ASTM E705 - 13a

    Standard Test Method for Measuring Reaction Rates by Radioactivation of Neptunium-237

    Active Standard ASTM E705 | Developed by Subcommittee: E10.05

    Book of Standards Volume: 12.02

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    Significance and Use

    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.4

    5.3 One or more fission products can be assayed. Pertinent data for relevant fission products are given in Table 1 and Table 2.

    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 0.662 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 (1).5

    5.5 Good agreement between neutron fluence measured by  237Np fission and the  54Fe(n,p) 54Mn reaction has been demonstrated (2). The reaction  237Np(n,f) F.P. is useful since it is responsive to a broader range of neutron energies than most threshold detectors.

    5.6 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 ENDF/B-VI cross section (MAT = 9346) revision 1 (3). Fig. 1 shows a plot of the recommended cross section versus neutron energy for the fast-neutron reaction   237Np(n,f)F.P.

    Note 1The data are taken from the Evaluated Nuclear Data file, ENDF/B-VI, rather than the later ENDF/B-VII. This is in accordance with Guide E1018 Guide for Application of ASTM Evaluated Cross Section Data File, 6.1. since the later ENDF/B-VII data files do not include covariance information. For more details see Section H of (10)

    1. Scope

    1.1 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 30 to 40 years.

    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 and health practices and determine the applicability of regulatory limitations prior to use.

    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    E170 Terminology Relating to Radiation Measurements and Dosimetry

    E181 Test Methods for Detector Calibration and Analysis of Radionuclides

    E261 Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques

    E262 Test Method for Determining Thermal Neutron Reaction Rates and Thermal Neutron Fluence Rates by Radioactivation Techniques

    E320 Test Method for Cesium-137 in Nuclear Fuel Solutions by Radiochemical Analysis

    E393 Test Method for Measuring Reaction Rates by Analysis of Barium-140 From Fission Dosimeters

    E704 Test Method for Measuring Reaction Rates by Radioactivation of Uranium-238

    E844 Guide for Sensor Set Design and Irradiation for Reactor Surveillance, E 706 (IIC)

    E944 Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance, E 706 (IIA)

    E1005 Test Method for Application and Analysis of Radiometric Monitors for Reactor Vessel Surveillance, E 706 (IIIA)

    E1018 Guide for Application of ASTM Evaluated Cross Section Data File, Matrix E706 (IIB)

    ICS Code

    ICS Number Code 17.240 (Radiation measurements); 27.120.30 (Fissile materials and nuclear fuel technology)

    UNSPSC Code

    UNSPSC Code 26142004(Neutron irradiators); 26141702(Dosimeters)

    Referencing This Standard
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    DOI: 10.1520/E0705-13A

    Citation Format

    ASTM E705-13a, Standard Test Method for Measuring Reaction Rates by Radioactivation of Neptunium-237, ASTM International, West Conshohocken, PA, 2013,

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