ASTM E496-14(2022)
(Test Method)Standard Test Method for Measuring Neutron Fluence and Average Energy from 3H(d,n)4He Neutron Generators by Radioactivation Techniques
Standard Test Method for Measuring Neutron Fluence and Average Energy from <sup >3</sup>H(d,n)<sup>4</sup>He Neutron Generators by Radioactivation Techniques
SIGNIFICANCE AND USE
5.1 Refer to Practice E261 for a general discussion of the measurement of fast-neutron fluence rates with threshold detectors.
5.5.1 Fig. 5 (2) shows how the neutron energy depends upon the angle of scattering in the laboratory coordinate system when the incident deuteron has an energy of 150 keV and is incident on a thick and a thin tritiated target. For thick targets, the incident deuteron loses energy as it penetrates the target and produces neutrons of lower energy. A thick target is defined as a target thick enough to completely stop the incident deuteron. The two curves in Fig. 5, for both thick and thin targets, come from different sources. The dashed line calculations come from Ref (3); the solid curve calculations come from Ref (4); and the measured data come from Ref (5). The dash-dot curve and the right-hand axis give the difference between the calculated neutron energies for thin and thick targets. Computer codes are available to assist in calculating the expected thick and thin target yield and neutron spectrum for various incident deuteron energies (6).
FIG. 5 Dependence of 3H(d,n)4He Neutron Energy on Angle (2)
5.6 The Q-value for the primary 3H(d,n)4He reaction is +17.59 MeV. When the incident deuteron energy exceeds 3.71 MeV and 4.92 MeV, the break-up reactions 3H(d,np)3H and 3H(d,2n)3He, respectively, become energetically possible. Thus, at high deuteron energies (>3.71 MeV) this reaction is no longer monoenergetic. Monoenergetic neutron beams with energies from about 14.8 to 20.4 MeV can be produced by this reaction at forward laboratory angles (7).
5.7 It is recommended that the dosimetry sensors be fielded in the exact positions where the dosimetry results are wanted. There are a number of factors that can affect the monochromaticity or energy spread of the neutron beam (7, 8). These factors include the energy regulation of the incident deuteron energy, energy loss in retaining windows if a gas target is used or energy loss within t...
SCOPE
1.1 This test method covers a general procedure for the measurement of the fast-neutron fluence rate produced by neutron generators utilizing the 3H(d,n)4He reaction. Neutrons so produced are usually referred to as 14-MeV neutrons, but range in energy depending on a number of factors. This test method does not adequately cover fusion sources where the velocity of the plasma may be an important consideration.
1.2 This test method uses threshold activation reactions to determine the average energy of the neutrons and the neutron fluence at that energy. At least three activities, chosen from an appropriate set of dosimetry reactions, are required to characterize the average energy and fluence. The required activities are typically measured by gamma-ray spectroscopy.
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.
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
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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: E496 − 14 (Reapproved 2022)
Standard Test Method for
Measuring Neutron Fluence and Average Energy
3 4
from H(d,n) He Neutron Generators by Radioactivation
Techniques
This standard is issued under the fixed designation E496; 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
2.1 ASTM Standards:
1.1 This test method covers a general procedure for the
E170Terminology Relating to Radiation Measurements and
measurement of the fast-neutron fluence rate produced by
3 4
Dosimetry
neutron generators utilizing the H(d,n) He reaction. Neutrons
E181Test Methods for Detector Calibration andAnalysis of
so produced are usually referred to as 14-MeV neutrons, but
Radionuclides
range in energy depending on a number of factors. This test
E261Practice for Determining Neutron Fluence, Fluence
method does not adequately cover fusion sources where the
Rate, and Spectra by Radioactivation Techniques
velocity of the plasma may be an important consideration.
