  In the last decades huge theoretical effort was devoted to the development of
consistent theoretical models, aiming to solve the so-called "measurement
problem", to which John Bell dedicated part of his thoughts. Among these, the
Dynamical Reduction Models possess the unique characteristic to be
experimentally testable, thus enabling to set experimental upper bounds on the
reduction rate parameter $\lambda$ characterizing these models. Analysing the
X-ray spectrum emitted by an isolated slab of Germanium, we set the most
stringent limit on the parameter $\lambda$ up to date.
