Fluorescence Imaging

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

In order to limit the number of motors and detector to deal with for the various configurations, all relevant motors for FI have been assigned to spec version "image". This includes the various scanners and the energy-dispersive detectors.

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:

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

For the new high energy multilayers getting D-line up to 30 keV, getting D-line above the tin K-edge (29.1 keV), we have tested the high performance 5-element detector. Only one element was used (#1 is quite good, #3 has background problems). Data were acquired with a ORTEC Trump-PCA pulse-height analyzer which is implemented in the station computer.

ESRF MCA macros

For higher functionality with regard to scanning, the G2 version of the ESRF MCA macros was implemented at D1. Macros interfacing the ORTEC Trump-PCI board ran stable over a week. In terms of performance, it turned out that the Trump board was the limiting factor reaching saturation, while the detector signal still looked good on the scope (limited pile-up, no baseline shift). The PCI board also ran fine with the CHESS macros - I will implement an easy switch-over macro in the "setup" command, which already exists for the ESRF macros. Users can then choose between both macro packages.

NOTE: So far I have not succeeded running the Roentec controller with the ESRF macros.