E265Test Method for Measuring Reaction Rates and Fast-
1.2 This test method uses threshold activation reactions to Neutron Fluences by Radioactivation of Sulfur-32
determine the average energy of the neutrons and the neutron E720Guide for Selection and Use of Neutron Sensors for
Determining Neutron Spectra Employed in Radiation-
fluence at that energy.At least three activities, chosen from an
Hardness Testing of Electronics
appropriate set of dosimetry reactions, are required to charac-
terize the average energy and fluence. The required activities 2.2 International Commission on Radiation Units and Mea-
are typically measured by gamma-ray spectroscopy. surements (ICRU) Reports:
ICRU Report 13Neutron Fluence, Neutron Spectra and
1.3 The values stated in SI units are to be regarded as
Kerma
standard. No other units of measurement are included in this
ICRU Report 26Neutron Dosimetry for Biology and Medi-
standard.
cine
2.3 ISO Standard:
1.4 This standard does not purport to address all of the
Guide to the Expression of Uncertainty in Measurement
safety concerns, if any, associated with its use. It is the
2.4 NIST Document:
responsibility of the user of this standard to establish appro-
TechnicalNote1297GuidelinesforEvaluatingandExpress-
priate safety, health, and environmental practices and deter-
ing the Uncertainty of NIST Measurement Results
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions—Refer to Terminology E170.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
4. Summary of Test Method
mendations issued by the World Trade Organization Technical
4.1 This test method describes the determination of the
Barriers to Trade (TBT) Committee.
average neutron energy and fluence by use of three activities
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.
1 3
ThistestmethodisunderthejurisdictionofASTMCommitteeE10onNuclear Available from the International Commission on Radiation Units, 7910
Technology and Applications and is the direct responsibility of Subcommittee Woodmont Ave., Washington, DC 20014.
E10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
CurrenteditionapprovedJuly1,2022.PublishedJuly2022.Originallyapproved 4th Floor, New York, NY 10036, http://www.ansi.org.
in 1973. Last previous edition approved in 2014 as E496–14. DOI: 10.1520/ Available from National Institute of Standards and Technology (NIST), 100
E0496-14R22. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E496 − 14 (2022)
from a select list of dosimetry reactions. Three dosimetry 5.2 Refer to Test Method E265 for a general discussion of
reactionsarechosenbasedonanumberoffactorsincludingthe the measurement of fast-neutron fluence rates by radioactiva-
intensity of the neutron field, the reaction half-lives, the slope tion of sulfur-32.
of the dosimetry reaction cross section near 14 MeV, and the
5.3 Reactions used for the activity measurements can be
minimum time between sensor irradiation and the gamma
chosen to provide a convenient means for determining the
counting. The activities from these selected reactions are
absolutefluenceratesof14-MeVneutronsobtainedwith H(d,
measured. Two of the activities are used, in conjunction with
n) Heneutrongeneratorsoverarangeofirradiationtimesfrom
the nuclear data for the dosimetry reactions, to determine the
seconds to approximately 100 days. High-purity threshold
average neutron energy. The third activity is used, along with
sensors referenced in this test method are readily available.
theneutronenergyandnucleardatafortheselectedreaction,to
determine the neutron fluence. The uncertainty of the neutron
5.4 Theneutron-energyspectrummustbeknowninorderto
energy and the neutron fluence is determined from the activity measure fast-neutron fluence using a single threshold detector.
measurement uncertainty and from the nuclear data.
Neutrons produced by bombarding a tritiated target with
deuterons are commonly referred to as 14-MeV neutrons;
5. Significance and Use
however, they can have a range of energies depending on: (1)
5.1 Refer to Practice E261 for a general discussion of the the angle of neutron emission with respect to the deuteron
measurement of fast-neutron fluence rates with threshold beam,(2)thekineticenergyofthedeuterons,and(3)thetarget
detectors. thickness. In most available neutron generators of the
3 4
FIG. 1 Variation of 0 Degree H(d,n) He Differential Cross Section with Incident Deuteron Energy (1)
E496 − 14 (2022)
3 4
FIG. 2 Variation of 0 Degree H(d,n) He Differential Cross Section with Incident Deuteron Energy (1)
Cockroft-Walton type, a thick target is used to obtain high- magnitude,A , of the P (θ) term, and hence the asymmetry in
1 1
neutron yields.As deuterons penetrate through the surface and the differential cross section grows with increasing energy of
move into the bulk of the thick target, they lose energy, and
the incident deuteron.The nonrelativistic kinematics (valid for
3 4
interactions occurring deeper within the target produce neu-
E <20 MeV) for the H(d,n) He reaction show that:
d
trons with correspondingly lower energy.
