  Here, we report on the observation of a random to chaotic temperature
transition in the spacing of Fano-Feshbach resonances in the ultracold
polarized gas of thulium atoms. This transition is due to the appearance of
so-called d-resonances, which are not accessible at low temperatures, in the
spectra at high temperatures, which drastically changes thulium's overall
resonance statistic. In addition to this statistical change, it has been
observed that s- and d-resonances experience quite different temperature
shifts: s-resonances experience almost no shift with the temperature, while
d-resonances experience an obvious positive shift. In addition, careful
analysis of the broad Fano-Feshbach resonances enabled the determination of the
sign of thulium's background scattering length. A rethermalization experiment
made it possible to estimate a length value of a=144+-38a.u.. This proves that
thulium atoms are suitable for achieving Bose-Einstein Condensation.
