compres fifth annual meeting identify and broaden the ear neutron scattering community in the...
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COMPRES Fifth Annual Meeting
• Identify and broaden the EAR neutron Identify and broaden the EAR neutron scattering community in the U.S.scattering community in the U.S.
• Stimulate and promote the use of Stimulate and promote the use of neutron scattering in the Earth neutron scattering in the Earth Sciences.Sciences.
• Support educational activities Support educational activities • Identify needs of the community, Identify needs of the community,
including future requirements for including future requirements for instrumentation and sourcesinstrumentation and sources
COMPRES Neutron Initiative:COMPRES Neutron Initiative:
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COMPRES Fourth Annual Meeting
• Financial assistance tFinancial assistance to carry out neutron scattering experiments and/or to participate in workshops and conferences on neutron scattering
• H. Sitepu: design and carry out high-H. Sitepu: design and carry out high-P,T neutron experiments P,T neutron experiments
• Build user community by assisting Build user community by assisting members of community with members of community with experimentsexperiments
• Community informed about upcoming Community informed about upcoming neutron workshops, conferences, neutron workshops, conferences, deadlines for proposals, etc.deadlines for proposals, etc.
• Education materials available on Education materials available on www.vt.edu/compreswww.vt.edu/compres
COMPRES Neutron Initiative:COMPRES Neutron Initiative:
[email protected]@vt.edu
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COMPRES Fourth Annual Meeting
• “High-pressure neutron diffraction study of AlOOD” (ISIS) - C. Vanpeteghem, H. Sitepu (VT) and E. Ohtani, S. Asami
• “Feasibility high pressure study of lithium aluminum deuteride [LiAlD4] and calcite [CaCO3]” using a PE cell on HIPD at LANSCE – H. Sitepu, A. Llobet Megias, and Y. Zhao
• “Investigation of Mg-Al site disorder in shocked MgAl2O4 spinel using neutron diffraction“ (ISIS) O. Tschauner (UNLV), H. Sitepu (VT), P. Asimow and T.J. Ahrens (Cal Tech).
• “Quantitative texture analysis of deformed natural quartz vein from the Torridon area of NW Scotland using neutron diffraction” (FRM-II) R.D. Law (VT), H. Sitepu (VT) and Prof. H.-G. Brokmeier (Tech. Univ. Clausthal).
• “Compressibility of layered molybdite (MoO3) powders determine from neutron diffraction studies at high pressure” (LLB) H. Sitepu (VT) and Dr. I. Goncharenko (LLB).
Recent projects:Recent projects:
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Neutron Initiative in Compres II?Neutron Initiative in Compres II?
• Travel support will continue – to be administered by COMPRES Central
• Form high-pressure neutron “task-force” made up members of the COMPRES community, experienced neutron researchers and representatives from neutron facilities(i) form high-pressure neutron network for exchange of information between high-pressure neutron facilities within the United States (LANSCE, IPNS, HIFR, SNS) and from around the world (ISIS, ILL, J-PARC) (ii) identify community needs and nurture infrastructure development projects and / or grand challenges as(iii) target, where appropriate, additional resources through which to leverage COMPRES funds
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New projects such as . . . • Temperature measurement using neutron reasonance
spectroscopy (synergy with high P-T calibration effort)
• Software development for on-line / off-line evaluation and processing of data (synergy with CEAD)
M. Dove, Y. Le Godec, S.A.T. Redfern, W.G. Marshall, H.J. Stone, M.G. Tucker,
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High P-T cells for community?
• Paris-Edinburgh cell
• Modified P-E cell with belt design (Dobson, 2005)
• Panoramic cell • or ???
200 m
m
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MSA Short Course:NEUTRON SCATTERING IN
EARTH SCIENCES
• December 7th and 8th, 2006 http://www.minsocam.org/msa/sc/
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Temperature measurement by radiography
Incoming neutron
beam
Sample in two sections
Thin foil
Transmitted neutron beam
Detector
WavelengthTra
nsm
itte
d inte
nsi
ty
NeutronAbsorptionresonance
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Effect of temperature
Wavelength
Tra
nsm
itte
d inte
nsi
ty
Width of resonance line can be used to calibrate temperature
Width of resonance line increases with temperature due to Doppler effect
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1.1
1.0
0.9
0.8
0.7
0.6
0.5
No
rma
lise
d t
ran
smis
sio
n
94x10-3
9290888684Neutron wavelength (Å)
181Ta 10.36eV resonanceRoom temperature
181Ta 10.36eV resonance1400°C
1.1
1.0
0.9
0.8
0.7
0.6
0.5
No
rma
lise
d t
ran
smis
sio
n
94x10-3
9290888684Neutron wavelength (Å)
1.0
0.8
0.6
0.4
0.2
0.0
Norm
alis
ed tra
nsm
issio
n
0.180.160.140.120.100.080.060.04Neutron wavelength (Å)
Doppler Broadening of Absorption Resonances: 181Ta (early data)
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Measured neutron resonance lineshape
EdEETrEREEPEI )()()()()(
))(exp()( EETr tot
EdEESEE BWtot
)()()(
Pulse sourcefunction
Detected signal:
Area density ofabsorbing nuclei
Detector efficiency
Instrumentresolution function
Energy transfer function(the Doppler broadening function)
Breit-Wigner lineshape
Transmitted signal:
Total cross-section:
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Example resonance absorption specta
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• The resonance lineshape for a stationary nuclei is well described by
the single-level Breit-Wigner equation
• Must account for the thermal motion of the nuclei in the lab frame (energy transfer function)
– For a free gas or classical solid assume a Maxwellian distribution of velocities
– For weak lattice binding can treat as a free gas replacing T by Teff
Doppler Broadening of Absorption Resonances - Theory
r(E)2gJnr
(E E r )2 ( 12)
2
S(E)1
exp (E En )
2 2
4mMEr kT
(mM )2where
kTeff 1
2d coth h
2kT
g( )
kTeff 1
2hE coth
hE2kT
For an Einstein solid: