2019 Vol. 36, No. 2
Special Issue on Nuclear Science and Technology for the 110th Anniversary of Lanzhou Univ
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2019, 36(2): .
Abstract:
2019, 36(2): 125-134.
doi: 10.11804/NuclPhysRev.36.02.125
Abstract:
The nature of strange axial-vector mesons are not well understood and can be investigated in D meson decays. In this work, it is found that the experimental data of D0 → K±K1∓(1270)(→ ρK or K*π) in the D0 → K+K-π+π- mode, disagree with the equality relation under the narrow width approximation and CP conservation of strong decays. Considering more other results of K1(1270) decays, the data of B(D0 → K-K1+(1270)(→ K*0π+)) is probably overestimated by one order of magnitude. We then calculate the branching fractions of the corresponding processes with K1(1400) in the factorization approach, and find B(D0 → K-K1+(1400)(→ K*0π+)) is comparable to the predicted B(D0 → K-K1+(1270)(→ K*0π+)) using the equality relation. Besides, we suggest to measure the ratios between K1(1270) → ρK and K*π or to test the equality relations in other D meson decay modes.
The nature of strange axial-vector mesons are not well understood and can be investigated in D meson decays. In this work, it is found that the experimental data of D0 → K±K1∓(1270)(→ ρK or K*π) in the D0 → K+K-π+π- mode, disagree with the equality relation under the narrow width approximation and CP conservation of strong decays. Considering more other results of K1(1270) decays, the data of B(D0 → K-K1+(1270)(→ K*0π+)) is probably overestimated by one order of magnitude. We then calculate the branching fractions of the corresponding processes with K1(1400) in the factorization approach, and find B(D0 → K-K1+(1400)(→ K*0π+)) is comparable to the predicted B(D0 → K-K1+(1270)(→ K*0π+)) using the equality relation. Besides, we suggest to measure the ratios between K1(1270) → ρK and K*π or to test the equality relations in other D meson decay modes.
2019, 36(2): 135-143.
doi: 10.11804/NuclPhysRev.36.02.135
Abstract:
The proton dripline nucleus 8B, with a proton separation energy of 0.137 5 MeV, is an archetypal proton halo candidate. The structure and mechanisms of reactions induced by this nucleus have received much attention from the experimental points of view. We review on the previous studies with measurements of reaction cross sections, longitudinal momentum distributions of fragments, electric quadruple moment, fusion cross sections, and elastic scattering angular distributions. More efforts, from both experimental and theoretical points of view, are needed to understand the nucleus 8B.
The proton dripline nucleus 8B, with a proton separation energy of 0.137 5 MeV, is an archetypal proton halo candidate. The structure and mechanisms of reactions induced by this nucleus have received much attention from the experimental points of view. We review on the previous studies with measurements of reaction cross sections, longitudinal momentum distributions of fragments, electric quadruple moment, fusion cross sections, and elastic scattering angular distributions. More efforts, from both experimental and theoretical points of view, are needed to understand the nucleus 8B.
2019, 36(2): 144-150.
doi: 10.11804/NuclPhysRev.36.02.144
Abstract:
The beyond-mean-field model is applied to study the octupole deformation and shape transition in 114-124Ba. Potential energy surfaces (PES), low-energy excitation spectra, electric transition rates, and probability density distributions in Ba isotopes are systematically analyzed using a quadrupole-octupole collective Hamiltonian (QOCH) model based on covariant density functional theory. The microscopic QOCH model is shown to accurately describe the empirical trend of low-energy positive-and negative-parity states. The theoretical results of PES, low-lying negative-parity bands, rather large B(E3;31- → 01+), and extended probability density distributions show evidence of strong octupole correlations in 114Ba. 116,118Ba present as transitional nuclei, while 120-124Ba are well quadrupole deformed nuclei.
The beyond-mean-field model is applied to study the octupole deformation and shape transition in 114-124Ba. Potential energy surfaces (PES), low-energy excitation spectra, electric transition rates, and probability density distributions in Ba isotopes are systematically analyzed using a quadrupole-octupole collective Hamiltonian (QOCH) model based on covariant density functional theory. The microscopic QOCH model is shown to accurately describe the empirical trend of low-energy positive-and negative-parity states. The theoretical results of PES, low-lying negative-parity bands, rather large B(E3;31- → 01+), and extended probability density distributions show evidence of strong octupole correlations in 114Ba. 116,118Ba present as transitional nuclei, while 120-124Ba are well quadrupole deformed nuclei.
