ALSNews is a biweekly electronic newsletter to keep users and other interested parties informed about developments at the Advanced Light Source, a national user facility located at Lawrence Berkeley National Laboratory, University of California. To be placed on the mailing list, send your name and complete internet address to ALSNews@lbl.gov. We welcome suggestions for topics and content.

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ALSNews           Vol. 13           February 14, 1995

Table of Contents


    1. BEAM STORED ON FIRST DAY OF OPERATIONS AFTER SUCCESSFUL CONCLUSION OF SHUTDOWN
       - BEAMTIME FOR USERS TO RESUME FEBRUARY 22
    2. MICROGRAM ACTINIDE SAMPLES SUCCESSFULLY STUDIED AT BEAMLINE 7.0
    3. VISITING RESEARCHERS -- ADAM HITCHCOCK
    4. DATE SET FOR ANNUAL ALS USERS' ASSOCIATION MEETING

There will be no ALSNews issue on February 21 because of the U.S. holiday, Presidents' Day. We will return to our weekly delivery on February 28.

1. BEAM STORED ON FIRST DAY OF OPERATIONS AFTER SUCCESSFUL CONCLUSION OF SHUTDOWN - BEAMTIME FOR USERS TO RESUME FEBRUARY 22
(contact: rmmiller@lbl.gov)

The storage ring came up instantaneously to 50 mA (the target current for initial startup) at approximately 2:00 a.m. this morning, marking the end of the shutdown for equipment installation and the start of commissioning the machine to resume operations for users. As expected, the beam lifetime was limited by high pressure in the new narrow-gap vacuum chamber of the U5 undulator in sector 7. The photons generated by the 50 mA electron beam are being used as a scrubbing tool to dislodge the unwanted gas molecules, which are then removed from the ring with vacuum pumps. The commissioning activities and equipment tests for accelerator operations will continue this week, with beam scheduled to be available to users again on February 22, as promised.

Operations for Feb. 21 - Mar. 1
1.5-GeV, 400-mA, 320-bunch operation for users:
    Feb. 22-26, 08:00-23:15
    Mar. 1, 16:00-23:15
Accelerator physics:
    Feb. 21, 16:00-23:15
    Feb. 28, 08:00-23:15
    Mar. 1, 08:00-16:00
Maintenance/system setup:
    Feb. 21, 08:00-16:00
    Feb. 27, 08:00-23:15

After the upcoming shutdown, the storage ring lattice-magnets will be operated on their lower hysteresis branches, to facilitate ramping up to 1.9 GeV. Even though orbit corrections at this new working point have been performed, we anticipate minor orbit changes (on the order of 100 microns) that may affect beamline source-point locations.

2. MICROGRAM ACTINIDE SAMPLES SUCCESSFULLY STUDIED AT BEAMLINE 7.0
(contact: dkshuh@lbl.gov)

Researchers at the Beamline 7.0 Spectromicroscopy Facility endstation have performed their second soft x-ray electron spectroscopy experiment with transuranic materials. The first such experiment was a proof-of-principle synchrotron "ultraESCA" (electron spectroscopy for chemical analysis) study of approximately one microgram (less than 20 nanocuries total activity) of the low-activity isotope curium-248. The sample was distributed non-uniformly on a platinum substrate. The data from this experiment were the first chemical information on a transuranic material obtained with a tunable photon source at a soft x-ray synchrotron radiation user facility.

The second transuranic investigation employed plutonium-242 (a low- activity isotope) as plutonium oxide, and a new sample of curium-248 as curium oxide. The samples were illuminated with x rays, and the resulting high-resolution electron energy distribution spectra were collected for photoelectrons emitted from curium and plutonium 4f, 4d, and valence-band energy levels, as well as the oxygen 1s core level. This was the first time that plutonium spectra have been measured with a tunable photon source at a facility like the ALS. Experimenters recorded elemental maps of the surface distributions of plutonium and curium. They also collected an absorption spectrum of the curium 4d levels (N-IV,V), the first absorption spectrum of a transuranic material in the soft x-ray regime.

The results of these initial transuranic electron spectroscopy investigations have major implications for future studies. They showed that microgram amounts of radioactive materials, which can be safely handled without elaborate precautions, are sufficient for detailed chemical and physical characterization, and that elemental and chemical state information can be mapped with sub-micron precision. The collaborators on these experiments were J. Denlinger and B. Tonner (U. of Wisconsin-Milwaukee); E. Rotenberg and S. Kevan (U. of Oregon); J. Bucher, N. Edelstein, D. Shuh, and A. Warwick (Lawrence Berkeley Laboratory); and J. Tobin (Lawrence Livermore National Laboratory).

3. VISITING RESEARCHERS -- ADAM HITCHCOCK
(contact: aph@mcmaster.ca)

Adam Hitchcock comes to the ALS on research leave from the Department of Chemistry and the Institute for Materials Research at McMaster University (Hamilton, Ontario, Canada). Hitchcock, who arrived at the ALS in August, also has active synchrotron radiation research projects at the Cornell High-Energy Synchrotron Source, the Synchrotron Radiation Center (U. of Wisconsin), and BESSY (Berlin).

One of Hitchcock's projects, with John Bozek (ALS) at Beamline 9.0, is to study ionic fragmentation mechanisms of core excited and ionized molecules using time-of-flight mass spectrometry and coincidence detection techniques. Time-of-flight techniques were described briefly in ALSNews Vol. 5 (Nov. 29, 1994). In this case, monochromated x rays ionize a molecule of a gas-phase sample to produce electrons and positive ions, which are accelerated in opposite directions by an electric field. Researchers measure the difference in time between detection of the photoelectron and all positive ions produced in a given photoionization event, and then determine the charge-to-mass ratio of each ion from its time of flight.

Hitchcock is also collaborating with the Beamline 7.0 group led by Brian Tonner (U. of Wisconsin, Milwaukee), using soft x-ray spectromicroscopy to study bulk and surface phase segregation phenomena in polymers. A scanning transmission x-ray microscope, which will undergo first tests in March, will be used to study phase segregation in various polyurethane foams, in particular to identify submicron inclusions. A second project in collaboration with John Brash (McMaster) will investigate surface compositions of polymeric materials used in contact with blood, seeking relationships between the surface composition of a polymer and the rate at which platelets at the surface activate the blood-clotting process. Such information would help the optimization of polymer surfaces for use in medical processes such as dialysis.

4. DATE SET FOR ANNUAL ALS USERS' ASSOCIATION MEETING

This year's meeting of the ALS Users' Association has been set for October 23-24, 1995. Past users' meetings have provided excellent opportunities to hear about new science emerging from the ALS, and about progress in improving and augmenting the tools available at this national user facility. Mark your calendars now!