Research at UKAL: Lessons
Learned and New Adventures
www.pa.uky.edu/accelerator/
Steven W. Yates
Inelastic Neutron Scattering
inelastically
scattered
neutron
Incident
Neutron
E**
E*
Target
Nucleus
Excited
Cooled
Nucleus
Nucleus
gs
(n,n') reaction
Neutron Production
3H(p,n)3He
Q = -1 MeV
2H(d,n)3He
Q = 3 MeV
Neutron Energies (Accelerator Voltage: 1.5 – 7.0 MV)
3H(p,n)
0.5 < En < 6 MeV
2H
2H(d,n)
4.5 < En < 10 MeV
or 3H gas
n
Target
Pulsed p or d beam
from VdG accelerator

Beam 
γ
(n,n') singles
(n,n') Singles Measurements
scattering
sample
gas cell
HPGe
BGO
(n,n') Singles Measurements
scattering
sample
Beam
gas cell
Gas
Handling
System
94Zr
(n,n)
Compton suppressed
TOF Gating
94Zr(n,n)
Angular Distribution
W() = 1 + a2 P2(cos ) + a4P4(cos )
Comparison with statistical model calculations (CINDY)
→ multipole mixing ratio () and spins
Doppler-Shift Attenuation Method


v
Detector
E() = E (1 + v/c cos )
The nucleus is recoiling into a viscous medium.
v  v(t) = F(t)vmax
E() = E (1 + F() v/c cos )
Level Lifetimes: Doppler-Shift
Attenuation Method (DSAM)
180°

v
γ
τ = 7.6(9) fs
0°
γ
• Scattered neutron causes
the nucleus to recoil.
τ = 76(7) fs
• Emitted γ rays experience a
Doppler shift.
• Level lifetimes in the
femtosecond region can be
determined.
T. Belgya, G. Molnár, and S.W. Yates, Nucl. Phys. A607, 43 (1996).
E.E. Peters et al., Phys. Rev. C 88, 024317 (2013).
DSAM
Calculated curve
Completely
Dopplershifted
F()exp
v


E γ θ )  E γ 1  Fexp τ ) cm cos θ
c


τ = 76(7) fs

Not Dopplershifted
K.B. Winterbon, Nucl. Phys.
A246, 293 (1975).
T. Belgya, G. Molnár, and S. W. Yates, Nucl. Phys. A607, 43 (1996).
Scattering Sample
Lithium Carbonate
Loaded Paraffin
Beam 
Paraffin-Filled Shielding
Gas Cell
Kentucky Gamma-ray Spectrometer
KEGS
KEGS
gas cell
“Monoenergetic” Neutron Production
3H(p,n)3He
Scattering
Sample

n
Gas cell with Mo foil window
Neutron energy at center of the gas cell
1.75 MeV
3.19 MeV
Straggling in 3.3-μm Mo entrance foil (keV)
dE/dgas, 3-cm tritium cell at 1 atm (keV)
32
31
81
55
dE/d, outgoing neutron energy deviation
over the sample (keV)
23
40
Diagnostic MCNPX calculations of neutron production in gas cell
Inelastic Neutron Scattering with
Accelerator-Produced Neutrons




