Advances in Radiation Detector Materials and Technologies

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Advances in Radiation Detector Materials and
Technologies
Lynn A. Boatner Center for Radiation Detection
Materials and Systems (CRDMS) Oak Ridge National
Laboratory Presented at Rutgers
University January 8, 2011
Research at the CRDMS is supported in part by the
DOE Office of Nonproliferation Research and
Development, NA-22, in the Nuclear Security
Administration and in part by the Domestic
Nuclear Detection Office of the Department of
Homeland Security.
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Radiation Detection by Scintillators or
Electronic Materials
Scintillator
Detector
Photomultiplier
Incident Radiation
Si Photodiode
Eye
IncidentRadiation
Light Output (usually visible to near visible)
SCINTILLATION DETECTION
ELECTRONIC DETECTION
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Gamma-Ray Scintillators

• 3 Major Processess
• ABSORPTION OF GAMMA- OR X-RAY PHOTONS AND
  CONVERSION INTO CHARGED PARTICLES (ELECTRON-HOLE
  PAIRS).
• Direct process for Egt 1.02 MeV the gamma ray
  directly produces an electron-positron pair with
  the same total energy (pair production).
• Compton scattering gamma-ray energy is
  divided between a scattered photon and a recoil
  electron
• Photoelectric effect the absorbed photon
  generates a fast electron and a hole in a deep
  core level of an ion with the two carrying all of
  the energy of the original photon.
• ENERGY TRANSFER FROM THE ELECTRONIC EXCITATIONS
  TO THE LUMINESCENCE CENTERS.
• A complex and not well-understood process.
• EMISSION OF THE SCINTILLATION PHOTONS
• Occurs with a quantum efficiency Q that
  represents the fraction of excited centers that
  actually emit a scintillation photon.

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?-Ray Detection Using a Scintillation Crystal
Requirements for a Good Scintillator 1. High
Light Output (Photons/Mev) NaI
Thallium ? 38,000 BGO ? 8,200 2.
Short Decay Time (Nano Sec) 3. Wavelength Match
to Detector 4. High Density (gt6 g/cm3) 5.
Chemical Stability 6. Radiation Hardness 7.
Cost 8. Crystal Growth NaI
Thallium ? 1948, Hufstader BGO
(Bi4Ge3O12) ? 1973, Weber Monchamp
LSO (Lu2SiO5) ? 1992, Melcher Schweitzer
ß ?-ray to electronic excitation S
fraction transferred to luminescence centers Q
quantum efficiency of the emission step
http//scintillator.lbl.gov/
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State of the Art Scintillators
Material Light Yield (photons/MeV) Resolution _at_ 662keV ()
NaI(Tl) 38,000 5.5
CsI (Tl) 65,000 6.2
BGO 8,200 12.7
LaBr3(Ce) 70,000 2.8
CeCl3 46,000 3.4
LSO(Ce) 39,000 7.9
SrI2 Eu (6) 120,000 2.7
BC-408 Plastic 10,600 -
GS-20 Li Glass (2930 for 1-inch round, 2mm thick/ 4,739 for 6.2-inch square, 2mm thick plate) 4,100 17
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Among the alkaline earth halides, Strontium
Iodide (Eu) possesses the most promising
characteristics
Advantages Low melting point ? reduced
temperature gradients Size and structure match
between SrI2 and EuI2 ? unity distribution
coefficient High light yield, proportional ?
superior resolution Congruent, since binary
compound ? no compositional gradients Near-UV
emission ? ideal match to PMT response Microsecon
d decay ? enlarges dynamic range for pulse height
spectrum
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A New Grain Selector
A new grain-selector geometry has been
incorporated into the 2.5 OD Bridgman growth
ampoules since it was found that two grains would
sometimes propagate into the large-diameter
growth chamber during the growth process even
the case of long straight grain selectors that
incorporated a bulb configuration. Similar
grain-selector geometries are uses in the growth
of the metal and alloy single crystals
including single crystal high-performance-alloy
turbine blades for nucleation suppression.
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Strontium Iodide Eu2 Crystal Growth
Enlarged view of the quartz frit that is used to
filter the molten SrI2Eu2 salt that then flows
into the Bridgman ampoule prior to sealing under
vacuum.
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Two-inch diameter single crystal of SrI2(Eu)
grown at Oak Ridge National Laboratory.
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Crystal 68f (Fisk University) was encapsulated in
a standard aluminum can, and its performance is
equivalent to the best RMD crystal.
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Elpasolites

