ASTM E385-22

Standard Test Method for Oxygen Content Using a 14-MeV Neutron Activation and Direct-Counting Technique

SIGNIFICANCE AND USE
5.1 The conventional determination of oxygen content in liquid or solid samples is a relatively difficult chemical procedure. It is slow and usually of limited sensitivity. The 14-MeV neutron activation and direct counting technique provides a rapid, highly sensitive, nondestructive procedure for oxygen determination in a wide range of matrices. This test method is independent of the chemical form of the oxygen.  
5.2 This test method can be used for quality and process control in the metals, coal, and petroleum industries, and for research purposes in a broad spectrum of applications.
SCOPE
1.1 This test method covers the measurement of oxygen concentration in almost any matrix by using a 14-MeV neutron activation and direct-counting technique. Essentially, the same system may be used to determine oxygen concentrations ranging from under 10 μg/g to over 500 mg/g, depending on the sample size and available 14-MeV neutron fluence rates.  
Note 1: The range of analysis may be extended by using higher neutron fluence rates, larger samples, and higher counting efficiency detectors.  
1.2 This test method may be used on either solid or liquid samples, provided that they can be made to conform in size, shape, and macroscopic density during irradiation and counting to a standard sample of known oxygen content. Several variants of this method have been described in the technical literature. A monograph is available which provides a comprehensive description of the principles of activation analysis using a neutron generator (1).2  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.Specific precautions are given in Section 8.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Jan-2022
• 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

• Refers: ASTM E170-17 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2017
• Refers: ASTM E170-16a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Oct-2016
• Refers: ASTM E170-16 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Feb-2016
• Refers: ASTM E170-15a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2015
• Refers: ASTM E170-15 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Mar-2015
• Refers: ASTM E170-14a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Oct-2014
• Refers: ASTM E170-14 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2014
• Refers: ASTM E496-14 - Standard Test Method for Measuring Neutron Fluence and Average Energy from&#8201;<sup>3</sup >H&#40;d,n&#41;⁴He Neutron Generators by Radioactivation Techniques
• Effective Date: 01-Jan-2014
• Refers: ASTM E170-10 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2010
• Refers: ASTM E181-10 - Standard Test Methods for Detector Calibration and Analysis of Radionuclides
• Effective Date: 01-Jan-2010
• Refers: ASTM E170-09a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Aug-2009
• Refers: ASTM E170-09 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Jun-2009
• Refers: ASTM E496-09 - Standard Test Method for Measuring Neutron Fluence and Average Energy from ³H(<i>d,n</i>)⁴He Neutron Generators by Radioactivation Techniques ¹
• Effective Date: 15-Jun-2009
• Refers: ASTM E170-08d - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Nov-2008
• Refers: ASTM E170-08c - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2008

Overview

ASTM E385-22, titled Standard Test Method for Oxygen Content Using a 14-MeV Neutron Activation and Direct-Counting Technique, outlines a highly sensitive, non-destructive analytical procedure for determining oxygen content in solid and liquid samples. Developed by ASTM International, this method addresses the limitations of traditional chemical tests for oxygen by leveraging neutron activation analysis and direct gamma counting, making it suitable for precise, rapid assessment of oxygen levels in a wide variety of matrices. The standard is applicable to industries where monitoring oxygen content is critical, such as metals, coal, petroleum, and research laboratories.

Key Topics

• Neutron Activation Analysis: Utilizes 14-MeV neutrons generated by particle accelerators to induce specific nuclear reactions in oxygen present within the sample.
• Direct Counting Technique: High-energy gamma rays, emitted from activated oxygen nuclei, are directly counted using sensitive detectors, providing a quantifiable measure of oxygen.
• Wide Measurement Range: Capable of detecting oxygen in concentrations from less than 10 μg/g up to over 500 mg/g, accommodating both trace and bulk analysis.
• Nondestructive Testing: The method preserves sample integrity, enabling subsequent or repeated analyses if required.
• Rapid and Sensitive: Offers faster results and greater sensitivity than conventional chemical methods, independent of the chemical form of oxygen present.
• Applicability to Diverse Matrices: Effective for analyzing samples of varying density, size, and composition, including solids and liquids, provided they conform to calibration standards during testing.
• Interference and Calibration: Addresses possible interferences from elements like fluorine, boron, and argon, emphasizing stringent calibration and correction procedures for accuracy.

Applications

The ASTM E385-22 test method for oxygen analysis is widely used in various industrial and research settings:

• Metals Industry: Monitoring and controlling oxygen levels during metal production and processing to prevent defects and ensure product quality.
• Coal and Petroleum Industries: Assessing oxygen in raw materials and end-products for process optimization and quality assurance.
• Material Research: Investigating oxygen content in advanced materials, ceramics, polymers, and composites for improved material properties and performance.
• Quality and Process Control: Providing a reliable, standardized approach for routine inspection and compliance with technical specifications.
• Environmental and Energy Sectors: Examining fuel samples for oxygen content to evaluate combustion efficiency and emissions.

Related Standards

To implement ASTM E385-22 effectively, reference to associated documents and standards is valuable:

• ASTM E170: Terminology Relating to Radiation Measurements and Dosimetry.
• ASTM E181: Test Methods for Detector Calibration and Analysis of Radionuclides.
• ASTM E496: Test Method for Measuring Neutron Fluence and Average Energy from Neutron Generators.
• Regulatory References: Compliance with U.S. NRC regulations (10 CFR Part 20) and local safety requirements for radiation protection.
• International Guidelines: Alignment with principles established by the WTO Technical Barriers to Trade Committee for standardization.

Summary

By following ASTM E385-22, laboratories and industries can achieve rapid, sensitive, and nondestructive measurement of oxygen content in a broad spectrum of samples. This method delivers significant advantages in quality control, process monitoring, and research, ensuring reliable data and global recognition through adherence to internationally accepted procedures for oxygen determination. For organizations handling metals, fuels, or advanced materials, integrating this standard into their testing protocols enhances analytical precision and operational efficiency.

