Combined Detectors With Neutron Sensitive Boron Coated Material And Experimental Tests In N/γ Radiation Field

There are always many kinds of particles in actual radiation field, which make it necessary todevelop the measuring devices and technology of mixed fields. Aiming at n/γ radiation field, acombined detector with wide measuring range and high sensitivity is developed in this work, which iscomposed of a cylindrical boron-lined proportional counter（BLPC） and a flat boron-lined ionizationchamber（BLIC）. The BLPC is used to monitor the small flux neutron field when working in pulsemode; while the BLIC directs at the large flux neutron field when working in accumulative currentmode due to its high sensitivity.Above all, the laboratorial manufacturing technology of the neutron sensitive layer has beenbroken through in this work, which is a bottleneck of boron-lined neutron detectors. After debuggedin labs and tested in radiation fields, the detectors show good parameters of neutron measurement,plateau characteristics and sensitivities etc.. Considering the lack of domestic laboratorialresin-dipped boron coating technics currently, two simple and practical boron film coated technics aredeveloped, as well as the production programs are optimized. The technics are named as dip-coatedboron deposition（DCBD） and hand-painted boron deposition （HPBD）, where Formvar resin is used asbinder and1,2-dichloroethane acts as solution. Experiments show that the smallest mass ratio ofFormvar resin and boron powder in DCBD is5.0, while the optimal value of that in HPBD is0.2. Inaddition, the preparation of the mixed solution, the dip-coated and hand-painted process, and thedrying by the thermostat are also detailed in this work. Finally the two technics have beensummarized and evaluated.After undergoing many segments, such as simulation, material performance test, machine designand process, system assembly, testing of vacuum system and working gas, unit test and combined testetc., the cylindrical BLPC showes good characteristics. In the neutron field of a100mCi Am-Besource, after0.4atm P10gas had been filled, the BLPC shows a plateau with the length is100V andthe slope is13.2%/100V, the operating voltage is800V. The width of the output pulse from theBLPC’s amplifier is1.26μs and the rise time is370ns. Working at the count rate of1.0×10⁵count/s,the pulse pile-up probability of the BLPC is found to be about3.6%.In the neutron field of a100mCi Am-Be source, after0.4atm P10gas had been filled, the BLICshows a complete charge collection until200V, which results a500V plateau length with a slope of3.72%/100V. Leakage current of the BLIC at200V is0.2pA, which results a neutron sensitivity of1.0×10^-15A/(cm^-2·s^-1). In the gamma field of a10mCi¹³⁷Cs source, the average signal current at the plateau region is1.23pA, and it turns into1.63pA when a10mCi⁹⁰Sr source is subjoined. The gammasensitivity of the BLIC is9.0×10^-16A/(MeV cm^-2·s^-1), it can also be converted into conventional unit1.42×10^-12A/(R h^-1).A simple and practical laboratorial resin-dipped boron coating technics developed in this workrealize the coating of neutron sensitive layer without any large experimental platforms. Now theleakage current of domestic BLICs usually range from50to100pA, their neutron sensitivities are ofthe order of10^-1410^-13A/(cm^-2·s^-1) and gamma sensitivities are10^-1210-11A/(R h^-1). By comparisonwe can conclude that the BLIC made in this work reaches the advanced domestic level. Furthermore,the combined detector realizes the measurements of neutron energy spectrum by using Bonner Spheretechnique.