How we can improve nuclear fission
data for applications and fundamental
physics
Alexander Laptev
Los Alamos Neutron Science Center (LANSCE)
Neutron & Nuclear Science
Physics with Secondary Hadron Beams in 21st Century
The GWU Virginia Science and Technology Campus
Ashburn, Virginia, April 7, 2012
LA-UR-12-20350
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Slide 1
Why neutrons?

High demand from nuclear industry for good quality
data, first of all neutron-induced reaction cross
sections for actinides and sub-actinides
-
Development of new advanced nuclear reactors
-
Decreasing nuclear data uncertainties will decrease
nuclear reactor construction safety margins incorporated
into reactor’s design
-
Industry keeps developing: in Dec. 2011 NRC approved
first nuclear power plant license since 1978 for the power
plant expansion in Georgia
-
Public pressure is as high as ever
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Slide 2
Why neutrons (cntd)?

Defense physics needs

Accelerator-based conversion of weapon’s grade
plutonium

Transmutation of nuclear waste, especially actinides
-

Yucca Mountain nuclear waste repository doesn’t accept
new waste effective in 2011
Basic understanding of fission process, fundamental
physics, etc.
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Slide 3
Why a pulsed neutron source?

The most accurate and effective method to measure
neutron energy is the time-of-flight method
T
Proton pulse
injection
τ
Time
TOF Distance (L)
0.15
0.10
En/En
Ew
E3
E2
t = 5 ns
L = 20 m
0.05
E1
0
T1
T2
T3
Time-of-Flight (t)
Cartoon idea is from the KENS web-page
Tw = T
Wrap-around
0.00
0.1
1
10
100
En, MeV
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Slide 4
What is the energy range of interest?
3
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
Fast Reactor
U-235
(ENDF/B)
Pu-239
(ENDF/B)
Thermal Reactor
U-238
(ENDF/B)
Th-232
(ENDF/B)
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
6
10
15
10
14
10
13
10
12
10
11
10
10
10
9
7
Neutron Energy, eV
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
Neutron flux shapes
folded with cross
sections determine
the region of interest
(both energy and
isotopes)

The magnitude of the
neutron flux drives
cross section
uncertainty
requirements
2
10
10
Neutron Flux, n/(cm ·s)
Fission Cross Section, barn
Fission Cross Section and Fluxes
Slide 5
History of neutron source development
Highlighted
are active
facilities in
the US
IAEA-TECDOC-1439, 2005
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Slide 6
Spallation sources: n/p yield and neutron energies
(thick Pb target)
Ep = 800 MeV
Two components:
- The cascade
component up to the
energy of the incident
protons
- The evaporation
component which is
dominant up to ~20 MeV
NIM A 374 (1996) 70
Preprint INR RAS 1280, 2011
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Report LA-4789, 1972
NIM A 242 (1985) 121
Slide 7
Moderated neutron sources


Enrich neutron flux with
epithermal neutrons
-
High content hydrogen material
is used for effective neutron
moderation, e.g. polyethylene,
water, etc.
-
Varying of moderator thickness
one can change the ratio of
faster/slower neutrons
Neutron flux of moderated source, LANSCE
PR C 79, 014613 (2009)
Time resolution of moderated source, GNEIS
Very specific moderator – liquid
hydrogen – provides cold and
ultra cold neutrons. This is a very
unique field of neutron physics
Details about this field are in the following report of S.Dewey
NIM A 242 (1985) 121
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Slide 8
What facilities are available for fast neutrons?
WNR
GNEIS
n_TOF
SNS
J-PARC
Proton energy, MeV
800
1,000
20,000
1,000
3,000
Proton current, μA
1.8
2.3
0.5
1,400
300
Target
Number of produced
neutrons per proton
Total neutron yield
per second
Proton pulse length
on target, ns
Pulse frequency, Hz
W
Pb
Pb
Hg
Hg
10
20
250
25
75
1∙1014
3∙1014
8∙1014
2∙1017
1.5∙1017
0.2
10
6
700
1,000
13,900
50
0.4
60
25
Handbook of Nuclear Engineering, Springer, 2010
NIM A 242(1985)121
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Slide 9
Existing 235U(n,f) XS data for fast neutrons
Fission cross section, b

