(a) Aggregate relative positions (top) and rotations (bottom) of 32 pairs of
application-specific integrated circuits (ASICs), each pair bump-bonded to a pixel array
sensor of the CSPAD detector. The two ASICs on each sensor are manufactured to be aligned
along the long axis, separated by a 3.0-pixel gap. These calibration results bear out this
expectation within the tolerances shown. (b) Impact of positional accuracy on
the indexing and integration success rate. Perturbing the ASICs away from their true
positions reduces both the total number of indexed images (blue) and the number of images
that contain successfully integrated reflections at high (1.8–2.2 Å)
resolution (red). Error bars are the standard deviation from five different sets of
perturbations drawn from a twodimensional normal distribution with a standard deviation
σr. Separate perturbations were drawn for each
ASIC. Squares: failure to apply final subpixel corrections from iterative least squares
refinement. Circles: failure to apply nearest-whole pixel corrections. (c)
Detail of four Bragg reflections on a thermolysin diffraction pattern, showing pronounced
(seven pixel) radial elongation for the [27 –34
–7] reflection and lesser elongation for those nearby. Solution
of Bragg’s law for each pixel (black arrows) identifies the spread of photon
energies that contribute to each reflection. Red disks delineate integration masks from a
three-parameter model with wavelength limits λhigh
= 1.297 (9.556 keV) and λlow = 1.313
(9.443 keV), and full-width mosaic spread δ =
0.174°. (d) Reciprocal space diagram indicating how different-shaped
reflections arise. Reciprocal lattice points (arcs) all have a constant angular extent
δ due to their mosaic spread. Points are in reflecting
condition if they are within the zone between the high-energy (red) and low-energy (blue)
Ewald spheres. Therefore, a greater fraction of the [27 –34
–7] mosaic distribution is within the reflecting condition,
leading to a reflection that subtends a greater radial angle
Δθ. (e) Paired refinements of the
thermolysin structure. Red and green bars indicate the change in
Rwork and Rfree, respectively,
as higher-resolution data are added to the refinement. Dark and light blue bars show
changes to the R-factors when the newly added high-resolution structure
factors are randomly permuted. The data are interpreted as containing statistically
significant signal for the resolution shells where
ΔRfree is continuously negative,
i.e. out to 2.1 Å.