ANSTO
LUCAS HEIGHTS, AUSTRALIA
15 NOVEMBER 2012
History of Spallation Neutron
Sources
John M. Carpenter
IPNS, Argonne National Laboratory
and
SNS, Oak Ridge National Laboratory
“Spallation”: the word
W. H. Sullivan and Glenn T. Seaborg, at Lawrence Radiation
Laboratory, Berkeley, California, coined the term “spallation”
on 20 August 1947*. They intended the word to designate the
process, already fairly well-known, in which a nucleus struck by
a high-energy particle emits a rather large number of nucleons
(mostly neutrons) or fragments. The products include practically
all the nuclei of smaller mass number than the target nucleus that
lie on the neutron-poor side of the line of stability, and most of the
lighter nuclei.
* B. G. Harvey, Ch. 3 “Spallation” in Progress in Nuclear Physics, Editor O. R.
Outline
Early Knowledge
Early Spallation Sources
The 10-GeV Question
Spallation Source Development
Target Developments
Operational Experience
Present Day Sources
The Spallation-Fission Process
Schematic
illustration of
our modern
understanding of the
spallation-fission
(when fission
is possible) process.
(Courtesy L. Waters,
LANL.)
π
First stage:
intranuclear
cascade
high-energy
proton
p
n
α
Intermediate stage:
preequilibrium
d
Second stage:
evaporation and/or
fission
t
Final stage: residual
deexcitation
e±
γ
Frisch, Vol. 7, Pergamon Press pp 90-120 (1959).
Cosmic Ray Protons
Cosmic-ray protons (of extra-solar origin) impinge isotropically and
steadily on the Earth. Consequently, there is no daily or annual variation
in the incident cosmic ray proton flux.
Discovery of Cosmic Rays
Victor Hess, 1912
International Herald Tribune 8 August, 2012
The energy spectrum of the incident cosmic-ray protons extends up to
tens of GeV, higher than that of solar protons, and can penetrate the
Earth’s magnetic field and the atmosphere.
The average energy of cosmic-ray protons is higher at lower latitudes
than at high latitudes near the poles. The Earth’s field deflects lowestenergy protons, (about 4. GeV at Chicago), depending on the observer’s
magnetic
latitude.
Solar protons cannot penetrate the Earth’s magnetic field because of
their lower energies, except near the magnetic poles. The intensity of
solar protons varies according to the level of solar activity.
Victor Hess received the Nobel Prize in Physics in 1932
1
Harold Agnew’s 1944 Flying Neutron Detector
(B-29)
Atmospheric Spallation Neutrons:
Fermi notes
The figure, from Enrico Fermi’s
University of Chicago lectures of
1948*, illustrates the cosmic-rayproton-induced neutron flux as a
function of atmo-spheric depth.
There are always neutrons
around us; the thermal neutron
flux at the Earth’s surface is on
the order of 10-4—10-3 n/cm2sec.
Agnew’s result,
exp(-0.083 Pcm Hg),
corresponds to that in Fermi’s book for low magnetic latitudes,
exp(-xgm/cm2/160),
when related according to the density of mercury,
0.083 Pcm Hg/13.55gm/cm3= xgm/cm2/163.
Earth’s atmosphere is equivalent to a layer of about 10 meters of water.
The cosmic-ray-induced neutron flux varies considerably according to the
barometric pressure (daily weather-dependent variations in the thickness
of the atmosphere). Heavy shielding around detectors can increase the
neutron flux nearby. This is important in detector testing activities and in
measurements of low counting rate phenomena.
*J. Orear, A. H. Rosenfeld, and R. A. Schluter,
“Nuclear Physics,” revised ed.,
The University of Chicago Press, Chicago (1949).
Tidal Effects
The rising tide
covers and the
receding tide
exposes heavy
material (rocks)
that produce
more spallation
neutrons than the
water. The local
cosmic-rayproduced neutron
background varies
with the tides.
Harold Agnew, APS Mtg. 1946
The neutron flux is lower but less strongly attenuated by the atmosphere
at low magnetic latitudes (nearer the magnetic equator: 190 gm/cm2 )
than at high latitudes (nearer the pole: 160 gm/cm2), indicating that near
the pole, the average energy of incident protons is lower than far from the
pole(s). The locations of the magnetic poles wander slowly, a few
degrees per decade.
Measurements have recently extended to
ocean depths
Rolando Granada’s 1989 Submarine Neutron Detector
ARA SANTA CRUZ S-41
2
Proton cyclotrons generated the first accelerator-produced
neutrons, starting in early 1930s. Glenn T. Seaborg was
among the first workers.
