ASTM E942-96
(Guide)Standard Guide for Simulation of Helium Effects in Irradiated Metals
Standard Guide for Simulation of Helium Effects in Irradiated Metals
SCOPE
1.1 This guide provides advice for conducting experiments to investigate the effects of helium on the properties of metals where the technique for introducing the helium differs in some way from the actual mechanism of introduction of helium in service. Simulation techniques considered for introducing helium shall include charged particle implantation, exposure to [alpha]-emitting radioisotopes, and tritium decay techniques. Procedures for the analysis of helium content and helium distribution within the specimen are also recommended.
1.2 Two other methods for introducing helium into irradiated materials are not covered in this guide. They are the enhancement of helium production in nickel-bearing alloys by spectral tailoring in mixed-spectrum fission reactors, and isotopic tailoring in both fast and mixed-spectrum fission reactors. These techniques are described in Refs (1-5). Dual ion beam techniques (6) for simultaneously implanting helium and generating displacement damage are also not included here. This latter method is discussed in Practice E521.
1.3 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.
General Information
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Standards Content (Sample)
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Designation: E 942 – 96
Standard Guide for
Simulation of Helium Effects in Irradiated Metals
This standard is issued under the fixed designation E 942; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This guide provides advice for conducting experiments 3.1 Descriptions of relevant terms are found in Terminology
to investigate the effects of helium on the properties of metals C 859 and Terminology E 170.
where the technique for introducing the helium differs in some
4. Significance and Use
way from the actual mechanism of introduction of helium in
4.1 Helium is introduced into metals as a consequence of
service. Simulation techniques considered for introducing he-
lium shall include charged particle implantation, exposure to nuclear reactions, such as (n, a), or by the injection of helium
into metals from the plasma in fusion reactors. The character-
a-emitting radioisotopes, and tritium decay techniques. Proce-
dures for the analysis of helium content and helium distribution ization of the effect of helium on the properties of metals using
within the specimen are also recommended. direct irradiation methods may be impractical because of the
time required to perform the irradiation or the lack of a
1.2 Two other methods for introducing helium into irradi-
ated materials are not covered in this guide. They are the radiation facility, as in the case of the fusion reactor. Simula-
tion techniques can accelerate the research by identifying and
enhancement of helium production in nickel-bearing alloys by
spectral tailoring in mixed-spectrum fission reactors, and isolating major effects caused by the presence of helium. The
word simulation is used here in a broad sense to imply an
isotopic tailoring in both fast and mixed-spectrum fission
reactors. These techniques are described in Refs (1-5). Dual approximation of the relevant irradiation environment. There
are many complex interactions between the helium produced
ion beam techniques (6) for simultaneously implanting helium
and generating displacement damage are also not included during irradiation and other irradiation effects, so care must be
exercised to ensure that the effects being studied are a suitable
here. This latter method is discussed in Practice E 521.
1.3 This standard does not purport to address all of the approximation of the real effect. By way of illustration, details
of helium introduction, especially the implantation tempera-
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- ture, may determine the subsequent distribution of the helium
(that is, dispersed atomistically, in small clusters in bubbles,
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. etc.)
5. Techniques for Introducing Helium
2. Referenced Documents
2.1 ASTM Standards: 5.1 Implantation of Helium Using Charged Particle Accel-
erators:
C 859 Terminology Relating to Nuclear Materials
E 170 Terminology Relating to Radiation Measurements 5.1.1 Summary of Method—Charged particle accelerators
and Dosimetry are designed to deliver well defined, intense beams of monoen-
ergetic particles on a target. They thus provide a convenient,
E 521 Practice for Neutron Radiation Damage Simulation
by Charged-Particle Irradiation rapid, and relatively inexpensive means of introducing large
concentrations of helium into thin specimens. An energetic
E 706 Master Matrix for Light-Water Reactor Pressure
Vessel Surveillance Standards, E706(0) alpha particle impinging on a target loses energy by exciting or
ionizing the target atoms, or both, and by inelastic collisions
E 910 Test Method for Application and Analysis of Helium
Accumulation Fluence Monitors for Reactor Vessel Sur- with the target atom nuclei. Particle ranges for a variety of
materials can be obtained from tabulated range tables (7-11).
veillance, E706(IIIC)
5.1.1.1 To obtain a uniform concentration of helium through
the thickness of a sample, it is necessary to vary the energy of
This guide is under the jurisdiction of ASTM Committee E-10 on Nuclear
the incident beam, rock the sample (12), or, more commonly, to
Technology and Applications and is the direct responsibility of Subcommittee
degrade the energy of the beam by interposing a thin sheet or
E10.08 on Procedures for Neutron Radiation Damage Simulation.
