### Syntax

`spectra = sw_neutron(spectra,Name,Value)`

### Description

`spectra = sw_neutron(spectra,Name,Value)`

calculates the neutron
scattering cross section for polarised and unpolarised neutrons. The
function reads the calculated spin-spin correlation function
and calculates the neutron
scattering cross section for unpolarized neutrons using the formula:

It also calculates spin-spin correlation function in the Blume-Maleev coordinate system and the complete polarised neutron scattering cross section.

**Note:**The Blume-Maleev coordinate system is a cartesian coordinate system with , and basis vectors defined as:

parallel to the momentum transfer ,

perpendicular to in the scattering plane,

perpendicular to the scattering plane.

### Input Arguments

`spectra`

- Input structure, contains spin-spin correlation functions. Supported inputs are produced by spinw.spinwave, spinw.powspec and [spinw.scga].

### Name-Value Pair Arguments

`'n'`

- Normal vector to the scattering plane, in real space (
coordinate system), stored in a row vector with 3 elements. Default
value is
`[0 0 1]`

. `'uv'`

- Cell, that contains two vectors defining the scattering
plane in rlu. If given overwrites the
`n`

parameter value. For example:`{[1 0 0] [0 1 0]}`

stands for the scattering plane. `'pol'`

- If
`true`

the cross sections in the Blume-Maleev coordinate system will be also calculated (`inP`

,`Pab`

and`Mab`

fields of the output`spectra`

). Default value is`false`

.

### Output Arguments

`spectra`

- Same as the input
`spectra`

plus the following additional fields:`param`

Input parameters.`Sperp`

unpolarised neutron scattering cross section, stored in a matrix with dimensions of .`intP`

polarised neutron scattering cross section, when only the incident neutron polarization is analyzed. It is stored in a matrix with dimensions of .`Pab`

complete polarised neutron scattering cross section, when the polarisation of both the incident () and the scattered () neutrons are analyzed. Stored in a matrix with dimensions of .`Mab`

components of the spin-spin correlation function in the blume-Maleev coordinate system, stored in a matrix with dimensions of .

If several domains exist in the sample, `Sperp`

, `intP`

, `Pab`

and `Mab`

will be packaged into a cell, that contains number of
matrices.

The meaning of the indices above:

- : index of incident polarisation (, or ),
- : index of final polarisation (, or ),
- : index of spin wave mode,
- : index of momentum transfer.