C-Line Windowless Operation:
Very successful…well done CHESS!
Easier alignment
More light at lower energy
Slit stage allows for a lot of flexibility
and experiments which will lead to more accurate fitting functions.
TASLITX=
+46 : wide open NO filter
+31.4 : 171 micron, no filter
+21.4 : 105 micron, no filter
+10.8 : 58 micron, no filter
+ 0.8 : 35 micron, no filter
-9.45 : open,
diamond filter (fine tuned position)
-19.0 : 35 micron, diamond
-29.4 : 105 micron, diamond
-39.63 : open,
Molybdenum filter (fine tuned position)
( Straight through - No horizontal limit at optic )
Why are we doing this?
In the simplest case, the Coded Aperture fitting function depends on the aperture sizes and positions.
It also depends on gold thickness which determines the transparency and phase shift (January 2012),
and on the x-ray energy spectrum (power distribution) seen by the optic (everything other than the gold).
We have been largely guessing the power distribution which is determined by…
synchrotron radiation ( electron energy, bending radius and Jackson )
absorbers: silicon, diamond, and protective layers on the diode
diode junction energy dependent efficiency .
The relative pulse height transmission with the application of the diamond, or molybdenum, absorber
is a additional guide (along with the image shape) to understanding the effective x-ray energy spectrum.
The diamond absorber low energy cut-off (50% of high energy
transmission) at about 1.6 keV.
The molybdenum absorber has a peak at 2.5 keV,
but also a high energy tail.
The Coded Aperture “transparent” silicon substrate blocks out
much of the power between 1.8 – 2.4 keV.
The diamond absorber, with the silicon substrate, causes
significantly more power loss below 1.8 keV, than above 2.4 keV.
For example
Application of the diamond filter
to Pinhole and Coded Aperture
at 2.085 GeV
indicates that the energy spectrum
should be push to a lower average
energy.
However,
the shape between the
main peaks in the CA image
diamond transmission with Pinhole
no diamond, affected by detector only
run 23661, G=15, Ibeam= 0.59, area= 925
σ (image) = 1.28 pixel
filtering with Diamond
run 23660, G=15, Ibeam= 0.61, area= 508
σ (image) = 1.05 pixel
Diamond transmission = 0.53 for energy spectrum without silicon filtering;
a significant fraction of the energy spectrum is below 1.6 keV.
indicates a strong
high energy component,
>3 keV.
The image calculator
now includes the
energy dependent filtering.
Improved fitting functions
will come in the next
few weeks.
diamond transmission with Coded Aperture
filtering with Silicon and Gold
run 23648, G=8, Ibeam= 0.64, area= 2919
filtering with Silicon and Gold and with Diamond
run 23649, G=8, Ibeam= 0.53, area= 1481
Diamond transmission = 0.61 for energy spectrum pre-filtered by Silicon and Gold;
there is still a significant fraction of the energy spectrum below 1.8 keV.