ASTM E798-96(2003)

Standard Practice for Conducting Irradiations at Accelerator-Based Neutron Sources

ABSTRACT
This practice covers procedures for irradiations at accelerator-based neutron sources. The discussion focuses on nearly monoenergetic 14-MeV neutrons from the deuterium-tritium T(d,n) interaction, and broad spectrum neutrons from stopping deuterium beams in thick beryllium or lithium targets. However, most of the recommendations also apply to other types of accelerator-based sources, including spallation neutron sources. The procedures to be considered include methods for characterizing the accelerator beam and target, the irradiated sample, and the neutron flux and spectrum, as well as procedures for recording and reporting irradiation data.
SCOPE
1.1 This practice covers procedures for irradiations at accelerator-based neutron sources. The discussion focuses on two types of sources, namely nearly monoenergetic 14-MeV neutrons from the deuterium-tritium T(d,n) interaction, and broad spectrum neutrons from stopping deuterium beams in thick beryllium or lithium targets. However, most of the recommendations also apply to other types of accelerator-based sources, including spallation neutron sources (). Interest in spallation sources has increased recently due to their proposed use for transmutation of fission reactor waste ().
1.2 Many of the experiments conducted using such neutron sources are intended to simulate irradiation in another neutron spectrum, for example, that from a DT fusion reaction. 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. In general, the intent of these simulations is to establish the fundamental relationships between irradiation or material parameters and the material response. The extrapolation of data from such experiments requires that the differences in neutron spectra be considered.
1.3 The procedures to be considered include methods for characterizing the accelerator beam and target, the irradiated sample, and the neutron flux and spectrum, as well as procedures for recording and reporting irradiation data.
1.4 Other experimental problems, such as temperature control, are not included.
1.5 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

• Status: Historical
• Publication Date: 09-Jan-1996
• ICS: 27.120.10 - Reactor engineering
• Technical Committee: E10 - Nuclear Technology and Applications

Relations

• Replaces: ASTM E798-96 - Standard Practice for Conducting Irradiations at Accelerator-Based Neutron Sources
• Effective Date: 10-Jan-1996
• Replaced By: ASTM E798-96(2009) - Standard Practice for Conducting Irradiations at Accelerator-Based Neutron Sources
• Effective Date: 01-Aug-2009
• Referred By: ASTM E1854-19 - Standard Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
• Effective Date: 10-Jan-1996

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 798 – 96 (Reapproved 2003)
Standard Practice for
Conducting Irradiations at Accelerator-Based Neutron
Sources
This standard is issued under the fixed designation E798; 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
1.1 This practice covers procedures for irradiations at 2.1 ASTM Standards:
accelerator-based neutron sources. The discussion focuses on C859 Terminology Relating to Nuclear Materials
two types of sources, namely nearly monoenergetic 14-MeV E170 Terminology Relating to Radiation Measurements
neutrons from the deuterium-tritium T(d,n) interaction, and and Dosimetry
broad spectrum neutrons from stopping deuterium beams in E181 Test Methods for Detector Calibration and Analysis
thick beryllium or lithium targets. However, most of the of Radionuclides
recommendations also apply to other types of accelerator- E261 Practice for Determining Neutron Fluence Rate, Flu-
2 4
based sources, including spallation neutron sources (1). Inter- ence, and Spectra by Radioactivation Techniques
est in spallation sources has increased recently due to their E263 Test Method for Measuring Fast-Neutron Reaction
proposed use for transmutation of fission reactor waste (2). Rates by Radioactivation of Iron
1.2 Many of the experiments conducted using such neutron E264 Test Method for Measuring Fast-Neutron Reaction
sources are intended to simulate irradiation in another neutron Rates by Radioactivation of Nickel
spectrum, for example, that from a DT fusion reaction. The E265 Test Method for Measuring Reaction Rates and
word simulation is used here in a broad sense to imply an Fast-Neutron Fluences by Radioactivation of Sulfur-32
approximation of the relevant neutron irradiation environment. E266 Test Method for Measuring Fast-Neutron Reaction
The degree of conformity can range from poor to nearly exact. Rates by Radioactivation of Aluminum
In general, the intent of these simulations is to establish the E393 TestMethodforMeasuringReactionRatesbyAnaly-
fundamental relationships between irradiation or material pa- sis of Barium-140 from Fission Dosimeters
rameters and the material response. The extrapolation of data E854 Test Method for Application and Analysis of Solid
from such experiments requires that the differences in neutron State Track Recorder (SSTR) Monitors for Reactor Sur-
spectra be considered. veillance, E706 (IIIB)
1.3 The procedures to be considered include methods for E910 Specification forApplication andAnalysis of Helium
characterizing the accelerator beam and target, the irradiated Accumulation Fluence Monitors for Reactor Vessel Sur-
sample, and the neutron flux and spectrum, as well as proce- veillance, E706 (IIIC)
dures for recording and reporting irradiation data.
