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Using a nonlinear least-squares fitting technique, the group parameters for 245 sets of experimentally-measured delayed neutron group constants for 20 fissionable isotopes have been expanded into an 8-group delayed neutron model based on a consistent set of group half-lives. During the expansion process, the reactivity scale for positive reactivities is conserved, as well as the time-dependent behavior of the reactor system as predicted by the original delayed neutron model. In addition, the mean half-life of the original delayed neutron set is conserved, as well as the overall uncertainty of the reactivity scale as quoted by the original experimenter.  相似文献   

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The most probable decays by spontaneous emission of heavy ions are listed for nuclides with Z = 47−106 and total half-lives > 1 μsec. Partial half-lives, branching ratios relative to α decay, kinetic energies, and Q values are estimated by using the analytical superasymmetric fission model, a semi-empirical formula for those α-decay lifetimes which have not been measured, and the new Wapstra-Audi mass tables. Numerous “stable” nuclides with Z > 40 are found to be metastable with respect to the new decay modes. The current experimental status is briefly reviewed.  相似文献   

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常宏钧 《核技术》1992,15(10):635-638
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Presented here is an annotated list of sources of information in the neutron cross-section field.  相似文献   

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The energy spectra and double differential cross sections of neutron and proton emissions for n+54,56,57,58Fe reactions are studied at incident neutron energies below 200 MeV based on the nuclear theoretical models, which are based on pre-equilibrium and equilibrium reaction theories. Theoretical calculated results are compared with existing experimental data.  相似文献   

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Gamma-ray emission probabilities of 241, 243Am and 239Np have been precisely measured with gamma- and alpha-ray spectroscopic methods. The activities of the samples were determined by measuring alpha particles using a Si semiconductor detector. Gamma rays emitted from the samples were measured with a planar type High-Purity Germanium (HPGe) detector. An efficiency curve of the HPGe detector was derived with uncertainties from 0.7% to 2.5% by combining measured efficiencies and Monte Carlo simulation. The gamma-ray emission probabilities for the major gamma rays of these nuclides were determined with uncertainties less than 1.2%.  相似文献   

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ABSTRACT

Accurate data of gamma-ray emission probabilities are frequently needed when one quantitatively determines the amount of isotope by gamma-ray measurements or obtains neutron capture cross-sections using them. Americium-243, one of the most important minor actinides, produces 244Am after neutron capture. The 744-keV gamma-ray decaying from the ground state of 244Am has a relatively large gamma-ray emission probability about 66%; however, its uncertainty is as large as 29%. The uncertainty of the gamma-ray emission probability leads to a major factor of the systematic uncertainty on determining an amount of isotope, and therefore the gamma-ray emission probability was measured by using an activation method and an examined level structure of 244Cm. In this study, the emission probability of 744-keV gamma-ray was derived as 66.5 ± 1.1%, and its uncertainty was improved from 29% to 2%.  相似文献   

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经堆中子辐照过的^154Sm样品,用阳离子交换法分离纯化,得到^155Eu核素。用4πβ-γ符合法测量放射性活度和用小平面Ge探测器测量^155Eu衰变发射的γ光子数,精确测定了γ射线的发射几率。对于强γ射线和弱γ射线的不确定度分别为1.7%和4.5%。与文献报道值相比较,本测量结果明显改善。  相似文献   

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In preparation of homogeneous Kr and Rb sources,the Kr activity was determined by the decay relationship between 88Kr and 88Rb using an HPGe detector.The peak efficiencies of 88Kr and 88Rbγ-rays were calibrated.The results show that the absolute probabilities of 196.3,834.8,1529.8,2195.8 and 2392.1 keVγ-rays of 88Kr were 25.1(5)%,12.9(2)%,10.7(2)%,13.3(2)%and 34.9(5)%,respectively.  相似文献   

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A weighted maximum likelihood method is developed for estimating the parameters of the statistical distribution of capture widths (average and number of degrees of freedom) taking into account experimental errors. Results are obtained for 224Cm, 238U and 235U.A formalism is developed for the area analysis of capture and fission neutron cross sections using maximum likelihood methods for deducing the most likely values for the capture widths. This formalism is applied to the analysis of 244Cm resonance data.  相似文献   

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Neutron nuclear data on 69,71Ga have been evaluated for the next version of the Japanese Evaluated Nuclear Data Library (JENDL) general purpose file in the energy region from eV to 20 MeV. The resolved resonance parameters at negative energies were adjusted so as to reproduce measured thermal capture cross sections. The statistical model was applied to calculate the cross sections above the resolved resonance region. In the calculations, coupled-channel optical model parameters were used for neutrons. Pre-equilibrium and direct-reaction processes were taken into account in addition to the compound process. The present evaluation is consistent with available experimental data. The evaluated data are compiled into an ENDF-formatted data file.  相似文献   

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Neutron nuclear data on 162,164,166,167,168.170Er have been evaluated for the next version of JENDL general purpose file in the energy region from 10?5 eV to 20 MeV. The resolved resonance parameters remain unchanged from JENDL-4.0, while the unresolved resonance parameters were revised. The statistical model was applied to calculate the cross sections above the resolved resonance region. In the calculations, coupled-channel optical model parameters were used for neutrons. Pre-equilibrium and direct-reaction processes were taken into account in addition to the compound process. A modified Lorentzian was employed for E1 gamma-ray strength functions. The present evaluation is consistent with available experimental data. The evaluated data are compiled into an ENDF-formatted data file.  相似文献   

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Fuel rods with burnup values beyond 50 GWd/t are characterised by relatively large amounts of fission products and a high abundance of major and minor actinides. Of particular interest is the change in the reactivity of the fuel as a function of burnup and the capability of modern codes to predict this change. In addition, the neutron emission from burnt fuel has important implications for the design of transport and storage facilities. Measurements have been made of the reactivity effects and the neutron emission rates of highly burnt uranium oxide and mixed oxide fuel rod samples coming from a pressurised water reactor (PWR). The reactivity measurements have been made in a PWR lattice in the PROTEUS zero-energy reactor moderated in turn with: water, a water and heavy water mixture and water containing boron. A combined transport flask and sample changer was used to insert the 400 mm long burnt fuel rod segments into the reactor. Both control rod compensation and reactor period methods were used to determine the reactivities of the samples. For the range of burnup values investigated, an interesting exponential relationship has been found between the neutron emission rate and the measured reactivity.  相似文献   

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