Evaporation Neutron Spectrum
The function shown in the inset has
a mean energy of 1.98 MeV.
A more accurate form is
f(E) = exp(-1.036E)sinh √(2.29E),
where E is expressed in MeV.
This is, strictly speaking, the
spectrum of neutrons produced by
fission in 235U, but it applies
approximately and in form to most
other evaporation neutron spectra.
A. M. Weinberg and E. P. Wigner,
The Physical Theory of Neutron
Chain Reactors, The University of
Chicago Press (1958). See 111-115.
Early Spallation Sources: MTA
The MTA
E. O. Lawrence conceived the Materials Testing Accelerator (MTA)
project in the late 1940s. Despite its name, MTA was never
intended for materials research, rather, bomb stuff. The required
production rate set the parameters of the accelerator—particles,
deuterons; beam energy, 500 MeV; CW operation; current, 320 mA;
beam power, 160 MW. RF was 12 MHz. Work went on at the site
of the present Lawrence Livermore Laboratory. Efforts continued
until 1955 when exploration revealed large uranium ore reserves in
the US and the project terminated. By that time the preaccelerator
had delivered CW proton currents of 100 mA and deuteron currents
of 30 mA. The work was declassified in 1957.
people
A. P. Armagnac, “The Most Fantastic Atom Smasher,”
Popular Science, p. 115 (Nov. 1959).
MTA Linac
The accelerating
cavities were very
large because
available highpower
klystrons operated
at only 12 MHz.
(Now, commonly,
800 MHz.)
ING
In 1963, the Chalk River Laboratory of Atomic Energy of Canada
launched the Intense Neutron Generator (ING) project. The goal
was a “versatile machine” providing a high neutron flux for
isotope production and neutron beam experiments. The effort
continued until 1968 when the project was cancelled. The
proposed installation was based on a 1.5-km-long proton linac
delivering 1.0-GeV, 65. mA (65 MW). The target was to have
been of flowing lead-bismuth eutectic (LBE), 20. cm in diameter,
60. cm long, with the proton beam incident vertically downward,
surrounded by an annular beryllium “multiplier” 20 cm thick.
Technical developments that resulted from the ING project were
significant, even seminal.
3
The ING Facility
Canadian scientists conceived the
Intense Neutron Generator project
in the early 1960s. ING was never
built because the proposed
accelerator was not feasible at
that time. The figure shows the
facility layout.
ING
Conceptual illustration of the
ING target arrangement, a
flow-through design in which
the protons impinge on the free
surface of the LBE.
“ING Status Report, July 1967:
The AECL Study for an Intense
Neutron Generator,” T. G. Church, Ed.,
Atomic Energy of Canada, Ltd.,
report AECL-2750 (1967).
Also,
“The AECL Study for an Intense
Neutron Generator, Technical Details,”
AECL report AECL 2600 (1966).
Neutron Yields
Fraser’s data permit a simple fit for energies up to 1.5 GeV,
Y(E, A) =
{
0.1(E GeV – 0.120)( A + 20), except fissionable materials;
238U .
50.(E GeV – 0.120),
Global neutron yields fall off as Ep0.8 for Ep > 1.0 GeV.
Also in the mid-1960s, Bertini, notably, and others developed
codes to compute the details of the spallation process. The Fraser
data stand essentially unchanged in the light of subsequent
experience, and the current generation of codes, exemplified by
the Los Alamos MCNPX code, are the basis for spallation
source design as well as for design of high-energy particle physics
detectors.
ING Machine Specifications
Proton linac
Energy, 1 GeV
Length: Alvarez section, 110 m,
Waveguide section, 1430 m
Total RF power, 90 MW
Current, 65 mA (CW)
Proton beam power, 65 MW
Neutron Yields
In 1965, in support of the ING project, John Fraser and his
colleagues studied thick-target neutron yields as a function of
proton energy. The figure shows their results.
These were the first systematic
neutron yield data, which
enabled quantitative design of
neutron sources and inspired
the creation of modern highenergy particle transport
simulation codes such as
MCNP.
The 10,000,000,000 eV Question: What’s the
best energy for spallation neutron production?
The power density variation as a
function of axial position in a
tantalum metal target (no coolant), for
various proton energies. Beyond a short
buildup range, the neutron production
and the power densities diminish
exponentially as governed by the
~constant proton-nuclear collision cross
section. (At the higher proton energies
the end-of-range Bragg peak is
insignificant.) The power density and
radiation damage rate per unit of beam
power at the entry (proton window) end
is considerably smaller for the higher
energies than for the lower energies.