• High light yield 70,000 to 180,000 ph/neutron
• High gamma equivalent gt 3 MeV
• High energy resolution 2-3
• Pulse height discrimination
• Pulse shape discrimination
• Cubic structure

www.rmdinc.com a dynasil member company
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Summary of Properties
Cs2LiLaCl6Ce CLLC Cs2LiLaBr6Ce CLLB Cs2LiYCl6Ce CLYC
Density, g/cm3 3.5 4.2 3.3
Emission, nm 290CVL, 400Ce3 410Ce3 290CVL, 390Ce3
Decay time, ns 1 CVL,60, 400, 55, 270, 1 CVL,40, 1800,
Max. light yield, ph/MeV 35,000 60,000 20,000
Light yield ph/n 110,000 180,000 70,000
GEE, MeV 3.1 3.2 3.1
Best ER _at_662 keV 3.4 2.9 3.9
PSD Excellent Possible Excellent
www.rmdinc.com a dynasil member company
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Bridgman Grown Crystals
?1 in CLYC
?1 in
CLLC
CLLB
www.rmdinc.com a dynasil member company
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CLYC 6Li vs. natLi
Enrichment significantly improves detection of
thermal neutrons.
www.rmdinc.com a dynasil member company
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New Metal-Organic Scintillators

• Investigations of alternate methods for growing
  large single crystals of rare-earth halide
  scintillators from organic solutions have led to
  the discovery of a new metal-organic scintillator
  crystal. This new scintillator material is a
  methanol adduct of cerium trichloride with the
  formula CeCl3(CH3OH)4.
• Large transparent single crystals of this
  material were grown from a seeded anhydrous
  methanol solution in a controlled-temperature
  bath, and the molecular structure was
  subsequently determined by single-crystal x-ray
  structure analysis.
• The CeCl3(CH3OH)4 metal-organic scintillator is
  applicable to x-ray, gamma-ray, alpha-particle,
  and neutron detection, and this new finding
  offers the promise of identifying other similar
  metal-organic molecular systems that offer the
  potential for serving as efficient radiation
  detector materials that can potentially be grown
  in large sizes using solution-growth methods.
• Most recently the scintillator
  La(4Ce)Br3(CH3OH)4 has been discovered.

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Crystal Structure
Perspective view of the CeCl3(CH3OH)4 adduct
showing the bridging role of the chlorine atoms.
The basic CeCl3(CH3OH)4 crystal data resulting
from the single crystal x-ray structural
refinement are M 374.64, monoclinic structure,
space group P21/c (no. 14), a 8.7092(5), b
18.5100(9), c 8.2392(4) Å, ß 108.946(1), V
1256.2(1) Å3, Z 4, and Dcalc 1.981 g/cm3.
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Large faceted single crystal of CeCl3(CH3OH)4
grown from an anhydrous methanol solution - shown
on a cm scale. The platinum wires used to hold
the seed crystal on the growth platform are
visible through the crystal. Crystal growth was
allowed to continue for a total growth time of 24
hrs - at which time the crystals were removed
from the vessel, rinsed clean of the solution in
fresh anhydrous methanol, dried, and sealed under
dry inert gas.
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Energy Spectra
Energy spectrum of the CeCl3(CH3OH)4
metal-organic scintillator single crystal
obtained using 662 keV gamma rays from a 137 Cs
1 ? Curie source. The light yield is 230 of
that of a BGO reference crystal - yielding a
light yield of 16,600 photons/MeV without
corrections for the photomultiplier tube
efficiency. The energy resolution was determined
to be 11.4 for this specimen.
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X-ray Luminescence
X-ray-excited luminescence spectrum for a single
crystal of CeCl3(CH3OH)4 measured in both
transmission and reflection geometries using an
x-ray tube operated at 35 kV as an excitation
source. The peak of the luminescence occurs at
365 nm.
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Transparent Polycrystalline Ceramic
ScintillatorsGlass Scintillators