The most popular
detector is a parallelplate fission ionization
chamber (FIC)
2.4
1955 Goldanskiy+
1957 Smith+
1963 Pankratov
1965 White
1975 Czirr+
1976 Leugers+
1978 Kari+
1983 Alkhazov+
1986 Alkhazov+
1988 Johnson+
1997 Lisowski+
2007 Nolte+
Standard ver.1997
Standard ver.2007
JENDL/HE
2.2
2.0
1.8
1.6
235
U
1.4
1.2
15%
1.0
1
100
10
1000
Neutron energy, MeV
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Slide 10
Existing 239Pu(n,f) XS data for fast neutrons
2.6
5.6%
Fission Cross Section, b
2.4
239
Pu
1%
2.2
2.0
LANL(88)
LANL(98)
PNPI(02)
LANL(10)
ENDF/B-VII.0
JENDL/HE
1.8
1.6
10%
1.4
1
10
100
Neutron Energy, MeV
Ref.:
LANL(88): Lisowski et al., ND-1988(1988)97
LANL(98): Staples et al., Nucl.Sci.Eng. 129(1998)149
PNPI(02): Shcherbakov et al., J.Nucl.Sci.Tech. S2(2002)230
LANL(10): Tovesson et al., Nucl.Sci.Eng. 165(2010)224
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Slide 11
0.0
1
10
Neutron energy, MeV
100
Existing 238U(n,f) XS data for fast neutrons
1.8
Fission cross section, b
1.6

Data were taken using
FIC as a ration to 235U
(LANL and PNPI)

Data of Nolte were
obtained relative to
np-scattering
7%
238
U
1.4
1.2
1.0
0.8
0.6
Lisowski+(1992)
Shcherbakov+(2001)
Nolte+(2007)
0.4
0.2
0.0
1
10
100
Neutron energy, MeV
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Ref.:
Lisowski: Lisowski et al., ND-1991(1992)732
Shcherbakov: Shcherbakov et al., J.Nucl.Sci.Tech. S2(2002)230
Nolte: Nolte et al., Nucl.Sci.Eng. 156(2007)197
Slide 12
Existing data for fast neutron-induced fission of some
minor actinides
3.5
244
2.5
2.0
Fursov+, 1997
Fomushkin+, 1991
Vorotnikov+, 1981
Fomushkin+, 1980
Moore+, 1971
Koontz+, 1968
Fomushkin+, 1967
ENDF/B-VII.0
JEFF-3.1
JENDL-3.3
JENDL/AC-2008
1.5
1.0
0.5
0.0
0.1
245
3.0
Cm
1
10
Fission cross section, b
Fission cross section, b
3.0
3.0
100
Cm
2.5
2.5
2.0
Fursov+, 1997
Ivanin+, 1997
Fomushkin+, 1991
Fomushkin+, 1987
White+, 1982
Gokhberg+, 1972
Moore+, 1971
ENDF/B-VII.0
JEFF-3.1
JENDL-3.3
JENDL/AC-2008
1.5
1.0
0.5
0.1
1
Energy, MeV
10
Fission cross section, b
3.5
100
Energy, MeV
248
Cm
2.0
1.5
Fursov+, 1997
Fomushkin+, 1991
Fomushkin+, 1980
Moore+, 1971
ENDF/B-VII.0
JEFF-3.1
JENDL-3.3
JENDL/AC-2008
1.0
0.5
0.0
0.1
1
10
100
Energy, MeV
From the NEA Nuclear Data High Priority Request List
for fission cross section of minor actinides
244
Cm
Initial vs target
uncertainties (%)
245
Cm
Initial vs target
uncertainties (%)
Energy Range
Initial
ADMAB
Energy Range
Initial
ADMAB
6.07 - 2.23 MeV
31
3
2.23 - 6.07 MeV
31
7
2.23 - 1.35 MeV
44
3
1.35 - 2.23 MeV
44
6
1.35 - 0.498 MeV
50
2
0.498 - 1.35 MeV
49
3
llllll
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Requested accuracy is
defined by the AcceleratorDriven Minor Actinides
Burner (ADMAB)
Slide 13
Systematic errors associated with conventional FICs
1.
Separation of fission and background events in pulseheight spectra:
-
Spallation and fragmentation inputs
-
Radioactivity of used targets
-
Electronic noise
2.
Anisotropy of emitted fission fragments
3.
Neutron flux normalization: mostly data were obtained from
235U ratio, very few were normalized to (n,p)-scattering
4.
Beam profile and sample uniformity
5.
Charged particle contamination of neutron beam
6.
…
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Slide 14
TPC can address most of the systematic uncertainties
associated with conventional FICs

