ASTM E261-16(2021)
(Practice)Standard Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques
Standard Practice for Determining Neutron Fluence, Fluence Rate, and Spectra by Radioactivation Techniques
SIGNIFICANCE AND USE
5.1 Transmutation Processes—The effect on materials of bombardment by neutrons depends on the energy of the neutrons; therefore, it is important that the energy distribution of the neutron fluence, as well as the total fluence, be determined.
SCOPE
1.1 This practice describes procedures for the determination of neutron fluence rate, fluence, and energy spectra from the radioactivity that is induced in a detector specimen.
1.2 The practice is directed toward the determination of these quantities in connection with radiation effects on materials.
1.3 For application of these techniques to reactor vessel surveillance, see also Test Methods E1005.
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.
Note 1: Detailed methods for individual detectors are given in the following ASTM test methods: E262, E263, E264, E265, E266, E343, E393, E481, E523, E526, E704, E705, and E854.
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
Relations
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: E261 − 16 (Reapproved 2021)
Standard Practice for
Determining Neutron Fluence, Fluence Rate, and Spectra by
Radioactivation Techniques
This standard is issued under the fixed designation E261; 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 tion Rates and Thermal Neutron Fluence Rates by Radio-
activation Techniques
1.1 Thispracticedescribesproceduresforthedetermination
E263Test Method for Measuring Fast-Neutron Reaction
of neutron fluence rate, fluence, and energy spectra from the
Rates by Radioactivation of Iron
radioactivity that is induced in a detector specimen.
E264Test Method for Measuring Fast-Neutron Reaction
1.2 The practice is directed toward the determination of
Rates by Radioactivation of Nickel
these quantities in connection with radiation effects on mate-
E265Test Method for Measuring Reaction Rates and Fast-
rials.
Neutron Fluences by Radioactivation of Sulfur-32
1.3 For application of these techniques to reactor vessel E266Test Method for Measuring Fast-Neutron Reaction
Rates by Radioactivation of Aluminum
surveillance, see also Test Methods E1005.
E343Test Method for Measuring Reaction Rates by Analy-
1.4 This standard does not purport to address all of the
sis of Molybdenum-99 Radioactivity From Fission Do-
safety concerns, if any, associated with its use. It is the
simeters (Withdrawn 2002)
responsibility of the user of this standard to establish appro-
E393Test Method for Measuring Reaction Rates by Analy-
priate safety, health, and environmental practices and deter-
sis of Barium-140 From Fission Dosimeters
mine the applicability of regulatory limitations prior to use.
E481Test Method for Measuring Neutron Fluence Rates by
NOTE 1—Detailed methods for individual detectors are given in the
Radioactivation of Cobalt and Silver
following ASTM test methods: E262, E263, E264, E265, E266, E343,
E523Test Method for Measuring Fast-Neutron Reaction
E393, E481, E523, E526, E704, E705, and E854.
Rates by Radioactivation of Copper
1.5 This international standard was developed in accor-
E526Test Method for Measuring Fast-Neutron Reaction
dance with internationally recognized principles on standard-
Rates by Radioactivation of Titanium
ization established in the Decision on Principles for the
E693Practice for Characterizing Neutron Exposures in Iron
Development of International Standards, Guides and Recom-
and Low Alloy Steels in Terms of Displacements Per
mendations issued by the World Trade Organization Technical
Atom (DPA)
Barriers to Trade (TBT) Committee.
E704Test Method for Measuring Reaction Rates by Radio-
activation of Uranium-238
2. Referenced Documents
E705Test Method for Measuring Reaction Rates by Radio-
2.1 ASTM Standards:
activation of Neptunium-237
E170Terminology Relating to Radiation Measurements and
E722PracticeforCharacterizingNeutronFluenceSpectrain
Dosimetry
Terms of an Equivalent Monoenergetic Neutron Fluence
E181Test Methods for Detector Calibration andAnalysis of
for Radiation-Hardness Testing of Electronics
Radionuclides
E844Guide for Sensor Set Design and Irradiation for
E262Test Method for Determining Thermal Neutron Reac-
Reactor Surveillance
E854Test Method for Application and Analysis of Solid
State Track Recorder (SSTR) Monitors for Reactor Sur-
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
veillance
Technology and Applications and is the direct responsibility of Subcommittee
E944Guide for Application of Neutron Spectrum Adjust-
E10.05 on Nuclear Radiation Metrology.
ment Methods in Reactor Surveillance
Current edition approved Sept. 1, 2021. Published October 2021. Originally
approved in 1965 as E261–65T. Last previous edition approved in 2016 as E1005Test Method for Application and Analysis of Radio-
E261–16. DOI: 10.1520/E0261-16R21.
