In fluorescence imaging (FI) x-ray fluorescence lines excited by the intense incident beam are simultaneously recorded on an energy-dispersive detector, as the sample is scanned through the beam. This way, maps of the concentration of specific chemical elements in the sample are obtained. Applications range from materials science, environmental science, soil science, and biology to archeology and fine arts.

spec multi-configuration set-up

spec setup for XFlash detector

The detector is connected by custom cables to the XFlash controller through the labyrinth. The serial port of the XFlash controller is connected to the second serial port of the control computer (ttyS1).

The following lines have to be added in the spec config file:

MCA- and CCD-Acquisition Type Device Configuration

MCA-like       DEVICE   ADDR  <>MODE                                      <>TYPE
 0  YES    /dev/ttyS1     <>  115200                      Roentec XFlash MAX MCA
 1   NO

The following lines were added to the image setup file:

# macros for fluorescence spectroscopy

# qdofile("~/Macros/donrong.mac")

# create sufficiently large scanfile for fluorescence spectroscopy mesh scans
# data_grp(0,0,2)

# query max size of default data group
# p data_grp(-1,0,0)
# typical output:
# The current data group configuration is:
#     Group  Width  Last_Added  Max_Pts
#       0      2           0    32768

NOTE: By uncommenting the respective lines macros can be invoked.

Halting scans during CESR refills

The presently used macro compares the XFlash counting time and the spec counting time. The latter gets gated with the "HEP in Progress" signal from the cross connect. If spec and XFlash counting time differ by more than 5sec (default used in the "mcasmode" macro - see below), the data point is remeasured, until it is measured outside a refill.

A home-built CHESS logic box allows various conditions to be checked. We typically only make use of the "HEP in Progress" signal which goes to the "CESR TTL IN" input. The "TTL LOW ON INHIBIT" output gets connected to the gating logic array in the CAMAC crate.

Note: Always check whether the "HEP in Progress" cable is correctly connected at the cross connect. As only 4 of the 10 channels of the crossconnect patch panel at the station are working (to be fixed), sometimes channels get reassigned (e.g. for CESR timing signal).
 

CHESS MCA macros

Most FI users like to use the CHESS macros, as the generated output files are compatible with Rong Huang's analysis software. Here are a couple of the most useful commands:

• mcasetup
setup and initialize detector and mca
• detector: 1 [XFlash]
• 
  
• pulser frequency: 100Hz per 100sec/spectrum, 1000Hz per 10sec/spectrum (for deadtime calibration)
• energy range: (as needed)
• mcasmode
enables/disables saving of spectra during scans as well as a live display using "uct [time]"
bug: the detector is still read out, even if mcasmode is disabled
• mcad
save spectrum after "ct" or "uct" (which are not saved by default)

• mcadisp [xmin] [xmax] [ymax]
displays a spectrum or part of a spectrum as specified by xmin, xmax, and ymax
• mcahelp
displays all CHESS mca macros
note: some macros seem to be obsolete (use "prdef" or "lsdef" to see whether the macro is known to spec)

• uct
provides a life display using spec's uct command when mcasmode is on

NOTE: some macros seem to be obsolete (use "prdef" or "lsdef" to see whether the macro is known to spec

Rong Huang's macros and MatLab

There is presently an incompatibility between Rong's program and the new MatLab version 7.0 for LINUX, with the effect that Rong's program can't run on the station computer. Please use the Windows computer in the trailer.

5-element Ge detector

ESRF MCA macros