2019, 36(2): 151-160.
doi: 10.11804/NuclPhysRev.36.02.151
Abstract:
The polarized helium-3 target offers a great opportunity of expanding the nuclear physics experiment to observe the impacts of the spin dimension in the initial state on the nuclear reaction. In this work by illustrating the possible applications of the target in the polarized three-body force experiment and in the polarized heavy ion charge exchange reaction, the unique advantage of the polarized helium-3 target was described. In the proton scattering experiment, by measuring the distribution of various products in the final state with various polarization direction, it is possible to further verify the 3-body-force part of the chiral effective theory. In the charge exchange reaction with the heavy ion beam, by control the polarization direction it is possible to distinguish the pion-exchange and rho-meson-exchange terms in the nucleon spin-isospin excitation. Thus it offers a unique opportunity to study the dynamic evolution of nucleon in different nuclear environments. Under the background of constructing the new generation large science facilities in China, specifically the ADS, HIAF, and CNS as the great representations of advanced platform for nuclear physics study, new technology will exploit both the width and depth of reaches on them. Thus the polarized helium-3 target as a unique research method owns a bright perspective.
The polarized helium-3 target offers a great opportunity of expanding the nuclear physics experiment to observe the impacts of the spin dimension in the initial state on the nuclear reaction. In this work by illustrating the possible applications of the target in the polarized three-body force experiment and in the polarized heavy ion charge exchange reaction, the unique advantage of the polarized helium-3 target was described. In the proton scattering experiment, by measuring the distribution of various products in the final state with various polarization direction, it is possible to further verify the 3-body-force part of the chiral effective theory. In the charge exchange reaction with the heavy ion beam, by control the polarization direction it is possible to distinguish the pion-exchange and rho-meson-exchange terms in the nucleon spin-isospin excitation. Thus it offers a unique opportunity to study the dynamic evolution of nucleon in different nuclear environments. Under the background of constructing the new generation large science facilities in China, specifically the ADS, HIAF, and CNS as the great representations of advanced platform for nuclear physics study, new technology will exploit both the width and depth of reaches on them. Thus the polarized helium-3 target as a unique research method owns a bright perspective.
2019, 36(2): 161-169.
doi: 10.11804/NuclPhysRev.36.02.161
Abstract:
The nuclear properties (spin, mass, life-time, magnetic moment, electric quadrupole moment and charge radius) of the ground and long-lived states of unstable nuclei can be used to explore the exotic nuclear structure phenomenon, and also will be a prominent input for the nuclear theory methods and nuclear interactions. Experimentally, we can nuclear-model independently determine the nuclear spins, magnetic moments, electric quadrupole moments and mean square charge radii simultaneously from hyperfine structure and isotope shift, measured with the interdisciplinary laser spectroscopy techniques. In recent years, with the continuous efforts, various laser spectroscopy techniques with high resolution and high efficiency have been developed in order to study the short-lived isotopes produced at the radioactive ion beam facilities with very low production yield. Here, we will introduce the basic principle of laser spectroscopy measurement and discuss in detail the various complementary laser spectroscopy techniques developed for the nuclear structure study of unstable isotopes. The advantages and disadvantages of these techniques, such as collinear laser spectroscopy (high resolution, low sensitivity), in-source laser spectroscopy (high sensitivity, low resolution), as well as collinear resonant ionization (high resolution, high sensitivity), are discussed regarding to the resolution and sensitivity, which is highly related to the application of the technique in different mass region of nuclear chart. In addition, future plan and prospect on the development of the precision laser spectroscopy techniques will be discussed, which, with the hope, will be used for nuclear physics study at the next-generation facilities constructed and planed in China.
The nuclear properties (spin, mass, life-time, magnetic moment, electric quadrupole moment and charge radius) of the ground and long-lived states of unstable nuclei can be used to explore the exotic nuclear structure phenomenon, and also will be a prominent input for the nuclear theory methods and nuclear interactions. Experimentally, we can nuclear-model independently determine the nuclear spins, magnetic moments, electric quadrupole moments and mean square charge radii simultaneously from hyperfine structure and isotope shift, measured with the interdisciplinary laser spectroscopy techniques. In recent years, with the continuous efforts, various laser spectroscopy techniques with high resolution and high efficiency have been developed in order to study the short-lived isotopes produced at the radioactive ion beam facilities with very low production yield. Here, we will introduce the basic principle of laser spectroscopy measurement and discuss in detail the various complementary laser spectroscopy techniques developed for the nuclear structure study of unstable isotopes. The advantages and disadvantages of these techniques, such as collinear laser spectroscopy (high resolution, low sensitivity), in-source laser spectroscopy (high sensitivity, low resolution), as well as collinear resonant ionization (high resolution, high sensitivity), are discussed regarding to the resolution and sensitivity, which is highly related to the application of the technique in different mass region of nuclear chart. In addition, future plan and prospect on the development of the precision laser spectroscopy techniques will be discussed, which, with the hope, will be used for nuclear physics study at the next-generation facilities constructed and planed in China.
