Speaker
Description
Gaseous wavelength shifting (GWS) plays a key role in the optical readout of modern micropattern gaseous detectors (MPGDs).
It is closely analogous to Penning transfer, although occurring between excited states. In principle, GWS enables the use of minute
additive concentrations to tailor both the spectrum and intensity of gas scintillation.
Indirect, mostly qualitative evidence suggests that GWS is present in CF₄-based mixtures under conditions relevant to gaseous detectors.
Here, we demonstrate the power of combining systematic measurements of primary (X-ray-induced) and secondary (avalanche-induced)
scintillation in Ar–CF₄ and He–CF₄ mixtures. We develop a simple kinetic model based on the atomic and molecular states populated during
electron transport, as estimated using state-of-the-art Garfield++ cross-sections. The model simultaneously reproduces scintillation yields
and emission spectra for both primary and secondary processes.
We argue that the combination of Garfield++ electron transport with the proposed kinetic model provides a robust framework for predicting
scintillation in the technologically relevant wavelength range (400–800 nm), over pressures from 50 mbar to 10 bar, and for arbitrary CF₄
concentrations. The data indicate a strong wavelength-shifting capability in Ar-based mixtures—likely driven by transfer processes from
Ar p-states—while no such effect is observed in He mixtures, consistent with their lower scintillation yields.
We conclude by comparing the model parameters with existing experimental data and state-of-the-art theoretical predictions (including DFT
and coupled-cluster calculations), and outline the next steps toward a first-principles description extending into the UV region.
| Name of the speaker | Diego González Díaz |
|---|---|
| Eligible for the Georges Charpak Young Scientist Award. | no |