Double-multilayer monochromators for high-energy and large-field X-ray imaging applications with intense pink beams at SPring-8 BL20B2

Abstract

In this study, double-multilayer monochromators that generate intense, high-energy, pink X-ray beams are designed, installed and evaluated at the SPring-8 medium-length (215 m) bending-magnet beamline BL20B2 for imaging applications. Two pairs of W/B₄C multilayer mirrors are designed to utilize photon energies of 110 keV and 40 keV with bandwidths of 0.8% and 4.8%, respectively, which are more than 100 times larger when compared with the Si double-crystal monochromator (DCM) with a bandwidth of less than 0.01%. At an experimental hutch located 210 m away from the source, a large and uniform beam of size 14 mm (V) × 300 mm (H) [21 mm (V) × 300 mm (H)] was generated with a high flux density of 1.6 × 10⁹ photons s^-1 mm^-2 (6.9 × 10¹⁰ photons s^-1 mm^-2) at 110 keV (40 keV), which marked a 300 (190) times increase in the photon flux when compared with a DCM with Si 511 (111) diffraction. The intense pink beams facilitate advanced X-ray imaging for large-sized objects such as fossils, rocks, organs and electronic devices with high speed and high spatial resolution.

Keywords: X-ray imaging; double-multilayer monochromator; high energy; large field of view; multilayer mirror.

Figure 1

Schematic of the beamline with the optics hutch (OH) and the experimental hutches (EH1, EH2 and EH3). The main optical components, that is, the multilayer mirrors (M1a, M1b and M2a/b) and DCM, are located in the OH.

Figure 2

Schematics of the optical configurations for the 110 keV DMM (M1a–M2a), 40 keV DMM (M1b–M2b) and DCM modes. TC slit: transport channel slit; SCM: screen monitor; DCM: double-crystal monochromator; DSS: downstream shutter.

Figure 3

Calculated multilayer reflectivities (single reflection) plotted as functions of the X-ray energy for the 40 keV and 110 keV multilayer mirrors. The vertical axes of the graphs are drawn in linear (upper) and log (lower) scales.

Figure 4

Photographs of the insides of the M1a (a) and M2a/b (b) chambers.

Figure 5

Calculated photon flux densities at EH3 under various conditions. The black line represents the photon flux density generated by the source. The green and brown lines represent the densities obtained using the 110 keV DMM (M1a–M2a) and 0.3 mm Cu filter, respectively. The blue line represents the density obtained using both the 110 keV DMM and 0.3 mm Cu filter. The inset depicts an enlarged representation of the plot enclosed in the dashed square. The vertical axes of the graphs are drawn in linear (upper) and log (lower) scales.

Figure 6

Calculated photon flux densities at EH3 under various conditions. The black line represents the photon flux density generated by the source. The green and orange lines represent the densities obtained using the 40 keV DMM (M1b–M2b) and 2 mm SiC filter, respectively. The red line represents the density obtained using both the 40 keV DMM and 2 mm SiC filter. The vertical axes of the graphs are drawn in linear (upper) and log (lower) scales.

Figure 7

Beam profiles of the (a) 110 keV DMM at EH3 and (b) 40 keV DMM at EH3.

Figure 8

(a) Schematic of the spectrum measurement for the 110 keV DMM and (b) the measured spectrum.

Figure 9

(a) Schematic of the spectrum measurement for the 40 keV DMM and (b) the measured spectrum.

Figure 10

(a) Calculated power incident on M1b plotted as a function of the TC slit width (w). The blue (red) line indicates the incident power without a filter (with a 2 mm SiC filter). (b) Vertical beam size at EH3 as a function of w. The size is normalized by the beam size at w = 5 mm. The blue (red) symbols represent the beam size without a filter (with a 2 mm SiC filter).

Figure 11

Result of stability measurements for the 40 keV and 110 keV DMM. (a) Vertical image gravity centers plotted as a function of time. (b) Variations in relative intensity plotted as a function of time.