1、Designation: E942 96 (Reapproved 2011)E942 16Standard Guide forSimulation Investigating the Effects of Helium Effects inIrradiated Metals1This standard is issued under the fixed designation E942; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides advice for conducting experiments to investigate the effects of helium on
3、 the properties of metals wherethe technique for introducing the helium differs in some way from the actual mechanism of introduction of helium in service.Simulation techniques Techniques considered for introducing helium shallmay include charged particle implantation, exposure to-emitting radioisot
4、opes, and tritium decay techniques. Procedures for the analysis of helium content and helium distributionwithin the specimen are also recommended.1.2 TwoThree other methods for introducing helium into irradiated materials are not covered in this guide. They are are: (1) theenhancement of helium prod
5、uction in nickel-bearing alloys by spectral tailoring in mixed-spectrum fission reactors, (2and ) arelated technique that uses a thin layer of NiAl on the specimen surface to inject helium, and (3) isotopic tailoring in both fast andmixed-spectrum fission reactors. These techniques are described in
6、Refs (1-56).2 Dual ion beam techniques (67) for simultaneouslyimplanting helium and generating displacement damage are also not included here. This latter method is discussed in PracticeE521.1.3 In addition to helium, hydrogen is also produced in many materials by nuclear transmutation. In some case
7、s it appears toact synergistically with helium (8-10). The specific impact of hydrogen is not addressed in this guide.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the
8、 safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C859 Terminology Relating to N
9、uclear MaterialsE170 Terminology Relating to Radiation Measurements and DosimetryE521 Practice for Investigating the Effects of Neutron Radiation Damage Using Charged-Particle IrradiationE706 Master Matrix for Light-Water Reactor Pressure Vessel Surveillance Standards, E 706(0) (Withdrawn 2011)4E910
10、 Test Method for Application and Analysis of Helium Accumulation Fluence Monitors for Reactor Vessel Surveillance,E706 (IIIC)3. Terminology3.1 Descriptions of relevant terms are found in Terminology C859 and Terminology E170.4. Significance and Use4.1 Helium is introduced into metals as a consequenc
11、e of nuclear reactions, such as (n, ), or by the injection of helium intometals from the plasma in fusion reactors. The characterization of the effect of helium on the properties of metals using direct1 This guide is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications
12、and is the direct responsibility of Subcommittee E10.08 onProcedures for Neutron Radiation Damage Simulation.Current edition approved June 15, 2011Dec. 1, 2016. Published July 2011January 2017. Originally approved in 1983. Last previous edition approved in 20032011 asE942 96 (2011).(2003). DOI: 10.1
13、520/E0942-96R11.10.1520/E0942-16.2 The boldface numbers in parentheses refer to a list of references at the end of this guide.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information,
14、refer to the standards Document Summary page on the ASTM website.4 The last approved version of this historical standard is referenced on www.astm.org.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 th
15、e previous version. Becauseit 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 versionof the standard as published by ASTM is to be considered the official document.Copyright A
16、STM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1irradiation methods may be impractical because of the time required to perform the irradiation or the lack of a radiation facility,as in the case of the fusion reactor. Simulation techniques can ac
17、celerate the research by identifying and isolating major effectscaused by the presence of helium. The word simulationsimulationis used here in a broad sense to imply an approximation of therelevant irradiation environment. There are many complex interactions between the helium produced during irradi
18、ation and otherirradiation effects, so care must be exercised to ensure that the effects being studied are a suitable approximation of the real effect.By way of illustration, details of helium introduction, especially the implantation temperature, may determine the subsequentdistribution of the heli
19、um (that is, dispersed atomistically, in small clusters in bubbles, etc.)etc.).5. Techniques for Introducing Helium5.1 Implantation of Helium Using Charged Particle Accelerators:5.1.1 Summary of MethodCharged particle accelerators are designed to deliver well defined, intense beams of monoenergeticp
20、articles on a target. They thus provide a convenient, rapid, and relatively inexpensive means of introducing large concentrationsof helium into thin specimens. An energetic alpha particle impinging on a target loses energy by exciting or ionizing the targetatoms, or both, and by inelastic collisions
21、 with the target atom nuclei. Particle ranges for a variety of materials can be obtainedfrom tabulated range tables (7-10-1114) or calculated using a Monte Carlo code such as SRIM (15).5.1.1.1 To obtain a uniform concentration of helium through the thickness of a sample, it is necessary to vary the
