Some problems associated with the use of boron carbide neutron filters for reactor epithermal neutron activation analysis (ENAA)

The radiation heating caused by the¹⁰B(n, )⁷Li-reaction in boron carbide (B₄ C) neutron filters used for epithermal neutron activation analysis has been examined by measuring rates of temperature rise and steady-state temperatures of sintered and powdered B₄C filters placed in dry air and reactor pool-water during irradiation, respectively. Maximum equilibrium temperatures of 195°C for air-cooled sintered, and 50°C for water-cooled powdered B₄C were observed, confirming the necessity for efficient cooling of the filter during irradiation. It is noted that the accumulation of the¹⁰B(n, )⁷Li-reaction products in B₄C and other boron compounds may severely limit the reuse of the filters in subsequent irradiations.