Scattering spectra from X-ray, electron or neutron 
diffraction experiments are sufficient to describe the 
phase behaviour of noble gas clusters and to determine 
their temperature. Using classical Monte Carlo 
simulations combined with optimized data analysis and 
Path Integral Monte Carlo calculations as ''idealized 
experiments'' we obtain scattering spectra of Ar- and 
Ne-clusters. Starting from the classical and quantum 
mechanical hypervirial theorems we devise a method to 
estimate the temperature and the caloric curves (which 
describe the phase behaviour of the noble gas clusters) 
directly from these scattering spectra using an 
interatomic potential function as input. As applications 
we studied for Ar-clusters the effect of different model 
potentials on the temperature estimate thus contributing 
to the intricate question of what experimentally is the 
temperature of an isolated cluster. For Ne-clusters we 
investigate the differences between classical and quantum
mechanical treatment.