2019, 36(2): 170-183.
doi: 10.11804/NuclPhysRev.36.02.170
Abstract:
Currently the 99mTc is most widely used medical radioisotope as a tracer in clinical diagnosis. The supply of the 99mTc mainly depends on the production of the 99Mo in the research reactors by irradiating High Enriched Uranium targets. The traditional production technique has disadvantages of complex process, high cost, long-distance transportation loss and the risk of nuclear weapons proliferation, etc. In addition, the number of research reactors and processing facilities are limited and most of the facilities will be decommissioned soon. Sometime the supply of 99Mo/99mTc has a problem due to unexpected reactor shutdown or planned maintenance. So, during recent years, a variety of new production techniques, such as the methods using facilities of linear/cyclotron accelerators and new types of reactors, have been proposed to restore the stable supply of 99Mo/99mTc. Starting from the current supply and demand situation of 99Mo/99mTc, this paper analyses the main problems existing in the current supply chain, and mainly introduces the principle, research progress and economic benefits of six traditional and new production technologies of 99Mo/99mTc. Following three separation and purification processes of 99Mo/99mTc, the development trend and prospect of 99Mo/99mTc production were discussed. Among them, the technology of accelerator-driven fission low-enriched-uranium solution is the key research direction in the future for no reactor, no high-enriched uranium, less radioactive waste. It is also imperative to develop and optimize the separation and purification process suitable for the production system in order to reduce the loss of 99Mo/99mTc and improve product quality. The theoretical output of the99Mo sub-critical production system driven by the deuterium-tritium fusion neutron source, designed by the Institute of Nuclear Safety Technology of the Chinese Academy of Sciences, is 27 Ci/day, which can meet the medical diagnostic needs of a province in China.
Currently the 99mTc is most widely used medical radioisotope as a tracer in clinical diagnosis. The supply of the 99mTc mainly depends on the production of the 99Mo in the research reactors by irradiating High Enriched Uranium targets. The traditional production technique has disadvantages of complex process, high cost, long-distance transportation loss and the risk of nuclear weapons proliferation, etc. In addition, the number of research reactors and processing facilities are limited and most of the facilities will be decommissioned soon. Sometime the supply of 99Mo/99mTc has a problem due to unexpected reactor shutdown or planned maintenance. So, during recent years, a variety of new production techniques, such as the methods using facilities of linear/cyclotron accelerators and new types of reactors, have been proposed to restore the stable supply of 99Mo/99mTc. Starting from the current supply and demand situation of 99Mo/99mTc, this paper analyses the main problems existing in the current supply chain, and mainly introduces the principle, research progress and economic benefits of six traditional and new production technologies of 99Mo/99mTc. Following three separation and purification processes of 99Mo/99mTc, the development trend and prospect of 99Mo/99mTc production were discussed. Among them, the technology of accelerator-driven fission low-enriched-uranium solution is the key research direction in the future for no reactor, no high-enriched uranium, less radioactive waste. It is also imperative to develop and optimize the separation and purification process suitable for the production system in order to reduce the loss of 99Mo/99mTc and improve product quality. The theoretical output of the99Mo sub-critical production system driven by the deuterium-tritium fusion neutron source, designed by the Institute of Nuclear Safety Technology of the Chinese Academy of Sciences, is 27 Ci/day, which can meet the medical diagnostic needs of a province in China.
2019, 36(2): 184-189.
doi: 10.11804/NuclPhysRev.36.02.184
Abstract:
Direct charge radioisotope battery having the advantages of long service lifetime, simple structure, high open circuit voltage and easily miniaturized, is a promising source for the great power of Micro-ElectroMechanical System. Although the beta sources are the main choice for direct charge nuclear battery in the present studies,but no systematic analysis and comparison on beta sources is presented. In this work, the properties of six beta sources (including 3H(Ti3H2), 14C, 35S, 45Ca, 63Ni and 147Pm) were studied by software simulation and theoretical calculation. This study includes the differences of energy conversion efficiency and the theoretical output power for direct charge nuclear battery. The calculated results showed that the energy conversion efficiency was positively correlated with the average energy of emitted radioactive particles, and the theoretical output power was negatively correlated with half-life of beta source. 147Pm was the preferred choice considering long life, the energy conversion efficiency and the theoretical output power.
Direct charge radioisotope battery having the advantages of long service lifetime, simple structure, high open circuit voltage and easily miniaturized, is a promising source for the great power of Micro-ElectroMechanical System. Although the beta sources are the main choice for direct charge nuclear battery in the present studies,but no systematic analysis and comparison on beta sources is presented. In this work, the properties of six beta sources (including 3H(Ti3H2), 14C, 35S, 45Ca, 63Ni and 147Pm) were studied by software simulation and theoretical calculation. This study includes the differences of energy conversion efficiency and the theoretical output power for direct charge nuclear battery. The calculated results showed that the energy conversion efficiency was positively correlated with the average energy of emitted radioactive particles, and the theoretical output power was negatively correlated with half-life of beta source. 147Pm was the preferred choice considering long life, the energy conversion efficiency and the theoretical output power.