3. Terminology
1.4 Other experimental problems, such as temperature con-
3.1 DescriptionsofrelevanttermsarefoundinTerminology
trol, are not included.
1.5 This standard does not purport to address all of the C859 and Terminology E170.
safety concerns, if any, associated with its use. It is the
4. Summary of Existing and Proposed Facilities
responsibility of the user of this standard to establish appro-
4.1 T(d,n) Sources:
priate safety and health practices and determine the applica-
4.1.1 Neutronsareproducedbythehighlyexoergicreaction
bility of regulatory limitations prior to use.
d+t→ n+ a. The total nuclear energy released is 17.589
MeV, resulting in about a 14.8-MeV neutron and a 2.8-MeV
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
alpha particle at low deuterium beam energies (3). The
Technology and Applications and is the direct responsibility of Subcommittee
deuteron energy (generally 150 to 400 keV) is chosen to
E10.08 on Procedures for Neutron Radiation Damage Simulation.
Current edition approved July 10, 2003. Published March 1996. Originally
published as E798–81. Last previous edition E798–89.
2 3
The boldface numbers in parentheses refer to a list of references at the end of Annual Book of ASTM Standards, Vol 12.01.
this practice. 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.
E 798 – 96 (2003)
maximize the neutron yield (for a particular target configura- spite of tritium burn-up in the target. Samples could be placed
tion) from the resonance in the d-t cross section near 100 keV. as close as 2.5 to 4.0 mm from the region of maximum d-t
13 2
The number of neutrons emitted as a function of angle (u) interaction resulting in a typical flux of 10 n/cm ·s over a
between the neutron direction and the incident deuteron beam small sample. The neutron fields were well characterized by a
is very nearly isotropic in the center-of-mass system. At a variety of methods and the absolute fluence could be routinely
deuteron energy of 400 keV in the laboratory system, the determined to 67%. Calculated neutron flux contours for
neutronfluxintheforwarddirectionisabout14%greaterthan RTNS-II are shown in Fig. 1.
in the backward direction, while the corresponding neutron 4.2 Be or Li(d,n) Sources (9):
energy decreases from 15.6 to 13.8 MeV (4). In practice, the 4.2.1 When a high-energy (typically 30- to 40-MeV) deu-
neutron field also depends on the gradual loss of the target teron beam is stopped in a beryllium (or lithium) target, a
material and the tritium deposition profile. Detailed calcula- continuous spectrum of neutrons is produced extending from
tions should then be made for a specific facility. thermal energies to about 4 MeV (15 MeV for lithium) above
4.1.2 The flux seen at a point (r, u, z) in cylindrical the incident deuteron energy (see Figs. 2-4). In existing
coordinates from a uniform T(d,n) source of diameter a is facilities,cyclotronswithdeuteronbeamintensitiesof20to40
given by the following (5): µA provide neutron source strengths in the range of 10 n/s,
using solid beryllium targets with water cooling. A more
4 2 2 1/2 2
Y ~k 14r z ! 1 k
f~r, u, z! 5 ln (1) intense source (>10 n/s) is now being designed employing
2 H 2 J
4pa 2z
liquid lithium targets. In the remainder of this document the
term Be(d,n) source is meant as a generic term including
where:
2 2 2 2
Li(d,n) sources, whether solid or liquid targets.
k = a + z − r , and
4.2.2 Neutrons are produced by several competing nuclear
Y = the total source strength.
