ASTM E521-96(2003)
(Practice)Standard Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation
Standard Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation
SIGNIFICANCE AND USE
A characteristic advantage of charged-particle irradiation experiments is precise, individual, control over most of the important irradiation conditions such as dose, dose rate, temperature, and quantity of gases present. Additional attributes are the lack of induced radioactivation of specimens and, in general, a substantial compression of irradiation time, from years to hours, to achieve comparable damage as measured in displacements per atom (dpa). An important application of such experiments is the investigation of radiation effects in not-yet-existing environments, such as fusion reactors.
The primary shortcoming of ion bombardments stems from the damage rate, or temperature dependences of the microstructural evolutionary processes in complex alloys, or both. It cannot be assumed that the time scale for damage evolution can be comparably compressed for all processes by increasing the displacement rate, even with a corresponding shift in irradiation temperature. In addition, the confinement of damage production to a thin layer just (often ∼ 1 μm) below the irradiated surface can present substantial complications. It must be emphasized, therefore, that these experiments and this practice are intended for research purposes and not for the certification or the qualification of equipment.
This practice relates to the generation of irradiation-induced changes in the microstructure of metals and alloys using charged particles. The investigation of mechanical behavior using charged particles is covered in Practice E 821.
SCOPE
1.1 This practice provides guidance on performing charged-particle irradiations of metals and alloys. It is generally confined to studies of microstructural and microchemical changes carried out with ions of low-penetrating power that come to rest in the specimen. Density changes can be measured directly and changes in other properties can be inferred. This information can be used to estimate similar changes that would result from neutron irradiation. More generally, this information is of value in deducing the fundamental mechanisms of radiation damage for a wide range of materials and irradiation conditions.
1.2 The word simulation is used here in a broad sense to imply an approximation of the relevant neutron irradiation environment. The degree of conformity can range from poor to nearly exact. The intent is to produce a correspondence between one or more aspects of the neutron and charged particle irradiations such that fundamental relationships are established between irradiation or material parameters and the material response.
1.3 The practice appears as follows:SectionApparatus4Specimen Preparation5-10Irradiation Techniques (including Helium Injection)11-12Damage Calculations13Postirradiation Examination14-16Reporting of Results17Correlation and Interpretation18-22
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:E521–96 (Reapproved 2003)
Standard Practice for
Neutron Radiation Damage Simulation by Charged-Particle
Irradiation
This standard is issued under the fixed designation E521; 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 (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Thispracticeisintendedtoprovidethenuclearresearchcommunitywithrecommendedprocedures
for the simulation of neutron radiation damage by charged-particle irradiation. It recognizes the
diversity of energetic-ion producing devices, the complexities in experimental procedures, and the
difficulties in correlating the experimental results with those produced by reactor neutron irradiation.
Such results may be used to estimate density changes and the changes in microstructure that would
be caused by neutron irradiation. The information can also be useful in elucidating fundamental
mechanisms of radiation damage in reactor materials.
1. Scope
Reporting of Results 17
Correlation and Interpretation 18-22
1.1 Thispracticeprovidesguidanceonperformingcharged-
1.4 This standard does not purport to address all of the
particle irradiations of metals and alloys. It is generally
confined to studies of microstructural and microchemical safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
changes carried out with ions of low-penetrating power that
cometorestinthespecimen.Densitychangescanbemeasured priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
directly and changes in other properties can be inferred. This
informationcanbeusedtoestimatesimilarchangesthatwould
2. Referenced Documents
result from neutron irradiation. More generally, this informa-
2.1 ASTM Standards:
tion is of value in deducing the fundamental mechanisms of
C859 Terminology Relating to Nuclear Materials
radiation damage for a wide range of materials and irradiation
E798 Practice for Conducting Irradiations at Accelerator-
conditions.
Based Neutron Sources
1.2 The word simulation is used here in a broad sense to
E821 Practice for Measurement of Mechanical Properties
imply an approximation of the relevant neutron irradiation
During Charged-Particle Irradiation
environment.Thedegreeofconformitycanrangefrompoorto
E910 Test Method forApplication andAnalysis of Helium
nearly exact. The intent is to produce a correspondence
Accumulation Fluence Monitors for Reactor Vessel Sur-
between one or more aspects of the neutron and charged
veillance, E706 (IIIC)
particle irradiations such that fundamental relationships are
E942 Guide for Simulation of Helium Effects in Irradiated
established between irradiation or material parameters and the
Metals
material response.
1.3 The practice appears as follows:
3. Terminology
Section
Apparatus 4 3.1 Definitions of Terms Specific to This Standard:
Specimen Preparation 5-10
3.1.1 Descriptions of relevant terms are found in Terminol-
Irradiation Techniques (including Helium Injection) 11–12
ogy C859 and Terminology E170.