Time Projection Chamber (TPC)
technology based on highly pixelated
readout anodes

Full 3D event reconstruction gives a
“snapshot” of ionization tracks in
a fill gas

Particle identification based on specific
ionization loss

The TPC experiment, involving a
collaboration of 4 national labs and 6
universities, is currently running at the
fast neutron beam facility WNR at LANL
Fission
fragment
track
Fission
fragment
Alpha
particle
track
Alpha
particle
There are more details in following report of F.Tovesson
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Ref.: Heffner, AIP Conf.Proc. 1005(2008)182
Slide 15
Other ways to avoid systematic uncertainties associated
with conventional FICs

An ionization fission chamber with gaseous
actinide target doesn’t lose fission fragments
emitted at steep angles

Uranium hexafluoride UF6 can be a suitable
compound for investigating U isotopes as it
has a boiling point at 56.5oC
-
-
There is no “edge-effect” due to two fragment emission
It is expected much better resolution between fission
fragments and small PH signals in a pulse height
spectrum
Separate active volume outside the main one should be
used for the background neutron input estimation
Neutron
beam
Ref.: Laptev, Strakovsky, Briscoe, Afanasev,
Proposal NSF-ARI-MA (DNDO) Grant ECCS-1139985, 2011

For the Pu isotopes, plutonium hexacarbonyl
Pu(CO)6 can be considered.
Ref.: Thanks to W.Loveland, Oregon State University,
for pointing out this opportunity
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Slide 16
Prompt Fission Neutron Study

Existing data establish the prompt fission
neutron spectrum quite well in the energy
range from 1 to about 5 MeV

The Chi-Nu experiment to study the prompt
fission neutron spectrum will also run at the WNR
-

Parallel plate avalanche counter as a fission trigger
6Li-glass
-
20
1 MeV
detectors to measure neutron output below
-
50 liquid scintillator detectors to measure neutron
output from 0.5 to 12 MeV
~35 % less
than 1 MeV
Important
region for
rad-chem:
(n,2n) etc.
Chi-Nu goals are
-
Below 1 MeV, to reduce the neutron output uncertainties
from ~10% to ~5%
-
Above 6 MeV, to reduce uncertainties from 20-50% to
10-20%
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Ref.: Noda, Haight et al., Phys.Rev.C 83, 034604 (2011)
Slide 17
Angular distribution of PFN relative to FF
Recent measurement for thermal neutrons





Fission neutrons from the 235U(nth,f) reaction
were detected at several angles
Angular resolution is 18o
Model calculation was done on the basis of
the assumption that neutrons are emitted
only from fully accelerated fragments
Obtained an estimate of upper limit for
“scission” neutrons less than 5% of the total
neutron output
From all existing works: the contribution of
scission neutrons to the total yield of PFN
ranges from 1% to 20%, so even existence
of “scission” neutrons can hardly be
considered proven
Ref.: A.Vorobyev et al., NIM A 598 (2009) 795
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Slide 18
Fission fragment yield distribution

The fission fragment yield distribution changes drastically with
neutron energy above ~10 MeV, from asymmetric to symmetric

There are no data above neutron energy of about 20 MeV
except for 238U and 232Th. No data for the most important nuclei
235U and 239Pu !

