Neutron Spectrum Measurements in a Homogeneous Erbium System and Erbium Cross Sections

Careful measurements and calculations of the neutron spectrum in an aqueous solution of erbium nitrate are described. The validity of the infinite medium calculation is scrutinizingly studied. As a result it is shown that the discrepancy between measurement and calculation is caused by a too high (by about 10%) absorption cross section of erbium. This result is substantiated by two independent integral tests; the fundamental time eigenvalue of the system and the neutron conservation test.