# Basic understanding of instrument components

In the McStas formulation of a neutron scattering instrument, all objects apart from the neutron ray are referred to as components. This includes for instance

- Source The exit of a neutron production facility, where neutron rays of certain velocities are emitted into some portion of space
- Monochromator (Idealized) crystal used to select a neutrons of a single wavelength 1 to probe the sample with (monochromator) or to analyze (analyzer)
- Sample An object altering the neutron physical properties in some sense, examples used here are
  - Vanadium. Scatters incoming neutron rays incoherently
  - PowderN. Can be thought of as a large number of crystals, each scattering neutron rays according to the Bragg law, thereby producing N concentric Debye Scherrer cones. This sample also has the posibility of adding inchoherent, eleasticly scattered neutron rays.
- Monitors Objects monitoring or registering neutron ray characteristics. In the exercises below are used different types of detectors or monitors:
  - Monitor. Single monitor, detecting the number of flying through a plane. (User defined opening size)
  - PSD_monitor. Square monitor, detecting the number of neutron rays passing through a plane, divided into pixels. Square regions of a plane. (User defined resolution and opening size)
  - PSD_monitor_4PI. As PSD_monitor but shaped like a sphere.
  - L_monitor. Wavelength monitor, measuring the different wavelengths of the passing neutron rays. (L is for )
  - Monitor_nD. General monitor for detecting all sorts of physical properties of the neutron ray. In our cases used with options
    - 'single' - as PSD_monitor but only one small square
    - 'banana' - as PSD_monitor but shaped like a curved, horizontal band
- Collimators Devices controling the direction and divergence of the neutron ray.
  - Collimator_linear A series of parallel absorbing neutron plates that limits the beam divergence. Typical values are to .

More information on the McStas components is available by using the `mcdoc` program (You may need to set the BROWSER system variable to your webbrowser of choice):

- `mcdoc -s` , Shows a html list of all the components
- `mcdoc Monitor.comp` , Shows the documentation for a given component
- `mcdoc -M` , brings up the McStas manual in PDF format
- `mcdoc -c` , brings up the McStas component manual in PDF format