For z>>a and r =0 (on beam axis) this reduces to Y/4pz , reaction mechanisms. The most important one for radiation
damage studies is the direct, stripping reaction since it pro-
as expected for a point source. The available irradiation
volume at maximum flux is usually small. For a sample placed duces almost all of the high-energy neutrons. When the
incident deuteron passes close to a target nucleus, the proton is
close to the target, the flux will decrease very rapidly with
increasingradialdistanceoffthebeamaxis.However,sincethe captured and the neutron tends to continue on in a forward
direction. The high energy neutrons are thus preferentially
neutron energy is nearly constant, this drop in flux is relatively
easy to measure by foil activation techniques. emitted in the direction of the incident deuteron beam. How-
ever, as the deuterons slow down in the target, lower energy
4.1.3 Other existing sources, such as Cockroft-Walton type
accelerators, are similar in nature although the available neutrons will be produced with angular distributions that are
neutron source strengths are much lower. much less forward peaked. Furthermore, when the residual
4.1.4 Rotating Target Neutron Source (RTNS) I and II nucleus is left in an excited state, the angular effects are also
(5-7)—RTNS I and II, which formerly were operated at the muchlesspronounced.Theselattertwoeffectstendtodecrease
the average neutron energy at angles other than 0° in the
Lawrence Livermore National Laboratory, provided 14 MeV
12 13
neutron source strengths of about 6 310 and 4 310 direction of the beam.
neutrons/s, respectively. Although these facilities have been 4.2.3 Neutrons can also be produced by compound nuclear
shut down, they were the most intense sources of 14 MeV reactions in which the entire deuteron is captured by the target
neutronsbuilttodateforresearchpurposes.Theyarediscussed nucleus and neutrons are subsequently evaporated. Neutrons
here because of their relevance to any future neutron sources. are preferentially emitted with energies less than a few MeV
Their characteristics are summarized in Table 1. A discussion and the angular distribution approaches isotropy at neutron
of similar sources can be found in Ref (8). The deuteron beam energiesbelow1MeV.Neutronsalsoareproducedbydeuteron
break-up, in which the deuteron simply breaks apart in the
energy was 400 keV and the target was a copper-zirconium
alloy (or copper with dispersed alumina) vapor-plated with Coulomb field of the nucleus, although this effect is very small
for low-Z materials.
tritium-occluded titanium. The beam spot size was about 10
mm in diameter. In addition to being rotated, the target also 4.2.4 The neutron spectrum thus depends very strongly on
wasrockedeveryfewhoursandthedeuteronbeamcurrentwas the angle from the incident deuteron direction, and the flux is
increased slowly in an attempt to maintain a constant flux in very sharply peaked in the forward direction (see Fig. 2).
TABLE 1 Characteristics of T(d,n) and Be or Li(d,n) Neutron Sources
Experimental
Source Maximum Flux
Volume for
Facility Availability Beam Target Strength, at Sample,
Maximum
n/s n/cm ·s
Flux, cm
12 12
RTNS I No longer available 400 keV d t 6 3 10 >10 0.2
13 13
RTNS II No longer available 400 keV d t 4 3 10 >10 0.2
>10 5.0
A 13 12
Existing Be or Li(d,n) U.C. Davis Cyclotron 30–40 MeV d Solid Be or Li ;10 >10 ;1.0
16 15
Proposed Li(d,n) Conceptual design (9) 30–40 MeV d Liquid Li 3 3 10 >10 10.0
>10 600.0
A
This is the only existing facility that has been well characterized and is readily available, although other facilities can be used.
E 798 – 96 (2003)
MeV) neutron energies, since these regions are either difficult
to measure with existing techniques, or the required nuclear
data are insufficient. In these cases, neutron dosimetry data
should be reported directly to allow reanalysis as procedures
and nuclear data improve in the future.
