Performing mu x measurement in transmission

The attenuation coefficient µx is calculated from the following equation:

In the equation, I is the measured count rate of the beam transmitted through the sample, I₀ is the count rate of the direct beam, and y_bg and y_0,bg are their smoothed background count rates. The recorded counts are corrected for dead time by

where N is the number of recorded counts, T is the counting time and τ is the dead time. For the scintillator setup τ = 2.1 µs. The Python routines perform this automatically.

The signals I and I₀ are obtained by scanning the “energy” pseudomotor which positions have units of keV. For example, to scan over the energy from 7.7 keV to 7.8 keV, with 301 points and 1 second per point, run command

ascan energy 7.7 7.8 300 1

The background count rates can be measured with

set_detx_offset 10ascan energy 7.7 7.8 100 1set_detx_offset -10ascan energy 7.7 7.8 100 1set_detx_offset 0

The set_detx_offset sets the constant offset to the detx position in units of mm. To obtain the estimate of the background at the focus, the plus and minus offset scans are averaged and smoothed with a low order polynomial fit.