ASTM E1297-18

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
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Designation: E1297 − 08 (Reapproved 2013) E1297 − 18
Standard Test Method for
Measuring Fast-Neutron Reaction Rates by Radioactivation
of Niobium
This standard is issued under the fixed designation E1297; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
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1.1 This test method describes procedures for measuring reaction rates by the activation reaction Nb(n,n') Nb.
1.2 This activation reaction is useful for monitoring neutrons with energies above approximately 0.5 MeV and for irradiation
times up to about 30 years.48 years (three half-lives), provided that the analysis methods described in Practice E261 are followed.
1.3 With suitable techniques, fast-neutron reaction rates for neutrons with energy distribution similar to fission neutrons can be
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determined in fast-neutron fluences above about 10 cm . In the presence of high thermal-neutron fluence rates (>10 cm ·s ),
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the transmutation of Nb due to neutron capture should be investigated. In the presence of high-energy neutron spectra such as
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are associated with fusion and spallation sources, the transmutation of Nb by reactions such as (n,2n) may occur and should
be investigated.
1.4 Procedures for other fast-neutron monitors are referenced in Practice E261.
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 safety, health, and healthenvironmental 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
2.1 ASTM Standards:
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
This test method is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applicationsand is the direct responsibility of Subcommittee E10.05 on
Nuclear Radiation Metrology.
Current edition approved Jan. 1, 2013June 1, 2018. Published January 2013August 2018. Originally approved in 1989. Last previous edition approved in 20082013 as
E1297 – 08.E1297 – 08(2013). DOI: 10.1520/E1297-08R13.10.1520/E1297-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1297 − 18
E1018 Guide for Application of ASTM Evaluated Cross Section Data File
3. Terminology
3.1 Definitions—The definitions stated in Terminology E170 and E456 are applicable to this test method.
4. Summary of Test Method
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4.1 High purity niobium is irradiated in a neutron field producing radioactive Nb from the Nb(n,n') Nb reaction. The
metastable state decays to the ground state by the virtual emission of 30 keV gamma rays that are all internally converted giving
rise to the actual emission of orbital electrons followed by X rays.
4.2 Sources of the irradiated niobium are prepared for X ray or liquid scintillation counting.
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4.3 The X rays emitted as a result of the decay of Nb are counted, and the reaction rate, as defined in Practice E261, is
calculated from the decay rate and irradiation conditions.
4.4 The neutron fluence rate may then be calculated from the appropriate spectral-weighted neutron activation cross section as
defined by Practice E261.
5. Significance and Use
5.1 Refer to Practice E261 for a general discussion of the determination of decay rates, reaction rates, and neutron fluence rates
with threshold detectors (1-29). Refer to Practice E1006, Practice E185 and Guide E1018 for the use and application of results
obtained by this test method.(30-32)
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5.2 The half-life of Nb is 5730 616.1 (2) 220 yearsdays (3334) and has a K X-ray emission probability of 0.10990.11442
6 0.0025 3.356 % per decay (3335). The K and K X-rays of niobium are at 16.5213–16.15216.521–16.615 and
α β
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18.618–18.95318.607–18.9852 keV, respectively.respectively (35). The recommended Nb (n,n')Nb(n,n') Nb cross section
comes from the IRDF-90 International Reactor Dosimetry and Fusion File (IRDFF version 1.05, cross section compendium (3436),
was drawn from and is shown in Fig. 1the RRDF-98 . This nuclear data evaluation is part of the Russian Reactor Dosimetry File
(RRDF), cross section evaluations (3537). The nuclear decay data referenced here are not taken from the latest dosimetry
recommended database (33) and is shown but are selected to be consistent with the nuclear data used in Fig. 1.the recommended
IRDFF evaluation.
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.
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FIG. 1 IRDF-90RRDF/IRDFF-1.05 Cross Section Versus Energy for the Nb(n,n') Nb Reaction
The boldface numbers in parentheses refer to the list of references at the end of this test method.
The value of uncertainty, in parenthesis, refers to the corresponding last digits, thus 16.1(2) corresponds to 16.1 6 0.2, which corresponds to 16.1 6 1.24 %.
One year is defined to be 365.242198 days – 31556926 seconds in the source documents referenced (33).
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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.
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5.5 The Nb(n,n') Nb 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 4048 years). Monitoring long exposures is useful in
determining the long-term integrity of nuclear facility components.
