ASTM E798-96

Standard Practice for Conducting Irradiations at Accelerator-Based Neutron Sources

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 (1). Interest in spallation sources has increased recently due to their proposed use for transmutation of fission reactor waste (2).  
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: 31-Dec-1995
• ICS: 27.120.10 - Reactor engineering
• Technical Committee: E10 - Nuclear Technology and Applications

Relations

• Replaced By: ASTM E798-96(2003) - Standard Practice for Conducting Irradiations at Accelerator-Based Neutron Sources
• Effective Date: 10-Jan-1996
• Referred By: ASTM E1854-19 - Standard Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic Parts
• Effective Date: 01-Jan-1996

Standards Content (Sample)

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.
Designation: E 798 – 96
Standard Practice for
Conducting Irradiations at Accelerator-Based Neutron
Sources
This standard is issued under the fixed designation E 798; 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 C 859 Terminology Relating to Nuclear Materials
E 170 Terminology Relating to Radiation Measurements
1.1 This practice covers procedures for irradiations at
and Dosimetry
accelerator-based neutron sources. The discussion focuses on
E 181 Test Methods for Detector Calibration and Analysis
two types of sources, namely nearly monoenergetic 14-MeV
of Radionuclides
neutrons from the deuterium-tritium T(d,n) interaction, and
E 261 Practice for Determining Neutron Fluence Rate, Flu-
broad spectrum neutrons from stopping deuterium beams in
ence, and Spectra by Radioactivation Techniques
thick beryllium or lithium targets. However, most of the
E 263 Test Method for Measuring Fast-Neutron Reaction
recommendations also apply to other types of accelerator-
Rates by Radioactivation of Iron
based sources, including spallation neutron sources (1). Inter-
E 264 Test Method for Measuring Fast-Neutron Reaction
est in spallation sources has increased recently due to their
Rates by Radioactivation of Nickel
proposed use for transmutation of fission reactor waste (2).
E 265 Test Method for Measuring Reaction Rates and
1.2 Many of the experiments conducted using such neutron
Fast-Neutron Fluences by Radioactivation of Sulfur-32
sources are intended to simulate irradiation in another neutron
E 266 Test Method for Measuring Fast-Neutron Reaction
spectrum, for example, that from a DT fusion reaction. The
Rates by Radioactivation of Aluminum
word simulation is used here in a broad sense to imply an
E 393 Test Method for Measuring Reaction Rates by Analy-
approximation of the relevant neutron irradiation environment.
sis of Barium-140 from Fission Dosimeters
The degree of conformity can range from poor to nearly exact.
E 854 Test Method for Application and Analysis of Solid
In general, the intent of these simulations is to establish the
State Track Recorder (SSTR) Monitors for Reactor Sur-
fundamental relationships between irradiation or material pa-
veillance, E 706 (IIIB)
rameters and the material response. The extrapolation of data
E 910 Specification for Application and Analysis of Helium
from such experiments requires that the differences in neutron
Accumulation Fluence Monitors for Reactor Vessel Sur-
spectra be considered.
veillance, E 706 (IIIC)
1.3 The procedures to be considered include methods for
characterizing the accelerator beam and target, the irradiated
3. Terminology
sample, and the neutron flux and spectrum, as well as proce-
3.1 Descriptions of relevant terms are found in Terminology
dures for recording and reporting irradiation data.
C 859 and Terminology E 170.
1.4 Other experimental problems, such as temperature con-
trol, are not included.
4. Summary of Existing and Proposed Facilities
1.5 This standard does not purport to address all of the
4.1 T(d,n) Sources:
safety concerns, if any, associated with its use. It is the
4.1.1 Neutrons are produced by the highly exoergic reaction
responsibility of the user of this standard to establish appro-
d+t → n+ a. The total nuclear energy released is 17.589
priate safety and health practices and determine the applica-
MeV, resulting in about a 14.8-MeV neutron and a 2.8-MeV
bility of regulatory limitations prior to use.
alpha particle at low deuterium beam energies (3). The
deuteron energy (generally 150 to 400 keV) is chosen to
2. Referenced Documents
maximize the neutron yield (for a particular target configura-
2.1 ASTM Standards:
tion) from the resonance in the d-t cross section near 100 keV.
The number of neutrons emitted as a function of angle (u)
between the neutron direction and the incident deuteron beam
This practice is under the jurisdiction of ASTM Committee E-10 on Nuclear
is very nearly isotropic in the center-of-mass system. At a
Technology and Applicationsand is the direct responsibility of Subcommittee
deuteron energy of 400 keV in the laboratory system, the
E10.08on Procedures for Neutron Radiation Damage Simulation.
Current edition approved Jan. 10, 1996. Published March 1996. Originally
published as E 798 – 81. Last previous edition E 798 – 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, 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 798
neutron flux in the forward direction is about 14 % greater than
in the backward direction, while the corresponding neutron
energy decreases from 15.6 to 13.8 MeV (4). In practice, the
neutron field also depends on the gradual loss of the target
material and the tritium deposition profile. Detailed calcula-
tions should then be made for a specific facility.
4.1.2 The flux seen at a point (r, u, z) in cylindrical
coordinates from a uniform T(d,n) source of diameter a is
given by the following (5):
4 2 2 1/2 2
Y ~k 1 4r z ! 1 k
f~r, u, z! 5 ln (1)
H J
2 2
4pa 2z
where:
2 2 2 2
k 5 a + z − r , and
Y 5 the total source strength.
Forz>>a and r 5 0 (on beam axis) this reduces to Y/4pz ,
as expected for a point source. The available irradiation
volume at maximum flux is usually small. For a sample placed
close to the target, the flux will decrease very rapidly with
increasing radial distance off the beam axis. However, since the
neutron energy is nearly constant, this drop in flux is relatively
easy to measure by foil activation techniques.
4.1.3 Other existing sources, such as Cockroft-Walton type