Current edition approved Jan. 10, 1996. Published March 1996. Originally
wedge of material ahead of the target. The range of monoen-
published as E 942 – 83. Last previous edition E 942 – 89.
ergetic particles is described by a Gaussian distribution around
The boldface numbers in parentheses refer to a list of references at the end of
the mean range. This range straggling provides a means of
this guide.
Annual Book of ASTM Standards, Vol 12.01.
implanting uniform concentrations through the thickness of a
Annual Book of ASTM Standards, Vol 12.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 942
specimen by superimposing the Gaussian profiles that result procedure offers the additional advantages that range straggling
from beam energy degradation of different thicknesses of increases with energy, thus producing a broader depth profile,
material. The uniformity of the implant depends on the number
and the angular divergence of the beam increases as a conse-
of superpositions. Charged particle beams have dimensions of
quence of the electronic energy loss process, thus increasing
the order of a few millimetres so that some means of translating
the spot size and reducing the localized beam heating. The
the specimen in the beam or of rastering the beam across the
beam energy degrader requires that a known thickness of
specimen must be employed to uniformly implant specimens of
material be placed in front of the beam with provisions for
the size required for tensile or creep tests. The rate of helium
remotely changing the thickness and for removal of heat from
deposition is usually limited by the heat removal rate from the
the beam energy degrader. Acceptable methods include a
specimens and the limits on temperature rise for a given
rotating stepped or wedged wheel, a movable wedge, or a stack
experiment. Care must be exercised that phase transformations
of foils. Beam degrader materials can be beryllium, aluminum,
or annealing of microstructural components do not result from
or graphite. The wedge or rotating tapered wheel designs
beam heating.
provide a continuous change in energy deposition, so as to
5.1.2 Limitations—One of the major limitations of the
provide a uniform distribution of helium in the specimen but
technique is that the thickness of a specimen that can be
introduce the additional complexity of moving parts and
implanted with helium is limited to the range of the most
cooling of thick sections of material. The stacked foil designs
energetic alpha particle beam available (or twice the range if
are simpler, can be cooled adequately by an air jet, and have
the specimen is implanted from both sides). Thus a stainless
well calibrated thickness. The design must be selected on the
steel tensile specimen is limited to 1.2 mm thickness using a
basis of experiment purpose and facility flexibility. Concentra-
70-MeV beam to implant the specimen from both sides. This
tions of helium uniform to within 65 % can be achieved by
limiting thickness is greater for light elements such as alumi-
superposition of the depth profiles produced by 25-μm incre-
num and less for heavier elements such as molybdenum.
ments in the thickness of aluminum beam degrader foils.
5.1.2.1 One of the primary reasons for interest in helium
Uniformity of 610 % is recommended for all material experi-
implantation is to simulate the effects resulting from the
ments. Distributing helium over more limited depth ranges (as,
production of helium by transmutation reactions in nuclear
for example, when it is only required to spread helium about
reactors. It should be appreciated that the property changes in
the peak region of heavy ion damage, in specimens that will be
irradiated metals result from complex interactions between the
examined by transmission electron microscopy) can be done by
helium atoms and the radiation damage produced during the
cycling the energy of the helium-implanting accelerator (15) in
irradiation in ways that are not fully understood. Energetic
place of degrader techniques.
alpha particles do produce atomic displacements, but in a
5.1.3.3 Specimen Holder—The essential features of the
manner atypical of most neutron irradiations. The displacement
specimen holder are provisions for accurately placing the
rate is generally higher than that in fast reactor, but the ratio of
specimen in the beam and for cooling the specimens. Addi-
helium atoms to displaced atoms is some 10 times greater for
tional features may include systems for handling and irradiat-
implantation of stainless steel with a 50-MeV alpha beam.