Standards Content (Sample)

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.
Designation: E385 − 22
Standard Test Method for
Oxygen Content Using a 14-MeV Neutron Activation and
Direct-Counting Technique
This standard is issued under the fixed designation E385; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the measurement of oxygen 2.1 ASTM Standards:
concentrationinalmostanymatrixbyusinga14-MeVneutron E170Terminology Relating to Radiation Measurements and
activation and direct-counting technique. Essentially, the same Dosimetry
system may be used to determine oxygen concentrations E181Test Methods for Detector Calibration andAnalysis of
ranging from under 10 µg/g to over 500 mg/g, depending on Radionuclides
the sample size and available 14-MeV neutron fluence rates. E496Test Method for Measuring Neutron Fluence and
3 4
Average Energy from H(d,n) He Neutron Generators by
NOTE 1—The range of analysis may be extended by using higher
Radioactivation Techniques
neutron fluence rates, larger samples, and higher counting efficiency
detectors.
2.2 U.S. Government Document:
Code of Federal Regulations, Title 10,Part 20
1.2 This test method may be used on either solid or liquid
samples, provided that they can be made to conform in size,
3. Terminology
shape,andmacroscopicdensityduringirradiationandcounting
to a standard sample of known oxygen content. Several 3.1 Definitions (see also Terminology E170):
variants of this method have been described in the technical 3.1.1 accelerator—a machine that ionizes a gas and electri-
literature.Amonograph is available which provides a compre- cally accelerates the ions onto a target.The accelerator may be
based on the Cockroft-Walton, Van de Graaff, or other design
hensive description of the principles of activation analysis
using a neutron generator (1). types (1). Compact sealed-tube, mixed deuterium and tritium
gas, Cockcroft-Walton neutron generators are most commonly
1.3 The values stated in SI units are to be regarded as
used for 14-MeV neutron activation analysis. However,
standard. No other units of measurement are included in this
“pumped” drift-tube accelerators that use replaceable tritium-
standard.
containing targets are also still in use. Reviews of operational
1.4 This standard does not purport to address all of the
characteristics, descriptions of accessory instrumentation, and
safety concerns, if any, associated with its use. It is the
applications of accelerators used as fast neutron generators for
responsibility of the user of this standard to establish appro-
activation analysis are available (2, 3).
priate safety, health, and environmental practices and deter-
3.1.2 comparator standard—a reference standard of known
mine the applicability of regulatory limitations prior to us-
−1
oxygencontentwhosespecificcountingrate(countsmin [mg
e.Specific precautions are given in Section 8.
−1
of oxygen] ) may be used to quantify the oxygen content of a
1.5 This international standard was developed in accor-
sample irradiated and counted under the same conditions.
dance with internationally recognized principles on standard-
Often, a comparator standard is selected to have a matrix
ization established in the Decision on Principles for the
composition, physical size, density and shape very similar to
Development of International Standards, Guides and Recom-
the corresponding parameters of the sample to be analyzed.
mendations issued by the World Trade Organization Technical
3.1.3 14-MeV neutron fluence rate—the areal density of
Barriers to Trade (TBT) Committee.
neutrons passing through a sample, measured in terms of
−2 −1
neutrons cm s , that is produced by the fusion reaction of
ThistestmethodisunderthejurisdictionofASTMCommitteeE10onNuclear
Technology and Applications and is the direct responsibility of Subcommittee
E10.05 on Nuclear Radiation Metrology. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 1, 2022. Published March 2022. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1969. Last previous edition approved in 2016 as E385–16. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0385-22. the ASTM website.
2 4
The boldface numbers in parentheses refer to a list of references at the end of Available from the Superintendent of Documents, U.S. Government Printing
the text. Office, Washington, DC 20402.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E385 − 22
deuterium and tritium ions accelerated to energies of typically (all chemical forms) in the sample is proportional to the
150 to 200 keV in a small accelerator. Fluence rate has been correctedandnormalizedsamplecountandisquantifiedbyuse
commonly referred to as “flux density.” The total neutron of the corrected and normalized specific activity of the com-
fluence is the fluence rate integrated over time. parator standard(s).
3 4 16 5
3.1.3.1 Discussion—The H(d,n) He reaction is used to 4.1.1 N decays with a half-life of 7.13 (2) sby
produceapproximately14.7-MeVneutrons.Thisreactionhasa β-emission (7),thusreturningto O.FromRef (7),67.0(6)%
Q-value of+17.586 MeV. of the decays are accompanied by 6.12863 (4)MeV gamma
rays, 4.9 (4)% by 7.11515 (14)MeV gamma rays, and 0.82
3.1.4 monitor—any type of detector or comparison refer-
(6)% by 2.7415(5)MeV gamma rays. Other lower intensity
ence material that can be used to produce a response propor-
gamma rays are also observed. About 28% of the beta
tional to the 14-MeV neutron fluence rate in the irradiation
transitions are directly to the ground state of O. Useful
position, or to the radionuclide decay events recorded by the
elemental data including calculated sensitivities and reaction
sample detector.Aplastic pellet with a relatively high oxygen
cross-sections for (14-MeV INAA) are provided in Refs (3)
content is often used as a monitor reference in dual sample
and (8). (See also Test Methods E181.)
transfer systems. It is never removed from the system regard-
less of the characteristics of the sample to be analyzed. It is
5. Significance and Use
important to distinguish that the monitor, whether an indepen-
5.1 The conventional determination of oxygen content in
dent detector or an activated reference material, is not a
standard used to scale the oxygen content of the samples to be liquid or solid samples is a relatively difficult chemical
procedure. It is slow and usually of limited sensitivity. The
measured, but rather is used to normalize the analysis system
among successive analytial passes within the procedure. 14-MeV neutron activation and direct counting technique
providesarapid,highlysensitive,nondestructiveprocedurefor
3.1.5 multichannel pulse-height analyzer—an instrument
oxygen determination in a wide range of matrices. This test
