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[en] This thesis describes an experiment in which about four thousand radioactive 21Na (tl/2 = 22 sec) atoms were trapped in a magneto-optical trap with laser beams. Trapped 21Na atoms can be used as a beta source in a precision measurement of the beta-asymmetry parameter of the decay of 21Na → 21Ne + Β+ + ve, which is a promising way to search for an anomalous right-handed current coupling in charged weak interactions. Although the number o trapped atoms that we have achieved is still about two orders of magnitude lower than what is needed to conduct a measurement of the beta-asymmetry parameter at 1% of precision level, the result of this experiment proved the feasibility of trapping short-lived radioactive atoms. In this experiment, 21Na atoms were produced by bombarding 24Mg with protons of 25 MeV at the 88 in. Cyclotron of Lawrence Berkeley Laboratory. A few recently developed techniques of laser manipulation of neutral atoms were applied in this experiment. The 21Na atoms emerging from a heated oven were first transversely cooled. As a result, the on-axis atomic beam intensity was increased by a factor of 16. The atoms in the beam were then slowed down from thermal speed by applying Zeeman-tuned slowing technique, and subsequently loaded into a magneto-optical trap at the end of the slowing path. The last two chapters of this thesis present two studies on the magneto-optical trap of sodium atoms. In particular, the mechanisms of magneto-optical traps at various laser frequencies and the collisional loss mechanisms of these traps were examined
[en] Since radiocarbon dating was first demonstrated in 1949, the field of trace analyses of long-lived cosmogenic isotopes has seen steady growth in both analytical methods and applicable isotopes. The impact of such analyses has reached a wide range of scientific and technological areas. A new method, named Atom Trap Trace Analysis (ATTA), was developed by our group and used to analyze 81Kr (t1/2 = 2.3 x 105 years, isotopic abundance ∼ 1 x 10-12) in environmental samples. In this method, individual 81Kr atoms are selectively captured and detected with a laser-based atom trap. 81Kr is produced by cosmic rays in the upper atmosphere. It is the ideal tracer for dating ice and groundwater in the age range of 104-106 years. As the first real-world application of ATTA, we have determined the mean residence time of the old groundwater in the Nubian Aquifer located underneath the Sahara Desert. Moreover, this method of capturing and probing atoms of rare isotopes is also applied to experiments that study exotic nuclear structure and test fundamental symmetries.
[en] The understanding of radiation-induced grain boundary segregation (RIS) has considerably improved over the past decade. New models have been introduced and much effort has been devoted to obtaining comprehensive information on segregation from the literature. Analytical techniques have also improved so that chemical analysis of layers 1 nm thick is almost routine. This invited paper will review the major methods used currently for RIS prediction: namely, Rate Theory, Inverse Kirkendall, and Solute Drag approaches. A summary is made of the available data on phosphorus RIS in reactor pressure vessel (RPV) steels. This will be discussed in the light of the predictions of the various models in an effort to show which models are the most reliable and easy to use for forecasting P segregation behaviour in steels. A consequence of RIS in RPV steels is a radiation induced shift in the ductile to brittle transition temperature (DBTT). It will be shown how it is possible to relate radiation-induced P segregation levels to DBTT shift. Examples of this exercise will be given for RPV steels and for ferritic steels being considered for first wall fusion applications. Cr RIS in high alloy stainless steels and associated irradiation-assisted stress corrosion cracking (IASCC) will be briefly discussed. (authors)
[en] Abstract Background: The main design feature of Generation III passive power plant is that the passive safety principles are adopted, so the system, equipment and structure are simplified significantly, and the plant safety, reliability and economy are greatly improved. And the utility requirements document(URD) requirements are met by Generation III passive power plant. Purpose: In this paper, a calculation is made to analyze and verify that the requirement in URD volume III chapter 5 which is related to the automatic depressurization system(ADS) function is met. The requirement is that sufficient reactor coolant system(RCS) inventory and/or makeup shall be provided so that ADS initiation shall not be required for 8-h following a small leak of reactor coolant system, i.e.,2.27-m3·h-1 of cold fluid in excess of available charging capacity. Methods: The small break loss of coolant accident(LOCA) safety analysis code NOTRUMP is used in this calculation. And NOTRUMP is a one dimension, system analysis code. Results: The results show that the core makeup tanks(CMTs) remain in recirculation phase during the 2.27-m3·h-1 leak of RCS transient. The water levels in CMTs do not decrease, and the ADS are not actuated accordingly. Conclusion: The URD requirement described above that ADS initiation shall not be required for 8-h following a small leak of reactor coolant system, i.e.,2.27-m3·h-1 of cold fluid in excess of available charging capacity is met for AP1000 nuclear power plant. (authors)