accelerators, are similar in nature although the available
neutron source strengths are much lower.
NOTE 1—Flux contours assume a symmetric, Gaussian beam profile.
4.1.4 Rotating Target Neutron Source (RTNS) I and II
Figure from Ref. (5).
(5-7)—RTNS I and II, which formerly were operated at the
FIG. 1 Flux Contours for RTNS II
Lawrence Livermore National Laboratory, provided 14 MeV
12 13
neutron source strengths of about 6 3 10 and 4 3 10 4.2 Be or Li(d,n) Sources (9):
neutrons/s, respectively. Although these facilities have been 4.2.1 When a high-energy (typically 30- to 40-MeV) deu-
shut down, they were the most intense sources of 14 MeV teron beam is stopped in a beryllium (or lithium) target, a
neutrons built to date for research purposes. They are discussed continuous spectrum of neutrons is produced extending from
here because of their relevance to any future neutron sources. thermal energies to about 4 MeV (15 MeV for lithium) above
Their characteristics are summarized in Table 1. A discussion the incident deuteron energy (see Figs. 2-4). In existing
of similar sources can be found in Ref (8). The deuteron beam facilities, cyclotrons with deuteron beam intensities of 20 to 40
energy was 400 keV and the target was a copper-zirconium μA provide neutron source strengths in the range of 10 n/s,
alloy (or copper with dispersed alumina) vapor-plated with
using solid beryllium targets with water cooling. A more
tritium-occluded titanium. The beam spot size was about 10 intense source (>10 n/s) is now being designed employing
mm in diameter. In addition to being rotated, the target also liquid lithium targets. In the remainder of this document the
was rocked every few hours and the deuteron beam current was term Be(d,n) source is meant as a generic term including
increased slowly in an attempt to maintain a constant flux in Li(d,n) sources, whether solid or liquid targets.
spite of tritium burn-up in the target. Samples could be placed 4.2.2 Neutrons are produced by several competing nuclear
as close as 2.5 to 4.0 mm from the region of maximum d-t reaction mechanisms. The most important one for radiation
13 2
interaction resulting in a typical flux of 10 n/cm ·s over a damage studies is the direct, stripping reaction since it pro-
small sample. The neutron fields were well characterized by a duces almost all of the high-energy neutrons. When the
variety of methods and the absolute fluence could be routinely incident deuteron passes close to a target nucleus, the proton is
determined to 67 %. Calculated neutron flux contours for captured and the neutron tends to continue on in a forward
RTNS-II are shown in Fig. 1. direction. The high energy neutrons are thus preferentially
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.
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 798
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, experimenters are faced with the problem of nonuniform
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
NOTE 1—Neutron spectra as a function of energy and angle for Be(d,n)
so severely affected and may in fact show an overall improve-
source at ORNL, E 5 40 MeV. (Data from Ref (8).)
d
ment in average fluence and neutron energy.
FIG. 2 Neutron Spectra as a Function of Energy and Angle from
4.2.6.3 At present, the neutron field can be determined
the Forward Direction of the Deuteron Beam
reasonably well at existing facilities. The flux-spectrum can be
measured to within 610 to 30 % in the 2- to 30-MeV energy
emitted in the direction of the incident deuteron beam. How-
region where about 90 % of neutron damage is initiated
ever, as the deuterons slow down in the target, lower energy
(assuming E 5 30 to 40 MeV). Highly accurate (610 %)
d
neutrons will be produced with angular distributions that are
time-of-flight spectrometry has been used to study the field far
much less forward peaked. Furthermore, when the residual
from the source, except for the energy region below a few MeV
nucleus is left in an excited state, the angular effects are also
(11). However, close geometry irradiations must rely on
much less pronounced. These latter two effects tend to decrease
passive dosimetry with larger errors due to uncertainties in the
the average neutron energy at angles other than 0° in the
nuclear cross sections, especially above 30 MeV (12).
direction of the beam.
4.2.7 Conceptual Design for Li(d,n) Source (9,14)—A con-
4.2.3 Neutrons can also be produced by compound nuclear
ceptual design for a fusion materials irradiation facility was
reactions in which the entire deuteron is captured by the target
done at the Hanford Engineering Development Laboratory
nucleus and neutrons are subsequently evaporated. Neutrons
(HEDL). The design consisted of a high-current (100-mA)
are preferentially emitted with energies less than a few MeV
deuteron accelerator and a liquid lithium target. This was
and the angular distribution approaches isotropy at neutron
expected to produce a neutron source strength of about
energies below 1 MeV. Neutrons also are produced by deuteron
3 3 10 n/s (14). The designs called for a wide-area beam spot
break-up, in which the deuteron simply breaks apart in the
on the target (for example, 3 by 1 cm), thereby moderating the
Coulomb field of the nucleus, although this effect is very small
steep neutron field gradients in close geometry. Neutron fluxes
for low-Z materials.
15 2
up to 10 n/cm ·s could be produced over a volume of several
4.2.4 The neutron spectrum thus depends very strongly on
cubic centimetres, allowing much larger samples than with
the angle from the incident deuteron direction, and the flux is
present sources. This facility would thus have a higher flux of
very sharply peaked in the forward direction (see Fig. 2).
high-energy neutrons over a larger volume than any available
Materials studies for which the maximum total neutron fluence
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
subtend a large range of forward angles (for example, 0 to 60°).
(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 such as the Intense Pulsed Neutron Source (IPNS) (16) and the
MeV) neutron energies, since these regions are either difficult Los Alamos Meson Physics Facility (LAMPF) (17,18) have
to measure with existing techniques, or the required nuclear also been used. For example
...