that receives, counts, separates, and stores, as a function of
method is independent of the chemical form of the oxygen.
their energy, pulses from a scintillation or semi-conductor
gamma-raydetectorandamplifier.Inthe14-MeVinstrumental
5.2 This test method can be used for quality and process
neutron activation analysis (INAA) determination of oxygen, control in the metals, coal, and petroleum industries, and for
the multichannel analyzer may also be used to receive and
research purposes in a broad spectrum of applications.
record both the BF neutron detector monitor counts and the
6. Interferences
sample gamma-ray detector counts as a function of stepped
time increments (4-6). In the latter case, operation of the
6.1 Because of the high energy of the gamma rays emitted
analyzer in the multichannel scaler (MCS) mode, an electronic
in the decay of N, there are very few elements that will
gating circuit is used to select only gamma rays within the
produce interfering radiations; nevertheless, caution should be
energy range of interest.
exercised. F, for example, will undergo an (n,α) reaction to
produce N, the same indicator radionuclide produced from
3.1.6 transfer system—a system, normally pneumatic, used
19 16
to transport the sample from an injection port (sometimes oxygen. Because the cross section for the F(n,α) N reaction
16 16
connected to an automatic sample changer) to the irradiation is approximately one-half that of the O(n,p) N reaction, a
station, and then to the counting station where the activity of correction must be made if fluorine is present in an amount
the sample is measured. The system may include components comparable to the statistical uncertainty in the oxygen deter-
to ensure uniform positioning of the sample at the irradiation mination.Another possible interfering reaction may arise from
and counting stations. the presence of boron. B will undergo an (n,p) reaction to
produce Be. This isotope decays with a half-life of 13.76
4. Summary of Test Method
(7)s, and beta decays to populate excited states in B which
4.1 The weighed sample to be analyzed is placed in a subsequently decay by emitting several high-energy gamma
rays with energies up to 7.97473 MeV (9, 10). In addition,
container for automatic transfer from a sample-loading port to
the 14-MeV neutron irradiation position of a particle accelera- there is Bremsstrahlung radiation produced by the high energy
beta particles emitted by Be. These radiations can interfere
tor. After irradiation for a pre-selected time, the sample is
with the oxygen determination if the oxygen content does not
automatically returned to the counting area. A gamma-ray
exceed 1% of the boron present.
detector measures the high-energy gamma radiation from the
radioactive decay of the N produced by the (n,p) nuclear
6.2 Another possible elemental interference can arise from
reaction on O. The number of counts in a pre-selected
thepresenceoffissionablematerialssuchasthorium,uranium,
counting interval is recorded by a gated scaler, or by a
and plutonium. Many short-lived fission products emit high-
multichannel analyzer operating in either the pulse-height, or
energygammarayscapableofinterferingwiththosefrom N.
gated multiscaler modes. The number of events recorded for
40 40 40
NOTE 2—Argon produces an interferent, Cl, by the Ar(n,p) Cl
samples and monitor reference standard are corrected for
reaction. Therefore, argon should not be used for the inert atmosphere
background and normalized to identical irradiation and count-
duringsamplepreparationforoxygenanalysis. Cl(t ⁄2 =1.35(3)m)has
ing conditions. If the sample and a monitor reference sample
are not irradiated simultaneously, the neutron dose received
during each irradiation must be recorded, typically by use of a
The value of uncertainty, in parentheses, refers to the corresponding last digits,
BF neutron proportional counter. The amount of total oxygen thus 14.958 (2) corresponds to 14.958 6 0.002.
E385 − 22
several high-energy gamma rays, including one at 5.8796 (12)MeV with
the counting geometry to reduce the solid angle. Since the
a yield of 4.1 (5)%.
decay of these “coincidence” events are subject to the half-life
6.3 An important aspect of this analysis that must be of the radionuclide from which they are emitted, it may be
controlled is the geometry during both irradiation and count-
possible to differentiate the interfering signal from oxygen
ing. The neutron source is usually a disk source. Hence, the counts by decay rate if using an MCS-based sytem (15).
fluence rate decreases as the inverse square at points distant
from the target, and less rapidly close to the target. Because of
7. Apparatus
thesefluencerategradients,theirradiationgeometryshouldbe
7.1 14-MeV Neutron Generator—Typically, this is a high-
reproducedasaccuratelyaspossible.Similarly,thepositioning
voltage sealed-tube machine to accelerate both deuterium and
of the sample at the detector is critical and must be accurately
tritium ions onto a target to produce 14-MeV neutrons by the
reproducible. For example, if the sample is considered to be a
3 4
H(d,n) He reaction. In the older “pumped” drift-tube
point source located 6 mm from a cylindrical sodium iodide
accelerators,andalsoinsomeofthenewersealed-tubeneutron
(NaI) detector, a 1mm change in position of the sample along
generators, deuterium ions are accelerated into copper targets
the detector axis was found to result in a 3.5% to 5% change
containingadepositoftitaniumintowhichtritiumisabsorbed.
in detector efficiency (11). Since efficiency is defined as the
Detailed descriptions of both sealed-tube and drift-tube ma-
fraction of gamma rays emitted from the source that interact
chines have been published (1, 3).
withthedetector,itisevidentthatachangeinefficiencywould
7.1.1 Other nuclear reactions may be used, but the neutron
result in an equal percentage change in measured activity and
16 16
energy must exceed 10.24451 MeV (16) for the O(n,p) N
in apparent oxygen content. The sample and monitor (if
reaction to take place. The 14-MeV neutron output of the
present) may be rotated during exposure or counting, or both,
9 12 −1
generator should be 10 to 10 neutrons s , with a usable
to ensure exposure and counting uniformity. See, for example,
7 9 −2 −1
fluence rate at the sample of 10 to 10 neutrons cm s .The
Ref (12).Forcounting,dualdetectorsat180°canbeusedasan
14-MeV fluence rate may be measured as described in Test
alternative to rotation to minimize positioning errors at the
Method E496.
counting station.
7.1.2 Theneutronoutputfromtargetsindrift-tubemachines
6.4 Since N emits high-energy gamma rays, determina-
