Abstract
The on-site calibration system of stationary neutron ambient dose equivalent instrument is mainly comprised of a small controllable neutron source and a reference neutron ambient dose equivalent instrument. According to the principle of “relative calibration method”, a small controllable neutron source continuously emits neutrons at the calibration site to construct a neutron radiation field.
The calibration factor (NB) can be obtained by comparing the response numbers from two instrument, the instrument to be calibrated and the reference instrument, which are symmetrically placed in the neutron radiation field. In order to complete the transfer of the ambient dose equivalent calibration coefficient of the reference instrument from National Metrology Center (252CfStandard radiation field) to nuclear facility site, the calibration coefficient needs to be corrected, that is, multiplied by the “energy correction coefficient”. Energy correction coefficient includes: (1) “Instrument Energy Response Correction Coefficient” kε for neutron fluence to neutron counting of the instrument, (2) “Conversion Correction Coefficient” kΦ for neutron fluence to neutron ambient dose equivalent.
Tests have shown that the ambient dose equivalent rate measurement error of the instrument which have been calibrated but without energy correction was 16.5%, by contrast the measurement error was 2.9% with energy correction. It can be seen that the energy correction is necessary and effective for the measuring instrument of neutron ambient dose equivalent during the on-site calibration process.
Analysis of neutron streaming through penetrations in the JET biological shielding