• Why would we want these?
• Single crystal growth is a time-consuming,
  expensive, and rate-limiting process.
• Transparent polycrystalline ceramic scintillators
  and glass scintillators offer an alternative
  approach to scintillator synthesis that
  eliminates single crystal growth.

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• Lu2O3Eu
• Synthesis and Post Synthesis Treatment
• Lu2O3 and Eu2O3 (5 wt. ) powders combined
  physically
• Powder heated in vacuum to dry
• Hot pressed at 1530C with 262 kg/cm2 of pressure
• Annealed with flowing oxygen for 72 hours at
  1050C

Photograph of a Lu2O3Eu ceramic before (right)
and after (left) annealing in an oxygen
atmosphere. Hot pressing technique tends to draw
oxygen out of the host lattice, creating a dark
color in the densified body. This coloration can
be removed by annealing in an O2.
Photograph of a Lu2O3Eu ceramic excited by a
30kV continuous X-ray source.
Photographs of a transparent Lu2O3Eu ceramic
(1mm thick)
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• LSOCe
• Synthesis and Post-synthesis Treatment
• High quality LSOCe powder produced by Nichia
  Corporation (Japan) used
• Powder heated in vacuum to dry
• Hot pressed at 1400C with 337 kg/cm2 of pressure
  for 2 hours
• Annealed in vacuum at 1050C/108h
• Annealed in water vapor at 1050C/32h
• Annealed in air at 1150C/32h

Photograph of a LSOCe ceramic before (left) and
after (right) annealing in vacuum
Photograph of an LSOCe ceramic (0.6 mm thick).
Note that no back-light is used in this
photograph.
Scanning electron microscopy (SEM) image of
LSOCe powder from Nichia Corporation.
Transmission electron microscopy (TEM) image of
LSOCe powder from Nichia Corporation
Particle size distribution of the Nichia LSOCe
powder used to make the LSO ceramic.
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Scintillating pulse shape of a LSOCe
polycrystalline ceramic excited by 662 KeV gamma
photons. The solid line represents single- and
three-exponential ( noise) fits to the
experimental data . The decay time constants and
contribution of faster components in comparison
to the decay time of about 42 ns generally
accepted for single crystal LSO.
Energy spectra (for 662 keV excitation photons)
of the LSOCe refernce crystal (the light yield
for this crystal was 30,000 photons/MeV) and the
LSOCe ceramic at various post-sintering
annealing stages. Symbol A denotes a ceramic
with a 2 mm thickness after annealing in vacuum,
A1 denotes a 0.7 mm thick piece of the former
ceramic after additional annealing in water
vapor, and A1a the same after additional
annealing in air.
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New scintillators for gamma ray spectroscopy
developed for DHS and DOE. (upper left) SrI2(Eu)
single crystal under UV excitation, (upper right)
GYGAG(Ce) ceramic, (bottom) two Bi-loaded
polymers under UV excitation.
Comparative Gamma Spectroscopy with SrI2(Eu),
GYGAG(Ce) and Bi-loaded Plastic Scintillators
N.J. Cherepy, Member, IEEE, S.A. Payne, Member,
IEEE, B.W. Sturm, Member, IEEE, J.D. Kuntz, Z.M.
Seeley, B.L. Rupert, R.D. Sanner, O.B. Drury,
T.A. Hurst, S.E. Fisher, M. Groza, L. Matei, A.
Burger, Member, IEEE, R. Hawrami, Member, IEEE,
K.S. Shah, Member, IEEE, and L.A. Boatner
IEEE Transactions on Nuclear Science, IEEE/NSS
Proceedings 2010 (Submitted for publication)
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GLASS SCINTILLATORS HOW CAN WE IMPROVE THEIR
PERFORMANCE?Glass Scintillator Parameter Space
Composition (Glass-forming space) Cladding
Phosphate Lead Phosphate Silicate Germanate Arsen
ate
Activation Ce,Pr,Nd,Eu,Tb,Yb Co-doping
Structure Phosphate glass only Phosphate chain
length
Post-synthesis Treatment Time Temperature Atmosphe
re
B. C. Sales, J. O. Ramey, L. A. Boatner, and J.
C McCallum, Structural in equivalence of the
Ion-Damaged-Produced Amorphous State and the
Glass State in Lead Pyrophosphate, Phys. Rev.
Lett. 62, (10) 1138-1141 (1989).
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Energy Spectra of Ce Doped Ca-Na Phosphate Glasses
137Cs 1µCi ? source 662 keV ? photons 0.5 µs
shaping time
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Current Uses of 3He