decreases quite rapidly during use because of depletion of the
tions are less subject to effects of self-absorption than are
tritium content of the target in the pumped system.
determinations based on the use of indicator radionuclides
Consequently, the target must be replaced frequently. The use
emittinglowerenergygammarays.Correctionsforgamma-ray
of a sealed-tube-type neutron generator obviates the need to
attenuation during counting are usually negligible, except for
handle tritium targets and provides for longer stable operation.
large samples as may be needed in the highest sensitivity
7.2 Sample Transfer System—The short half-life (7.13 s) of
determinations.
the Nrequiresthatthesamplebetransferredrapidlybetween
6.5 The oxygen content of the transfer container (“rabbit”)
theirradiationpositionandthecountingstationbyapneumatic
must be kept as low as possible to avoid a large “blank”
system to minimize decay of the N. If the oxygen content in
correction. Suggested materials that combine light weight and
thesampleislow,itisdesirabletousedrynitrogen,ratherthan
low oxygen content are polypropylene and high-density poly-
air, in the pneumatic system to avoid an increase in radioac-
ethylene (molded under a nitrogen atmosphere), high purity
tivity due to recoil of N atoms produced in the air onto the
Cu, and high-purity nickel.Asimple subtraction of the counts
sample surface or other transfer of irradiated air back to the
fromtheblankvialintheabsenceofthesampleisnotadequate
counting station. The transfer system and data processing may
for oxygen determinations below 200 µg/g, since large sample
be controlled directly by laboratory computers (17),orby
sizes may be required for these high-sensitivity measurements
programmable logic controllers (5, 6). Dual transfer systems
andgamma-rayattenuationmaybeimportantwhenthesample
transport the sample and a monitor reference standard simul-
is present (13). If the total oxygen content of the sample is as
taneously. In this case, two independent counting systems are
lowasthatofthecontainer(typicallyabout0.5mgofoxygen),
often used. Single sample transfer systems based on sequential
the sample should be removed from the irradiation container
irradiations of a sample and a comparator standard, are also
prior to counting. Statistical errors increase rapidly as true
used.
sample activities decrease, while container contamination ac-
tivities remain constant. For certain shapable solids, it may be
NOTE 3—As mentioned previously in 6.2, argon should be avoided in
possible to use no container at all (14). This “containerless”
thetransfergas,aswellasinsamplepackaging,becauseoftheinterferent
Cl produced.
approach provides optimum sensitivity for low-level
determinations, but care must be taken to avoid contamination
7.3 Monitor—The number of counts obtained from any
of the transfer system.
given irradiation is dependent upon the oxygen content of the
6.6 Although the discriminator is used to eliminate the sample, the length of irradiation, the neutron fluence rate, the
signal originating from gamma rays of energy less than neutron energy spectrum, the delay time between irradiation
4.5MeV, it is possible when analyzing certain materials that and counting, and the length of the count. It is desirable to
very high matrix activities can result in multiple gammas of make a measurement in which the result obtained is a function
lowerenergybeingsummed,therebygeneratingasignalinthe of only the oxygen content and independent of other variables.
energy window. This effect can be minimized by reducing the This can be achieved by standardizing the experimental con-
specific activity of the interfering radionuclide or by altering ditions and use of a monitor.
E385 − 22
7.3.1 In the dual sample transfer approach, the monitor is bution to the oxygen counts over the remainder of the
ordinarily a high-oxygen containing material that is irradiated irradiation period. This produces a beam normalization value
with each sample in a position adjacent to the sample position, that is tailored to correct for beam variations during the
transferred to an independent detector, and counted simultane- irradiation as well as beam intensity differences between
ouslywiththesample.Thesamemonitorreferenceisusedwith irradiations.
each sample, and is never removed from the system. Since the
7.3.3 Variations in the positions of the sample or monitor
sample and monitor reference are irradiated and counted
reference relative to the neutron generator will cause a varia-
simultaneously, and N is measured in both, most changes in
tionintheratioofsamplecountstomonitorcounts.Inorderto
the experimental parameters affecting the sample counts will
avoidtheeffectsofthisnonuniformity,boththesampleandthe
affect the monitor counts equally. One possible exception is
monitorreferencestandardcanberotatedaboutanaxisparallel
that changes in the neutron energy spectrum due to incident
to the beam during irradiation. Selection of experimental
accelerator particle energy changes may affect the sample and
irradiation and counting geometries normally can be done in
monitor in different ways due to angular dependence factors.
such a way as to avoid significant errors (see 7.4.2).
However, a relatively constant particle energy can usually be 16
7.3.4 Theshorthalf-lifeof Nimposessomerestrictionson
achieved.Therefore,whilethenumberofcountsobtainedfrom
the timing of the various steps of the analysis. For maximum
any given sample may vary greatly from one irradiation to
accuracy in a single sample transfer system, the entire cycle of
another, the ratio of sample counts to monitor reference counts
irradiation, transfer, and counting should be controlled auto-
will be a constant. To determine the oxygen content of a
matically so that all times are reproduced within a few
sample, it is necessary to irradiate a comparator standard of
hundredths of a second. Alternately, the entire irradiation and
known oxygen content with physical and chemical properties
counting process may be recorded by a multichannel analyzer
similar to those of the sample and determine the ratio of its
operating in the multichannel scaler mode and the parameters
counts to that of the monitor reference as well.
later normalized by use of a computer program (4-6). Precise
7.3.2 If a single sample transfer system is used, it is
control or measurements of time and fluence rate are not
necessary to measure the neutron fluence rate during both the
usually necessary when a monitor reference is irradiated
irradiation of the sample and the irradiation of the comparator
simultaneously with the sample in a dual sample transfer and
standard. Variations in fluence rate from a neutron generator