Answer—It doesn’t make much difference: it’s what’s convenient.
4
Pulsed Spallation Neutron Sources
Pulsed Spallation Neutron
Sources
Developments of proton-driven spallation sources for slowneutron (below about ~100 eV) scattering applications began in the
early 1970s. Most of these are “short-pulsed” machines, but there is
one MW-level CW proton accelerator (SINQ). And ESS is to be a
“long-pulse” system.
Pulsed operation provides for momentarily high power and long
inter-pulse periods to dissipate heat from the target and components.
Based on the spallation reaction, these sources benefit from the
fact that the heat to be dissipated is only about 30-40 MeV per neutron,
about 60% of the proton beam power.
Dense hydrogenous moderators close by the source slow down
the ~ 1.-MeV neutrons from the source to useful energies,
< ~1. eV, and provide a well defined time origin for time-of-flight
spectroscopy. Nearby reflectors (e.g., beryllium) substantially
increase neutron beam intensities
Intense, high-emittance negative hydrogen (H-) ion sources developed
by the Russian scientists G. I. Budker and G. I. Dimov in the 1960s
made possible development of high-current synchrotrons using
stripping injection.
H- ions from the ion source are accelerated to modest energy (~50
MeV) in a linac, transported into the circular machine through a thin
foil in a magnetic field. Passing through the foil, the ion loses its
electrons and circulates as a proton, bending oppositely in the field
than the H- ions. Protons already captured in the ring pass again
through the foil, unaffected.
The process allows loading the ring with many (~1000) turns of
protons. The procedure does not violate Liouville’s theorem because
stripping is an irreversible process.
This discovery was adopted for the 500-MeV Booster-accelerator
injector for the 12-GeV Zero Gradient Synchrotron (ZGS) at Argonne.
Emission-Time Distribution
(pulse shape)
63.3 meV neutrons from a
300-K moderator at IPNS
Moderators
Pulsed-source moderators have designable features that can be tailored
to instrument needs:
Spectral temperature— 10K < T <300K;
Intensity—decoupled, poisoned < I < coupled;
Pulse width–2 microsec < Δt λ < 1 millisec.
( )
Physical temperature, material, geometry, size …
are variables to play off in instrument and moderator design.
The design tool is MCNP or equivalent. Calculations require tested
scattering functions, as functions of the temperature, especially for novel
moderator materials, O/P L-H2, NH3, CxHy, means for measuring O/P,
small neutron sources, … .
Reactor and Pulsed Source Spectra
FRM-2
IPNS
5
Sketch of the First
Prototype, ZING-P
ZING-P (Argonne, 1974-1975)
ZING-P was the first-ever
pulsed spallation neutron
source equipped in all the ways
of modern sources. It operated
with100 nano-amps of 200-MeV
protons delivered in short pulses
at 30 Hz.
That comes to 20 W!
And we actually did meaningful
research measurements.
SNS, now 1 MW, will have 1.4-2 MW!
IPNS (Argonne, 1981-2008)
The IPNS Booster Target
In 1988, IPNS installed a subcritical “Booster” target
constructed of highly enriched (77.5%) uranium, having a
computed keff = 0.80, and designed to provide short pulses of
fast neutrons. The Booster target replaced the previous
depleted uranium target of similar design, with the intent to
provide higher neutron beam intensities. The Booster
operated satisfactorily and according to expectations until
1991, when the cladding on one of the target disks failed.
The Booster target produced about 2.5 times higher neutron
beam intensities than the depleted uranium targets, accompanied
about 5 times higher delayed neutron component (which we
learned to manage.
The IPNS Booster Target
Material, alpha-uranium
Enrichment 77.5 %
Disks, 12.5 mm & 25. mm,
10-cm diameter
Clad, 0.5-mm Zircaloy-2,
HIP bonding
Coolant, H2O
Vessel, 304 stainless steel
Decoupler, 10B-Cu
Reflector, graphite & Be
keff = 0.80 (in place)
Power, 50 kW for
15 µA, 450 MeV protons
IPNS Booster Target
The expected heat power and beam intensities do not scale as
1/(1- keff): For the depleted uranium target, the target power is about
10 kW (beam power 6.75 kW), and the multiplication factor is about
keff = 0.10 (not zero). Gains for the Booster case do not follow the
1/(1-k) rule because the proton-induced source neutrons are not
(by far) distributed in the 6-dimensional phase space as are neutrons
in the most-nearly-critical mode. The neutron beam intensity gain
was expected to be about 3.0, not 5.0 on these accounts. The
same observation has important implications for startup criticality
monitoring.
