ASTM E481-03
Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver

Standard No.

ASTM E481-03

Release Date

2003

Published By

American Society for Testing and Materials (ASTM)

Status

Be replaced

Replace By

ASTM E481-10

Latest

ASTM E481-23

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 E 262, 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 E 170). The reaction ⁵⁹Co(n,)⁶⁰Co results in a well-defined gamma emitter having a half-life of 1925.5 days (1). The reaction ¹⁰⁹Ag(n,) ^110mAg results in a nuclide with a complex decay scheme which is well known and having a half-life of 249.76 days (14). 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.

Note 0

Westcott fluence rate = Equation 1 - v00n(v)dv.

1.3 The values stated in SI units are to be regarded as the standard.

1.4 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.

ASTM E481-03 Referenced Document

• ASTM E170 Standard Terminology Relating to Radiation Measurements and Dosimetry
• ASTM E177 Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E181 Standard Test Methods for Detector Calibration and Analysis of Radionuclides
• ASTM E262 Standard Method for Determining Thermal Neutron Reaction and Fluence Rates by Radioactivation Techniques

ASTM E481-03 history

• 2023 ASTM E481-23 Standard Practice for Measuring Neutron Fluence Rates by Radioactivation of Cobalt and Silver
• 2016 ASTM E481-16 Standard Test Method for Measuring Neutron Fluence Rates by Radioactivation of Cobalt and Silver
• 2015 ASTM E481-15 Standard Test Method for Measuring Neutron Fluence Rates by Radioactivation of Cobalt and Silver
• 2010 ASTM E481-10 Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver
• 2003 ASTM E481-03 Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver
• 1997 ASTM E481-97 Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver