Home > Scripts > Treatment > Sab > Sab_Sqw.m

# iFit/Sab_Sqw

## PURPOSE

Sqw = Sab_Sqw(Sqw, M, T)

## SYNOPSIS

function Sqw = Sab_Sqw(s, M, T)

## DESCRIPTION

``` Sqw = Sab_Sqw(Sqw, M, T)
Sab_Sqw: convert a 2D S(q,w) into an S(alpha,beta) suitable for e.g. ENDF/MCNP.

The S(alpha,beta) is a representation of the dynamic structure factor
using unitless momentum and energy variables defined as:
alpha= h2q2/2MkT  = (Ei+Ef-2*mu*sqrt(Ei*Ef))/AkT
beta = -hw/kT     = (Ef-Ei)/kT
A    = M/m
mu   = cos(theta) = (Ki.^2 + Kf.^2 - q.^2) ./ (2*Ki.*Kf)

input:
s:  Sqw data set e.g. 2D data set with beta as 1st axis (rows), alpha as 2nd axis (columns).
M:  molar weight of the atom/molecule in [g/mol].
when omitted or empty, it is searched as 'weight' or 'mass' is the object.
T: when given, Temperature to use. When not given or empty, the Temperature
is searched in the object. The temperature is in [K]. 1 meV=11.605 K.
output:
Sqw: S(alpha,beta) 2D data set (iData)

conventions:
w = omega = Ei-Ef = energy lost by the neutron [meV]
omega > 0, neutron looses energy, can not be higher than Ei (Stokes)
omega < 0, neutron gains energy, anti-Stokes

references: M. Mattes and J. Keinert, IAEA INDC(NDS)-0470, 2005.
R. E. MacFarlane, LA-12639-MS (ENDF-356), 1994.

Example: Sqw = iData( fullfile(ifitpath,'Data','SQW_coh_lGe.nc') );
Sab = Sqw_Sab(Sqw,72.6,300);
Sqw2= Sab_Sqw(Sab);
subplot(log([Sqw Sab Sqw2))

(c) E.Farhi, ILL. License: EUPL.```

## CROSS-REFERENCE INFORMATION

This function calls:
• Sab_check Sab_check: check if a 2D iData is a S(alpha,beta).
• Sab_check Sab_check: check if a 2D iData is a S(alpha,beta).
This function is called by:

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