Damage Calculations 13
Postirradiation Examination 14-16 3.2 Definitions:
3.2.1 damage energy, n—that portion of the energy lost by
an ion moving through a solid that is transferred as kinetic
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
energy to atoms of the medium; strictly speaking, the energy
Technology and Applications and is the direct responsibility of Subcommittee
E10.08 on Procedures for Neutron Radiation Damage Simulation.
Current edition approved Jan. 10, 1996. Published March 1996. Originally Annual Book of ASTM Standards, Vol 12.01.
published as E521–76. Last previous edition E521–89. Annual Book of ASTM Standards, Vol 12.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E521–96 (2003)
transfer in a single encounter must exceed the energy required damage production to a thin layer just (often ; 1 µm) below
to displace an atom from its lattice cite. the irradiated surface can present substantial complications. It
3.2.2 displacement, n—the process of dislodging an atom must be emphasized, therefore, that these experiments and this
from its normal site in the lattice. practice are intended for research purposes and not for the
3.2.3 path length, n—the total length of path measured certification or the qualification of equipment.
along the actual path of the particle. 4.3 This practice relates to the generation of irradiation-
3.2.4 penetration depth, n—a projection of the range along induced changes in the microstructure of metals and alloys
the normal to the entry face of the target. using charged particles. The investigation of mechanical be-
3.2.5 projected range, n—the projection of the range along havior using charged particles is covered in Practice E821.
the direction of the incidence ion prior to entering the target.
3.2.6 range, n—the distance from the point of entry at the 5. Apparatus
surface of the target to the point at which the particle comes to
5.1 Accelerator—The major item is the accelerator, which
rest.
in size and complexity dwarfs any associated equipment.
3.2.7 stopping power (or stopping cross section), n—the
Therefore, it is most likely that irradiations will be performed
energy lost per unit path length due to a particular process;
at a limited number of sites where accelerators are available (a
usually expressed in differential form as−dE/dx.
1-MeV electron microscope may also be considered an accel-
3.2.8 straggling, n—the statistical fluctuation due to atomic
erator).
or electronic scattering of some quantity such as particle range
5.2 Fixtures for holding specimens during irradiation are
or particle energy at a given depth.
generally custom-made as are devices to measure and control
3.3 Symbols:Symbols:
particle energy, particle flux, and specimen temperature. Deci-
A,Z —the atomic weight and the number of the bombard-
1 1
sions regarding apparatus are therefore left to individual
ing ion.
workerswiththerequestthataccuratedataontheperformance
A,Z —the atomic weight and number of the atoms of the
2 2
of their equipment be reported with their results.
medium undergoing irradiation.
depa—damage energy per atom; a unit of radiation expo-
6. Composition of Specimen
sure. It can be expressed as the product of s¯ and the fluence.
de
6.1 An elemental analysis of stock from which specimens
dpa—displacements per atom; a unit of radiation exposure
are fabricated should be known. The manufacturer’s heat
giving the mean number of times an atom is displaced from its
number and analysis are usually sufficient in the case of
lattice site. It can be expressed as the product of s¯ and the
d
commercally produced metals. Additional analysis should be
fluence.
performed after other steps in the experimental procedure if
heavy ion—used here to denote an ion of mass >4.
there is cause to believe that the composition of the specimen
light ion—an arbitrary designation used here for conve-
may have been altered. It is desirable that uncertainties in the
nience to denote an ion of mass#4.
analyses be stated and that an atomic basis be reported in
T —an effective value of the energy required to displace an
d
addition to a weight basis.
atom from its lattice site.
s (E)—anenergy-dependentdisplacementcrosssection; s¯
d d
7. Preirradiation Heat Treatment of Specimen
denotes a spectrum-averaged value. Usual unit is barns.
7.1 Temperature and time of heat treatments should be well
s (E)—an energy-dependent damage energy cross section;
de
controlled and reported. This applies to intermediate anneals
s¯ denotes a spectrum-averaged value. Usual unit is barns-eV
de
during fabrication, especially if a metal specimen is to be
or barns-keV.
irradiated in the cold-worked condition, and it also applies to
4. Significance and Use
operations where specimens are bonded to metal holders by
4.1 A characteristic advantage of charged-particle irradia- diffusion or by brazing. The cooling rate between annealing
tionexperimentsisprecise,individual,controlovermostofthe steps and between the final annealing temperature and room
temperature should also be controlled and reported.
important irradiation conditions such as dose, dose rate,
temperature, and quantity of gases present. Additional at- 7.2 The environment of the specimen during heat treatment
tributes are the lack of induced radioactivation of specimens should be reported. This includes description of container,
and, in general, a substantial compression of irradiation time, measureofvacuum,presenceofgases(flowingorsteady),and
from years to hours, to achieve comparable damage as mea- the presence of impurity absorbers such as metal sponge.Any
sured in displacements per atom (dpa). An important applica- discoloration of specimens following an anneal should be
tionofsuchexperimentsistheinvestigationofradiationeffects reported.