2019, 36(2): 190-196.
doi: 10.11804/NuclPhysRev.36.02.190
Abstract:
The construction of Chinese Spallation Neutron Source (CSNS) laid the foundation for the development and application of neutron scattering technology General Purpose Powder Diffractometer (GPPD), which is one of the three spectrometers of CSNS in the first phase. The large area scintillator detector array for GPPD was developed and the key performance parameters of the detector has been tested on the BL20 of CSNS. The test results showed that the detection efficiency for 1.4 Å and 2.8 Å neutrons is (38.5±1.7)% and (56.1±1.1)% respectively. In accordance with simulation results, the detection efficiency is about (46.1±2.0)% for 2.0 Å neutrons. The position resolution of the detector is 4.0 mm×4.0 mm, the maximun counting rate is about 79 kHz and the count nonuniformity is about 19.6% and reduced to 14.9% after optimization. The performance of the detector unit can fulfill the physical requirements of GPPD.
The construction of Chinese Spallation Neutron Source (CSNS) laid the foundation for the development and application of neutron scattering technology General Purpose Powder Diffractometer (GPPD), which is one of the three spectrometers of CSNS in the first phase. The large area scintillator detector array for GPPD was developed and the key performance parameters of the detector has been tested on the BL20 of CSNS. The test results showed that the detection efficiency for 1.4 Å and 2.8 Å neutrons is (38.5±1.7)% and (56.1±1.1)% respectively. In accordance with simulation results, the detection efficiency is about (46.1±2.0)% for 2.0 Å neutrons. The position resolution of the detector is 4.0 mm×4.0 mm, the maximun counting rate is about 79 kHz and the count nonuniformity is about 19.6% and reduced to 14.9% after optimization. The performance of the detector unit can fulfill the physical requirements of GPPD.
2019, 36(2): 197-203.
doi: 10.11804/NuclPhysRev.36.02.197
Abstract:
The fission time projection chamber based on GEM technology has the advantages of GEM technology such as high counting rate and high spatial resolution. Therefore, we plan to obtain nuclear charge number, mass number and energy of fission products in a single measurement through fission time projection chamber. This paper mainly discusses the types of working gas, pressure, energy loss and effective charge of fission fragments in the fission time projection chamber based on GEM process. It is found that for the energy loss of light and heavy fission fragments, the distribution width of heavy fission fragments is narrower than that of the light fission fragments. Based on the energy loss of fission fragments in gas chamber, a method to obtain nuclear charge from the effective charge of fission fragments is proposed, which is very important for the development of fission time projection chamber and the multi-parameter measurement of fission products.
The fission time projection chamber based on GEM technology has the advantages of GEM technology such as high counting rate and high spatial resolution. Therefore, we plan to obtain nuclear charge number, mass number and energy of fission products in a single measurement through fission time projection chamber. This paper mainly discusses the types of working gas, pressure, energy loss and effective charge of fission fragments in the fission time projection chamber based on GEM process. It is found that for the energy loss of light and heavy fission fragments, the distribution width of heavy fission fragments is narrower than that of the light fission fragments. Based on the energy loss of fission fragments in gas chamber, a method to obtain nuclear charge from the effective charge of fission fragments is proposed, which is very important for the development of fission time projection chamber and the multi-parameter measurement of fission products.
2019, 36(2): 204-210.
doi: 10.11804/NuclPhysRev.36.02.204
Abstract:
The detector of SANS is one of the key instruments for Small Angle Neutron Scattering (SANS) Spectrometer. It needs large areas of detection, high efficiencies of detection and high spatial resolutions. It is also required to be able to work stably and move forward and backward in a vacuum tube. Two-dimensional detector array of an effective area of 1 000 mm (X)×1 020 mm (Y) is constructed using 120 position-sensitive 3He tubes of 8 mm in diameter. The SANS detector array is divided into 10 modules, each of which is completely independent and includes 12 3He tubes and corresponding readout electronics and data acquisition systems. The readout electronics located in the back of the detector is developed by CSNS independently. It takes 3 years in total since the detector of SANS was designed, selected, tested and installed. The experimental result of neutron beams shows that the detection efficiency of the detector is more than 50% (@2 Å) and the spatial resolution of the detector is below 10 mm (FWHM). The performances fully meets the requirements of designs. The detector is working at the SANS of CSNS now.
The detector of SANS is one of the key instruments for Small Angle Neutron Scattering (SANS) Spectrometer. It needs large areas of detection, high efficiencies of detection and high spatial resolutions. It is also required to be able to work stably and move forward and backward in a vacuum tube. Two-dimensional detector array of an effective area of 1 000 mm (X)×1 020 mm (Y) is constructed using 120 position-sensitive 3He tubes of 8 mm in diameter. The SANS detector array is divided into 10 modules, each of which is completely independent and includes 12 3He tubes and corresponding readout electronics and data acquisition systems. The readout electronics located in the back of the detector is developed by CSNS independently. It takes 3 years in total since the detector of SANS was designed, selected, tested and installed. The experimental result of neutron beams shows that the detection efficiency of the detector is more than 50% (@2 Å) and the spatial resolution of the detector is below 10 mm (FWHM). The performances fully meets the requirements of designs. The detector is working at the SANS of CSNS now.