22、energy of theincident beam, rock the sample (126), or, more commonly, to degrade the energy of the beam by interposing a thin sheet or wedgeof material ahead of the target.The range of monoenergetic particles is described by a Gaussian distribution around the mean range.This range straggling provide
23、s a means of implanting uniform concentrations through the thickness of a specimen bysuperimposing the Gaussian profiles that result from beam energy degradation of different thicknesses of material. The uniformityof the implant depends on the number of superpositions. Charged particle beams have di
24、mensions of the order of a few millimetresso that some means of translating the specimen in the beam or of rastering the beam across the specimen must be employed touniformly implant specimens of the size required for tensile or creep tests. The rate of helium deposition is usually limited by thehea
25、t removal rate from the specimens and the limits on temperature rise for a given experiment. Care must be exercised that phasetransformations or annealing of microstructural components do not result from beam heating.5.1.2 LimitationsOne of the major limitations of the technique is that the thicknes
26、s of a specimen that can be implanted withhelium is limited to the range of the most energetic alpha particle beam available (or twice the range if the specimen is implantedfrom both sides). Thus a stainless steel tensile specimen is limited to 1.2 mm thickness using a 70-MeV beam to implant thespec
27、imen from both sides. This limiting thickness is greater for light elements such as aluminum and less for heavier elements suchas molybdenum.5.1.2.1 One of the primary reasons for interest in helium implantation is to simulateinvestigate the effects resulting from theproduction of helium by transmut
28、ation reactions in nuclear reactors. It should be appreciated that the property changes in irradiatedmetals result from complex interactions between the helium atoms and the radiation damage produced during the irradiation inways that are not fully understood. Energetic Implantation of energetic alp
29、ha particles dodoes produce atomic displacements, butin a manner atypical of most neutron irradiations. The displacement rate is generally higher than that in fast reactor, but the ratioof helium atoms to displaced atoms is some 103 times greater for implantation of stainless steel with a 50-MeV alp
30、ha beam.5.1.3 ApparatusApparatus for helium implantation is usually custom designed and built at each research center and thereforemuch variety exists in the approach to solving each problem. The general literature should be consulted for detailed information(12-16-1620). Paragraphs 5.1.3 5.1.3.4 pr
31、ovide comments on the major components of the helium implantation apparatus.5.1.3.1 AcceleratorCyclotrons or other accelerators are used for helium implantation experiments because they are well suitedto accelerate light ions to the high potentials required for implantation. Typical Cyclotron operat
32、ing characteristics are 20 to 80MeV with a beam current of 20 A at the source. It should be noted, however, that the usable beam current delivered to thespecimen is limited by the ability to remove heat from the specimens which restricts beam currents to a limit of 4 to 5 A. Abeam-rastering system i
33、s the most practical method for moving the beam across the sample surface to uniformly implant heliumover large areas of the specimen.5.1.3.2 Beam Energy DegraderThe most efficient procedure for implanting helium with an accelerator, because of the timeinvolved in changing the energy, is to operate
34、the accelerator at the maximum energy and to control the depth of the helium implantby degrading the beam energy. This procedure offers the additional advantages that range straggling increases with energy, thusproducing a broader depth profile, and the angular divergence of the beam increases as a
35、consequence of the electronic energy lossprocess, thus increasing the spot size and reducing the localized beam heating. The beam energy degrader requires that a knownthickness of material be placed in front of the beam with provisions for remotely changing the thickness and for removal of heatfrom
36、the beam energy degrader. Acceptable methods include a rotating stepped or wedged wheel, a movable wedge, or a stack offoils. Beam degrader materials can be beryllium, aluminum, or graphite. The wedge or rotating tapered wheel designs provide acontinuous change in energy deposition, so as to provide
37、 a uniform distribution of helium in the specimen but introduce theadditional complexity of moving parts and cooling of thick sections of material. The stacked foil designs are simpler, can be cooledadequately by an air jet, and have well calibrated thickness. The design must be selected on the basi
38、s of experiment purpose andfacility flexibility. Concentrations of helium uniform to within 65 % can be achieved by superposition of the depth profilesproduced by 25-m increments in the thickness of aluminum beam degrader foils. Uniformity of 610 % is recommended for allE942 162material experiments.
