Post on 20-Jan-2016
Steven W. Yates
Research at UKAL: Lessons Learned and New Adventures
www.pa.uky.edu/accelerator/
E*
E**
gsgs
Excited
Nucleus
IncidentNeutron
TargetNucleus
Inelastic Neutron Scatteringinelasticallyscatteredneutron
(n,n') reaction
E**
gs
E*CooledNucleus
n
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(d,n) 4.5 < En < 10 MeV
2H or 3H gas
Pulsed p or d beamfrom VdG accelerator
Target
Beam
γ (n,n') singles
(n,n') Singles Measurements
scatteringsample
gas cell
HPGe
BGO
Beam
(n,n') Singles Measurements
scatteringsample
gas cell
Beam
GasHandlingSystem
94Zr (n,n) Compton suppressed TOF Gating
94Zr(n,n) Angular Distribution
W() = 1 + a2 P
2(cos ) + a
4P
4(cos )
Comparison with statistical model calculations (CINDY)
→ multipole mixing ratio () and spins
Detector
Doppler-Shift Attenuation Method
v
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)
T. Belgya, G. Molnár, and S.W. Yates, Nucl. Phys. A607, 43 (1996).E.E. Peters et al., Phys. Rev. C 88, 024317 (2013).
• Scattered neutron causes the nucleus to recoil.
• Emitted γ rays experience a Doppler shift.
• Level lifetimes in the femtosecond region can be determined.
γγ
v
0°180°
τ = 7.6(9) fs
τ = 76(7) fs
DSAM
Not Doppler-shifted
CompletelyDoppler-shifted
Calculated curve
F()exp
θ cos
c
vτF1EθE cm
expγγ
τ = 76(7) fs
K.B. Winterbon, Nucl. Phys. A246, 293 (1975).
T. Belgya, G. Molnár, and S. W. Yates, Nucl. Phys. A607, 43 (1996).
Paraffin-Filled Shielding
Lithium CarbonateLoaded Paraffin
Bea
m
Gas Cell
Scattering Sample
HPGe
HPGe
HPGe
HPGe
Kentucky Gamma-ray SpectrometerKEGS
KEGS
gas cell
Beam
“Monoenergetic” Neutron Production
ScatteringSample
3H(p,n)3He
n
Neutron energy at center of the gas cell 1.75 MeV 3.19 MeV
Straggling in 3.3-μm Mo entrance foil (keV) 32 31
dE/dgas, 3-cm tritium cell at 1 atm (keV) 81 55
dE/d, outgoing neutron energy deviation over the sample (keV)
23 40
Diagnostic MCNPX calculations of neutron production in gas cell
Gas cell with Mo foil window
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
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 ResearchDirections 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 ResearchDirections at UKAL
2νββ 0νββ?
52 53 54 55 56 57 58 59 Z
BE
b-
b-
136Te
136I
136Xe
136Cs
b-
136Ba
EC
136Ce136La
136Pr
Is the neutrino its own antiparticle?What is the mass of the neutrino?
EC
M. Auger et al., PRL 109, 032505 (2012) Pictures from R. Neilson TIPP 2011 andhttp://www-project.slac.stanford.edu/exo/
EXO-200: 200 kg of Xe (l) • 80.6% enriched in 136Xe • (remaining 19.4% is 134Xe)• Q-value: 2457.83 ± 0.37 keV
1000 2000 E(keV)
Cou
nts
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).
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.
Neutron Backgrounds from Cosmic-ray Muons
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• Transition probabilities
• Solid XeF2 samples of 130Xe, 132Xe, 134Xe, 136Xe Highly enriched, solid targets not used previously
XeF2 in Teflon vial
New Level: 2485 keV
134Xe
1614
847
2485 fs 328 9162
0.20 0.48 0.32
New Level: 2485 keV871 1638 2485
2485-keV Transitionbg
σ Measurement
Q-value: 2458 keV
Other New Levels
847847
25022440
1593 1655
fs 310 260110
fs 221 4032
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 ResearchDirections at UKAL
S. F. HicksUniversity of Dallas, Irving, TX
J. R. VanhoyUS Naval Academy, Annapolis, MD
M. T. McEllistrem and S. W. YatesUniversity of Kentucky, Lexington, KY
Applied Science with Monoenergetic Pulsed Neutrons from the University of Kentucky Accelerator Laboratory
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)
Part of the Advanced Fuel Cycle Initiative (AFCI) to develop safe, clean, and affordable energy sources
http://www.gen-4.org/Technology/evolution.htm
Goals of Gen IV:i) Saferii) Sustainableiii) Economicaliv) Physically Secure
“A Technology Roadmap for Generation IV Nuclear Energy Systems,” Generation IV International Forum, December 2002.
One of the Six Generation IV Nuclear Energy
SystemsInelastic Neutron
Scattering
Energy Loss Mechanism
<http://nuclearpowertraining.tpub.com/h1019v1/css/h1019v1_69.htm.>
Fe*
Neutron elastic and inelastic scattering cross sections are needed from structural materials such as Fe and coolants such as Na.
Forward monitor
Long counter
Neutron detector
Gas cell
Beam line
Copper shielding
(n,n') TOF
> 2-meter deep scattering pit
Typical adjustment of wedge with cell and sample
Tungsten wedge
Na sample
Gas cell Beam line
Neutron
detector
3H(p,n) Q= -0.76 MeV2H(d,n) Q= 3.3 MeV3H(d,n) Q= 17.6 MeV
• 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 (1x5.5).
•Pulse Shape Discrimination
Neutron Detection: Main
Understanding background generation in TOF spectra
1000 2000 30000
500
1000
1500
2000
23Na(n,ng) En=4.0 MeV, 125o
HPGe Channel Number
Coun
ts3000 5000 7000 90000
100
200
300
400
500
HPGe Channel Number
Coun
ts23Na
Inelastic Cross Sections --Two Techniques
(n,n')
(n,n'γ)
EVALUATIONS EXPERIMENTAL DATA
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 ResearchDirections at UKAL
Glodo-IEEETransNuclSci.60.864.2012
http://www.rmdinc.com/
SCINTILLATOR DEVELOPMENT
• Multi-radiation detectors– CLYC: Cs2LiYCl6
– CNYC: Cs2NaYCl6
– CLLC: Cs2LiLaCl6
– CLLB: Cs2LiLaBr6
Measured detector response forEn = 0.5 - 22 MeV
~7 scintillators in 36 hours.
http://atguelph.uoguelph.ca/2011/11/guelph-physicist-leads-project-at-triumf-lab/
http://www.physics.uoguelph.ca/Nucweb/tigress.html
DETECTOR DESIGN & CHARACTERIZATION
• Neutron Detectors– Efficiency(En)– Pulse Shape Discrimination– Amplitude Distribution
e
n
n
D
g
DEuterated SCintillator Array for Neutron Tagging@ TRIUMF
scintillator fluidC6D6
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/
https://www.facebook.com/photo.php?fbid=645033412191460&set=pb.114964088531731.-2207520000.1373380138.&type=3&theater
http://www.physics.uoguelph.ca/Nucweb/tigress.html
DESCANT neutron detector array
TIGRESS g-ray detector array
Our ColleaguesUniversity of Dallas
U.S. Naval AcademyUniversity of Guelph
University of Wisconsin at Lacrosse Georgia Institute of Technology
University of Notre Dame Radiation Monitoring Devices
University of Cologne HIgS at TUNL
Yale UniversityTechnical University Darmstadt
University of the West of Scotland University of the Western Cape (South Africa)
iThemba Labs TRIUMF ANU