Experience operating the Booster target was consistent with
expectations.
J. M. Carpenter and A. G. Hins, “Experience with IPNS Targets,” Proc. ICANS
XII, Abingdon, England, 24-28 May 1993, Rutherford-Appleton Laboratory report
94-025, Vol. 2, pp. T1-T11 (1994).
6
Pulsed Spallation Sources
A representative configuration has an H- ion source, linac, and a
synchrotron or accumulator ring with stripping injection and singleturn extraction. “Long-pulse” sources do not employ a ring.
Steady Spallation Sources
One steady spallation source operated early-on. There is
one steady spallation source in operation.
New Projects
Present Target Concepts
A number of projects have been completed or are under way.
Targets in the older, lower-power spallation sources are all based
on solid material with H2O or D2O cooling. All cases have been
successful, and the lifetimes in service acceptable at their
power levels. Operators have removed and examined tungsten
and tantalum targets before real events indicated end of life.
The cladding of targets constructed of orthorhombic (anisotropic)
alpha-phase uranium fails because of anisotropic grain growth in
the uranium, well correlated to the accumulated fission density; in
IPNS, depleted uranium targets last about 275 mA-hr in the
25-mm-diameter 450-MeV proton beam.
All targets have yielded neutron intensities and sensible heat
consistent with Monte Carlo predictions, verifying the codes.
Liquid Targets
The SNS Target
In pulsed sources, solid targets lose at high power in competition
with liquid targets because at high power the thinner plates and
larger coolant volume fractions dilute the target material to
densities lower than liquid target material.
The current high-power sources have adopted liquid
mercury as target material. Its high density and high atomic
number provide efficient conversion of proton energy to
neutrons and, being liquid at ambient temperatures, it enables
heat removal by mass transport rather than by conductionconvection as in the solid targets. The liquid is not
subject to cumulative radiation damage effects but high
instantaneous pressures result in cavitation and erosion damage
to the vessel, which are the subject of current research.
The SNS target—designed for 2 MW of 1-GeV protons distributed
with a maximum current density of 25 µA/cm2. The shell is stainless
steel. To avoid a hot spot at the center of the window where symmetry
would otherwise produce a flow stagnation, design provides a
secondary flow through a window coolant channel. Maximum flow
velocity in the target is about 3.5 m/sec.
M. W. Wendel, “SNS Target Thermal-Hydraulic Design”, Third International
Workshop on Mercury Target Development, Oak Ridge, November 16-19, 2001.
7
MEGAPIE
The Megawatt Proton Irradiation Experiment (MEGAPIE)
started in the year 2000 on an initiative of the Paul Scherrer
Institute (PSI), Commisariat a l’Energie Atomique (CEA), and
Forschungszentrum Karlsruhe (FZK).
Aims, which have been accomplished, are:
•Design, build, and test a liquid lead-bismuth eutectic (LBE)
spallation target of 1-MW beam power.
•Demonstrate the feasibility of targets for accelerator driven
systems (ADS) and provide for PSI’s SINQ neutron source
a target that increases the neutron flux in that facility.
•Demonstrate at least one year’s service (6000 mA-hr),
prototypical of the needs for an ADS target.
The MEGAPIE Target
Parameters:
Beam power 1 MW
Vertical entry from below
Target material LBE
Electromagnetic pump
Secondary coolant diphenyl
F. Groeschel, “The MEGAPIE
Project: An Overview,”
MEGAPIE Technical Review
Meeting, Bologna,
5-6 March 2002.
Flow diagram
Entry window
APT Irradiation Tests
The conceptual design study of the Accelerator Production of
Tritium (APT, ~ 100 MW, ~1 GeV proton beam), carried out from
1995-2000 at Los Alamos, supported an extensive materials
irradiation testing program at the LAMPF (800-MeV) beam stop*.
APT Concept
APT Irradiation Facility
Protons come from the left.
Rotating Targets
A solution to the problems of heat removal and radiation damage in
spallation targets is to rotate the target in the proton beam. In this
scheme, the target revolves sufficiently that the beam strikes a
cooled portion of the target while the heated portion moves onward
and cools slowly. Damage to the beam window and to solid target
material, which accumulates very slowly, and heat, which is
continuously removed, are spread out into larger volumes than in
stationary targets. Rotating-anode targets are common in
laboratory x-ray sources and rotating targets are used in some
high-power low-energy charged-particle neutron sources.