2019, 36(2): 211-217.
doi: 10.11804/NuclPhysRev.36.02.211
Abstract:
The imaging quality of the CT system is influenced by many factors. It is necessary to study the influence caused by each factor in order to get a better imaging result. Based on a cone-beam CT system developed by our group, and under the near detector condition, using a standard workpiece of aluminum to study the influences on the imaging quality of CT system, produced by the factors of projection acquisition range and step, tube voltage and current, focal spot size, object position on turntable, beam-hardening correction and image optimizing. The results show that the influence of projection acquisition range on imaging quality is very small, and the smaller acquisition step can improve imaging quality; appropriately increasing the tube voltage can reduce the beam-hardening artifacts and enlarging the tube current can reduce image noise; the smaller focal spot size can enhance the spatial resolution of the image, but was not obvious under the near detector geometry; sample position on turntable does not affect the reconstruction result; hardening correction can greatly eliminate beam-hardening artifacts. Finally, image optimizing can improve image quality effectively. This work provides a reference for the development and application of the CT system.
The imaging quality of the CT system is influenced by many factors. It is necessary to study the influence caused by each factor in order to get a better imaging result. Based on a cone-beam CT system developed by our group, and under the near detector condition, using a standard workpiece of aluminum to study the influences on the imaging quality of CT system, produced by the factors of projection acquisition range and step, tube voltage and current, focal spot size, object position on turntable, beam-hardening correction and image optimizing. The results show that the influence of projection acquisition range on imaging quality is very small, and the smaller acquisition step can improve imaging quality; appropriately increasing the tube voltage can reduce the beam-hardening artifacts and enlarging the tube current can reduce image noise; the smaller focal spot size can enhance the spatial resolution of the image, but was not obvious under the near detector geometry; sample position on turntable does not affect the reconstruction result; hardening correction can greatly eliminate beam-hardening artifacts. Finally, image optimizing can improve image quality effectively. This work provides a reference for the development and application of the CT system.
2019, 36(2): 218-223.
doi: 10.11804/NuclPhysRev.36.02.218
Abstract:
Developed a set of two-dimensional position sensitive detector based on micro-channel plate (MCP) and conducted a series of X-ray imaging tests. Image of Vernier-caliper proves our equipment has an edge resolution of about 500 μm. Imaging tests were carried out on the composite samples. When the X-ray machine's target flow was 1 mA, the clear imaging could be realized within 1 ms. Image rebuilding has also been adapted afterwards, median filtering combined with sharpen, blind deconvolution and Wiener filtering have been used respectively to reconstruct the original image of Vernier caliper. All of the three methods have a positive effect on image's quality but wiener filtering becomes the optimal method among those three which improves the edge resolution by 7%.
Developed a set of two-dimensional position sensitive detector based on micro-channel plate (MCP) and conducted a series of X-ray imaging tests. Image of Vernier-caliper proves our equipment has an edge resolution of about 500 μm. Imaging tests were carried out on the composite samples. When the X-ray machine's target flow was 1 mA, the clear imaging could be realized within 1 ms. Image rebuilding has also been adapted afterwards, median filtering combined with sharpen, blind deconvolution and Wiener filtering have been used respectively to reconstruct the original image of Vernier caliper. All of the three methods have a positive effect on image's quality but wiener filtering becomes the optimal method among those three which improves the edge resolution by 7%.
2019, 36(2): 224-229.
doi: 10.11804/NuclPhysRev.36.02.224
Abstract:
The apatite structure material Ca8LnNa(PO4)6F2(Ln=La, Nd and Sm) were successfully synthesized by the solid state reaction method, and the single phase was confirmed by normal X-ray diffraction(XRD). Three kinds of samples were irradiated with 800 keV Kr2+ at room temperature, then the irradiated samples were characterized by grazing incidence X-ray diffraction(GIXRD) to identify the structures of irradiation layer. Crystalline to amorphization phase transition was observed in these three kinds of samples within the irradiation dose (1.0×1014~7.0×1014 cm-2). However, the abilities to resist amorphization of the three samples are different, the relationship of the ability to resist amorphization is Ca8LaNa(PO4)6F2 > Ca8NdNa(PO4)6F2 > Ca8SmNa(PO4)6F2. The ion radius of the lanthanide nuclides in Ca8LnNa(PO4)6F2 are more smaller, more lanthanide nuclides will occupy the Ca(2) positions and form ionic bonds with F. Meanwhile, the ionic bonding between lanthanide nuclides and Ca are weaker than Ca-F. Therefore, the ion radius of the lanthanide nuclides are more smaller, the more point defects will remain under irradiation, and the crystalline to amorphous phase transition is more likely to occur.