counting system.
are to be expected, not only with time, but also with position.
7.4 Counting Equipment:
Compensation for these variations must be provided. It is not
7.4.1 Irradiation Container Receiver and Stopping
necessarytomakeanabsolutemeasurementofthefluencerate
Devices—These are devices to accept the sample following
at the irradiation position, but only to obtain a value that is
−2 −1
irradiation, and to position it reproducibly for counting.
proportional to the neutrons cm s passing through the
sample.Awidevarietyofingenioussystemshavebeendevised 7.4.2 Gamma Detector, or Detectors—Detectors at least
and used for this purpose (18). Probably the most commonly equalinsensitivitytoasingle3-in.by3-in.(76mmby76mm)
used and simplest system is a boron trifluoride (BF ) counter thallium-activated sodium iodide (NaI(T1)) scintillation coun-
coupled to a rate meter, scaler, or multichannel analyzer ter should be used. Both the sensitivity and reproducibility of
operatinginthemultichannelscalermodetodetectthermalized the measurement will be affected by the choice of radiation
neutrons. The greatest difficulty with this system is that it detectors. Where energy discrimination is required, the supe-
detects thermal neutrons, while the oxygen reaction proceeds rior resolution of a semi-conductor high-purity Ge (HPGe)
onlywithfastneutrons.Therefore,theBF monitor,encasedin detectormaybedesirable.However,useofanaffordableHPGe
a polyethylene cover to thermalize the fast neutrons from the detectormayalsoresultinsomelossofefficiency,ascompared
generator, does not directly measure neutrons of the energy to use of a NaI(T1) detector. Systems based on use of a large
used for the analyses. Hence, the presumption of proportion- well-type NaI(T1) detector, or two 5-in. by 5-in. (127mm by
127mm) solid NaI(T1) detectors mounted at 180 °C are
ality may not always be valid unless the neutron spectrum is
constant. Fortunately, most newer sealed-tube generators pro- commonly used for higher efficiency counting. Bismuth germ-
vide consistent incident particle energies, reducing the likeli- anate (BGO) scintillation detectors have higher efficiencies
hoodofavariableenergyspectrumduringasingleexperiment. than NaI(T1) detectors for the high-energy gamma rays from
Another difficulty is that, if only a single scaler is used, total N, but are also presently much more costly than equivalent-
neutron fluence during the irradiation and not a representative size NaI(T1) crystals. BGO detectors also have poorer energy
fluence rate is measured. Since the length of irradiation is resolution than NaI(T1) detectors and this could be a consid-
eration in some types of analyses. In general, the sensitivity of
ordinarily at least as long as the half-life of the N, any
changes in fluence rate during irradiation will introduce an oxygen analysis will be increased by increasing the volume of
error. This error can be overcome by using a pulse-height thedetector,andanaly
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
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
of the standard as published by ASTM is to be considered the official document.
Designation: E385 − 16 E385 − 22
Standard Test Method for
Oxygen Content Using a 14-MeV Neutron Activation and
Direct-Counting Technique
This standard is issued under the fixed designation E385; 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
1.1 This test method covers the measurement of oxygen concentration in almost any matrix by using a 14-MeV neutron activation
and direct-counting technique. Essentially, the same system may be used to determine oxygen concentrations ranging from under
10 μg/g to over 500 mg/g, depending on the sample size and available 14-MeV neutron fluence rates.
NOTE 1—The range of analysis may be extended by using higher neutron fluence rates, larger samples, and higher counting efficiency detectors.
1.2 This test method may be used on either solid or liquid samples, provided that they can be made to conform in size, shape, and
macroscopic density during irradiation and counting to a standard sample of known oxygen content. Several variants of this method
have been described in the technical literature. A monograph is available which provides a comprehensive description of the
principles of activation analysis using a neutron generator (1).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.Specific precautions are given in Section 8.
1.5 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:
E170 Terminology Relating to Radiation Measurements and Dosimetry
E181 Test Methods for Detector Calibration and Analysis of Radionuclides
3 4
E496 Test Method for Measuring Neutron Fluence and Average Energy from H(d,n) He Neutron Generators by Radioactivation
Techniques
This test method is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications and is the direct responsibility of Subcommittee E10.05
on Nuclear Radiation Metrology.
Current edition approved Jan. 1, 2016Feb. 1, 2022. Published February 2016March 2022. Originally approved in 1969. Last previous edition approved in 20112016 as
E385 – 11.E385 – 16. DOI: 10.1520/E0385-16.10.1520/E0385-22.
The boldface numbers in parentheses refer to a list of references at the end of the text.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
E385 − 22
2.2 U.S. Government Document:
Code of Federal Regulations, Title 10, Part 20
3. Terminology
3.1 Definitions (see also Terminology E170):
3.1.1 accelerator—a machine that ionizes a gas and electrically accelerates the ions onto a target. The accelerator may be based
on the Cockroft-Walton, Van de Graaff, or other design types (1). Compact sealed-tube, mixed deuterium and tritium gas,
Cockcroft-Walton neutron generators are most commonly used for 14-MeV neutron activation analysis. However, “pumped”
drift-tube accelerators that use replaceable tritium-containing targets are also still in use. Reviews of operational characteristics,
descriptions of accessory instrumentation, and applications of accelerators used as fast neutron generators for activation analysis
are available (2, 3).
−1
3.1.2 comparator standard—a reference standard of known oxygen content whose specific counting rate (counts min [mg of
−1
oxygen] ) may be used to quantify the oxygen content of a sample irradiated and counted under the same conditions. Often, a
comparator standard is selected to have a matrix composition, physical size, density and shape very similar to the corresponding
parameters of the sample to be analyzed.
−2
3.1.3 14-MeV neutron fluence rate—the areal density of neutrons passing through a sample, measured in terms of neutrons cm
−1
