An Introduction to Neutron Scattering - Spallation Neutron Source
An Introduction to Neutron Scattering - Spallation Neutron Source
An Introduction to Neutron Scattering - Spallation Neutron Source
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In NSE*, <strong>Neutron</strong> Spins Precess Before and After <strong>Scattering</strong> & a<br />
y Polarization Echo is Obtained if <strong>Scattering</strong> is Elastic<br />
z x π/2<br />
F S<br />
π/2<br />
π<br />
Initially,<br />
neutrons<br />
are polarized<br />
along z<br />
F<br />
Rotate spins in<strong>to</strong><br />
x-y precession plane<br />
Final Polarization,<br />
P<br />
S<br />
Allow spins <strong>to</strong><br />
precess around z:<br />
slower neutrons<br />
precess further over<br />
a fixed path-length<br />
=<br />
cos( φ −<br />
Rotate spins<br />
through π about<br />
x axis<br />
1 φ2<br />
)<br />
Elastic<br />
<strong>Scattering</strong><br />
Event<br />
Rotate spins<br />
<strong>to</strong> z and<br />
measure<br />
polarization<br />
Allow spins <strong>to</strong> precess<br />
around z: all spins are in<br />
the same direction at the<br />
echo point if ∆E = 0<br />
* F. Mezei, Z. Physik, 255 (1972) 145
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