6. Interferences
6.1 Pure niobium in the forms of foil and wire is available and easily handled as a metal. When thin niobium is irradiated, it
may become brittle and fragile, thus requiring careful handling or encapsulation to prevent damage or loss of the niobium. Refer
to Guide E844 for the selection, irradiation, and quality control of neutron dosimeters.
6.2 There are some distinct advantages and limitations to three measurement techniques identified in 5.3. It is the responsibility
of the user to evaluate these and determine the optimum technique for the situation.
6.2.1 Low mass source X-ray spectrometry advantages include sufficient energy resolution to eliminate other X-ray emissions,
stable long life sources, reduced interference fluorescence due to other radionuclides, small and precise background corrections,
and minimal X-ray source self-absorption corrections. Limitations are low counting efficiency, complex source preparation, and
use of hazardous chemicals.
6.2.2 Direct X-ray spectrometry of metal (foil or wire) sources has the advantages of simple source preparation, stable long life
sources, sufficient energy resolution to eliminate other X-ray emissions, small and precise background corrections, and no use of
hazardous chemicals. Limitations are low counting efficiency, large X-ray source self-absorption corrections, larger corrections for
interference fluorescence due to the other radionuclides, and source geometry control.
6.2.3 Liquid scintillation counting advantages include very high detection efficiency, reproducible source preparation, and no
source self absorption corrections. Limitations include specialized calibration techniques to reduce interference from other
radionuclides, limited source stability, use of hazardous chemicals, and disposal of hazardous chemical waste.
7. Apparatus
7.1 X-ray Spectrometer, using a Si(Li) detector or a Ge detector and a multichannel pulse-height analyzer. For more information,
refer to Test Methods E181 and E1005.
7.2 Precision Balance, able to achieve the required accuracy.
7.3 Beakers, 50 mL polyethylene; pycnometer (weighing bottle), 50 mL polyethylene; volumetric pipets, 10 μL to 5 mL.
7.4 Gamma Ray Spectrometer, using a Ge detector and a multichannel pulse-height analyzer. Refer to Test Method E181.
7.5 Liquid Scintillation Counter.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such
specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
8.2 Purity of Water—Unless otherwise indicated, any water used shall be understood to mean reagent water as defined by Type
I of Specification D1193.
8.3 Hydrofluoric Acid—Concentrated (32M) hydrofluoric acid (HF).
8.4 Nitric Acid—Concentrated (16M) nitric acid (HNO ).
8.5 Niobium Metal—The purity of the niobium is important in that no impurities (such as tantalum) should be present to produce
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long-lived radionuclides that interfere with the Nb activity determination. To avoid problems from tantalum, the niobium should
have the lowest tantalum content possible. Niobium metal in the form of foil and wire with tantalum content of about 5 ppm (parts
per million) or less is obtainable and can be used under most conditions. The niobium material should be tested for interfering
radioactivity by neutron activation techniques.
8.6 Encapsulation Material—The encapsulation material (such as quartz, stainless steel, aluminum, etc.) should be selected to
prevent corrosion of the niobium during irradiation and to be compatible with the irradiation environment and post-irradiation
“Reagent Chemicals, American Chemical Society Specifications,” Am. Chemical Soc., Washington, DC. For suggestions on the testing of reagents not listed by the
American Chemical Society, see “Reagent Chemicals and Standards,” by Joseph Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States Pharmacopeia.”
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handling. If thermal and epithermal neutron filters or shrouds are used, these materials (such as cadmium, tantalum, gadolinium,
etc.) must also be compatible with the encapsulation and irradiation environment.
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8.7 Analytical Paper—Analytical grade filter paper of uniform thickness (about 0.076 cm) and density (about 8 mg cm ). The
paper can be cut or obtained precut to the desired size (usually between 0.5 and 1.5 cm diameter) that is compatible with the
activity concentration of the solution and the counting conditions. The paper should be able to absorb as much liquid as is necessary
and not decompose from the acid. TFE-fluorocarbon rings with an inside diameter matching the outside diameter of the filter paper
disks so they fit together with light contact.
8.8 Support and Cover Materials—Thin plastic film and plastic tape materials are useful to support and cover the filter paper
sources. They should be strong enough to contain the sources and thin enough to minimize attenuation of the X rays.
8.9 Source Holder—A source holder must be used to accurately and reproducibly position the sources for the counting geometry
to be used. The source holder should be constructed of low density materials such as aluminum or plastic.
8.10 Liquid Scintillation Materials—Vials, emulsion scintillant (xylene-based), chelating agent (di-2-ethylhexyl phosphoric
acid).
