Neutron Scattering

the similar intensity distribution of that part of the spectra for different angles- follows
from the fact that the main contribution to Q at high energy gain stems from the length
difference of k and k' (sec fig . 10 .1) . The variation of IQI may be compensated within
certain limits by combining the data from different detectors (angles), however that does
net apply for the direction change of Q . Therefore TOF-instruments -in contrast to tripleaxis
spectrometers- are better suited for isotropic samples (liquids, powders, amorphous
substances) than for single crystals or other highly oriented samples .
10.2 .3 Transforms
Since the physics of the systems under investigation is
usually expressed in terms of
S(Q, cw), a transformation of the raw data representing 1(28, t) into the (Q, cw)-space is
necessary. With t = L /v' and t o = L/v inserted in Eqn . 10 .2 yields
and
2 2
w (t) = m n L2t - to
t2 t2
t 2
2h
+t2 - 2cos(20)tot
t 2 t 2 0
The nonlinear mapping frein channels to energy given by Eqn .
varying energy-width of TOF-channels, K.
er somewhat simpler
with
z(2o, K) a
KD7
(K-1)4r
kt
47rb2S(Q, w(t))
dt dt
(10 .5)
(10 .6)
10 .5 also causes a strongly
(10 .7)
I(20, K) x k/47rb2S(Q, w(KO7))wOT (10 .8)
and
the result
k'
k
to
t
dcw(t) = Mn L2 1
dt fii t3
(10 .9)
(10.10)
I(2(9, K)
1
S(Q, w(KOT) (10.11)
10-9