[en] Pre-alloyed powders of oxide dispersion strengthened (ODS) steels were produced by atomization. The atomized powders without mechanical alloying (MA) and with short-time MA were consolidated by hot isostatic pressing (HIP). The morphology and microstructure of the atomized and the MA powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of 9Cr–ODS steels with different MA time was characterized by high-resolution transmission electron microscopy (HRTEM), electron backscatter diffraction (EBSD) and atom probe tomography (APT). The results showed that high-density of nanosized precipitates and ultrafine grains are formed in the ODS steels using the processing route, which remarkably reduce MA time. The yield strength and ultimate tensile strength of ODS steels are improved with the increase of MA time
[en] The feasible researches on reducing fuel enrichment and deriving of thermal neutron beam are carried out for current miniature neutron source reactor (MNSR). The nuclear parameters of reactor and formation of thermal neutron beam are analyzed and calculated. The research provides profitable suggestion for enhancing application and reducing fuel enrichment on MNSR
[en] Porous calcium carbonate/carboxymethylcellulose (CaCO3/CMC) microspheres were prepared by the biomimetic mineralization method for lysozyme immobilization via adsorption. The size and morphology of CaCO3/CMC microspheres were characterized by transmitted electron microscopy (TEM) and zeta potential measurement. The lysozyme immobilization was verified by Fourier transform infrared (FTIR) spectroscopy. The effects of pHs and temperatures on lysozyme adsorption were investigated as well. It was revealed that CaCO3/CMC microspheres could immobilize lysozyme efficiently via electrostatic interactions and a maximum adsorption capacity of 450 mg/g was achieved at pH 9.2 and 25 °C. Moreover, it was found that the adsorption process fitted well with the Langmuir isothermal model. In addition, UV, fluorescence, and circular dichroism (CD) spectroscopic studies showed that lysozyme maintained its original secondary structure during the adsorption/desorption process. Our study therefore demonstrated that CaCO3/CMC microsphere can be used as a cost-effective and efficient support for lysozyme immobilization. - Graphical abstract: CaCO3/CMC microsphere was prepared by a facile biomimetic mineralization method and can be used as an efficient and cost-effective support for lysozyme immobilization. Highlights: ► CaCO3/CMC microspheres were prepared by the biomimetic mineralization method. ► Lysozyme was efficiently immobilized to CaCO3/CMC microspheres via adsorption. ► A maximum adsorption capacity of 450 mg/g was obtained at pH 9.2 and 25 °C. ► The original secondary structure of lysozyme was maintained upon immobilization.
[en] In order to analyze the influence on dynamics characteristics from delayed gamma-induced neutron for nuclear reactor of in-hospital neutron irradiator, which used to cure cancer with technology of boron neutron capture therapy (BNCT), the dynamics equation of point-reactor included the quantity, worth and decay constant of gamma-induced neutron was set by introducing neutron worth in reactor core and reflector in the one group diffusion equation. The calculation methods on generation rate of delayed gamma-induced neutron, the worth of neutrons generated from fission reaction or gamma-induced were also introduced. The total numerical calculation methods were studied with help of current calculation software and its sketch was shown. The mentioned parameters were calculated and analyzed for the nuclear reactor of in-hospital neutron irradiator. As a result, parameters of 9 groups delayed neutron were added to normal 6 groups. The tendency was analyzed and the good coincidence was verified with experiments from other research reactors which consist of beryllium in reactor complex. (authors)
[en] The theory and method of China Advanced Research Reactor (CARR) first critical experiment were briefly introduced. Without referenced reactor and zero-power device, the theoretical calculation was used to simulate the whole process of CARR first critical experiment. The simulative extrapolate graph of fuel assembly number and control rods height were given, which predicted the critical fuel number and control rod height. This work provides necessary referenced data for the first critical experiment which will be carried out soon. (authors)
[en] CITATOOL, a nuclear parameters management interface code needed by China advanced research reactor (CARR) physics analysis, is presented. It's used to supply cross-section parameters for CITATION code, which is an international famous code among nuclear reactor designer. With CITATOOL, special useful data, keff, neutron fluence, burn-up, etc., can be drawn from the complex result file of CITATION code