Beryllium radioactive isotopes as a probe to measure residence time of Cosmic Rays in the Galaxy and halo thickness.

Cosmic Rays (CR) are a powerful tool for the investigation of the structure of the magnetic fields in the galactic halo and the property of the Inter-Stellar Medium. In particular the ratio of secondary CR (as Li,Be,B) over the primary CR (as He,C,O) is able to provide the grammage, that is the amount of material crossed by CR in their journey through the Galaxy. Two parameters of the CR propagation models: the galactic halo thickness, H, and the diffusion coefficient, D, are loosely constrained by such a grammage measurement, in particular a large degeneracy exist being only H/D well measured. The uncertainties on D and H parameters (this last one know to be in the range 3-8 kpc) also reflects on the accuracy of the determination of secondary anti-proton and positrons fluxes that are the background for the Dark Matter or exotic (astro-)physics searches. The ¹⁰Be/⁹Be isotopic flux ratio (thanks to the 2 My lifetime of ¹⁰Be) can be used as a radioactive clock providing the measurement of CR residence time in the galaxy. This is an important tool to solve the H/D degeneracy. Past measurements of ¹⁰Be/⁹Be isotopic flux ratio in CR are scarce, limited to low energy and affected by large uncertainties. Here a new technique to measure ¹⁰Be/⁹Be isotopic flux ratio with a Data-Driven approach in magnetic spectrometers is presented. As an example by applying the method to Beryllium data collected and published by PAMELA collaboration it is now possible to determine this important measurement avoiding the prohibitive uncertainties coming from the Monte Carlo simulation. It is shown that the accuracy of PAMELA data permits to infer a value of the halo thickness H within 20% precision.