These data are vitally important for both fission theory and
many applications including fast reactors, ADS systems, and
special nuclear devices

This gives strong motivation for the new LANL experiment
SPIDER, designed to obtain fission fragment yields with mass
resolution up to 1 amu following fast neutron-induced fission
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Slide 19
Existing data for fission fragment yield distribution as a
function of neutron energy for 232Th
FF mass resolution is ~ 8 amu

The fission fragment yield distribution
experiences drastic change in the
energy range from 10 to 60 MeV
Ref.: Simutkin et al., AIP Conf.Proc. 1175(2009)393
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Slide 20
High resolution fission fragment yield measurements

Measured at ILL,
France for
thermal neutron
229Th(n ,f)
th
with COSI-FAN-TUTTE spectrometer
FF yield
Nuclear charge
distribution for
A=87
FF mass resolution
is ~ 0.64 amu
Ref.: Boucheneb et al., Nuc.Phys.A 502(1989)261c

SPIDER experiment to measure energy-dependent neutroninduced FF yields with high resolution in progress at LANL
Ref.: White, Tovesson et al.,
Report LA-UR-11-01125
FF mass resolution
is expected ~1 amu
There are more details about SPIDER in following report of F.Tovesson
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Slide 21
Correlation between PFN multiplicity & FF properties
Search for correlation between PFN multiplicity & FF properties
in SF of 252Cf, 244Cm, and 248Cm was done using a 4π neutron
detector and twin Frisch gridded FIC



Ref.: V.Kalinin et al., Fission: Pont d’Oye V (2003)73
Fission fragment mass distribution for fixed
numbers of emitted neutrons νL / νH for
spontaneous fission of 248Cm
There are no such data for fast neutroninduced fission. The very first attempt of
such measurement was done for thermal
and 0.3 eV neutron induced fission of 235U
and 239Pu [Batenkov et al., AIP Conf. Proc. 769
(2005)1003]
Fission theories are most sensitive for
correlated data, source: LANL-LLNL fission
workshop, Feb 3-6, 2009
FF mass resolution is ~ 1.5 amu (for 252Cf)
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Slide 22
Average fission neutron multiplicity

Average fission neutron multiplicity as a function of incident neutron energy
is known quite well for nuclei 235U, 238U, and 237Np, up to 200 MeV
14
14
Average Neutron Multiplicity
U
10
8
6
4
Howe(1984)
Ethvignot+(2005)
2
0
0
20
40
238
12
60
80 100 120 140 160 180 200
Average Neutron Multiplicity
235
12
Ref. (235U):
R.Howe,
Nucl.Sci.Eng. 86(1984)157
T.Ethvignot et al.,
PRL 94(2005)052701
10
8
6
4
Frehaut(1980)
Taieb+(2007)
2
0
0
20
Incident Neutron Energy, MeV

U
40
60
Ref. (238U):
J.Frehaut ,
EXFOR data 21685.003
J.Taieb et al.,
ND-2007 (2007)429
80 100 120 140 160 180 200
Incident Neutron Energy, MeV
For other nuclei important to the nuclear cycle the data are limited:
for 232Th < 50 MeV, 239Pu < 30 MeV, 233U < 15 MeV, 243,241Am < 11 MeV, etc.
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Slide 23
Total kinetic energy of fission fragments as a function
of neutron energy

