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Significance and Use
5.1 Refer to Practice for a general discussion of the determination of decay rates, reaction rates, and neutron fluence rates with threshold detectors (. ) Refer to Practice , Practice and Guide for the use and application of results obtained by this test method.()
5.2 The half-life of 93mNb is 16.1 (2) years( and has a K X-ray emission probability of 0.11442 ± 3.356 % per decay )(. The K )α and Kβ X-rays of niobium are at 16.521–16.615 and 18.607–18.9852 keV, respectively (. The recommended 93Nb(n,n )′)93mNb cross section comes from the International Reactor Dosimetry and Fusion File (IRDFF version 1.05, cross section compendium (, and is shown in ) . This nuclear data evaluation is part of the Russian Reactor Dosimetry File (RRDF), cross section evaluations (. The nuclear decay data referenced here are not taken from the latest dosimetry recommended database )( but are selected to be consistent with the nuclear data used in the recommended IRDFF evaluation. )
FIG. 1 RRDF/IRDFF-1.05 Cross Section Versus Energy for the 93Nb(n,n′) 93mNb Reaction
5.3 Chemical dissolution of the irradiated niobium to produce very low mass-per-unit area sources is an effective way to obtain consistent results. The direct counting of foils or wires can produce satisfactory results provided appropriate methods and interpretations are employed. It is possible to use liquid scintillation methods to measure the niobium activity provided the radioactive material can be kept uniformly in solution and appropriate corrections can be made for interfering activities.
5.4 The measured reaction rates can be used to correlate neutron exposures, provide comparison with calculated reaction rates, and determine neutron fluences. Reaction rates can be determined with greater accuracy than fluence rates because of the current uncertainty in the cross section versus energy shape.
5.5 The 93Nb(n,n′)93mNb reaction has the desirable properties of monitoring neutron exposures related to neutron damage of nuclear facility structural components. It has an energy response range corresponding to the damage function of steel and has a half-life sufficiently long to allow its use in very long exposures (up to about 48 years). Monitoring long exposures is useful in determining the long-term integrity of nuclear facility components.
1.1 This test method describes procedures for measuring reaction rates by the activation reaction 93Nb(n,n′) 93mNb.
1.2 This activation reaction is useful for monitoring neutrons with energies above approximately 0.5 MeV and for irradiation times up to about 48 years (three half-lives), provided that the analysis methods described in Practice are followed.
1.3 With suitable techniques, fast-neutron reaction rates for neutrons with energy distribution similar to fission neutrons can be determined in fast-neutron fluences above about 1016 cm−2. In the presence of high thermal-neutron fluence rates (>1012cm−2·s−1), the transmutation of 93mNb due to neutron capture should be investigated. In the presence of high-energy neutron spectra such as are associated with fusion and spallation sources, the transmutation of 93mNb by reactions such as (n,2n) may occur and should be investigated.
1.4 Procedures for other fast-neutron monitors are referenced in Practice .
1.5 Fast-neutron fluence rates can be determined from the reaction rates provided that the appropriate cross section information is available to meet the accuracy requirements.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 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.
1.8 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.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D1193 Specification for Reagent Water
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
E185 Practice for Design of Surveillance Programs for Light-Water Moderated Nuclear Power Reactor Vessels
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
E456 Terminology Relating to Quality and Statistics
E844 Guide for Sensor Set Design and Irradiation for Reactor Surveillance
E944 Guide for Application of Neutron Spectrum Adjustment Methods in Reactor Surveillance
E1005 Test Method for Application and Analysis of Radiometric Monitors for Reactor Vessel Surveillance
E1006 Practice for Analysis and Interpretation of Physics Dosimetry Results from Test Reactor Experiments
E1018 Guide for Application of ASTM Evaluated Cross Section Data File
ICS Number Code 27.120.01 (Nuclear energy in general)
UNSPSC Code 26140000(Atomic and nuclear energy machinery and equipment)
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ASTM E1297-18, Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Niobium, ASTM International, West Conshohocken, PA, 2018, www.astm.orgBack to Top