Optimization Design Of Detectors For Dose Equivalent And Fluence Measurement In Neutron Spectrum

A spherical neutron detector applied for neutron ambient dose equivalent measurementhas been designed by MCNP-4C code in this work. This detector consists of a central SP93Heproportional counter, a polyethylene moderator, a cadmium layer, a lead layer and some airguides. The spherical cadmium layer and the lead layer share the center of the sphericaldetector, and the air guides are regularly positioned along the radical of the sphericalmoderator. After optimization of the geometric parameters of these basic structures, includingthe diameter of this detector, the number, diameter and position of air guides, the position andthickness of cadmium layer and lead layer and so on, a satisfying energy response cure wasgained. The optimized relative energy response cure, with a maximum2.04at energy5.0keVand a minimum0.42at energy0.2MeV, was approximately located in a2factor interval.Energy responses of some broad neutron spectra were also calculated. The results showed thatthe relative response of this detector ranged from0.55to1.05, and the deviation of the revisedneutron ambient dose equivalent estimation was less than±31%.Another novel neutron detector mainly applied for neutron fluence rate measurement inneutron radiation filed is also given in this paper. The performance of the detector wasoptimized by MCNP-4C code. A type SP93He proportional counter is placed in the center ofthis spherical detector,50air guides are regularly positioned along the radical of the sphericalmoderator, and two pitchblende layers are introduced into the detector. It has been detailedinvestigated the influence of these parameters, such as the diameter of the detector, the radiusof the air guides, and the position, thickness and its uranium235concentration of thepitchblende lawyers. The results show that the ratio between the maximum and minimum ofthe optimized energy response curve is2.40, and this ratio is just1.35below2.0MeV. Thedeviation of the calculated angel independence response is less than15%in the range fromthermal to20.0MeV. The response of some broad neutron spectra has also been investigated.The results reveal that theirs relative energy response is between0.8and1.6, and thedeviation of the revised neutron fluence estimation is less than±33%. With the assistance ofFLUKA code, some improvements have been taken to suppress the overestimated response ofthis neutron fluence rate detector to high-energy neutron above1.0GeV. The technicalmeasurements are mainly about decreasing the thickness of the lead shield, and decreasing thethickness and uranium235concentration of the pitchblende lawyers. After optimization, therelative energy response cure of improved detector varies from0.5to1.87for neutronbetween thermal and10.0GeV. Compared with unimproved detector, the relative energyresponse of10.0GeV neutron has been dramatically decreased from4.37to1.87. Some experiments have been taken to verify the credibility of detector optimizationresults. The deviation of the measured cosmic secondary neutron fluence rate is+13.8%, andthe measured neutron fluence rate deviation in a252Cf neutron radiation filed is+8.87%.