[en] The relative abundance of nuclear species measured in cosmic rays at earth has often been interpreted with the simple leaky box model. Recently new accurate cross sections of key importance for propagation calculations have been measured. Their statistical uncertainties are often better than 4% and their values significantly different from those previously accepted. In this paper we use these new cross sections to compare the observed B/C+O and (Sc to Cr)/Fe ratio to those predicted with the simple leaky box model