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Scanning EXAFS beamline (BL-9) [an error occurred while processing this directive]

Introduction

Primarily, scanning EXAFS beamline is designed to perform experiments which have requirements that fall beyond the capabilities of Dispersive EXAFS beamline (BL-08), like requiring high resolution & fluorescence mode of EXAFS measurements. The key component of the beamline is Double Crystal Monochromator (DCM) which is used for energy selection from the white synchrotron beam.

Beamline Specification

Source

              

2.5 GeV, Bending Magnet

BM port

10° Port of bending magnet (BM 4)


BL-09
Photon energy range
4-25 keV
Energy resolution (E/ΔE)
104
Flux
1011ph/sec/0.1 % band width @2.5 GeV, 300mA
Beam size (H x V)
1 mm x 0.2 mm
BL acceptance
3mrad (H) x 0.2 mrad (V)


Beamline Optics

Mainly BL-09 optics consists of

  • Two Rh and Pt coated meridional cylindrical mirrors (reflectivity shown in Fig. 1):
    • Pre-mirror : Used for collimation, which is horizontally mounted on hexapod.
    • Rh and Pt mirror reflectivity as function of energy at 0.2° incidence angle.
      Figure 1: Rh and Pt mirror reflectivity as function of energy at 0.2° incidence angle.
    • Post-mirror : Used For focusing the beam vertically at sample position.
  • Si(111) Double Crystal Monochromator (DCM): Highly monochromatic radiation is obtained using two Si(111) crystals. First one is plane crystal and second one is mechanically bendable (Sagittal) crystal which helps to focus beam horizontally at the fixed sample position.
Schematic layout
Schematic layout
View of optics & experimental Hutch of BL-09
Si(111) Double Crystal monochromator
Sample Position
Sample Environment

In-situ experimental facility over a wide temperature range from 4 K to 1000K and also under various gaseous environments is possible using closed cycle cryostat and high temperature reaction cell.
4 K Closed Cycle Cryostat
4 K Closed Cycle Cryostat
 
In-situ High Temperature Reaction Cell
In-situ High Temperature Reaction Cell


Mode of Operation

Transmission Mode: The absorption coefficient in transmission mode is given by
I = I0 exp[-μ(E)x]

Fluorescence Mode: The absorption coefficient in fluorescence mode is given by
μ=If /I0
Where I0 is the incident photon beam, I is the transmitted beam from the sample and If is the florescence intensity from sample, x is the distance travelled through the material, and μ(E) is the absorption coefficient of the material.

For transmission mode EXAFS experiment, three Ionisation chambers are used filled with suitable mixture of gases depending upon the photon energy.

For fluorescence mode EXAFS experiment, Ionisation chamber based Lytle detector or Vortex detector is used.


Recent Results
Recent Results
Recent Results
Application

The beamline can be used to study local structural properties around a specific element in materials like: liquids/solutions, single and polycrystalline materials, amorphous & highly disordered solids, thin film and doped material. The energy range (4-25 keV) available from the beamline is sufficient for K-edge studies of many elements in the range 20 < Z < 47(viz. Ti, Zn, Cu, Ga , Zr, Rb, Sr, Mo etc.). For Z > 47(viz. Rare earth elements, Au, Pt, Th, U etc.) one can probe L-edges instead of K edge. The sample thicknesses for experiments are in the μm range for transmission experiments. However, thin film and/or dilute systems studies are possible in fluorescence mode.

Publication:

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Contact Number : 244 2509/ 244 2104

Contacts

Dr. M. N. Deo, mndeo(at)barc.gov.in, Head - Atomic & Molecular Physics Division (A&MPD), BARC, Mumbai-85

Dr. S. N. Jha, snjha(at)rrcat.gov.in, A&MPD, RRCAT, Indore

Dr. D. Bhattacharyya, dibyendu(at)barc.gov.in, A&MPD, BARC, Mumbai Mr. A. K. Poswal, anshu(at)barc.gov.in, A&MPD, BARC, Mumbai