½ ½
E 50.28445E 3cosθ1 (1)
n d
5.5 Wide variations in neutron energy are not generally
2 ½
2.031E 3cosθ 1352.6422819.95998E
encountered in commercially available neutron generators of ~ !
d d
5.01017
theCockroft-Waltontype.Figs.1and2 (1) showthevariation
3 4
ofthezerodegree H(d,n) Heneutronproductioncrosssection
where:
with energy, and clearly indicate that maximum neutron yield
E = the neutron energy in MeV,
n
is obtained with deuterons having energies near the 107 keV
E = the incident deuteron energy in MeV, and
d
resonance. Since most generators are designed for high yield,
θ = the neutron emission angle with respect to the incident
the deuteron energy is typically about 200 keV, giving a range
deuteron in the laboratory system.
of neutron energies from approximately 14 to 15 MeV. The
5.5.1 Fig.5 (2)showshowtheneutronenergydependsupon
differentialcenter-of-masscrosssectionistypicallyparameter-
the angle of scattering in the laboratory coordinate system
izedasasummationofLegendrepolynomials.Figs.3and4 (1,
2) show how the neutron yield varies with the emission angle when the incident deuteron has an energy of 150 keV and is
in the laboratory system. The insert in Fig. 4 shows how the incident on a thick and a thin tritiated target. For thick targets,
the incident deuteron loses energy as it penetrates the target
6 andproducesneutronsoflowerenergy.Athicktargetisdefined
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard. as a target thick enough to completely stop the incident
E496 − 14 (2022)
3 4
FIG. 4 Change in Neutron Energy from H(d,n) He Reaction with
Laboratory Emission Angle (2)
3 4
FIG. 3 Energy and Angle Dependence of the H(d,n) He
Differential Cross Section (1)
energy, energy loss in retaining windows if a gas target is used
orenergylosswithinthetargetifasolidtritiatedtargetisused,
deuteron. The two curves in Fig. 5, for both thick and thin
the irradiation geometry, and background neutrons from scat-
targets, come from different sources. The dashed line calcula-
tering with the walls and floors within the irradiation chamber.
tions come from Ref (3); the solid curve calculations come
from Ref (4); and the measured data come from Ref (5). The
6. Apparatus
dash-dot curve and the right-hand axis give the difference
6.1 Either a NaI(Tl) or a Ge semiconductor gamma-ray
between the calculated neutron energies for thin and thick
spectrometer, incorporating a multichannel pulse-height ana-
targets. Computer codes are available to assist in calculating
lyzer is required. See Test Methods E181 for a discussion of
the expected thick and thin target yield and neutron spectrum
spectrometer systems and their use.
for various incident deuteron energies (6).
3 4
6.2 If sulfur is used as a sensor, then a beta particle detector
5.6 The Q-value for the primary H(d,n) He reaction
is required. The apparatus required for beta counting of sulfur
is+17.59 MeV. When the incident deuteron energy exceeds
3 3
is described in Test Methods E181 and E265.
3.71 MeV and 4.92 MeV, the break-up reactions H(d,np) H
3 3
and H(d,2n) He, respectively, become energetically possible.
6.3 A precision balance for determining foil masses is
Thus,athighdeuteronenergies(>3.71MeV)thisreactionisno
required.
longer monoenergetic. Monoenergetic neutron beams with
energies from about 14.8 to 20.4 MeVcan be produced by this 7. Materials and Manufacture
reaction at forward laboratory angles (7).
