Using the test beam data is also possible to obtain informations about some electromagnetic features of the absorber.
The calorimeter critical energy Ec and the radiation length X0 can be obtained looking at the longitudinal profile of electron initiated showers. Such distribution can be parametrised by using the relation:
 
 
 

where t=x/X0 .
The following figure shows the distribution of the longitudinal profile of a 2 GeV electron initiated shower and the fit obtained using  the previous equation, giving Ec =59.7 MeV and  X0=5.0 cm.
 
 

Using 4 GeV electrons the fit results are Ec  =56.8 MeV and   X0 =5.0 cm.