The apatite structure material Ca8LnNa(PO4)6F2(Ln=La, Nd and Sm) were successfully synthesized by the solid state reaction method, and the single phase was confirmed by normal X-ray diffraction(XRD). Three kinds of samples were irradiated with 800 keV Kr2+ at room temperature, then the irradiated samples were characterized by grazing incidence X-ray diffraction(GIXRD) to identify the structures of irradiation layer. Crystalline to amorphization phase transition was observed in these three kinds of samples within the irradiation dose (1.0×1014~7.0×1014 cm-2). However, the abilities to resist amorphization of the three samples are different, the relationship of the ability to resist amorphization is Ca8LaNa(PO4)6F2 > Ca8NdNa(PO4)6F2 > Ca8SmNa(PO4)6F2. The ion radius of the lanthanide nuclides in Ca8LnNa(PO4)6F2 are more smaller, more lanthanide nuclides will occupy the Ca(2) positions and form ionic bonds with F. Meanwhile, the ionic bonding between lanthanide nuclides and Ca are weaker than Ca-F. Therefore, the ion radius of the lanthanide nuclides are more smaller, the more point defects will remain under irradiation, and the crystalline to amorphous phase transition is more likely to occur.
2019, 36(2): 230-234.
doi: 10.11804/NuclPhysRev.36.02.230
Abstract:
Titanate are one of the important candidates for solidifying high-level radioactive nuclear waste (HLW) and lanthanide (Plutonium) due to its excellent physical and chemical durability. Polycrystalline Lu2Ti2O7 and Lu2TiO5 ceramic materials were prepared by a conventional ceramic sintering process, then the samples were irradiated with 800 keV Kr2+ at room temperature, and were subsequently characterized by GIXRD method. In the two kinds of samples, lattice swelling was observed firstly, and then amorphization phase transition took place. However, the lattice swelling of Lu2Ti2O7 is greater than that of Lu2TiO5. In addition, when Lu2Ti2O7 and Lu2TiO5 were irradiated to a fluence of 2×1014 ions/cm2, the amorphous content of Lu2TiO5 sample reaches 95.54%, while the amorphous content of Lu2Ti2O7 sample is only 74.66%. The first-principle was used to calculate the lattice swelling of Lu2Ti2O7 with increasing of anti-sites concentration. The results show that the lattice swelling of Lu2Ti2O7 before amorphization is mainly caused by the cation anti-sites. While the pristine Lu2TiO5 is a disordered fluorite structure, so that no cation anti-sites will contribute to the lattice swelling of Lu2TiO during the ion irradiation process. Therefore, the lattice swelling of Lu2TiO5 is lower compared to that of Lu2Ti2O7.
Titanate are one of the important candidates for solidifying high-level radioactive nuclear waste (HLW) and lanthanide (Plutonium) due to its excellent physical and chemical durability. Polycrystalline Lu2Ti2O7 and Lu2TiO5 ceramic materials were prepared by a conventional ceramic sintering process, then the samples were irradiated with 800 keV Kr2+ at room temperature, and were subsequently characterized by GIXRD method. In the two kinds of samples, lattice swelling was observed firstly, and then amorphization phase transition took place. However, the lattice swelling of Lu2Ti2O7 is greater than that of Lu2TiO5. In addition, when Lu2Ti2O7 and Lu2TiO5 were irradiated to a fluence of 2×1014 ions/cm2, the amorphous content of Lu2TiO5 sample reaches 95.54%, while the amorphous content of Lu2Ti2O7 sample is only 74.66%. The first-principle was used to calculate the lattice swelling of Lu2Ti2O7 with increasing of anti-sites concentration. The results show that the lattice swelling of Lu2Ti2O7 before amorphization is mainly caused by the cation anti-sites. While the pristine Lu2TiO5 is a disordered fluorite structure, so that no cation anti-sites will contribute to the lattice swelling of Lu2TiO during the ion irradiation process. Therefore, the lattice swelling of Lu2TiO5 is lower compared to that of Lu2Ti2O7.
2019, 36(2): 235-241.
doi: 10.11804/NuclPhysRev.36.02.235
Abstract:
The formation of Cu film on Fe (001) surface by depositing Cu13 clusters was investigated via the molecular dynamics simulation. The incident energy range of Cu13 clusters was from 0.1 to 10.0 eV/atom, and the deposition rate was 1 clusters/ps. The temperature of substrate was 300, 700 and 1 000 K, respectively. The effects of incident energy of cluster and substrate temperature on the growth mode, surface roughness, defects distribution and epitaxy degree of film were studied. The simulation results show that the incident energy of Cu13 clusters plays a dominant role in the growth mode of film. In addition, when the incident energy of Cu13 clusters is 7.5 eV/atom and the substrate temperature is 300 K, the Cu film formed on Fe(001) surface is smoother, few defects and better epitaxy degree.
The formation of Cu film on Fe (001) surface by depositing Cu13 clusters was investigated via the molecular dynamics simulation. The incident energy range of Cu13 clusters was from 0.1 to 10.0 eV/atom, and the deposition rate was 1 clusters/ps. The temperature of substrate was 300, 700 and 1 000 K, respectively. The effects of incident energy of cluster and substrate temperature on the growth mode, surface roughness, defects distribution and epitaxy degree of film were studied. The simulation results show that the incident energy of Cu13 clusters plays a dominant role in the growth mode of film. In addition, when the incident energy of Cu13 clusters is 7.5 eV/atom and the substrate temperature is 300 K, the Cu film formed on Fe(001) surface is smoother, few defects and better epitaxy degree.