s , that is produced by the fusion reaction of deuterium and tritium ions accelerated to energies of typically 150 to 200 keV in
a small accelerator. Fluence rate has been commonly referred to as “flux density.” The total neutron fluence is the fluence rate
integrated over time.
3.1.3.1 Discussion—
3 4
The H(d,n) He reaction is used to produce approximately 14.7-MeV neutrons. This reaction has a Q-value of + 17.586 MeV.
3.1.4 monitor—any type of detector or comparison reference material that can be used to produce a response proportional to the
14-MeV neutron fluence rate in the irradiation position, or to the radionuclide decay events recorded by the sample detector. A
plastic pellet with a relatively high oxygen content is often used as a monitor reference in dual sample transfer systems. It is never
removed from the system regardless of the characteristics of the sample to be analyzed. It is important to distinguish that the
monitor, whether an independent detector or an activated reference material, is not a standard used to scale the oxygen content of
the samples to be measured, but rather is used to normalize the analysis system among successive analytial passes within the
procedure.
3.1.5 multichannel pulse-height analyzer—an instrument that receives, counts, separates, and stores, as a function of their energy,
pulses from a scintillation or semi-conductor gamma-ray detector and amplifier. In the 14-MeV instrumental neutron activation
analysis (INAA) determination of oxygen, the multichannel analyzer may also be used to receive and record both the BF neutron
detector monitor counts and the sample gamma-ray detector counts as a function of stepped time increments (4-6). In the latter
case, operation of the analyzer in the multichannel scaler (MCS) mode, an electronic gating circuit is used to select only gamma
rays within the energy range of interest.
3.1.6 transfer system—a system, normally pneumatic, used to transport the sample from an injection port (sometimes connected
to an automatic sample changer) to the irradiation station, and then to the counting station where the activity of the sample is
measured. The system may include components to ensure uniform positioning of the sample at the irradiation and counting
stations.
4. Summary of Test Method
4.1 The weighed sample to be analyzed is placed in a container for automatic transfer from a sample-loading port to the 14-MeV
neutron irradiation position of a particle accelerator. After irradiation for a pre-selected time, the sample is automatically returned
to the counting area. A gamma-ray detector measures the high-energy gamma radiation from the radioactive decay of the N
produced by the (n,p) nuclear reaction on O. The number of counts in a pre-selected counting interval is recorded by a gated
scaler, or by a multichannel analyzer operating in either the pulse-height, or gated multiscaler modes. The number of events
recorded for samples and monitor reference standard are corrected for background and normalized to identical irradiation and
counting conditions. If the sample and a monitor reference sample are not irradiated simultaneously, the neutron dose received
during each irradiation must be recorded, typically by use of a BF neutron proportional counter. The amount of total oxygen (all
Available from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.
E385 − 22
chemical forms) in the sample is proportional to the corrected and normalized sample count and is quantified by use of the
corrected and normalized specific activity of the comparator standard(s).
16 5 16
4.1.1 N decays with a half-life of 7.13 s(2) s by β-emission (7), thus returning to O. From Ref (87), sixty seven percent67.0
(6) % of the decays are accompanied by 6.12863-MeV 6.12863 (4) MeV gamma rays, 4.9 % by 7.11515-MeV 4.9 (4) % by
7.11515 (14) MeV gamma rays, and 0.82 % 0.82 (6) % by 2.7415-MeV2.7415 (5) MeV gamma rays. Other lower intensity gamma
rays are also observed. About 28 % of the beta transitions are directly to the ground state of O. Useful elemental data including
calculated sensitivities and reaction cross-sections for (14-MeV INAA) are provided in Refs (3) and (98). (See also Test Methods
E181.)
5. Significance and Use
5.1 The conventional determination of oxygen content in liquid or solid samples is a relatively difficult chemical procedure. It is
slow and usually of limited sensitivity. The 14-MeV neutron activation and direct counting technique provides a rapid, highly
sensitive, nondestructive procedure for oxygen determination in a wide range of matrices. This test method is independent of the
chemical form of the oxygen.
5.2 This test method can be used for quality and process control in the metals, coal, and petroleum industries, and for research
purposes in a broad spectrum of applications.
6. Interferences
6.1 Because of the high energy of the gamma rays emitted in the decay of N, there are very few elements that will produce
19 16
interfering radiations; nevertheless, caution should be exercised. F, for example, will undergo an (n,α) reaction to produce N,
19 16
the same indicator radionuclide produced from oxygen. Because the cross section for the F(n,α) N reaction is approximately
16 16
one-half that of the O(n,p) N reaction, a correction must be made if fluorine is present in an amount comparable to the statistical
uncertainty in the oxygen determination. Another possible interfering reaction may arise from the presence of boron. B will
undergo an (n,p) reaction to produce Be. This isotope decays with a half-life of 13.81 s, and emits 13.76 (7) s, and beta decays
to populate excited states in B which subsequently decay by emitting several high-energy gamma rays with energies in the range
of 4.67 to 7.98 MeV.up to 7.97473 MeV (9, 10). In addition, there is Bremsstrahlung radiation produced by the high energy beta
particles emitted by Be. These radiations can interfere with the oxygen determination if the oxygen content does not exceed 1 %
of the boron present.
6.2 Another possible elemental interference can arise from the presence of fissionable materials such as thorium, uranium, and
plutonium. Many short-lived fission products emit high-energy gamma rays capable of interfering with those from N.
40 40 40
NOTE 2—Argon produces an interferent, Cl, by the Ar(n,p) Cl reaction. Therefore, argon should not be used for the inert atmosphere during sample
preparation for oxygen analysis. Cl (t ⁄2 = 1.35 m)(3) m) has several high-energy gamma rays, including one at 5.8796 MeV(12) MeV with a yield of
4.1 %.(5) %.
6.3 An important aspect of this analysis that must be controlled is the geometry during both irradiation and counting. The neutron
