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X-Ray imaging and diffraction techniques at Sirius [1], the fourth-generation synchrotron light source operated by the Brazilian Synchrotron Light Laboratory (LNLS) which is part of Brazilian Center for Research in Energy and Materials (CNPEM), frequently utilize hybrid pixel detectors. They consist of photon-counting devices encompassing a photo-active semiconductor sensor integrated with a pulse processing Application Specific Integrated Circuit (ASIC) capable of performing input pulse counting across a pixelated array. This work discuss characterization results based on the PIMEGA detectors [2], large area hybrid assemblies using Medipix3RX [3] ASIC, with a 55 x 55 µm2 pixel size. We compare the physical responses of 300 and 675 µm thick silicon sensors. For this contribution, we have performed the slanted edge technique for measuring the Modulation Transfer Function (MTF) [4,5] and pixel response linearity for high photon-rate conditions [6].
The MTF experiment explored the thickness dependence of the detector’s spatial resolution and was conducted under 5.9 keV incident energy ($E_0$), for equivalent energy threshold values of 0.5 and 0.7$E_0$ , as shown in Figure 1. Our work demonstrates that, even though thicker sensors present higher absorption efficiencies, the MTF values decrease along the entire spatial frequency domain. Moreover, higher threshold settings yield larger MTF values for both probed thicknesses. These observations are a consequence of the charge diffusion lengths within the thickness of the semiconductors, this leads to more pronounced charge sharing effects in thicker sensors, which are inversely proportional to the threshold settings.
The count rate linearity experiment was conducted to investigate and characterize the electronic effect of pile-up and pixel electronics paralyzable effect under high-flux incident conditions. This experiment was simultaneously conducted at two beamlines, in which we were able to vary the incident flux in the detectors by controlling the current in the Sirius storage ring.
Two detectors with Silicon sensors with thicknesses of 300 and 675 microns were studied in this experiment, with varying energies applied in accordance with the beamline and their experimental capabilities. Consequently, the CATERETE beamline [7] employs the thinner Silicon sensor for 6 keV and EMA beamline [8] employs the thicker sensor for 25 keV photon energy.
For each set ring current value, the detector was subjected to direct beam irradiation. This method enables a direct correlation between the current levels and the incident flux by analyzing the count-rate observed under low flux conditions. Numerical adjustments based on the paralyzable model [6] demonstrated the value of μ=0.66 ± 0.08 μs, which resulted in a loss of linearity under 1.58 $10^5$ photons/px.s for 675 microns sensors. The μ value demonstrated is equal to those found for 300 microns Si sensors under 6 keV μ=0.66 ± 0.01 μs and loss of linearity under 1.60 $10^5$ photons/px.s.
Our results suggest a compromise between sensor absorption efficiency and spatial resolution. Given the fair energy resolution, excellent MTF performance and despite currently unavoidable spectral distortions due to charge sharing and pile up effect, these Silicon sensor detectors constitute a very attractive technological platform for imaging and diffraction applications, especially from the tender X-ray energy range to initial hard X-ray energies.
[1] ALVES, Murilo et al. Simulation of Sirius booster commissioning. In: 10th International Particle Accelerator Conference, 2019
[2] CAMPANELLI, R. B. et al. Large area hybrid detectors based on Medipix3RX: Commissioning and characterization at Sirius beamlines. Journal of Instrumentation, v. 18, n. 02, p. C02008, 2023.
[3] BALLABRIGA, Rafael et al. The Medipix3RX: A high resolution, zero dead-time pixel detectorreadout chip allowing spectroscopic imaging. Journal of Instrumentation, v. 8, n. 02, p. C02016, 2013.
[4] BOONE, John M.; SEIBERT, J. Anthony. An analytical edge spread function model for computer fitting and subsequent calculation of the LSF and MTF. Medical physics, v. 21, n. 10, p. 1541-1545, 1994.
[5] KOENIG, Thomas et al. How spectroscopic x-ray imaging benefits from inter-pixel communication. Physics in Medicine & Biology, v. 59, n. 20, p. 6195, 2014.
[6] FROJDH, Erik et al. Count rate linearity and spectral response of the Medipix3RX chip coupled to a 300μm silicon sensor under high flux conditions. Journal of Instrumentation, v. 9, n. 04, p. C04028, 2014.
[7] MENEAU, F. et al. Cateretê: The Coherent X-ray Scattering Beamline at the 4th generation synchrotron facility SIRIUS. Acta Crystallogr. Sect. A Found. Adv, v. 77, p. C283, 2021.
[8] DOS REIS, Ricardo D. et al. Preliminary overview of the extreme condition beamline (EMA) at the new Brazilian synchrotron source (Sirius). In: Journal of Physics: Conference Series. IOP Publishing, 2020.
The authors acknowledge funding from the Brazilian Ministry of Science, Technology, and Innovation.
| Workshop topics | Applications |
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