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Refs #6670 improved wiki page
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jmborr committed May 23, 2013
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13 changes: 12 additions & 1 deletion Code/Mantid/Framework/Algorithms/src/ModeratorTzero.cpp
Expand Up @@ -20,12 +20,23 @@ For an indirect geometry instrument, <math>E_1</math> is different for each neut
<math>t_2 = L_2/v_2</math> with <math>L_2</math> the distance from sample to detector, and <math>v_2</math> is the final fixed velocity ( <math>E_2=1/2*m*v_2^2</math>)<br />
We obtain <math>TOF^*</math> as an iterative process, taking into account the fact that the correction <math>t_0</math> is much smaller than <math>t_i+t_f</math>. Thus<br />
'''Note:''' We obtain <math>TOF^*</math> as an iterative process, taking into account the fact that the correction <math>t_0</math> is much smaller than <math>t_i+t_f</math>. Thus<br />
<math>TOF-t_0^{(n)} = L_1/v_1^{(n)} + L_2/v_2</math> , n=0, 1, 2,..<br />
Set <math>t_0^{(0)}=0</math> and obtain <math>v_1^{(0)}</math> from the previous formula. From <math>v_1^{(0)}</math> we obtain <math>E_1^{(0)}</math><br />
Set <math>t_0^{(1)}=func( E_1^{(0)} )</math> and repeat the steps until <math>|t_0^{(n+1)} - t_0^{(n+1)}| < tolTOF</math>. With tolTOF=0.1microsecond, only one iteration is needed for convergence.
Here's the result of applying ModeratorTzero to both the event list and the histogrammed data of a run in the VISION beamline. The transformation of either events or histograms shifts the curve to smaller TOF's.
The transformed curves are not supposed to be identical, but similar and differenciated from the original curve.
{| class="wikitable"
|-
! Sumed Histogram !! Elastic Line !! Inelastic Peaks
|-
| [[File:ModeratorTzero_Fig.1.jpeg|200px||center|]] || [[File:ModeratorTzero_Fig.2.jpeg|200px||center|]] || [[File:ModeratorTzero_Fig.3.jpeg|200px||center|]]
|}
For indirect instruments featuring an incoming neutron flux having a sufficiently narrow distribution of energies, a linear relationship between t_0 and
the wavelength of the incoming neutron can be established. This relation allows for coding of an algorithm with
faster execution times. For indirect instruments that comply with these conditions, use of [[ModeratorTzeroLinear]] is preferred.
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