source is usually a disk source. Hence, the fluence rate decreases as the inverse square at points distant from the target, and less
rapidly close to the target. Because of these fluence rate gradients, the irradiation geometry should be reproduced as accurately as
possible. Similarly, the positioning of the sample at the detector is critical and must be accurately reproducible. For example, if
the sample is considered to be a point source located 6 mm from a cylindrical sodium iodide (NaI) detector, a 1-mm1 mm change
in position of the sample along the detector axis was found to result in a 3.53.5 % to 5 % change in detector efficiency (1011). Since
efficiency is defined as the fraction of gamma rays emitted from the source that interact with the detector, it is evident that a change
in efficiency would result in an equal percentage change in measured activity and in apparent oxygen content. The sample and
monitor (if present) may be rotated during exposure or counting, or both, to ensure exposure and counting uniformity. See, for
example, Ref (1112). For counting, dual detectors at 180° can be used as an alternative to rotation to minimize positioning errors
at the counting station.
6.4 Since N emits high-energy gamma rays, determinations are less subject to effects of self-absorption than are determinations
based on the use of indicator radionuclides emitting lower energy gamma rays. Corrections for gamma-ray attenuation during
counting are usually negligible, except for large samples as may be needed in the highest sensitivity determinations.
The value of uncertainty, in parentheses, refers to the corresponding last digits, thus 14.958 (2) corresponds to 14.958 6 0.002.
E385 − 22
6.5 The oxygen content of the transfer container (“rabbit”) must be kept as low as possible to avoid a large “blank” correction.
Suggested materials that combine light weight and low oxygen content are polypropylene and high-density polyethylene (molded
under a nitrogen atmosphere), high purity Cu, and high-purity nickel. A simple subtraction of the counts from the blank vial in the
absence of the sample is not adequate for oxygen determinations below 200 μg/g, since large sample sizes may be required for
these high-sensitivity measurements and gamma-ray attenuation may be important when the sample is present (1213). If the total
oxygen content of the sample is as low as that of the container (typically about 0.5 mg of oxygen), the sample should be removed
from the irradiation container prior to counting. Statistical errors increase rapidly as true sample activities decrease, while container
contamination activities remain constant. For certain shapable solids, it may be possible to use no container at all (1314). This
“containerless” approach provides optimum sensitivity for low-level determinations, but care must be taken to avoid contamination
of the transfer system.
6.6 Although the discriminator is used to eliminate the signal originating from gamma rays of energy less than 4.5 MeV, 4.5 MeV,
it is possible when analyzing certain materials that very high matrix activities can result in multiple gammas of lower energy being
summed, thereby generating a signal in the energy window. This effect can be minimized by reducing the specific activity of the
interfering radionuclide or by altering the counting geometry to reduce the solid angle. Since the decay of these “coincidence”
events are subject to the half-life of the radionuclide from which they are emitted, it may be possible to differentiate the interfering
signal from oxygen counts by decay rate if using an MCS-based sytem (1415).
7. Apparatus
7.1 14-MeV Neutron Generator—Typically, this is a high-voltage sealed-tube machine to accelerate both deuterium and tritium
3 4
ions onto a target to produce 14-MeV neutrons by the H(d,n) He reaction. In the older “pumped” drift-tube accelerators, and also
in some of the newer sealed-tube neutron generators, deuterium ions are accelerated into copper targets containing a deposit of
titanium into which tritium is absorbed. Detailed descriptions of both sealed-tube and drift-tube machines have been published (1,
3).
16 16
7.1.1 Other nuclear reactions may be used, but the neutron energy must exceed 10.2210.24451 MeV (1516) for the O(n,p) N
9 12 −1
reaction to take place. The 14-MeV neutron output of the generator should be 10 to 10 neutrons s , with a usable fluence rate
7 9 −2 −1
at the sample of 10 to 10 neutrons cm s . The 14-MeV fluence rate may be measured as described in Test Method E496.
7.1.2 The neutron output from targets in drift-tube machines decreases quite rapidly during use because of depletion of the tritium
content of the target in the pumped system. Consequently, the target must be replaced frequently. The use of a sealed-tube-type
neutron generator obviates the need to handle tritium targets and provides for longer stable operation.
7.2 Sample Transfer System—The short half-life (7.13 s) of the N requires that the sample be transferred rapidly between the
irradiation position and the counting station by a pneumatic system to minimize decay of the N. If the oxygen content in the
sample is low, it is desirable to use dry nitrogen, rather than air, in the pneumatic system to avoid an increase in radioactivity due
to recoil of N atoms produced in the air onto the sample surface or other transfer of irradiated air back to the counting station.
The transfer system and data processing may be controlled directly by laboratory computers (1617), or by programmable logic
controllers (5, 6). Dual transfer systems transport the sample and a monitor reference standard simultaneously. In this case, two
independent counting systems are often used. Single sample transfer systems based on sequential irradiations of a sample and a
comparator standard, are also used.
NOTE 3—As mentioned previously in 6.2, argon should be avoided in the transfer gas, as well as in sample packaging, because of the interferent Cl
produced.
7.3 Monitor—The number of counts obtained from any given irradiation is dependent upon the oxygen content of the sample, the
length of irradiation, the neutron fluence rate, the neutron energy spectrum, the delay time between irradiation and counting, and
the length of the count. It is desirable to make a measurement in which the result obtained is a function of only the oxygen content
and independent of other variables. This can be achieved by standardizing the experimental conditions and use of a monitor.
7.3.1 In the dual sample transfer approach, the monitor is ordinarily a high-oxygen containing material that is irradiated with each
sample in a position adjacent to the sample position, transferred to an independent detector, and counted simultaneously with the