metric Monitors for Reactor Vessel Surveillance
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E261 − 16 (2021)
E1018Guide for Application of ASTM Evaluated Cross 8. Irradiation Procedures
Section Data File
8.1 The irradiations are carried out in two ways depending
E2005Guide for Benchmark Testing of Reactor Dosimetry
upon whether the instantaneous fluence rate or the fluence is
in Standard and Reference Neutron Fields
being determined. For fluence rate, irradiate the detector for a
2.2 ISO Standard: short period at sufficiently low power that handling difficulties
JCGM100:2008Evaluationofmeasurementdata—Guideto
and shielding requirements are minimized. Then extrapolate
the expression of uncertainty in measurement the resulting fluence rate value to the value anticipated for full
JCGM 104:2009Evaluation of measurement data—An in-
reactorpower.Thistechniqueissometimesusedforthefluence
troduction to the “Guide to the expression of uncertainty mapping of reactors (1, 2).
in measurement” and related documents
8.2 The determination of fluence is most often required in
JCGM 101:2008 Evaluation of measurement data—
experiments on radiation effects on materials. Irradiate the
Supplement 1 to the “Guide to the expression of uncer-
detectors for the same duration as the experiment at a position
tainty in measurement” – Propogation of distributions
in the reactor where, as closely as possible, they will experi-
using a Monte Carlo method
ence the same fluence, or will bracket the fluence of the
JCGM 102:2011 Evaluation of measurement data—
position of interest. When feasible, place the detectors in the
Supplement 2 to the “Guide to the expression of uncer-
experiment capsule. In this case, long-term irradiations are
tainty in measurement” – Extension to any number of
often required.
output quantities
8.3 Itisdesirable,butnotrequired,thattheneutrondetector
JCGM 106:2012Evaluation of measurement data—The role
be irradiated during the entire time period considered and that
of measurement uncertainty in conformity assessment
a measurable part of the activity generated during the initial
period of irradiation be present in the detector at the end of the
3. Terminology
irradiation. Therefore, the effective half-life, t' = 0.693/λ'
1/2
3.1 Descriptions of terms relating to dosimetry are found in
(seeEq6),ofthereactionproductshouldnotbemuchlessthan
Terminology E170.
the total elapsed time from the initial exposure to the final
shutdown.
4. Summary of Practice
8.4 Asmentionedin9.10through9.11,theuseofcadmium-
4.1 A sample containing a known amount of the nuclide to
shielded detectors is convenient in separating contributions to
be activated is placed in the neutron field. The sample is
the measured activity from thermal (E170) and epithermal
removed after a measured period of time and the induced
(E170) neutrons.Also, cadmium shielding is helpful in reduc-
activity is determined.
ing activities due to impurities and the loss of the activated
nuclide by thermal-neutron absorption. The recommended
5. Significance and Use
thicknesses of cadmium is 1 mm. When bare and cadmium-
shielded samples are placed in the same vicinity, take care to
5.1 Transmutation Processes—The effect on materials of
bombardment by neutrons depends on the energy of the avoid partial shielding of the bare detectors by the cadmium-
shielded ones.
neutrons; therefore, it is important that the energy distribution
of the neutron fluence, as well as the total fluence, be
9. Calculation
determined.
9.1 Fluence:
6. Counting Apparatus 9.1.1 φ(E, t) is the differential neutron fluence rate; that is,
the fluence rate per unit energy per unit time for neutrons with
6.1 A number of instruments are used to determine the
energies between E and E + dE.When focusing on the neutron
disintegration rate of the radioactive product of the neutron-
spectrum, the notation φ(E) is sometimes used. φ(E) has an
induced reaction. These include the scintillation counters,
implicit dependence on time. In many cases, the neutron
ionization chambers, proportional counters, Geiger tubes, and
spectrum does not vary with time.
solidstatedetectors.Recommendationsofcountersforparticu-
9.1.2 The neutron fluence rate φ is the integral over energy
lar applications are given in Test Methods E181.
of the differential neutron fluence rate.
7. Requirements for Activation-Detector Materials
φ 5 φ E dE (1)
* ~ !
7.1 Considerations concerning the suitability of a material φ has an implicit dependence on time.
for use as an activation detector are found in Guide E844.
9.1.3 φ(E) may be determined by computer calculations
7.2 The amounts of fissionable material needed for fission
using neutron transport codes or by adjustment techniques
threshold detectors are rather small and the availability of the
using radioactivation data from multiple-foil irradiations.
material is limited. Licenses from the U.S. Nuclear Regulatory
9.1.4 The neutron fluence, Φ, is related to the time varying
Commission are required for possession.
differential neutron fluence rate by the following expression:
7.3 A detailed description of procedures for the use of
fission threshold detectors is given in Test Methods E343,
The boldface numbers in parentheses refer to a list of references at the end of
E393, and E854, and Guide E844. this standard.