ing large numbers of specimens to improve the efficiency of the
5.1.3 Apparatus—Apparatus for helium implantation is
facility and to avoid handling the specimens until the radioac-
usually custom designed and built at each research center and
tivity induced during the implantation has had an opportunity
therefore much variety exists in the approach to solving each
to decay. Some method of specimen cooling is essential since
problem. The general literature should be consulted for de-
a degraded, singly charged beam of average energy of 20 MeV
tailed information (12-16). Paragraphs 5.1.3-5.1.3.4 provide
and current of 5 μA striking a 1-cm nickel target, 0.025 cm
comments on the major components of the helium implantation
thick, deposits 100 W of heat into a mass of 0.22 g. Assuming
apparatus.
only radiative heat loss to the surroundings, the resulting rise in
5.1.3.1 Accelerator—Cyclotrons or other accelerators are
−1
temperature would occur at an initial rate of about 1300 K·s
used for helium implantation experiments because they are
and would reach a value of about 2000 K. Techniques used for
well suited to accelerate light ions to the high potentials
specimen cooling will depend on whether the implantation is
required for implantation. Typical Cyclotron operating charac-
performed in air or in vacuum and on the physical character-
teristics are 20 to 80 MeV with a beam current of 20 μA at the
istics of the specimen. Conductive cooling with either air or an
source. It should be noted, however, that the usable beam
inert gas may be used if implants are not performed in vacuum.
current delivered to the specimen is limited by the ability to
Water cooling is a more effective method of heat removal and
remove heat from the specimens which restricts beam currents
to a limit of 4 to 5 μA. A beam-rastering system is the most permits higher current densities to be used on thick tensile
practical method for moving the beam across the sample specimens. The specimens may be bonded to a cooled support
surface to uniformly implant helium over large areas of the
block or may be in direct contact with the coolant. Care must
specimen. be exercised to ensure that metallurgical reactions do not occur
between the bonding material and the specimen as a conse-
5.1.3.2 Beam Energy Degrader—The most efficient proce-
quence of the beam heating, and that hot spots do not develop
dure for implanting helium with an accelerator, because of the
time involved in changing the energy, is to operate the as a consequence of debonding from thermal expansion of the
specimen. Silver conductive paint has been used successfully
accelerator at the maximum energy and to control the depth of
the helium implant by degrading the beam energy. This as a bonding agent where the temperature rise is minimal.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 942
Aluminum is recommended in preference to copper for con- holder will have high levels of induced activity and precautions
struction of the target holder because of the high levels of must be exercised in handling and storage of the specimens and
radioactivity induced in copper. target holder. Most of this activity is shortlived and decays
within a day. The induced activity can be used advantageously
5.1.3.4 Faraday Cup and Charge Integration System—A
to check the uniformity of the implant by standard autoradio-
Faraday cup should be used to measure the beam current
graphic techniques.
delivered to the target. A600 mm long by 50 mm diameter
aluminum tube closed on one end makes a satisfactory Faraday 5.1.5 Calculation and Interpretation of Results—The ranges
of energetic particles in solid media have been calculated
cup. An electron suppressor aperture insulated from the Fara-
day cup and positively charged is necessary to collect the (7-12) for a number of materials. The range increases with
increasing energy and is affected by target parameters such as
electrons emitted from the degrader foils so as to give accurate
beam current readings. Beam current density and beam profile electron density, atomic density, and atomic mass. Ranges are
−2
stated in units of mg·cm , which, when divided by the
can be determined by reading the current passed by a series of
−3
apertures of calibrated size that can be placed in the beam. The physical density of the target material, in g·cm gives a
distance in tens of μm. The total range is defined as the total
target holder assembly must be insulated from its surroundings,
and deionized (low conductivity) water must be used for path length from the point of entry at the target surface to the
cooling purposes to permit an integration of current delivered point at which the particle comes to rest. The projected range
to the target and thereby accurately measure the total helium or penetration depth is defined as the projection of the total
implanted independent of fluctuations in the beam current. A range along the normal to the entry face of the target, and is
negatively biased aperture must be placed between the target therefore a sensitive function of the angle of incidence of the a
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