Biological X-ray Absorption Spectroscopy at NSLS-II
We continue to be committed to transitioning our biological X-ray absorption spectroscopy program to NSLS-II. We have secured a partner user agreement with the NSLS-II ISS beamline, expected to become operational for general users in late 2016. In addition, we are working with NSLS-II management and funding agencies for longer-term options to develop a replacement for NSLS X3B at NSLS-II. In the interim, we are providing user access to biological XAS resources through an NSLS-II Transition Program for Hard X-ray Spectroscopy at SSRL, summarized below.
SSRL Transition Program
We are partners in an agreement between NSLS-II and the Stanford Synchrotron Radiation Lightsource to make SSRL beamline 2-2 available as a transition beamline for NSLS XAS users while NSLS-II X-ray spectroscopy beamlines are under construction. 80% of beamtime on SSRL BL 2-2 is dedicated to NSLS users, and 25% of this fraction is reserved specifically for proposals from the biological XAS community that we supported at NSLS X3A and X3B (approximately 2 months in each 9 month run year), with onsite user support provided by CSB personnel. Additional partners in this effort supplying manpower and equipment include the Synchrotron Catalysis Consortium and NSLS-II.
Figure 1. (left) The bioXAS endstation setup with He Displex cryostat and Ge fluorescence detector; (right) the SSRL BL 2-2 experimental hutch enclosure and user work area.
SSRL BL 2-2 is an unfocused bending magnet beamline equipped with a double crystal monochromator (Si(111) and Si(220) crystals available). Equipment specifically devoted to biological XAS experiments includes a He Displex cryostat and Lakeshore temperature controller for cryogenic and variable temperature studies (temperature range of 15-325K). In addition, the Canberra 13 element germanium detector (11 working elements) originally installed on NSLS X3A is available for fluorescence studies. The beamline is also equipped with the usual complement of ion chambers, and motorized stages, and there is provision for supply of various gases and non-energy discriminating Lytle and PIPS detectors. The available flux is on the order of 1010 photons/sec for large beam sizes, which is about an order of magnitude lower than was available at X3B. The lack of a mirror for harmonic rejection further constrains this flux as it is necessary to detune by 25-50% depending on energy. Practical experience in the first two cycles of operations suggests that ca. 1-2mM is a practical lower limit for late transition metals such as Co, Ni, Cu, and Zn, while Mn and Fe realistically require >3mM for acceptable EXAFS data. As such, the beamline is better suited for dilute model complex studies, although biological samples can be examined with careful planning.
Figure 2. Measured flux curve at SSRL BL 2-2 for Si(111) and Si(220) crystal sets and a fully tuned monochromator. SPEAR3 was operating at 3 GeV and 500mA, the premonochromator vertical slit was set to 1mm, and sample slits were set to 1x12mm (V/H). Actual sample flux will be somewhat less due to detuning to remove higher harmonics and smaller sample slits.
All proposals and requests for SSRL 2-2 beamtime will be submitted via the new NSLS-II PASS system and follow the NSLS-II GU Proposal submission calendar. SSRL plans to operate from November 9, 2015 to July 25, 2016 during the FY 2016 run. Deadlines for proposal submission through NSLS-II PASS are as follows:
November 2015 - February 2016: June 1, 2015
February 2016 - May 2016: September 30, 2015
May 2016 - August 2016: February 1, 2016
Please contact Erik Farquhar to discuss any questions about this program, including SSRL BL 2-2 access, the proposal submission process, sample feasibility discussions, and so on.
CSB Partnership with ISS
The Inner Shell Spectroscopy (ISS) beamline, being constructed as part of the NSLS-II NEXT Project by the Photon Sciences Directorate at BNL, under the leadership of Dr. Klaus Attenkofer. ISS is located on a an NSLS-II damping wiggler source, which provides an extremely bright source of broadband radiation with photon fluxes on the order of 1013 to 1014 photons/sec, 2-3 orders of magnitude greater than was available at NSLS X3B. ISS will provide versatile capabilities in ultra-dilute bulk XAS and X-ray emission spectroscopy. The ISS energy range of 4.9-36 keV will cover the K and L-edges of almost all metals of biological interest. Photon fluxes greater than 2 x 1013 photons/sec (for 4.9-22 keV) will be focused into typical beam spot sizes of 0.5mm x 2.0mm, with spots as small as 25um x 25um achievable using polycapillary focusing optics. Due to the very high photon flux, radiation damage is expected to be significant and ISS will therefore routinely operate using rapid energy scanning (1-10s per scan) and translation of the sample to mitigate radiation damage. The beamline will also have a second experimental hutch for user-provided equipment or other complex experiments.
The CSB has an active partner user agreement in which we will contribute scientific user support for biological X-ray spectroscopy users in return for a 10% fraction of total ISS beamtime, the majority of which will be specifically devoted to biological general users. We are working with the ISS team to define requirements for our biological X-ray spectroscopy user community and develop an early scientific program. At present, the beamline is expected to begin commissioning in the spring of 2016, with a general user program initiated in the fall of 2016.