 835 °C lên 850 °C. Ngoài ra, các phân tích độ dẫn điện thừa dựa trên lý thuyết Aslamazov - Larkin (AL) và Lawrence - Doniach (LD) cho thấy sự giảm đi của chiều dài hợp nhất (ξc(0)) từ 1.957 Å xuống 1.565 Å và khoảng cách giữa các lớp hiệu dụng (d) từ 79.7 Å xuống 64.5 Å. Trong khi đó, sức mạnh liên kết giữa hai mặt phẳng CuO2 (J) được ước lượng là tăng từ 0.00083 lên 0.00137. Những kết quả này có thể là bằng chứng để kết luận rằng việc tăng nhiệt độ nung rõ ràng cải thiện tính siêu dẫn trong hệ thống BPSCCO.