No Coulomb barrier/variable neutron energies
Excellent energy resolution ( rays detected)
Nonselective, but limited by angular momentum
Lifetimes by Doppler-shift attenuation method (DSAM)
 T. Belgya, G. Molnár, and S.W. Yates, Nucl. Phys. A607, 43 (1996)
 E.E. Peters et al., Phys. Rev. C 88, 024317 (2013).
 Gamma-gamma coincidence measurements
 C.A. McGrath et al., Nucl. Instrum. Meth. A421, 458 (1999)
 E. Elhami et al., Phys. Rev. C 78, 064303 (2008)
 Limited to stable nuclei
 Large amounts of enriched isotopes required
Current and Future Research
Directions at UKAL
 Fast neutron physics
 Nuclear shell structure and shape transitions
 Nuclear level lifetime determinations with the
Doppler-shift attenuation method
 Nuclear structure relevant to double-β decay
 Precision fast neutron reaction cross sections
 Corporate and homeland security applications
 Neutron detector development (with collaborators)
www.pa.uky.edu/accelerator/
Current and Future Research
Directions at UKAL
 Fast neutron physics
 Nuclear shell structure and shape transitions
 Nuclear level lifetime determinations with the
Doppler-shift attenuation method
 Nuclear structure relevant to double-β decay
 Precision fast neutron reaction cross sections
 Corporate and homeland security applications
 Neutron detector development (with collaborators)
www.pa.uky.edu/accelerator/
0νββ?
2νββ
BE
Is the neutrino its own antiparticle?
What is the mass of the neutrino?
136Te
136Pr
b-
136I
EC
b136La
136Ce
136Cs
136Xe
b-
EC
136Ba
52
53
54
55
56
57
58
59
Z
• 80.6% enriched in 136Xe
• (remaining 19.4% is 134Xe)
• Q-value: 2457.83 ± 0.37 keV
Counts
EXO-200: 200 kg of Xe (l)
1000
2000
E(keV)
M. Auger et al., PRL 109, 032505 (2012) Pictures from R. Neilson TIPP 2011 and
http://www-project.slac.stanford.edu/exo/
EXO Resolution
228Th
2615 keV
FWHM ≈ 100 keV
M. Auger et al., PRL 109, 032505 (2012)
Neutron Backgrounds from Radioactive Decay
Fig. 1. Neutron energy
spectrum from U and Th
traces in rock as calculated
with modified SOURCES.
Contributions from 60 ppb U
(filled squares and lower
curve), 300 ppb Th (open
circles and middle curve) and
the sum of the two (filled
circles and upper curve) are
shown.
M.J. Carson et al., Astroparticle Phys. 21, 667 (2004).
Neutron Backgrounds from Cosmic-ray Muons
Fig. 7. Energy spectra of muon-induced neutrons at various boundaries: (a) filled circles––
neutrons at the salt/cavern boundary, open circles––neutrons after the lead shielding; (b)
filled circles––neutrons at the salt/cavern boundary (the same as in (a)), open circles––
neutrons after the lead and hydrocarbon shielding.
M.J. Carson et al., Astroparticle Phys. 21, 667 (2004).
UKAL Experiments
• Inelastic neutron scattering
 Monoenergetic neutrons via 3H(p,n)3He
 Allows determination of :
• Level scheme
• Transition multipolarities
• Multipole mixing ratios
• Level lifetimes
XeF2 in
• Transition probabilities
Teflon vial
• Solid XeF2 samples of 130Xe, 132Xe, 134Xe, 136Xe
 Highly enriched, solid targets not used previously
New Level: 2485 keV
2485   32891
62 fs
0.20
0.48
0.32
1614
847
134Xe
New Level: 2485 keV
871
1638
2485
2485-keV Transition
bg
Q-value: 2458 keV
σ Measurement
Other New Levels
2502
2440
260
  310110
fs
  22140
32 fs
1655
1593
847
847
Current and Future Research
Directions at UKAL
 Fast neutron physics
 Nuclear shell structure and shape transitions
 Nuclear level lifetime determinations with the
Doppler-shift attenuation method
 Nuclear structure relevant to double-β decay
 Precision fast neutron reaction cross sections
 Corporate and homeland security applications
 Neutron detector development (with collaborators)
www.pa.uky.edu/accelerator/
Applied Science with Monoenergetic Pulsed Neutrons
