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