Research on the test, measurement and ambient dose equivalent conversion for a multisphere neutron spectrometer

[Background] Neutron ambient dose equivalent is closely related to neutron energy. Acquisition of the energy spectrum is necessary to calculate the ambient dose equivalent accurately in the neutron radiation field. [Purpose] This study aims at the ambient dose equivalent calculation by shakedown test of multi sphere neutron spectrometer (MNS). [Methods] First of all, pulse height analysis (PHA) method was used for neutron/γ discrimination to precisely measure neutron count rate. Then the neutron energy spectrum was successfully obtained and carefully analyzed in three neutron radiation fields: laboratory background, Am-Be neutron source and DD tube emergency neutron. Neutron fluence was converted into ambient dose equivalent consulting the conversion coefficient recommended by International Commission on Radiological Protection (ICRP) report No. 74, and dose contribution weight from neutron in different energy groups was analyzed. Finally, comparison test was made against three other instruments with mono moderator respectively, errors between MNS and them were analyzed theoretically. [Results] Neutron ambient dose equivalent converted from energy spectrum measured by MNS was consistent with the other three dose instruments. No matter what kind of the neutron radiation field is, fast neutrons are the main contributors to the dose. [Conclusion] PHA and pulse height spectrum monitoring is the critical point for neutron energy spectrum measurement. MNS can be used to measure and calculate neutron ambient dose equivalent directly, guide optimal reference radiation for other neutron dose instruments calibration, and radiation protection design against neutron of special energy groups. (authors)