sample. The same monitor reference is used with each sample, and is never removed from the system. Since the sample and
monitor reference are irradiated and counted simultaneously, and N is measured in both, most changes in the experimental
parameters affecting the sample counts will affect the monitor counts equally. One possible exception is that changes in the neutron
E385 − 22
energy spectrum due to incident accelerator particle energy changes may affect the sample and monitor in different ways due to
angular dependence factors. However, a relatively constant particle energy can usually be achieved. Therefore, while the number
of counts obtained from any given sample may vary greatly from one irradiation to another, the ratio of sample counts to monitor
reference counts will be a constant. To determine the oxygen content of a sample, it is necessary to irradiate a comparator standard
of known oxygen content with physical and chemical properties similar to those of the sample and determine the ratio of its counts
to that of the monitor reference as well.
7.3.2 If a single sample transfer system is used, it is necessary to measure the neutron fluence rate during both the irradiation of
the sample and the irradiation of the comparator standard. Variations in fluence rate from a neutron generator are to be expected,
not only with time, but also with position. Compensation for these variations must be provided. It is not necessary to make an
absolute measurement of the fluence rate at the irradiation position, but only to obtain a value that is proportional to the neutrons
−2 −1
cm s passing through the sample. A wide variety of ingenious systems have been devised and used for this purpose (1718).
Probably the most commonly used and simplest system is a boron trifluoride (BF ) counter coupled to a rate meter, scaler, or
multichannel analyzer operating in the multichannel scaler mode to detect thermalized neutrons. The greatest difficulty with this
system is that it detects thermal neutrons, while the oxygen reaction proceeds only with fast neutrons. Therefore, the BF monitor,
encased in a polyethylene cover to thermalize the fast neutrons from the generator, does not directly measure neutrons of the energy
used for the analyses. Hence, the presumption of proportionality may not always be valid unless the neutron spectrum is constant.
Fortunately, most newer sealed-tube generators provide consistent incident particle energies, reducing the likelihood of a variable
energy spectrum during a single experiment. Another difficulty is that, if only a single scaler is used, total neutron fluence during
the irradiation and not a representative fluence rate is measured. Since the length of irradiation is ordinarily at least as long as the
half-life of the N, any changes in fluence rate during irradiation will introduce an error. This error can be overcome by using a
pulse-height analyzer operating in the multichannel scaler mode and recording the BF monitor output and the induced N activity
on the same multiscaler pass (4-6, 1819). Changes in beam intensity can then be precisely compensated for by mathematically
treating each channel recording the relative neutron fluence rate as an individual irradiation and decay correcting its relative
contribution to the oxygen counts over the remainder of the irradiation period. This produces a beam normalization value that is
tailored to correct for beam variations during the irradiation as well as beam intensity differences between irradiations.
7.3.3 Variations in the positions of the sample or monitor reference relative to the neutron generator will cause a variation in the
ratio of sample counts to monitor counts. In order to avoid the effects of this nonuniformity, both the sample and the monitor
reference standard can be rotated about an axis parallel to the beam during irradiation. Selection of experimental irradiation and
counting geometries normally can be done in such a way as to avoid significant errors (see 7.4.2).
7.3.4 The short half-life of N imposes some restrictions on the timing of the various steps of the analysis. For maximum accuracy
in a single sample transfer system, the entire cycle of irradiation, transfer, and counting should be controlled automatically so that
all times are reproduced within a few hundredths of a second. Alternately, the entire irradiation and counting process may be
recorded by a multichannel analyzer operating in the multichannel scaler mode and the parameters later normalized by use of a
computer program (4-6). Precise control or measurements of time and fluence rate are not usually necessary when a monitor
reference is irradiated simultaneously with the sample in a dual sample transfer and counting system.
7.4 Counting Equipment:
7.4.1 Irradiation Container Receiver and Stopping Devices—These are devices to accept the sample following irradiation, and to
position it reproducibly for counting.
7.4.2 Gamma Detector, or Detectors—Detectors at least equal in sensitivity to a single 33-in. by 3-in. (76(76 mm by
76-mm)76 mm) thallium-activated sodium iodide (NaI(T1)) scintillation counter should be used. Both the sensitivity and
reproducibility of the measurement will be affected by the choice of radiation detectors. Where energy discrimination is required,
the superior resolution of a semi-conductor high-purity Ge (HPGe) detector may be desirable. However, use of an affordable HPGe
detector may also result in some loss of efficiency, as compared to use of a NaI(T1) detector. Systems based on use of a large
well-type NaI(T1) detector, or two 55-in. by 5-in. (127(127 mm by 127-mm)127 mm) solid NaI(T1) detectors mounted at 180°C
180 °C are commonly used for higher efficiency counting. Bismuth germanate (BGO) scintillation detectors have higher
efficiencies than NaI(T1) detectors for the high-energy gamma rays from N, but are also presently much more costly than
equivalent-size NaI(T1) crystals. BGO detectors also have poorer energy resolution than NaI(T1) detectors and this could be a
consideration in some types of analyses. In general, the sensitivity of oxygen analysis will be increased by increasing the volume
of the detector, and analytical reproducibility will be increased by the use of multiple detectors. If a single detector is used, but
not a well counter, the sample should be rotated during counting to minimize the effects of sample nonhomogeneity and
positioning. An external radiation shield of heavy metal sufficient to reduce the detector background to an acceptable level should
surround the detector assembly.
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