39、 Distributing helium over more limited depth ranges (as, for example, when it is only required to spreadhelium about the peak region of heavy ion damage, in specimens that will be examined by transmission electron microscopy) canbe done by cycling the energy of the helium-implanting accelerator (151
40、9) in place of degrader techniques.5.1.3.3 Specimen HolderThe essential features of the specimen holder are provisions for accurately placing the specimen inthe beam and for cooling the specimens. Additional features may include systems for handling and irradiating large numbers ofspecimens to impro
41、ve the efficiency of the facility and to avoid handling the specimens until the radioactivity induced during theimplantation has had an opportunity to decay. Some method of specimen cooling is essential since a degraded, singly charged beamof average energy of 20 MeV and current of 5 A striking a 1-
42、cm2 nickel target, 0.025 cm thick, deposits 100 W of heat into amass of 0.22 g. Assuming only radiative heat loss to the surroundings, the resulting rise in temperature would occur at an initialrate of about 1300 Ks1 and would reach a value of about 2000 K. Techniques used for specimen cooling will
43、depend on whetherthe implantation is performed in air or in vacuum and on the physical characteristics of the specimen. Conductive cooling witheither air or an inert gas may be used if implants are not performed in vacuum. Water cooling is a more effective method of heatremoval and permits higher cu
44、rrent densities to be used on thick tensile specimens. The specimens may be bonded to a cooledsupport block or may be in direct contact with the coolant. Care must be exercised to ensure that metallurgical reactions do notoccur between the bonding material and the specimen as a consequence of the be
45、am heating, and that hot spots do not developas a consequence of debonding from thermal expansion of the specimen. Silver conductive paint has been used successfully as abonding agent where the temperature rise is minimal. Aluminum is recommended in preference to copper for construction of thetarget
46、 holder because of the high levels of radioactivity induced in copper.5.1.3.4 Faraday Cup and Charge Integration SystemA Faraday cup should be used to measure the beam current delivered tothe target. A600 mmA 600 mm long by 50 mm 50 mm diameter aluminum tube closed on one end makes a satisfactory Fa
47、radaycup. An electron suppressor aperture insulated from the Faraday cup and positively charged is necessary to collect the electronsemitted from the degrader foils so as to give accurate beam current readings. Beam current density and beam profile can bedetermined by reading the current passed by a
48、 series of apertures of calibrated size that can be placed in the beam. The target holderassembly must be insulated from its surroundings, and deionized (low conductivity) water must be used for cooling purposes topermit an integration of current delivered to the target and thereby accurately measur
49、e the total helium implanted independent offluctuations in the beam current. A negatively biased aperture must be placed between the target holder and the degrader foils tosuppress secondary electrons emitted from the target that would give erroneously high values of total charge deposited on thespecimen.5.1.4 ProcedurePrior to the actual implantation of helium in a specimen, certain standardization and calibration proceduresshould be performed. The temperature rise to be expected from beam heating and the intended specimen cooling mode must bemeasured. Such me
