[continues from 4.3]
The reference characteristics of the calibration sources are stored in files
m{1,2,3}_calsource.coeff
and are used by the gain history accumulation program.
These characteristics are :
- a reference gain
- the X and Y coordinates of the two calibration sources in unlinearized
coordinates (these are converted in linearized coordinates of user selected
pixel size inside the program and are not reported here).
The term tauw is the transmission
of the Be window at a given energy and position, reported in
fig. 4.5-I.
Its dependencies are:
- on energy through the Be absorption cross section
(computed from atomic coefficients hardcoded in the programs), and
- through the typical thickness of the
window and of the
strongback
(currently stored in files
m{1,2,3}_thick_be.dat),
and equal to
- for M1 : 51.5 micron (window) plus 600 micron (strongback)
- for M2 : 54.5 micron (window) plus 600 micron (strongback)
- for M3 : 53.5 micron (window) plus 600 micron (strongback)
- and on position, due to the presence of the
strongback
structure (this must be
convolved with the
Point Spread Function
of the optics alone)
Fig. 4.5-I : Transmission of a Be layer with nominal thicknesses
of the MECS entrance window (solid) and its supporting strongback (dotted).
The dashed black line is the overall transmission in a point
at x,y = (0,5) mm, i.e. on the edge of the strongback.
Namely, the transmission at one given position x,y is computed combining the
transparencies of the two thicknesses twindow
and tstrongback
tauw = Z(E,x,y) exp (-mu(E)twindow) + (1-Z(E,x,y) exp (-mu(E)tstrongback)
where Z(E,x,y) is the convolution of a 1/0 mask representing the Be entrance window
with the optics PSF (i.e. the coverage fraction of
the window) and its complement 1-Z is the coverage fraction of the strongback.
Additional representations (as separately numbered figures) can be obtained via the following form. Please note that the time needed to compute images can be prohibitively long (more than 10 minutes)
and CPU-intensive : please reserve this option to off-peak hours.