lamp_mac/IN13/
quasi_slab.pro
top quasi_slab
result = quasi_slab(w_data, background_w=background_w, angle=angle, t_sample=t_sample, t_container=t_container, twice=twice, f=f, corr_w=corr_w)
******* ********** ** User callable ******************************************************************************* ** ** Evaluation of correction coefficients for transmission in the case of a ** flat sample. Both absorption and self shielding are taken into account. ** Calculations are made according to reference [1] (chapter 4) and following ** the fortran implementation in [2]. However some equations have been changed, ** as there are some errors in the expressions given in [1] for the reflection ** case. The factors obtained agree with the results given by the Self-shielding ** calculator for slab geometry of DAVE. ** ** Is: theoretical scattering from sample, without absorption ** Ic: theoretical scattering from container, without absorption ** Iscsc: scattering from sample plus container (i.e. measured scattering) ** Icc: scattering from container when alone (i.e. measured) ** Issc: scattering from sample itself when inside container ** Icsc: scattering from can itself when sample inside ** ** measured scattering Iscsc = Issc + Icsc ** ** Issc = Assc*Is , where Assc is the self-shielding of scattering by the sample (in sample measurement) ** Icsc = Acsc*Ic , where Acsc is the self-shielding of scattering by the container (in sample measurement) ** Icc = Acc*Ic , where Acc is the self-shielding of scattering by the container (in empty cell measurement) ** ** Is = (1/Assc) * [Iscsc - (Acsc/Acc)*Icc ] ** ** Also defined sample attenuation factor, SAF = Acsc/Acc, and ** self-shielding factor, SSF = Assc, so ** ** Is = (1/SSF) * (Iscsc - SAF*Icc) ** ** [1] "Quasielastic neutron scattering", M. Bee, Adam Hilger (1988) ** [2] Elascan, subroutine elsc_slab ** ** Call w6=elascan_slab (w1, background_w=2, angle=45, t_sample=0.90, t_container=0.99,twice=0.5, f=1.0, corr_w=20) ** Short call: w6=elascan-slab(w1,b=2,a=45,t_s=0.9,t_c=0.99,tw=0.5,f=1,c=20) ** ** where the data are in w1, 2 indicates that the background measurement to subtract is in w2, ** the slab is oriented pointing to 45 degrees, the transmission of the sample (without container) is 0.90, ** and the transmission of the empty cell is 0.99. ** ** 'twice' is the fraction of neutrons passing a second time through the sample in the way back from ** the analysers to the detectors. ** ** 'f' is a scaling factor for the background that can be used for example when the measured background ** does not correspond exactly to the real background during the sample measurement. ** ** 'corr_w' serves to indicate a workspace to store the correction factors: ** A_c,c , A_c,s+c , A_s,s+c , SAF = A_c,s+c / A_c,c , SSF = A_s,s+c. ** ** Apart from the input workspace containing the data, the only compulsory parameter to pass when calling ** the routine is the angle corresponding to the orientation of the slab. ** If the background workspace is not passed, then only the self-shielding correction is applied: ** Is = Iscsc / SSF. ** If a transmission value is not given, then its value is set to 1 (so no correction will take place), ** while the default values for twice and f are 0 (so no correction for passing a second time through ** the sample applies) and 1. ** ** With the above call the routine will give as output the corrected data in w6. ** Additionally an ASCII file called 'attenuation_factors.dat' is written. This file contains the ** self-shielding factors Assc, Acsc, and Acc applied in the correction. ** If twice > 0, another ASCII file named 'backthrough.dat' is written. It contains the attenuation ** factor applied to the neutrons passing a second time through the sample. ** ** If the background workspace contains more than one temperature measurement, for each point corresponding ** to a sample temperature the subtracted background is the empty cell measurement taken at the closest T. ** The file 'temperatures.dat' contains tje list of the sample temperatures and the corresponding ** background temperature used in the subraction. ** ** MAG (07/5/2009) ** JC (02/8/2012) MAG version modified for quasielastic measurements ** *******************************************************************************
Parameters
- w_data
Keywords
- background_w
- angle
- t_sample
- t_container
- twice
- f
- corr_w
File attributes
Modification date: | Tue Oct 1 14:41:21 2013 |
Lines: | 339 |