ASTM E481-97

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

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  59 Co(n,[gamma]) 60 Co results in a well-defined gamma emitter having a half-life of 5.271 years (1).  The reaction  109 Ag(n, [gamma] ) 110m Ag results in a nuclide with a complex decay scheme which is well known and having a half-life of 249.85 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 Bureau of Standards 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 10  cm -2 [dot]s -1  to 3 X 10 15  cm -2 [dot]s -1  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 1-Westcott fluence rate = v0[integral] [infinity] 0 n(v)dv .
1.3 The values stated in SI units are to be regarded as the standard.  
1.4 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems 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.

General Information

• Status: Historical
• Publication Date: 09-Jun-1997
• ICS: 17.240 - Radiation measurements
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: E10 - Nuclear Technology and Applications
• Drafting Committee: E10.05 - Nuclear Radiation Metrology

Relations

• Replaced By: ASTM E481-03 - Standard Test Method for Measuring Neutron Fluence Rate by Radioactivation of Cobalt and Silver
• Effective Date: 10-Feb-2003
• Referred By: ASTM E261-16(2021) - Standard Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques
• Effective Date: 10-Jun-1997
• Referred By: ASTM E1854-19 - Standard Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
• Effective Date: 10-Jun-1997
• Referred By: ASTM E1005-21 - Standard Test Method for Application and Analysis of Radiometric Monitors for Reactor Vessel Surveillance
• Effective Date: 10-Jun-1997
• Referred By: ASTM E262-17 - Standard Test Method for Determining Thermal Neutron Reaction Rates and Thermal Neutron Fluence Rates by Radioactivation Techniques
• Effective Date: 10-Jun-1997
• Referred By: ASTM E944-19 - Standard Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance
• Effective Date: 10-Jun-1997

Standards Content (Sample)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 481 – 97
Standard Test Method for
Measuring Neutron Fluence Rates by Radioactivation of
1
Cobalt and Silver
This standard is issued under the fixed designation E 481; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.3 The values stated in SI units are to be regarded as the
standard.
1.1 This test method covers a suitable means of obtaining
1.4 This standard does not purport to address all of the
the thermal neutron fluence rate, or fluence, in well moderated
safety concerns, if any, associated with its use. It is the
nuclear reactor environments where the use of cadmium, as a
responsibility of the user of this standard to establish appro-
thermal neutron shield as described in Method E 262, is
priate safety and health practices and determine the applica-
undesirable because of potential spectrum perturbations or of
bility of regulatory limitations prior to use.
temperatures above the melting point of cadmium.
1.2 This test method describes a means of measuring a
2. Referenced Documents
Westcott neutron fluence rate (Note 1) by activation of cobalt-
2.1 ASTM Standards:
and silver-foil monitors (See Terminology E 170). The
59 60 E 170 Terminology Relating to Radiation Measurements
reaction Co(n, ) Co results in a well-defined gamma emit-
g
4
2 and Dosimetry
ter having a half-life of 1925.5 days (1). The
109 110m E 177 Practice for Use of the Terms Precision and Bias in
reaction Ag(n,g˙) Ag results in a nuclide with a complex
5
ASTM Test Methods
decay scheme which is well known and having a half-life of
E 181 Test Methods for Detector Calibration and Analysis
249.76 days (2). Both cobalt and silver are available either in
4
of Radionuclides
very pure form or alloyed with other metals such as aluminum.
E 262 Test Method for Determining Thermal Neutron Re-
A reference source of cobalt in aluminum alloy to serve as a
4
action and Fluence Rates by Radioactivation Techniques
neutron fluence rate monitor wire standard is available from the
National Institute of Standards and Technology (NIST) as
3. Significance and Use
3
Standard Reference Material 953. The competing activities
3.1 The pertinent data for these two reactions are given in
from neutron activation of other isotopes are eliminated, for the
Table 1. This test method uses one monitor (cobalt) with a
most part, by waiting for the short-lived products to die out
nearly 1/v absorption cross-section curve and a second monitor
before counting. With suitable techniques, thermal neutron
9 −2 −1 15 −2 (silver) with a large resonance peak so that its resonance
fluence rate in the range from 10 cm ·s to 3 3 10 cm
−1
integral is large compared to the thermal cross section. The
·s can be measured. For this method to be applicable, the
equations are based on the Westcott formalism (3, 4) and
reactor must be well moderated and be well represented by a
determine a Westcott 2200 m/s neutron fluence rate nv and the
0
Maxwellian low-energy distribution and an (1/E) epithermal
Westcott epithermal index parameter r T/T . References 5,
=
0
distribution. These conditions are usually met in positions
6, and 7 contain a general discussion of the two-reaction test
surrounded by hydrogenous moderator without nearby strongly
method. In this test method, the absolute activities of both
absorbing materials. Otherwise the true spectrum must be
cobalt and silver monitors are determined. This differs from the
calculated to obtain effective activation cross sections over all
test method in the references wherein only one absolute
energies.
activity is determined.
‘
NOTE 1—Westcott fluence rate 5 v * n~v!dv.
0 0 3.2 The advantages of this test method are the elimination of
three difficulties associated with the use of cadmium: (1) the
perturbation of the field by the cadmium; (2) the inexact
cadmium cut-off energy; (3) the low melting temperature of
1
This test method is under the jurisdiction of ASTM Committee E-10 on Nuclear
cadmium. In addition, the reactivity changes accompanying the
Technology and Applications and is the direct responsibility of Subcommittee
rapid insertion and removal of cadmium may prohibit the use
E10.05 on Nuclear Radiation Metrology.
Current edition approved June 10, 1997. Published May 1998. Originally of the cadmium-ratio method. However, the self-shielding
published as E 481 – 73 T. Last previous edition E 481 – 86 (1991).
2
The boldface numbers in parentheses refer to references listed at the end of this
test method.
3 4
Standard Reference Material 953 is available from National Institute of Annual Book of ASTM Standards, Vol 12.
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