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定价： 1475元 / 折扣价： 1254 元 加购物车

定价： 1475元 / 折扣价： 1254 元 加购物车

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Specifies requirements for the Fibre Distributed Data Interface (FDDI) Part: Token ring low-cost fibre physical layer medium dependent (LCF-PMD). FDDI provides a high-bandwidth (100 Mbit/s), general-purpose interconnection among computers and peripheral

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5.1 Refer to Practice E261 for a general discussion of the determination of fast-neutron fluence rate with fission detectors.5.2 237Np is available as metal foil, wire, or oxide powder. For further information, see Guide E844. It is usually encapsulated in a suitable container to prevent loss of, and contamination by, the   237Np and its fission products.45.3 One or more fission products can be assayed. Pertinent data for relevant fission products are given in Table 15 and Table 2.(A) The lightface numbers in parentheses are the magnitude of plus or minus uncertainties in the last digit(s) listed.(B) With  137mBa (2.552 min) in equilibrium.(C) Probability of daughter  140La decay.(D) With  140La (1.67850 d) in transient equilibrium.(E) Primary reference for half-life, gamma energy, and gamma emission probability is Ref (1) when data is available. Note this reference is to the BIPM data that was recommended at the time of the recommended fission yields were set, that is, as of 2009, and not to the latest Vol 8 data that was published in 2016.(A) The JEFF-3.1/3.1.1 radioactive decay data and fission yields sub-libraries, JEFF Report 20, OECD 2009, Nuclear Energy Agency (2).(B) All yield data given as a %; RC represents a cumulative yield; RI represents an independent yield.(C) The neutron energy represents a generic “fast neutron” spectrum and has been characterized in the JEFF 3.1.1 fission yield library as having an average neutron energy of 0.4 MeV.5.3.1 137Cs-137mBa is chosen frequently for long irradiations. Radioactive products 134Cs and  136Cs may be present, which can interfere with the counting of the 0.661657 MeV  137Cs-137mBa gamma ray (see Test Methods E320).5.3.2 140Ba-140La is chosen frequently for short irradiations (see Test Method E393).5.3.3 95Zr can be counted directly, following chemical separation, or with its daughter 95Nb, using a high-resolution gamma detector system.5.3.4 144Ce is a high-yield fission product applicable to 2- to 3-year irradiations.5.4 It is necessary to surround the 237Np monitor with a thermal neutron absorber to minimize fission product production from trace quantities of fissionable nuclides in the 237Np target and from  238Np and  238Pu from (n,γ) reactions in the   237Np material. Assay of   238Pu and   239Pu concentration is recommended when a significant contribution is expected.5.4.1 Fission product production in a light-water reactor by neutron activation products   238Np and   238Pu has been calculated to be insignificant (1.2 %), compared to that from  237Np(n,f), for an irradiation period of 12 years at a fast neutron (E > 1 MeV) fluence rate of 1 × 1011 cm−2 ·s−1, provided the  237Np is shielded from thermal neutrons (see Fig. 2 of Guide E844).5.4.2 Fission product production from photonuclear reactions, that is, (γ,f) reactions, while negligible near-power and research reactor cores, can be large for deep-water penetrations (3).5.5 This dosimetry reaction is important in the area of reactor retrospective dosimetry (4, 5). Good agreement between neutron fluence measured by  237Np fission and the  54Fe(n,p) 54Mn reaction has been demonstrated (6, 7). The reaction  237Np(n,f) F.P. is useful since it is responsive to a broader range of neutron energies than most threshold detectors.5.5.1 Fig. 1 shows the energy-dependent cross section for this dosimetry reaction. The figure shows that, while it is not strictly a threshold detector, because of its sensitivity in the greater than 0.1 MeV neutron energy range it can function as a detector with good sensitivity in the fast neutron region. In the fast fission 252Cf spontaneous fission benchmark field, ~1 % of the 237Np fission dosimeter response comes from neutrons with an energy less than 0.1 MeV. In the cavity of a fast burst 235U reactor, ~5 % of the 237Np ifssion dosimeter response comes from neutrons with an energy less than 0.1 MeV. In the cavity of a well-moderated pool-type research reactor ~50 % of the fission response from the 237Np(n,f) reaction comes from energies less than 0.1 MeV. The importance of this low neutron energy sensitivity should be determined based on the aplication.5.6 The  237Np fission neutron spectrum-averaged cross section in several benchmark neutron fields are given in Table 3 of Practice E261. Sources for the latest recommended cross sections are given in Guide E1018. In the case of the  237Np(n,f)F.P. reaction, the recommended cross section source is the Russian Reactor Dosimetry File, RRDF (8). This recommended cross section is identical, for energies up to 20 MeV, to what is found in the latest International Atomic Energy (IAEA) International Reactor Dosimetry and Fusion File, IRDFF-1.05 (9) . Fig. 1 shows a plot of the recommended cross section versus neutron energy for the fast-neutron reaction   237Np(n,f)F.P.FIG. 1 RRDF/IRDFF-1.05 Cross Section Versus Energy for the 237Np(n,f)F.P. Reaction1.1 This test method covers procedures for measuring reaction rates by assaying a fission product (F.P.) from the fission reaction  237Np(n,f)F.P.1.2 The reaction is useful for measuring neutrons with energies from approximately 0.7 to 6 MeV and for irradiation times up to 90 years, provided that the analysis methods described in Practice E261 are followed. If dosimeters are analyzed after irradiation periods longer than 90 years, the information inferred about the fluence during irradiation periods more than 90 years before the end of the irradiation should not be relied upon without supporting data from dosimeters withdrawn earlier.1.3 Equivalent fission neutron fluence rates as defined in Practice E261 can be determined.1.4 Detailed procedures for other fast-neutron detectors are referenced in Practice E261.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 A soil sampling and analysis program provides a direct means of determining the concentration and distribution of radionuclides in soil. The presence and extent of neptunium-237 is of particular interest because it is one of the more mobile transuranics in terms of migration and plant uptake. Since soil is an integrator and a reservoir on long-lived radionuclides, and serves as an intermediary in several pathways of potential importance to humans, knowledge of the concentration of neptunium-237 in soil is essential.1.1 This guide covers the determination of neptunium-237 in soil by means of radiochemical separations and alpha spectrometry. This guide provides options in the selection of sample preparation, separation, and measurement. Although neptunium-237 is not a component of global fallout, it is a product of production reactors and spent fuel processing. This guide is designed for analysis of ten grams of soil previously collected and treated in accordance with Practices C998 and C999. Larger-size samples of environmental soil may also be analyzed, as long as the concentrations of interferences such as uranium and thorium are at or near environmental concentrations. Depending on the choice of a sample dissolution method, all chemical forms of neptunium may not be completely solubilized. This guide should allow the determination of neptunium-237 concentrations from sub becquerel per gram levels to applicable standards depending on count time, sample size, detector efficiency, background, and tracer yield.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 9.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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Specifies requirements for the Fibre Distributed Data Interface (FDDI) Part: Token ring low-cost fibre physical layer medium dependent (LCF-PMD). FDDI provides a high-bandwidth (100 Mbit/s), general-purpose interconnection among computers and peripheral

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