Speaker
Description
Several next-generation experiments for rare events require a further reduction of the $^{238}$U and $^{232}$Th contamination on material surfaces with respect to what is achievable with current technologies. Such a reduction can be achieved by improved cleaning techniques or surface coating, both of which can be optimized using sources with a well-known surface contamination and/or $^{222}$Rn emanation rate.
In this talk, we will report on the characterization of 19 samples of different materials irradiated with $^{226}$Ra at the ISOLDE facility (CERN). We performed a full characterization of all samples, including the measurement of the emitted $\alpha$ spectra with a silicon PIN diode, of the $\gamma$ spectrum with a HPGe detectors, and of the $^{222}$Rn emanation with an electrostatic radon monitor and miniaturized proportional counters.
In addition, we exposed some of the irradiated samples to clean targets, yielding a very shallow $^{222}$Rn distribution which is unaffected by the nuclear recoil contribution from $^{226}$Ra decay. We measured the α spectrum with a silicon PIN diode, and the $^{222}$Rn emanation resulting from a pure diffusion process using a cryogenic radon monitor.
Finally, we simulated the primary and secondary implantation processes, as well as the recoil-induced diffusion processes using the TRIDYN software.
The availability of all these independent measurements allows us to cross-validate the different experimental techniques against each other, and the validation of the simulation against the data, guaranteeing a robust predictive power for TRIDYN-based simulations of future applications to rare-events experiments.