INSTITUT MAX VON LAUE - PAUL LANGEVIN CERN, 12/5/09 Ken Andersen Neutron Optics • Optics – reflection – refraction – diffraction – polarization • Neutron Instruments – source – transport – focusing, divergence – wavelength encoding – polarization encoding
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INSTITUT MAX VON LAUE - PAUL LANGEVIN CERN, 12/5/09 Ken Andersen Neutron Optics Optics –reflection –refraction –diffraction –polarization Neutron Instruments.
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INSTITUT MAX VON LAUE - PAUL LANGEVINCERN, 12/5/09 Ken Andersen
• Flux impinging on sample < 108 n/s– strongly limited by Poisson statistics
• Sometimes S/N can be more important
INSTITUT MAX VON LAUE - PAUL LANGEVIN
Polarization Optics
• Magnetism– neutron magnetic moment interacts with
that of unpaired electrons– magnetic scattering depends strongly on
relative orientation of neutron spin, electron spin and momentum transfer
– unambiguous separation of magnetic and nuclear scattering
• Precession techniques– polarization vector precesses around field
direction– frequency ~ B– phase measurement gives time spent in
field neutron speed
21ns+½ħ
-½ħ
“Spin-up” (+)
“Spin-down” (-)
21ns
B
INSTITUT MAX VON LAUE - PAUL LANGEVIN
Polarizing Supermirrors
B
FeSi
Si
0
5
10
15
Si Fe Si Fe Si Fe Si substrate
N.b
(1
0-6 A
-2)
0
5
10
15
Si Fe Si Fe Si Fe Si substrate
N.b
(1
0-6 A
-2)
• with
B
0
5
10
15
Si Fe Si Fe Si Fe Si substrate
N.b
(1
0-6 A
-2)
B
B=0
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5
0 1 2 3 4
R+R-
Omega
m=/ c(Ni)
FeSi m=3.8
INSTITUT MAX VON LAUE - PAUL LANGEVIN
Cu2MnAl (Heusler) crystal
Polarizing Crystals
ILL is the only producer
INSTITUT MAX VON LAUE - PAUL LANGEVIN
MEOP
Metastability Exchange Optical Pumping
B0
OPC
3He bottle Purifier
Capillary
Optical pumping Cells
Yb fiber laser
OPC
Buffer 2,5l
5.2 liter compressor
Hydraulic piston
Polarised 3He Cells
Optical polarimeter
Mirrors
Discharge
Polarized-3He Spin-filters
INSTITUT MAX VON LAUE - PAUL LANGEVIN
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60
Transmission TBeam Polarization P
Figure of Merit P2T
Opacity (bar.cm.A)
Polarized-3He Spin-filters
Hen PΟΟT )(cosh)(exp)(
Hen PΟP )(tanh)(
where O(λ) = 7.28×10-2×P[bar] ×t[cm] ×λ[Å]
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 13He Polarization
Flipping ratio = 40P
n = 0.95
2002
2008
INSTITUT MAX VON LAUE - PAUL LANGEVIN
Polarized-3He Spin-filters
• 3He Polarization < 80%• World leaders
– Supplying 3He filling stations, spin-filter cells & magnetic-field environments to neutron labs in UK, Australia, Germany, Taiwan, USA
• Applications:– magnetic structures in single
crystals– magnetic domain structures in thin
films– disorder in frustrated magnetic
systems– magnetic excitations in high-Tc
superconductors• Medical applications
– functional lung imaging (MRI)
INSTITUT MAX VON LAUE - PAUL LANGEVIN
• User facilities– experiments performed mainly by outside groups– ILL: 200 days/yr, 40 instruments, 700 experiments/year, 1200 users/year– mainly solid-state physics, but also fundamental physics, chemistry,
biology• Sources
– thermalized Maxwellian spectrum– low brightness, large sources– beam distribution by guides