in not-yet-existing environments, such as fusion reactors. 7.3 High-temperature annealing of metals and alloys from
4.2 The primary shortcoming of ion bombardments stems Groups IV, V, and VI frequently results in changes, both
from the damage rate, or temperature dependences of the positive and negative, in their interstitial impurity content.
microstructural evolutionary processes in complex alloys, or Since the impurity content may have a significant influence on
both. It cannot be assumed that the time scale for damage void formation, an analysis of the specimen or of a companion
evolution can be comparably compressed for all processes by piecepriortoirradiationshouldbeperformed.Othersituations,
increasing the displacement rate, even with a corresponding such as selective vaporization of alloy constituents during
shift in irradiation temperature. In addition, the confinement of annealing, would also require a final analysis.
E521–96 (2003)
7.4 The need for care with regard to alterations in compo- investigated by analyses of polished and nonpolished speci-
sition is magnified by the nature of the specimens. They are mens. Deviations in the surface form the perfect-planar condi-
usually very thin with a high exposed surface-to-volume ratio. tion should not exceed, in dimension perpendicular to the
Information is obtained from regions whose distance from the plane, 10% of the expected particle range in the specimen.
surface may be small relative to atomic diffusion distances.
10.2 The specimen may be irradiated in a mechanically
polished condition provided damage produced by polishing
8. Plastic Deformation of Specimen does not extend into the region of postirradiation examination.
8.1 When plastic deformation is a variable in radiation
11. Dimension of Specimen Parallel to Particle Beam
damage, care must be taken in the geometrical measurements
used to compute the degree of deformation. The variations in
11.1 Specimens without support should be thick enough to
dimensions of the larger piece from which specimens are cut
resist deformation during handling. If a disk having a diameter
should be measured and reported to such a precision that a
of 3 mm is used, its thickness should be greater than 0.1 mm.
standard deviation in the degree of plastic deformation can be
11.2 Supportedspecimensmaybeconsiderablythinnerthan
assigned to the specimens. A measuring device more accurate
unsupported specimens. The minimum thickness should be at
and precise than the common hand micrometer will probably
least fourfold greater than the distance below any surface from
be necessary due to the thinness of specimens commonly
which significant amounts of radiation-produced defects could
irradiated.
escape.Thisdistancecansometimesbeobservedasavoid-free
8.2 The term cold-worked should not stand alone as a
zone near the free surface of an irradiated specimen.
description of state of deformation. Every effort should be
made to characterize completely the deformation. The param-
12. Helium
eters which should be stated are: (1) deformation process (for
12.1 Injection:
example, simple tension or compression, swaging, rolling,
12.1.1 Alpha-particle irradiation is frequently used to inject
rolling with applied tension); (2) total extent of deformation,
helium into specimens to simulate the production of helium
expressed in terms of the principal orthogonal natural strain
during neutron irradiations where helium is produced by
components (e , e , e ) or the geometric shape changes that
1 2 3
transmutation reactions. Helium injection may be completed
willallowthereadertocomputethestrains;(3)procedureused
before particle irradiation begins. It may also proceed incre-
to reach the total strain level (for example, number of rolling
mentally during interruptions in the particle irradiation or it
passes and reductions in each); (4) strain rate; and (5) defor-
may proceed simultaneously with particle irradiation. The last
mation temperature, including an estimate of temperature
case is the most desirable as it gives the closest simulation to
changes caused by adiabatic work.
neutron irradiation. Some techniques for introducing helium
8.2.1 Many commonly used deformation processes (for
are set forth in Guide E942.
example, rolling and swaging) tend to be nonhomogeneous. In
12.1.2 The influence of implantation temperature on helium
such cases the strain for each pass can be best stated by the
distribution (that is, dispersed atomistically, in small clusters,
dimensionsintheprincipalworkingdirectionsbeforeandafter
inbubbles,etc.)isknowntobeimportant.Theconsequencesof
each pass. The strain rate can then be specified sufficiently by
thechoiceofinjectiontemperatureonthesimulationshouldbe
stating the deformation time of each pass.
evaluated and reported.
12.2 Analysis and Distribution:
9. Preirradiation Metallography of Specimen
12.2.1 Analysis of the concentration of helium injected into
9.1 A general examination by light microscopy and
the specimens should be performed by mass spectrometry.
transmission-electron microscopy should be performed on the
Using this technique, the helium content is determined by
specimen in the condition in which it will be irradiated. In
vaporizing a helium-containing specimen under vacuum, add-
3 4 3
somecases,thismeansthattheexaminationshouldbedoneon
ingaknownquantityof He,andmeasuringthe He/ Heratio.
specimens that were mounted for irradiation and then un-
Thisinformation,alongwiththespecimenweight,willgivethe
mounted without being irradiated. The microstructure should
average hel
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