9. Procedure
9.1 Determine the size and shape of the niobium sample being irradiated. Consider the convenience in handling and available
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irradiation space. Ensure that sufficient Nb activity will be produced to permit accurate radioassay. Typically, samples of 0.2
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to 20 mg of niobium may be used, but a preliminary calculation of the expected production of Nb will aid in selecting the
appropriate mass for the irradiation.
9.2 Accurately weigh the niobium sample being irradiated.
9.3 Encapsulate the niobium sample so that it can be retrieved and identified following the irradiation. Record the sample
identification, sample weight, and exact details of the encapsulation. Shroud the niobium with neutron filter material if necessary.
If the thermal-to-fast neutron fluence rate ratio is high (greater than 5) or the tantalum impurity is high (greater than 10 ppm), use
neutron filter materials, if possible.
9.4 Irradiate the niobium samples. Keep an accurate record of the irradiation history including neutron level versus time, starting
and ending time of the irradiation, and the periods when the neutron level is zero. Record the spatial position of the sample in the
irradiation facility.
9.5 After the irradiation, retrieve and identify the irradiated sample. Take necessary precautions to avoid personnel overexposure
to radiation and the spread of radioactive contamination.
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9.6 A waiting time between the end of irradiation and the start of counting may be necessary to allow Nb or Nb, or both,
to decay to an insignificant level. Check the samples for activity from contamination by other materials or reactions (see Test
Method E262) and for any material adhering to the sample. Check the weight of the sample. If necessary, clean and reweigh the
sample.
9.7 X-Ray Source Preparation and Counting:
9.7.1 If the metal is being dissolved and reduced to a low mass-per-unit area source, dissolve the sample by placing it in a
preweighed 50 mL polyethylene or TFE-fluorocarbon (non-wettable) beaker and adding enough concentrated hydrofluoric acid to
cover the sample (usually about 1 to 10 mL of HF). Add concentrated nitric acid dropwise to start dissolution; as dissolution slows,
add additional drops to maintain a controlled slow rate of dissolution until the entire sample dissolves. After dissolution is
complete, bring the final volume of solution to the desired amount by adding distilled water. Weigh the solution in the beaker if
mass aliquoting is used. A preweighed polyethylene pycnometer (weighing bottle) is recommended for mass aliquoting. The ratio
of the niobium mass to the solution mass determines the concentration of niobium in the solution. When transferring the solution
from one container to another, ensure that all of the solution is transferred by using multiple rinses. Use accurately calibrated pipets
if volumetric aliquoting is performed.
9.7.2 Deposit the desired amount of the solution on a filter paper disk surrounded by a TFE-fluorocarbon ring to produce a
counting source. Deposit the solution on the paper drop-by-drop so the paper does not become saturated but is uniformly wetted.
The deposits are allowed to dry by evaporation of the solvent. Gently remove the paper disk from the TFE-fluorocarbon ring. Seal
the sources between thin layers of plastic or plastic tape to contain the niobium. Mount the sources on the source holder for the
counting geometry being used. Determine and record the amount of niobium in each source.
9.7.3 Count the prepared sources using an X-ray spectrometer with either an Si(Li) or a Ge detector with a beryllium window
and designed to count X rays in the energy range between about 5 and 50 keV. Refer to Test Methods E181 and Practice E261.
It is assumed that the persons doing the counting are knowledgeable in the operation and use of the counting apparatus and the
handling and counting of X-ray sources.
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9.7.4 The Nb activity can be determined from the K X-ray emission rates by direct comparison to a certified standard of
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Nb prepared and counted under the same conditions. Alternatively, the detection efficiency for the spectrometer system may be
determined from other standardized K X-ray sources and applied to the counting of the unknown sources as described in Test
Methods E181 and Ref (8).
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9.7.5 If the prepared sources contain significant and variable amounts of niobium relative to each other or to the standard source,
correction for self-attenuation may be necessary. These corrections can be determined as described in Test Methods E181. The
accuracy of these corrections will depend on the uniformity of the distribution of the niobium in the sources. If possible, sources
with less than 1 mg/cm of niobium should be prepared for counting to minimize the self-attenuation of the sources.
9.8 Comparison Counting:
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9.8.1 If direct counting of metal niobium foils or wires is being done by comparison with appropriate standard sources of Nb
in the same form and geometry as the unknown sources, or by comparison with certified standards and with appropriate corrections
made for geometry differences,
...