2019, 36(2): 242-247.
doi: 10.11804/NuclPhysRev.36.02.242
Abstract:
Single event effect (SEE) is an important reason that induces failures in space electronic components. Explanations of physical process are important to life evaluation of electronic devices and radiation hardening. Many models, in which cross section of SEE was related to the linear energy transfer (LET), were presented. However, according those models, temperature effects could not be explained. A new model, which is based on interactions of high-energy ion with material, is proposed. This model is employed to calculate the energy deposition, exchange and diffusion in material. The temperatures electron and lattice are obtained from thermal diffusion equations. Evolutions of electron and lattice with space and time are presented. The model suggested the concentration of free electrons and total collected charge induced by irradiation of ions were function of LET. The model explained an experimental effect that the cross sections of SEE increased with the temperature of device.
Single event effect (SEE) is an important reason that induces failures in space electronic components. Explanations of physical process are important to life evaluation of electronic devices and radiation hardening. Many models, in which cross section of SEE was related to the linear energy transfer (LET), were presented. However, according those models, temperature effects could not be explained. A new model, which is based on interactions of high-energy ion with material, is proposed. This model is employed to calculate the energy deposition, exchange and diffusion in material. The temperatures electron and lattice are obtained from thermal diffusion equations. Evolutions of electron and lattice with space and time are presented. The model suggested the concentration of free electrons and total collected charge induced by irradiation of ions were function of LET. The model explained an experimental effect that the cross sections of SEE increased with the temperature of device.
2019, 36(2): 248-255.
doi: 10.11804/NuclPhysRev.36.02.248
Abstract:
In this work, we studied the structural, mechanical, and thermal properties of RE2Ti2O7 (RE=Gd, Y, Ho, Er) pyrochlores by the first-principles calculations combining with the quasi-harmonic approximation. Our study reveals that RE2Ti2O7 possess excellent resistance to compression and shear at the ground state. Moreover, these compounds can be approximate to elastically isotropic materials because their Zener ratios are close to 1. The obtained thermal expansion coefficient agrees well with the experimental results at high temperature. The mean thermal expansion coefficient of the RE2Ti2O7 compound is about (10.4~13.1)×10-6 K-1 in the temperature range of 500~1 500 K. We also employed Slack's model to estimate thermal conductivity, and the results located in the range of 1.5~4.9 W·m-1·K-1 at 1 000 K.
In this work, we studied the structural, mechanical, and thermal properties of RE2Ti2O7 (RE=Gd, Y, Ho, Er) pyrochlores by the first-principles calculations combining with the quasi-harmonic approximation. Our study reveals that RE2Ti2O7 possess excellent resistance to compression and shear at the ground state. Moreover, these compounds can be approximate to elastically isotropic materials because their Zener ratios are close to 1. The obtained thermal expansion coefficient agrees well with the experimental results at high temperature. The mean thermal expansion coefficient of the RE2Ti2O7 compound is about (10.4~13.1)×10-6 K-1 in the temperature range of 500~1 500 K. We also employed Slack's model to estimate thermal conductivity, and the results located in the range of 1.5~4.9 W·m-1·K-1 at 1 000 K.
2019, 36(2): 256-260.
doi: 10.11804/NuclPhysRev.36.02.256
Abstract:
In this paper, the molecular dynamics method was used to study the binding energy of a helium atom with the helium-vacancy cluster (HenV22) in tungsten. As a result, when the heliumvacancy ratio was less than 4.5 the binding energy decreased with the helium-vacancy ratio linearly. When the heliumvacancy ratio was larger than 4.5 the binding energy appeared vibrating extremely. After analyzing kinetic processes, it was found that the phenomenon was due to the helium-vacancy cluster extruding dislocation loop form the tungsten body randomly which leading to the energy of the system droping sharply. At the same time, the helium-vacancy cluster was surrounded by some metastable fcc-tungsten and hcptungsten. Trying to explain the phenomenon, we employed the firstprinciples calculation to study the phase transformation of tungsten under high-pressure. We found that the phase transformation can not occur under hydrostatic pressure. Moreover after analyzing the charge density difference, we found that the stability of the tetrahedral interstitial helium atom was higher than that of the octahedral interstitial helium atom in bcc-tungsten, whereas the stability of the tetrahedral interstitial helium atom was weaker than the stability of the octahedral interstitial helium atom in the fcc-tungsten
In this paper, the molecular dynamics method was used to study the binding energy of a helium atom with the helium-vacancy cluster (HenV22) in tungsten. As a result, when the heliumvacancy ratio was less than 4.5 the binding energy decreased with the helium-vacancy ratio linearly. When the heliumvacancy ratio was larger than 4.5 the binding energy appeared vibrating extremely. After analyzing kinetic processes, it was found that the phenomenon was due to the helium-vacancy cluster extruding dislocation loop form the tungsten body randomly which leading to the energy of the system droping sharply. At the same time, the helium-vacancy cluster was surrounded by some metastable fcc-tungsten and hcptungsten. Trying to explain the phenomenon, we employed the firstprinciples calculation to study the phase transformation of tungsten under high-pressure. We found that the phase transformation can not occur under hydrostatic pressure. Moreover after analyzing the charge density difference, we found that the stability of the tetrahedral interstitial helium atom was higher than that of the octahedral interstitial helium atom in bcc-tungsten, whereas the stability of the tetrahedral interstitial helium atom was weaker than the stability of the octahedral interstitial helium atom in the fcc-tungsten
2019, 36(2): 261-265.