Data on total kinetic energy of fission fragment are required for both theory
and applications to calculate total energy release in fission (along with that for
Total Kinetic Energy, MeV
172
238
171
prompt and delay fission neutron, prompt
and delay fission gamma-ray energy, etc.)
U
Pre prompt neutron emission
170
169
168
167
Ref.:
Data: C.Zöller, PhD Theses (1991)
Fit: D.Madland, NP A 772(2006)113
Zoeller (1991)
Fit
0
5
10
15
20
25
30
Incident Neutron Energy, MeV

The quadratic fit doesn’t describe structure near different chance fission
thresholds because the corresponding experimental data for 235U and 239Pu
are much lower in quality and the energy range is limited (no data above
15 MeV)
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Slide 24
Angular anisotropy of fission fragments
2.0
140
238
238
100
80
1.6
1.4
o
d/d, mb/sr
o
120
U
1.8
d/d(0 ) / d/d(90 )
U
En = 14.1 MeV
Ouichaoui+(1988)
2
Fit ao+a2cos Lab
60
40
-30
1.2
0.8
0
30
60
90
Ouichaoui+(1988)
Shpak(1989)
Other data(<1981)
1.0
1
Lab, deg
10
En, MeV

It is used in fission cross section measurements to
calculate a correction for FF absorption in a target

Provide information about the projection of the total
angular momentum J of the fissioning nucleus along
the nuclear symmetry axis at saddle point deformation
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Ref.:
Ouichaoui et al., Acta Phys.Hung. 64(1988)209
Shpak, Yadernaya Fizika 50(1989)922
Slide 25
Ternary fission yields

Important for both fission theory and applications (gas emission
characteristics)

Studied quite well at thermal
energy:

-
235U
-
energy distribution of ternary
α’s measured
[C.Wagemans et al., NP A 742(2004)291];
-
etc.
E-distribution for the 235U(nth,f) ternary α’s
ratio binary/ternary
fission was measured quite
well: 536±10
[C.Wagemans et al., PR C 33(1986)943];
Confident separation of all ternary particles in SF 252Cf
[M.Mutterer et al., PR C 78(2008)064616]
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Slide 26
Prospective investigations of ternary fission

Very little data for fast neutron-induced fission. Better
understanding needed of:
-
Variation of ternary-to-binary fission ratios in the resonance energy
region. E.g., a correlation of ternary fission yields and the relative
contribution of standards I and II fission modes was found in
235U(n,f) resonances at energy from thermal to 2500 eV
[S.Pomme et al., NP A 587(1995)1]
-
Angular anisotropy in ternary nuclear fission and its dependence
on neutron energy. Most fission theories predict ternary particles to
be formed at scission. A way to confirm this assumption is to
analyze the angular distribution of fission fragments
[S.Dilger, PhD Theses(2004)]
-
“Quaternary” fission with an apparently independent emission of
two charged particles?
[M.Mutterer, Pont d'Oye V (2003)135]
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Slide 27
Subthreshold fission as a search for class-II states

Gives unique information about fission barriers

Direct demonstration of double-humped
structure of potential energy of heavy nuclei
and existence of class-II states

First systematic study of class-II clusters with
high energy resolution was done at the ORELA
facility, ORNL for 240Pu
The double-humped
fission barrier
Clustering of
fission strengths
1936 eV cluster in subthreshold
fission of 240Pu
Ref.: Mughabghab, Atlas of Neutron Resonances, 2006
Ref.: Auchampaugh, Weston,
PRC 12, 1850 (1975)

Clustering of subthreshold fission strengths observed in 240Pu
was explained in terms of the double-humped fission theory

Average level spacing of class-II states estimated of
DII = 450±50 eV. Based on that and known DI, a value of
EII = 1.52±.08 MeV was derived
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Slide 28
Search for γ-transitions to class-II states