4.2.6 Existing Sources:
4.2.6.1 Whereas virtually any deuteron accelerator with
reasonable energy and intensity can be used as a neutron
source, only two facilities have been used routinely for
materials effects irradiations, namely the cyclotrons at the
University of California at Davis (10) and at Oak Ridge
National Laboratory (11,12). Typical flux-spectra obtained are
shown in Figs. 2-4 (9,11,13), and typical characteristics are
listed in Table 1.
4.2.6.2 Since the neutron flux and spectral gradients are so
steep,experimentersarefacedwiththeproblemofnonuniform
irradiations over their samples unless specimen sizes are
severely limited. Alternatively, the field gradients may be
moderated by deliberately moving or enlarging the beam spot
on the target.This technique will result in a lower total fluence
as well as a lower average neutron energy for a small-size
sample on the beam axis, although larger samples will not be
so severely affected and may in fact show an overall improve-
ment in average fluence and neutron energy.
4.2.6.3 At present, the neutron field can be determined
NOTE 1—Flux contours assume a symmetric, Gaussian beam profile.
Figure from Ref. (5).
reasonably well at existing facilities.The flux-spectrum can be
FIG. 1 Flux Contours for RTNS II
measured to within 610 to 30% in the 2- to 30-MeV energy
region where about 90% of neutron damage is initiated
(assuming E =30 to 40 MeV). Highly accurate (610%)
d
time-of-flight spectrometry has been used to study the field far
fromthesource,exceptfortheenergyregionbelowafewMeV
(11). However, close geometry irradiations must rely on
passive dosimetry with larger errors due to uncertainties in the
nuclear cross sections, especially above 30 MeV (12).
4.2.7 Conceptual Design for Li(d,n) Source (9,14)—Acon-
ceptual design for a fusion materials irradiation facility was
done at the Hanford Engineering Development Laboratory
(HEDL). The design consisted of a high-current (100-mA)
deuteron accelerator and a liquid lithium target. This was
expected to produce a neutron source strength of about
3 310 n/s(14).Thedesignscalledforawide-areabeamspot
NOTE 1—Neutronspectraasafunctionofenergyandanglefor Be(d,n)
on the target (for example, 3 by 1 cm), thereby moderating the
source at ORNL, E =40 MeV. (Data from Ref (8).)
d steep neutron field gradients in close geometry. Neutron fluxes
15 2
FIG. 2 Neutron Spectra as a Function of Energy and Angle from
up to 10 n/cm ·s could be produced over a volume of several
the Forward Direction of the Deuteron Beam
cubic centimetres, allowing much larger samples than with
present sources. This facility would thus have a higher flux of
high-energy neutrons over a larger volume than any available
Materialsstudiesforwhichthemaximumtotalneutronfluence
accelerator source. A more recent design that takes advantage
is desired are usually conducted close to the target and may
of improvements in accelerator technology is discussed in Ref
subtendalargerangeofforwardangles(forexample,0to60°).
(15).
This practice primarily will be concerned with this close-
4.3 Other Sources:
geometry situation since it is the most difficult to handle
properly. 4.3.1 There are many other accelerator-based neutron
4.2.5 Other factors can also influence the neutron field sources available, generally having lower neutron energy and
during a particular irradiation, especially beam and target flux. Most are used for medical or nuclear research applica-
characteristics, as well as the perturbing influence of surround- tions. Van de Graaffs and cyclotrons have also been used with
ing materials. At present, these facilities have not been com- many other nuclear reactions such as d(d,n) He
7 7
pletely characterized for routine use. In particular, some and Li(n,p) Be. Facilities with much higher charged particles
uncertainties exist, especially at low (<2 MeV) and high (<30 suchastheIntensePulsedNeutronSource(IPNS)(16)andthe
E 798 – 96 (2003)
NOTE 1—The maximum occurs at about 40% of the deuteron energy. (Data from Ref (6).)
FIG. 3 Li(d,n) Spectra at 0°
...