determination of the thermal and epithermal neutron sensitivities of an lbo chamber an lbo li2b4o7 walled ionization chamber was designed to monitor the epithermal neutron fluence in boron neutron capture therapy clinical irradiation the thermal and epithermal neutron sensitivities of the device were evaluated using accelerator neutrons from the 9bed n reaction at a deuteron energy of 4 mev 4 mev dbe neutrons the response of the chamber in terms of the electric charge induced in the lbo chamber was compared with the thermal and epithermal neutron fluences measured using the goldfoil activation method the thermal and epithermal neutron sensitivities obtained were expressed in units of pc cm2 ie from the chamber response divided by neutron fluence cm2 the measured lbo chamber sensitivities were 223 107 034 107 pc cm2 for thermal neutrons and 200 105 012 105 pc cm2 for epithermal neutrons this shows that the lbo chamber is sufficiently sensitive to epithermal neutrons to be useful for epithermal neutron monitoring in bnct irradiation