An Introduction to Neutron Scattering - Spallation Neutron Source

Neutron Polarization at the Echo Point is a
Measure of the Intermediate Scattering Function
r
∫∫ I(
λ)
S(
Q,
ω)
cos( φ1
−φ
2 ) dλdω
r
r
P = r
≈ ∫ S(
Q,
ω)
cos( ωτ ) dω
= I( Q,τ)
∫∫ I(
λ)
S(
Q,
ω)
dλdω
Bd λ τ
2
m 3
where the " spin echo time" τ = γBd
λ
(T.m)
(nm) (ns)
2
2πh
1 0.4 12
• I(Q,t) is called the intermediate scattering function
– Time Fourier transform of S(Q,ω) or the Q Fourier transform of G(r,t), the two
particle correlation function
• NSE probes the sample dynamics as a function of time rather than
as a function of ω
• The spin echo time, τ, is the “correlation time”
1
1
0.6
1.0
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