7.1 High-purity threshold foils are available in a large
5.7 It is recommended that the dosimetry sensors be fielded variety of thicknesses. Foils of suitable diameter can be
in the exact positions where the dosimetry results are wanted. punched from stock material. Small diameter wire may also be
There are a number of factors that can affect the monochro- used. Pre-punched and weighed high-purity foils are also
maticity or energy spread of the neutron beam (7, 8). These available commercially. Guide E720 provides some details on
factors include the energy regulation of the incident deuteron typicalfoilmassesandpurity.Foilsof12.7and25.4mm(0.50
E496 − 14 (2022)
of each cross section is listed in the table.The SNLRMLcross
section compendium (13) is a single-point-of-reference alter-
nativesourceforthecrosssectionsanduncertaintydataforthe
reactions mentioned in Table 1, but somewhat dated, reflecting
larger uncertainties than IRDF 2002. The references for the
other nuclear data in Table 1 are given in the table.
9.1.3 Longerhigh-fluenceirradiationsarerecommendedfor
thedeterminationoftheneutronenergy.Table3andFig.7give
the neutron energy-dependent activity ratios for some com-
monly used sensor combinations. Fig. 8 displays some slopes
for these ratios. In general, the larger the slope, the more
sensitive the method is to the neutron energy. For the proce-
dures of this standard to work, it is necessary for the ratios of
the cross sections to be monotonic in the vicinity of 14 MeV,
but the slopes need not be monotonic.
9.1.4 Table 4 shows the energy resolutions of some specific
sensor combinations for a 14.5-MeV neutron source.
58 57
The Ni(n,2n) Ni-based combinations are recommended due
to their steep slope and accurate dosimetry cross section
evaluations.
9.2 Determine the Sensor Mass—Weigh each sensor to a
precision of 0.1%. Nonuniform foil thicknesses can result
from the use of dull punches and frequently result in weight
variation of 10% or more.
9.3 Irradiation of Sensors—Irradiate the sensors, making
certain that both sensors experience exactly the same fluence.
The fluence gradients near a 14-MeV source tend to be high
and it may be necessary to stack the sensors together or to
3 4
FIG. 5 Dependence of H(d,n) He Neutron Energy on Angle (2)
mount them on a rotating disk during irradiation. Note the
length of the irradiation, t, and the time the irradiation ended.
i
and 1.00 in.) diameter and 0.13 and 0.25 mm (0.005 and 0.010 Some sensors may have an interference reaction that is
in.) thickness are typical. sensitive to low-energy neutrons. The interference reaction
may be associated with the primary sensor element or with a
7.2 SeeTestMethodE265fordetailsontheavailabilityand
contaminant material in the sensor. Of the reactions listed in
preparation of sulfur sensors.
Table 1, the use of a Cu sensor is the only case where the
primary sensor element may be responsible for an interference
8. Calibration
65 64
reaction. In this case the useful Cu(n,2n) Cu reaction activ-
8.1 See Test Methods E181 for general detector calibration
63 64
ity must be distinguished from the Cu(n,γ) Cu interference
methods. Test Methods E181 addresses both gamma-ray spec-
reaction activity (for example, by using an isotopically pure
trometers and beta counting methods.
sensororbyexperimentallyverifyingboundsonthemaximum
possible level of interference). Other examples of interference
9. Procedure for Determining the Neutron Energy
reactions from contaminant materials include trace impurities
9.1 Selection of Sensors:
of Mn in Fe sensors and Na in Al sensors. Manganese is a
9.1.1 Use of an activity ratio method is recommended for
frequent contaminant in Fe foils. In this case the Mn(n,
the determination of the neutron energy. The activity ratio
γ) Mn reaction interferes with the desired sensor response
method has been described in Ref (9). This test method has
56 56
fromthe Fe(n,p) Mnreaction.SaltfromhandlingAlsensors
been validated for ENDF/B-VI cross sections (10) in Ref (11).
...
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