• Cryogenics below 1 K, laser research, guided
  missiles
• No known alternative
• Medical imaging of lungs
• Unique capability
• Security applications
• Looking for alternatives
• Oil well logging
• Need alternatives
• Nonproliferation
• Low probability of finding alternatives
• Neutron polarization
• No known alternatives
• Neutron scattering detectors
• Need alternatives for large area coverage

Ron Cooper 29 September, 2009
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Gas Detectors
25,000 ions and electrons (4x10-15 coulomb)
produced per neutron

• 1 part in 104 of natural helium
• Obtained from Tritium decay
• 3T ?  3He   e-  antineutrino
• Half-life is 12.3 years
• Tritium is produced in reactors mainly for
  nuclear weapons
• The Watts-Bar reactor, near Oak Ridge - scheduled
  for tritium production - delayed
• Accelerator option, 40 3MeV accelerators with 1A
  beam current each, -20k liters/year 120MW of beam
  power!

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Alternative Thermal Neutron Converters
6Li(n,a) reaction n 6Li ? 3H 4He
Q-value4.78 MeV E3H2.73 MeV E4He2.05
MeV Cross Section ? 940 b 6LiF coatings -
Chemical Stability Ranges 3H-32.1 microns
4He-6.11 microns nabs-174 microns 10B(n,a)
reaction n 10B ? 4He 7Li ground state
Q-value2.792 MeV n 10B ? 4He 7Li excited
state Q-value2.310 MeV ELi 0.84 MeV E4He
1.47 MeV Cross Section ? 3836 b 10B
coatings Ranges 7Li-1.6 microns 4He-3.6 microns
nabs -19.9 microns Boron straws 10BF3
(gas) Other reactions 157Gd(n,?) (Natural Gd,
cross section 49,000 b) 113Cd(n,?) Less useful
gamma-rays and conversion electrons
The challenge is to balance thermal neutron
conversion efficiency and charged particle
transport (while minimizing and/or rejecting
gamma-ray response)
Range calculations McGregor, D. S., et al., NIM
A 500 (2003) 272-308
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• Prototype 6Li-lined gas detector that
  incorporates a Li-coated Mo cathode, a 0.001
  stainless steel anode wire, and a Xe fill gas at
  one atmosphere.

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• Typical preamplifier output pulse from a neutron
  interaction. Note the large amplitude of the
  pulse, which after subsequent amplification in a
  spectroscopy amplifier, leads to a count in the
  neutron peak (gtchannel number 1000) shown in
  the pulse height spectra.

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DETAILS OF THE NEUTRON RESPONSE PORTION OF THE
PULSE HEIGHT SPECTRA ARE SHOWN FOR THE 6Li-LINED
PROPORTIONAL COUNTER USING AN AmLi MODERATED
NEUTRON SOURCE -- UNSHIELDED SOURCE (BLACK), A
2 THICK Pb-SHIELDED SOURCE (BLUE), AND FOR A
Cd-SHIELDED SOURCE (RED).