At least two prototype rotating targets have been tested but none
have integrated into operating pulsed spallation neutron sources.
*S.A. Maloy, W.F. Sommer, M.R. James, T. Romero, M. Lopez, E. Zimmermann,
J. Ledbetter, “The Accelerator Production of Tritium Materials Test Program,”
Nucl. Technology, Vol. 132, pp. 103-114 (2000).
APT Tests
Among the results, irradiation of clad tungsten to 23 displacements
per atom (dpa) (about 6 months) testing indicated that the material
retained some ductility but would then no longer be serviceable.
Inconel Window
Irradiation in the 800-MeV
LANSCE beam of a watercooled double-walled Inconel
718 proton beam window
for about 9 months (20 dpa)
resulted in a crack on the air
side, indicating “end-of-life”
at that dose. The failure was
a”soft” one—no catastrophe.
Aluminum widows are also
satisfactory.
20% compression
S.A. Maloy, M.R. James, W.F. Sommer, G.J. Willcutt, M. Lopez, T.J. Romero,
“The Effect of 800 MeV Proton Irradiation on the Mechanical Properties of
Tungsten,” Materials Transactions, Japan Institute of Metals, 43 [4], pp. 1-5 (2002).
M.R. James, S.A. Maloy, F.D. Gac, W.F. Sommer, J. Chen, and H. Ullmaier, “The
Mechanical Properties of an Alloy 718 Window after Irradiation in a Spallation
Environment,” J. Nuclear Materials, 296, pp. 139-144 (2001).
8
Fatigue
One expects that materials
irradiated in spallation environments may suffer different
effects on fatigue resistance
than in reactors. There is as
yet little data. The figure
compares results of recent irradiations of steels in SINQ,
with those of steels irradiated
in HFIR. There are no
obvious differences.
Courtesy of J. Haines and
K. Kikuchi, 2003.
Delayed Neutrons
We observed delayed neutrons (with precursor half-lives greater
than about one millisecond) in operations with uranium targets.
With the IPNS depleted uranium targets, we observe that delayed
neutrons constitute 0.44% (2.5% in the Booster target) of all
neutrons observed in the neutron beams (and produced in the target).
This is in spite of the fact that in fast-neutron-induced fission of 238U
the intrinsic delayed fraction is 1.48 %. The distinction comes about
because in the depleted targets, most of the neutrons come not from
fission but from proton-induced spallation-evaporation processes.
Calculations vs. Measurements
Experience shows that, with care, the experimental and calculated
epithermal neutron spectra from pulsed-source moderators can be
determined to within approximately 20% of one another. (At lower
neutron energies uncertainties in the modeled scattering function result
in larger discrepancies.) Such comparisons have been carried out
many times, and are as much tests of the capability to model
(in calculations) and to measure with sufficient accuracy to represent
a test, as they are tests of the intrinsic accuracy of the calculations.
We conclude that there is no significant uncertainty in the neutron
yields or in the modeling at that level. Current assessments of the relationship of calculations to measurements at lower energies indicate
shortcomings in the low-energy scattering models, S (α , β ).
Fission and Spallation Products
Light spallation-fragment nuclei include a number of beta-decaying
nuclei that lead to states that decay by neutron emission.
The process of delayed neutron production in spallation targets
is not well understood and not yet accurately calculable.
Delayed photoneutrons presumably are relatively simple to
understand.
Heat Deposited
Heat removal is a
primary target design
consideration. The figure
shows a summary of
calculations and
measurements of heat
deposited in spallation
targets. Agreement
among the data verifies
the codes predictions
with reasonable certainty.
Fission-related delayed
neutrons
Spallation-related delayed
neutrons
Afterheat
An important consideration in spallation target design is the Loss of
Coolant Accident (LOCA). Although the primary target turns off
quickly, radioactive nuclei in the target continue to decay and give off
heat, which must be accounted for to avoid damage. Ta and W are
desirable target components. The table illustrates the (n, γ) production
rates in Ta and W targets (product nuclei per incident proton) for
different neutron energy ranges and for different target/coolant
combinations. W is better than Ta when afterheat questions arise.
“IPNS Upgrade: A Feasibility Study,” Argonne National Laboratory report
ANL-95/13 (April 1995). See IV.2-7
9
Afterheat
Tungsten:
Dominant isotope 187W,
T1/2 = 24 hrs.
