ASTM E481 - 10

    Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver

    Active Standard ASTM E481 | Developed by Subcommittee: E10.05

    Book of Standards Volume: 12.02


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    Significance and Use

    The pertinent data for these two reactions are given in Table 1. This test method uses one monitor (cobalt) with a nearly 1/v absorption cross-section curve and a second monitor (silver) with a large resonance peak so that its resonance integral is large compared to the thermal cross section. The equations are based on the Westcott formalism (2, 3) and determine a Westcott 2200 m/s neutron fluence rate nv0 and the Westcott epithermal index parameter r

    1. Scope

    1.1 This test method covers a suitable means of obtaining the thermal neutron fluence rate, or fluence, in well moderated nuclear reactor environments where the use of cadmium, as a thermal neutron shield as described in Method E262, is undesirable because of potential spectrum perturbations or of temperatures above the melting point of cadmium.

    1.2 This test method describes a means of measuring a Westcott neutron fluence rate (Note 1) by activation of cobalt- and silver-foil monitors (See Terminology E170). The reaction 59Co(n,γ)60Co results in a well-defined gamma emitter having a half-life of 1925.28 days (1). The reaction 109Ag(n,˙γ) 110mAg results in a nuclide with a complex decay scheme which is well known and having a half-life of 249.76 days (1). Both cobalt and silver are available either in very pure form or alloyed with other metals such as aluminum. A reference source of cobalt in aluminum alloy to serve as a neutron fluence rate monitor wire standard is available from the National Institute of Standards and Technology (NIST) as Standard Reference Material 953. The competing activities from neutron activation of other isotopes are eliminated, for the most part, by waiting for the short-lived products to die out before counting. With suitable techniques, thermal neutron fluence rate in the range from 109 cm2 · s1 to 3 × 1015 cm2 · s1 can be measured. For this method to be applicable, the reactor must be well moderated and be well represented by a Maxwellian low-energy distribution and an (1/E) epithermal distribution. These conditions are usually met in positions surrounded by hydrogenous moderator without nearby strongly absorbing materials. Otherwise the true spectrum must be calculated to obtain effective activation cross sections over all energies.


    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

    E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

    E181 Test Methods for Detector Calibration and Analysis of Radionuclides

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


    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)


    Referencing This Standard

    DOI: 10.1520/E0481-10

    ASTM International is a member of CrossRef.

    Citation Format

    ASTM E481-10, Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver, ASTM International, West Conshohocken, PA, 2010, www.astm.org

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