doi: 10.11804/NuclPhysRev.36.02.261
Abstract:
The effect of uniaxial stress field along <100> and <111> crystal direction on the diffusion of a single helium atom in bcc tungsten was studied by molecular dynamics simulation. Our calculation shows that the stress strain caused the phase transition of tungsten metal and the initio phase transition strain decreases with the increase of temperature. The initial strain of phase transition is near the strain where stress reaches the maximum value. The diffusion coefficient of a single helium atom in tungsten metal decreases with the increase of strain. The helium diffusion coefficient decreases linearly along the <100> crystal direction, while the <111> crystal direction shows a fluctuating trend. Fitting the Arrhenius equation, the results show that when the crystal strain along <100> reaches +1.5% and the Arrhenius equation is no longer applicable; however, the Arrhenius equation still applies when the crystal strain along <111> increases by +5%. The helium diffusion activation energy along the crystal direction <111> was obtained, the results showed that the helium diffusion activation energy decreases with the increase of strain, indicating that the strain enhanceds the mobility of a single helium atom in tungsten.
The effect of uniaxial stress field along <100> and <111> crystal direction on the diffusion of a single helium atom in bcc tungsten was studied by molecular dynamics simulation. Our calculation shows that the stress strain caused the phase transition of tungsten metal and the initio phase transition strain decreases with the increase of temperature. The initial strain of phase transition is near the strain where stress reaches the maximum value. The diffusion coefficient of a single helium atom in tungsten metal decreases with the increase of strain. The helium diffusion coefficient decreases linearly along the <100> crystal direction, while the <111> crystal direction shows a fluctuating trend. Fitting the Arrhenius equation, the results show that when the crystal strain along <100> reaches +1.5% and the Arrhenius equation is no longer applicable; however, the Arrhenius equation still applies when the crystal strain along <111> increases by +5%. The helium diffusion activation energy along the crystal direction <111> was obtained, the results showed that the helium diffusion activation energy decreases with the increase of strain, indicating that the strain enhanceds the mobility of a single helium atom in tungsten.
2019, 36(2): 266-271.
doi: 10.11804/NuclPhysRev.36.02.266
Abstract:
Neutron multiplicity technique is commonly used to measure and verify nuclear materials, especially for objects with heavy shields. Plutonium material has high spontaneous fission rate and passive measurement is available. Currently, there are many different measurement devices. However, uranium material measurement can only be performed by active method due to its low spontaneous fission rate. The existing active well type coincidence counter (AWCC) is capable of performing active neutron multiplicity measurement of uranium. But the detection efficiency is low and there are lots of accidental coincidence counts caused by the Am-Li neutron source. In order to improve the efficiency and the accuracy it is necessary to carry out comprehensive investigation on active neutron multiplicity measurement method. A neutron multiplicity measurement system was modeled based on Geant4 referring to the AWCC structure. The effects of different gate width and delay time on the measurement deviation were studied. The optimal gate width of the counter is 44 μs and the range of the gate width is suitable for about 1.5 times of the counter die-away time; after the delay time is greater than 3 times the counter die-away time, the relative deviation is significantly reduced. The influence of 235U enrichment on the result was also discussed. This work provides a reference for the design of the active neutron multiplicity counter.
Neutron multiplicity technique is commonly used to measure and verify nuclear materials, especially for objects with heavy shields. Plutonium material has high spontaneous fission rate and passive measurement is available. Currently, there are many different measurement devices. However, uranium material measurement can only be performed by active method due to its low spontaneous fission rate. The existing active well type coincidence counter (AWCC) is capable of performing active neutron multiplicity measurement of uranium. But the detection efficiency is low and there are lots of accidental coincidence counts caused by the Am-Li neutron source. In order to improve the efficiency and the accuracy it is necessary to carry out comprehensive investigation on active neutron multiplicity measurement method. A neutron multiplicity measurement system was modeled based on Geant4 referring to the AWCC structure. The effects of different gate width and delay time on the measurement deviation were studied. The optimal gate width of the counter is 44 μs and the range of the gate width is suitable for about 1.5 times of the counter die-away time; after the delay time is greater than 3 times the counter die-away time, the relative deviation is significantly reduced. The influence of 235U enrichment on the result was also discussed. This work provides a reference for the design of the active neutron multiplicity counter.
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