Corrosion
30000
Most corrosion and materials compatibility problems probably
are easy to anticipate on the basis of the immense body of
materials experience in nuclear facilities.
Ta-HPTS
25000
Ta-IPNS
W-HPTS
W-IPNS
20000
15000
10000
Tantalum:
Dominant isotope 182Ta,
T1/2 = 114 days.
5000
0
0
50
100
150
200
250
300
350
400
450
time after irradiation starts (days)
Although we usually regard a spallation target as an energetic-particle
system, thermal-neutron capture is the dominant mechanism for
generation of the radionuclides responsible for long-term afterheat.
The figure shows calculated results for several cases, illustrating the
sensitivity to the presence of coolant and to thermal-neutron capture.
Stress Corrosion Cracking
SEM image of the fracture
surface of a high-strength
steel alloy bolt exposed in
the gaseous atmosphere
of irradiated air.
In IPNS, we experienced a set of problems, however, in the
relatively unfamiliar circumstances that stem from the passage of
high-energy protons and neutrons through air in the path
between the beam transport system and the target. The culprit
is nitric acid, HNO3.
We observed serious oxidation of exposed iron shielding
parts, stress corrosion cracking (yes, in the gaseous atmosphere)
of high-strength alloy steel bolts (stainless steel is not affected),
and corrosion of aluminum surfaces leading to heavy deposits of
Al(NO3)•9H2O.
Target Failure Mechanisms
Targets in pulsed spallation sources so far have expired in “soft”
ways, with no consequences beyond the targets.
Uranium target (alpha-phase, orthorhombic, anisotropic) breakdowns
in IPNS, ISIS, and KENS have all been the result of cracks in the
cladding with subsequent release of fission products, exacerbated
after the event by corrosion.
Tungsten in contact with coolant water releases corrosion products
into the coolant stream, requiring cladding. Tantalum targets in
ISIS have exhibited internal changes, which engendered change.
Tungsten and tantalum targets live much longer than the alphauranium targets employed to date.
Gamma-Phase Uranium
The 10,000,000,000-Volt Question
Developments in the Reduced Enrichment Research and
Test Reactor (RERTR) fuel development program have studied
gamma-phase uranium-molybdenum (~8 w% Mo), which has
cubic crystal structure and therefore isotropic physical properties.
The alloy is metastable but persists for long times at service
temperatures.
Irradiation tests show that that material is stable against
anisotropic grain growth up to about 10 times the fission
density that causes cracking of alpha-uranium, such as resulted
from approximately 275 mA-hrs/5cm2 irradiation in IPNS.
It is natural to speculate on the appropriate proton energy to drive a
spallation system. A summary observation is that the total neutron
yield, proportional to the proton energy in the neighborhood of
1 GeV, falls off at higher energies mainly due to the loss of energy
o
from the hadron cascade through the very rapid π decay (yielding
two 70-MeV photons, which escape the hadron cascade). For
energies above about 3.0 GeV, the yield of neutrons per proton
varies as E0.80.
In spite of this, it may be that to achieve given power or neutron
production rate, higher energies are preferable to lower ones, because
higher energy may be cheaper and easier to accomplish than higher
current.
10
ICANS
The International Collaboration on Advanced Neutron Sources
(ICANS) is an informal collaboration among laboratories involved
in spallation source development, founded in 1977. Twenty meetings
have taken place, at roughly 2-year intervals. Host laboratories
publish proceedings, which now amount to more than 10,000 pages.
These trace and report developments of pulsed and steady spallation
sources through most of their history. The ICANS website describes
the collaboration and provides references to the proceedings.
THE TREE OF
ICANS
ICANS has grown from its
roots in 1977 into a
spreading tree with many
branches, many fruits,
many related organizations,
and many hovering
periodical-birds.
ICANS XX took place in Bariloche, Argentina, in March 2012.
<www.pns.anl.gov/related/icans.shtml>
62
And now, SNS, 2012
J-PARC in January 2011
Summary and Conclusions
ESS in Lund, Sweden (2019)
Knowledge of the spallation process has a history that began with
its recognition as a nuclear physics phenomenon.
Early accelerators used spallation targets to produce neutrons for
physics research.
Some installations that might be called “neutron factories” for
various applications have been studied.
Operational experience verifies our quantitative understanding of
the spallation process and its engineering requirements.
Since the early 1970s, pulsed spallation sources of ever-increasing
power have evolved, designed for slow-neutron scattering
applications that are producing valuable data.
11
Thank You!
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