.. resolution_calculator_help.rst .. This is a port of the original SasView html help file to ReSTructured text .. by S King, ISIS, during SasView CodeCamp-III in Feb 2015. Q Resolution Estimator Tool =========================== Description ----------- This tool approximately estimates the resolution of $Q$ from SAS instrumental parameter values assuming that the detector is flat and normal to the incident beam. .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ Using the tool -------------- 1) Select *Q Resolution Estimator* from the *Tool* menu on the SasView toolbar. 2) Select the source and source type (Monochromatic or TOF). *NOTE! The computational difference between the sources is only the gravitational contribution due to the mass of the particles.* 3) Change the default values of the instrumental parameters as required. Be careful to note that distances are specified in cm! 4) Enter values for the source wavelength(s), $\lambda$, and its spread (= $\text{FWHM}/\lambda$). For monochromatic sources, the inputs are just one value. For TOF sources, the minimum and maximum values should be separated by a '-' to specify a range. Optionally, the wavelength (BUT NOT the wavelength spread) can be extended by adding '; nn' where the 'nn' specifies the number of the bins for the numerical integration. The default value is nn = 10. The same number of bins will be used for the corresponding wavelength spread. 5) For TOF, the default wavelength spectrum is flat. A custom spectral distribution file (2-column text: wavelength (|Ang|\) vs Intensity) can also be loaded by selecting *Add new* in the combo box. 6) When ready, click the *Compute* button. Depending on the computation the calculation time will vary. 7) 1D and 2D $dQ$ values will be displayed at the bottom of the panel, and a 2D resolution weight distribution (a 2D elliptical Gaussian function) will also be displayed in the plot panel. TOF only: green lines indicate the limits of the maximum $Q$ range accessible for the longest wavelength due to the size of the detector. Note that the effect from the beam block/stop is ignored. So, in the small $Q$ region near the beam block/stop [i.e., $Q < (2 \pi \cdot \text{beam block diameter}) / (\text{sample-to-detector distance} \cdot \lambda_\text{min})$] the variance is slightly under estimated. 8) A summary of the calculation is written to the SasView *Console* at the bottom of the main SasView window, below the plot. .. figure:: resolution_tutor.png .. 1) Define the source. Select *Photon* for X-ray. This selection only affects the gravitational contribution of the resolution 2) Select between *Monochromatic* or *TOF* 3) For *TOF*, there is the option of loading a custom spectral distribution using *Add New* in the combo box 4) *Wavelength* and *wavelength spread*: one value for *Monochromatic*, minimum and maximum of range for *TOF* 5) For *Source* and *Sample Size Aperture*, one value for a circular aperture (diameter) and two values separated by a comma (,) for a rectangular slit (side lengths) 6) One value for one ($Qx$, $Qy$) location or more values separated by a comma (,) for more locations. *Note: the $Qx$, $Qy$ input boxes should have the same number of values.* 7) Click on *Compute* button to start the calculation 8) *Sigma_x* and *Sigma_y* are the components of the 2D $dQ$ at the last ($Qx$, $Qy$) point of inputs 9) *Sigma_lamd* is the 2D $dQ_{\lambda}$ at the last point of inputs. *Note: $dQ_{\lambda}$ has only the Qr directional component* 10) *(1D Sigma)* is the 1D $dQ$ at the last ($Qx$, $Qy$) point of inputs 11) Plot of the result. For *TOF*, a green rectangle marks the limits of maximum $Q$ range accessible for the longest wavelength due to the size of the detector. .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ Theory ------ The scattering wave transfer vector is by definition .. image:: q.png In the small-angle limit, the variance of $Q$ is to a first-order approximation .. image:: sigma_q.png The geometric and gravitational contributions can then be summarised as .. image:: sigma_table.png Finally, a Gaussian function is used to describe the 2D weighting distribution of the uncertainty in $Q$. .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ References ---------- D.F.R. Mildner and J.M. Carpenter *J. Appl. Cryst.* 17 (1984) 249-256 D.F.R. Mildner, J.M. Carpenter and D.L. Worcester *J. Appl. Cryst.* 19 (1986) 311-319 .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ .. note:: This help document was last changed by Steve King, 01May2015