E261 − 16 (2021)
` t
A 5λD/ 1 2 exp 2λ t exp 2λ t (8)
@~ ~ !! ~ !#
c w
Φ 5 * * φ~E,t!dt dE (2)
0 t
where:
where:
λ = decay constant for the radioactive nuclide,
t –t = duration of the irradiation period
2 1
t = time interval for counting,
c
t = time elapsed between the end of the irradiation period
9.2 Spectrum-Averaged Cross Sections:
w
9.2.1 Spectrum-averaged cross sections (E170) are used in and the start of the counting period, and
D = number of disintegrations (net number of counts cor-
reactionratecalculations.Aspectrum-averagedcrosssectionis
rected for background, random and true coincidence
defined as follows:
losses, efficiency of the counting system, and fraction
`
σ E φ E dE
* ~ ! ~ !
of the sample counted) in the interval t .
c
σ¯ 5 (3)
`
φ E dE
* ~ !
9.5.2 If, as is often the case, the counting period is short
compared to the half-life (=0.693⁄λ) of the radioactive
where:
nuclide, the activity is well approximated as follows:
σ(E) = microscopiccrosssectionfortheisotopeandreaction
A 5 D/@t exp 2λ t # (9)
~ !
c w
of interest.σ¯ has an implicit dependence on time and
may change if the neutron spectrum changes.
9.5.3 The number of radioactive product nuclei, N,is
p
9.2.2 In order to calculate the spectrum-averaged cross
related to the reaction rate by the following equation:
section, the differential cross section of the nuclide and the
dN ⁄dt 5 NR 2 N λ' (10)
p R p
neutron spectrum over the neutron energy range for which the
nuclide has a non-negligible cross section must be known.
9.5.4 Solution of Eq 10, for the case where the neutron
When cross-section and spectrum information are not
spectrum and N are constant and N =0 at t=0, yields the
p
available, alternative procedures may be used; suggested alter-
following expression for the activity of a foil:
natives are discussed in 9.10 – 9.12, and in the methods for
' '
A 5 N λ 5 ~λ ⁄ λ !NR ~1 2 exp~2λ t !! (11)
p R i
individual detectors.
9.5.5 For irradiations at constant fluence rate, the saturation
9.3 Reaction Rate:
activity (E170), A , is calculated as follows:
9.3.1 The reaction rate per nucleus, R , for a given reaction
s
R
'
is related to the fluence rate by:
A 5 A/ 1 2 exp 2λ t (12)
~ ~ !!
s i
`
R 5 σ E φ E dE (4)
* ~ ! ~ !
where:
R R
t = exposure duration.
i
where:
It follows from Eq 11 and Eq 12 that:
σ (E) = microscopic cross section for the isotope and reac-
R
'
tion of interest.
A 5 ~λ ⁄ λ ! NR (13)
S R
9.3.2 It follows that:
The saturation activity corresponds to the number of disin-
R
R
tegrationsperfoilperunittimeforthesteady-stateconditionin
R 5σ¯ φ or φ 5 (5)
R R
σ¯
R
which the rate of production of the radioactive nuclide is equal
9.4 Effective Decay Constant: to the rate of loss by radioactive decay and transmutation. The
9.4.1 The effective decay constant, λ', which may be a activity A approaches the saturation activity, A , but does not
s
function of time, is related to the decay constant λ as follows:
surpass it, as the exposure duration increases (exp(-λ't)→0).
`
9.5.6 The isotopic content of the target nuclide may be
λ' 5λ1 σ E φ E dE (6)
* ~ ! ~ !
a
reduced during the irradiation by more than one transmutation
process and it may be increased by transmutation of other
where:
nuclides so that the rate of change of the number of target
σ (E) = theneutronabsorptioncrosssectionfortheproduct
a
nuclei with time is described by a number of terms:
nuclide.
n m
9.4.2 The effective decay constant accounts for burnup of a
dN/dt52N R 1 R 1 N R (14)
S D
R ( i ( j j
t51 j51
product nuclide during irradiation.Application of the effective
decay constant for irradiation under varying fluence rates is
where:
discussed in this section and in the detailed methods for
i = discrete transmutation path for removal of the target
individual detectors.
isotope, and
9.5 Activity:
j = discrete transmutation reaction whereby the target iso-
9.5.1 The activity of the sample, A, is the decay rate of the
topeisproducedfromisotope N andeachofthe R and
j i
product nuclei of interest, N .
R terms could be calculated from equations similar to
p
j
Eq 4, using the appropriate cross sections.
A 5 N λ (7)
p
9.5.6.1 The R termmaypredominateand,if R isconstant,
The activity at the end of the exposure period is calculated
R R
from an activation foil count rate as follows: Eq 14 can be solved as
E261 − 16 (2021)
N 5 N exp 2 R t (15) 9.6.4.4 Iftheproductof(λ' t)isverysmallforallirradiation
~ !
0 R
i i
using the approximation that the change in target composi-
periods,thevaluesof A calculatedfromEq17areproportional
i
tion is negligible and replacing N by N .
to (R ) and t.
s i i
9.6.4.5 If the spectrum averaged cross section is also con-
9.5.6.2 During irradiation, the effective decay rate may be
stant over
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.