Descriptive schematic of the
(n, γf) reaction mechanism


Differences in pulse-height γ-ray spectra for
weak (Γf < 10 meV) and strong (Γf > 10 meV)
fission 1+-resonances of 239Pu in epithermal
neutron energies
Few possible structures could be interpreted
as a γ-transitions between class-II states
Confident discovery of class-II γ-transitions
will give unique information about the
structure of the fission barrier
Ref.: J.Trochon, Physics & Chemistry of Fission, 1979, Vol. I, p.87
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Ref.: O.Shcherbakov et al., ASAP Proc. (2002) 123
Slide 29
Proton-induced fission of 235U
Fission cross section of
235
U

This energy range is important
for future ADC systems, e.g.,
for transmutation of nuclear
waste

Existing data are very scarce
and are in contradictory

The ALICE code calculation for
the JENDL-HE data file shows
a peak near 300 MeV, which
comes from a broad reaction
cross section shape from the
optical model [Private communication
from T.Kawano, 2009]. New
experimental data are needed
to confirm that result

Relevant proton energy range
should be available for the
JLab EIC booster
235
U(n,f), Standard ver. 2007
U(n,f), JENDL-HE
235
U(p,f), JENDL-HE
235
U(p,f), Kotov+, 2006
235
U(p,f), Yurevich+, 2002
235
U(p,f), Ohtsuki+, 1991
235
U(p,f), Bochagov+, 1978
235
U(p,f), Boyce+, 1974
235
U(p,f), Brandt+, 1972
235
U(p,f), Matusevich+, 1968
235
U(p,f), Konshin+, 1965
235
U(p,f), Fulmer, 1959
235
U(p,f), Steiner+, 1956
235
U(p,f), McCormick+, 1954
235
Fission cross section, b
2.0
1.5
1.0
0.5
1
10
100
1000
10000
Incoming Particle Energy, MeV
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Slide 30
Single-event effects (SEEs) in electronics investigations

Increasing complexity and density of an electronic
chips increases their susceptibility to cosmic
radiation. Most SEEs in avionic electronics at aircraft
cruising altitudes are caused by neutrons

Electronics industry is very interested in checking the
stability of their electronics against neutron irradiation

Spallation neutron sources can imitate cosmic
neutron flux but with intensities millions of times
higher

Many facilities all around the world built irradiation
facilities, which are in high demand
UNCLASSIFIED
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Slide 31
Active facilities in SEEs studies
Facility
Affiliation
Energy,
MeV*)
Neutron source
Ref.
ICE House
LANL, USA
800(p)
White spectrum
J.Korean Phys.Soc. 59
(2011) 1558
TRIUMF Neutron
Facility
TRIUMF, Canada
70-500(p)
White spectrum
IEEE Radiation Effects
Data Workshop, 2003,
p.149
180(p)
White spectrum
IEEE Radiation Effects
Data Workshop, 2009,
p.166
800(p)
White spectrum
Appl. Phys. Lett. 92,
114101 (2008)
ANITA
VESUVIO
The Svedberg Lab.,
Uppsala Univ.,
Sweden
Rutherford Appleton
Laboratory, UK
GNEIS
PNPI, Russia
1,000(p)
White spectrum
Instrum. Exper. Tech. 53
(2010) 469
RCNP
Research Center for
Nuclear Physics,
Osaka Univ., Japan
14-198(n)
Quasimonoenergetic
42nd Annual IEEE Int.
Reliability Physics Symp.,
2004, p.305
…
*)
Neutron flux of the ICE House
irradiation facility at LANL
Neutron flux of the irradiation
facility at GNEIS
(p) indicates proton beam energy on spallation target;
(n) energy of neutron beam is shown.

With the EIC booster proton energy of 3,000 MeV
it may be possible to obtain better imitation of
cosmic-ray neutron spectrum to higher energies
UNCLASSIFIED
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Slide 32
Summary

In many years of fission research, a large volume of
experimental data was accumulated

There is still a significant lack of fission data for fast
neutrons. Improving the quality of existing data will
make a crucial impact on important applications and
nuclear theory

The proposed EIC complex at JLab promises to be a
facility for acquiring high-quality experimental fission
data and to carry out applied research
UNCLASSIFIED
Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Slide 33