from the University of Kentucky Accelerator Laboratory
S. F. Hicks
University of Dallas, Irving, TX
J. R. Vanhoy
US Naval Academy, Annapolis, MD
M. T. McEllistrem and S. W. Yates
University of Kentucky, Lexington, KY
Part of the Advanced Fuel Cycle Initiative (AFCI) to develop
safe, clean, and affordable energy sources
Goals of Gen IV:
i) Safer
ii) Sustainable
iii) Economical
iv) Physically Secure
http://www.gen-4.org/Technology/evolution.htm
 Critical need for high-precision and accurate elastic and inelastic neutron
scattering data on materials important for fission reactor technology
 Critical need for trained individuals (NEUP initiative)
One of the Six
Generation IV Nuclear
Energy Systems
Inelastic Neutron
Scattering
Fe*
<http://nuclearpowertraining.tpub.com/h
1019v1/css/h1019v1_69.htm.>
“A Technology Roadmap for Generation IV Nuclear Energy Systems,” Generation
IV International Forum, December 2002.
Energy Loss Mechanism
Neutron elastic and inelastic scattering cross
sections are needed from structural materials such
as Fe and coolants such as Na.
Forward monitor
Long counter
Beam line
Neutron detector
Gas cell
Copper shielding
(n,n') TOF
> 2-meter deep
scattering pit
Tungsten wedge
3H(p,n) Q= 0.76 MeV
2H(d,n) Q= 3.3 MeV
3H(d,n) Q= 17.6 MeV
Gas cell
Na sample
Typical adjustment of wedge with cell and sample
Beam line
Neutron Detection: Main
• Flight paths to about 4 m can be used
for neutron scattering. Angles between
30 and 145 degrees are accessible with
the Na and Fe samples.
•Neutrons are detected by a deuterated
benzene liquid scintillation detector
(1x5.5).
•Pulse Shape Discrimination
Understanding background generation in TOF spectra
Inelastic Cross Sections --Two Techniques
23Na(n,n) En=4.0 MeV, 125o
2000
Counts
1500
1000
500
0
1000
2000
3000
HPGe Channel Number
500
Counts
400
300
200
100
23Na
0
3000
5000
7000
HPGe Channel Number
9000
EVALUATIONS
EXPERIMENTAL DATA
Current and Future Research
Directions at UKAL
 Fast neutron physics
 Nuclear shell structure and shape transitions
 Nuclear level lifetime determinations with the
Doppler-shift attenuation method
 Nuclear structure relevant to double-β decay
 Precision fast neutron reaction cross sections
 Corporate and homeland security applications
 Neutron detector development (with collaborators)
www.pa.uky.edu/accelerator/
SCINTILLATOR
DEVELOPMENT
• Multi-radiation detectors
–
–
–
–
CLYC: Cs2LiYCl6
CNYC: Cs2NaYCl6
CLLC: Cs2LiLaCl6
CLLB: Cs2LiLaBr6
http://www.rmdinc.com/
Measured detector response for
En = 0.5 - 22 MeV
~7 scintillators in 36 hours.
Glodo-IEEETransNuclSci.60.864.2012
DETECTOR DESIGN & CHARACTERIZATION
DEuterated SCintillator Array for Neutron Tagging
@ TRIUMF
• Neutron Detectors
– Efficiency(En)
– Pulse Shape Discrimination
– Amplitude Distribution
n
n
D

e
scintillator fluid
C6D6
Different recoiling ions excite the atomic/molecular structure
differently, and exhibit different characteristic decay times.
http://atguelph.uoguelph.ca/2011/11/guelph-physicist-leads-project-at-triumf-lab/
http://www.physics.uoguelph.ca/Nucweb/tigress.html
https://www.facebook.com/photo.php?fbid=645033412191460&set=pb.114964
088531731.-2207520000.1373380138.&type=3&theater
TIGRESS -ray detector array
http://atguelph.uoguelph.ca/2011/11/guelph-physicist-leads-project-at-triumf-lab/
DESCANT neutron detector array
http://www.physics.uoguelph.ca/Nucweb/tigress.html
Our Colleagues
University of Dallas
U.S. Naval Academy
University of Guelph
University of Wisconsin at Lacrosse
Georgia Institute of Technology
University of Notre Dame
Radiation Monitoring Devices
University of Cologne
HIS at TUNL
Yale University
Technical University Darmstadt
University of the West of Scotland
University of the Western Cape (South Africa)
iThemba Labs TRIUMF ANU