The `PowderN` Component

General powder sample (N lines, single scattering, incoherent scattering)

Identification

Author: P. Willendrup, L. Chapon, K. Lefmann, A.B.Abrahamsen, N.B.Christensen, E.M.Lauridsen.
Origin: McStas release
Date: 4.2.98
Version: 1.44
Modification history:
- KL, KN 20.03.98 (rewrite)
- KL, 28.09.01 (two lines)
- KL, 22.05.03 (background)
- KL, PW 01.05.05 (N lines)
- PW, LC 04.10.05 (Merge with Chapon Powder_multi)
- PW, KL 05.06.07 (Concentricity)

Description

General powder sample with
        many scattering vectors
        possibility for intrinsic line broadening
        incoherent backgorund ratio is specified by user.
        No multiple scattering. No secondary extinction.

Based on Powder1/Powder2/Single_crystal.
Geometry is a powder filled cylinder or a box.
Incoherent scattering is only provided here to account for a background
The efficient is highly improved when restricting the vertical scattering
range on the Debye-Scherrer cone (with 'd_phi').
The unit cell volume Vc may also be computed when giving the density,
the atomic/molecular weight and the number of atoms per unit cell.

Example: PowderN(reflections = "c60.lau", d_phi = 15 , radius = 0.01,
  yheight = 0.05, Vc = 1076.89, sigma_abs = 0, Delta_d=0, DW=1,
  format=Crystallographica)

Powder definition and file format

Powder structure is specified with an ascii data file 'reflections'.
The powder data are free-text column based files.
Lines begining by '#' are read as comments (ignored) but they may contain
the following keywords (in the header):
  #Vc           
  #sigma_abs    
  #sigma_inc    
  #Debye_Waller 
  #Delta_d/d    
These values are not read if entered as component parameters (Vc=...)

The signification of the columns in the numerical block may be
set using the 'format' parameter. Built-in formats are:
  format=Crystallographica
  format=Fullprof
  format=Lazy
and these specifications it is important NOT to use quotes, as shown.

An other possibility to define other formats is to set directly
the signification of the columns as a vector of indexes in the order
  format={j,d,F2,DW,Delta_d/d,1/2d,q,F}
Signification of the symbols is given below. Indexes start at 1.
Indexes with zero means that the column is not present, so that:
  Crystallographica={ 4,5,7,0,0,0,0,0 }
  Fullprof         ={ 4,0,8,0,0,5,0,0 }
  Lazy             ={17,6,0,0,0,0,0,13}
Here again, NO quotes should be around the 'format' value.

At last, the format may be overridden by direct definition of the
column indexes in the file itself by using the following keywords
in the header (e.g. '#column_j 4'):
  #column_j     
  #column_d     
  #column_F2    
  #column_F     
  #column_DW    
  #column_Dd    
  #column_inv2d 
  #column_q     

Concentricity

PowderN assumes 'concentric' shape, i.e. can contain other components inside its
optional inner hollow. Example, Sample in Al cryostat:


COMPONENT Cryo = PowderN(reflections="Al.laz", radius = 0.01, radius_i = 0.009,
                         concentric = 1)
AT (0,0,0) RELATIVE Somewhere

COMPONENT Sample = some_other_component(with geometry FULLY enclosed in the hollow)
AT (0,0,0) RELATIVE Somewhere

COMPONENT Cryo2 = COPY(Cryo)(concentric = 0)
AT (0,0,0) RELATIVE Somewhere


(The second instance of the cryostat component can also be written out completely
 using PowderN(...). In both cases, this second instance needs concentric = 0.)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
reflections	string	Input file for reflections. Use only incoherent scattering if NULL or ""
format	no quotes	name of the format, or list of column indexes (see Description).	Undefined
d_phi	deg,0-180	Angle corresponding to the vertical angular range to focus to, e.g. detector height. 0 for no focusing	0
radius	m	Outer radius of sample in (x,z) plane	0
radius_i	m	Radius of optional inner hollow	0
yheight	m	Height of sample y direction	0
pack	1	Packing factor	1
Vc	AA^3	Volume of unit cell=nb atoms per cell/density of atoms	0
sigma_abs	barns	Absorption cross section per unit cell at 2200 m/s	0
sigma_inc	barns	Incoherent cross section per unit cell	0
Delta_d	Angs	global relative Delta_d/d spreading when the 'w' column is not available. Use 0 if ideal.	0
frac	1	Fraction of incoherently scattered neutron rays	0.1
tfrac	1	Fraction of transmitted (only attenuated) neutron rays	0.1
xwidth	m	horiz. dimension of sample, as a width	0
zthick	m	thickness of sample	0
xwidth_i	m	horiz. dimension of optional inner hollow when in cubic geometry	0
yheight_i	m	vertical dimension of optional innher hollow in cubic and cyl geometry. If zero assumed == h.	0
zthick_i	m	thickness of optional innner hollow when in cubic geometry	0
h	m	the same as yheight	0
DW	1	global Debey-Waller factor when the 'DW' column is not available. Use 1 if included in F2	0
nb_atoms	1	number of atoms per unit cell	1
concentric	1	Flag to indicate if sample is 'concentric'	0
density	g/cm^3	density of material. V_rho=density/weight/1e24*N_A.	0
weight	g/mol	atomic/molecular weight of material	0
barns	1	Flag to indicate if \|F\|^2 from 'reflections' is in barns or fm^2 (barns=1 for laz, barns=0 for lau type files).	1

Output parameters

Name	Unit	Description	Default
line_info
Nq
my_s_v2
my_s_v2_sum
my_a_v
my_inc
q_v
w_v
isrect
columns

The PowderN Component

Identification

Description

Input parameters

Output parameters

Links

The `PowderN` Component