Research On Correction Methods For Water-Pumping-Injection Multi-Sphere Neutron Spectrometer

With the development of accelerator,reactor and spaceflight in China,it is more and more important to master the neutron dose of radiation field for the safety of personnel and the radiation resistance of spaceflight materials.It usually first obtains the neutron spectrum and then the dose.Accurate measurement of energy spectrum is very important to obtain accurate dose.In the neutron radiation field,due to the complex environment,there are many factors affecting neutron measurement:?1?The influence of scattered neutrons often leads to a large error in measurement and counting;?2?In the radiation field,high-energy neutrons account for a large proportion.However,the high-energy neutron conversion coefficient is much larger than the low-energy neutron conversion coefficient in the dose equivalent conversion coefficient around neutrons,which often leads to the phenomenon that it is underestimated when the neutron spectrometer measures the dose below 20Me V.How to eliminate these effects in the process of developing neutron spectrometers is an urgent problem.The Monte Carlo method is used to carry out relevant research on the calibration of scattered neutrons and neutron dose,and the following research results are mainly obtained:1)Firstly,the effect of wall thickness on the scattering count of neutron spectrometer was studied.According to the size of the calibration chamber model recommended by ISO,the influence of different calibration chamber models on the counting of multi-layer concentric neutron spectrometers for pumping water was studied,and a model of neutron calibration chambers suitable for pumping multi-layer concentric neutron spectrometers was established(According to ISO recommendations,four radioactive sources ²⁴¹Am-Be,²⁴¹Am-B,²⁵²Cf and ²⁵²Cf+D2O are used as calibration sources).The room is a 700×700×350 cm³ half cube.Influences of 32 kinds of sub-aqueous scattering,internal and external scattering of air,and“radiator-detector center”distance on scattering counts were obtained:When the water layer thickness of the spectrometer is less than 6 cm,the effect of air scattering is small,and the scattering rate is up to 5%;When the thickness of the moderated water layer is greater than 6cm,the effect of air scattering approaches to 0;The scattering of the wall in the calibration room has a great influence on the count of the water injection spectrometer.With the exponential attenuation of the water layer thickness,the scattering rate of the wall reaches the highest of 96%and the minimum of 10%.2)Secondly,a structural model of shadow cone for pumping water was designed.Comparison and analysis of the mass of the shadow cone and the shielding effect on neutrons of conventional shadow cones and different structures.When the extraction water shadow cone is Fe+water+boric acid,and the thickness is 15 cm,30 cm,and5 cm.The quality of the water-injected shadow cone is the smallest,and the shielding effect is 3 times better than that of the conventional shadow cone.3)Thirdly,using the shadow cone method recommended by ISO,the optimal extraction water shadow cone selected above,combined with the characteristics of the neutron spectrometer,The calibration model of neutron peripheral dose equivalent for multi-layer concentric spherical neutron spectrometer is established.Obtain the correction factor N and the spectrometer water layer thickness r in accordance with the formulaN=0.83868-0.06482r?10?0.01239r².And the semi-empirical method recommended by ISO was used to verify the correctness of the correction model.4)Finally,a high-energy neutron dose estimation correction model for a multi-layer concentric sphere neutron spectrometer was established.From the 37high-energy neutron spectra provided by IAEA 403 report,6 representative high-energy neutron spectra were selected?“KEK 12 Ge V Synchrotron Location 1”?“Tokyo University 1 Ge V Synchrotron On concrete roof,calculated”?“DESY,Leakage Neutron Spectra,1 Heavy concrete shielding”?“DESY,Leakage Neutron Spectra,2 Heavy concrete”?“KEK 12 Ge V Synchrotron Location 5”?“Tokyo University 1 Ge V Synchrotron On concrete roof,measured”?.The MCNP program was used to calculate the simulated neutron count CR of the spectrometer,and the neutron dose of the known correction chamber was used to obtain the correction factor CF.For the unknown neutron field,on the one hand,CF is used to obtain the theoretical neutron ambient dose equivalent H^*?10?_Cf-252;On the other hand,the calculated dose-equivalence value H^*?10?_spe of the water-injection neutron spectrometer under 6 high-energy neutron spectra was obtained by combining the response functions of 32 energy injection quantities and the conversion coefficient of neutron dose equivalent around the spectrometer;Finally get the spectral correction factor of the neutron field to be measured.The study found that when the thickness of the water layer is less than 8 cm,the correction coefficient gradually increases due to the increase in the thickness of the moderating layer and finally approaches 1;When the thickness of the water layer is greater than 8 cm,the correction coefficient gradually decreases with the increase of the thickness of the water layer,and the attenuation trend for different high-energy neutron spectra is different;By comparing the correction factors of high-energy neutron dose estimation of the spectrometer under the three standard neutron sources of ²⁴¹Am-Be and ²⁴¹Am-B,it is found that the difference of correction factors calculated by the three(²⁵²Cf,²⁴¹Am-Be and²⁴¹Am-B)is very small,except that the time difference value of the combination of water layer is 11Pb110?no water in the fifth layer from the inside out?and 11Pb111?full water layer?is higher than 10%.It may Be caused by the neutron counting error of the water injection spectrometer when measuring the neutron source energy spectrum of ²⁴¹Am-Be and ²⁴¹Am-B by the spectrometer under the combination of two water layers.Main innovations of this paper:1)A“Fe+water+boric acid”pumping water shadow cone model was designed based on pumping water multi-layer concentric neutron spectrometer.The intermediate water of this model can be pumped according to demand,which has the advantages of low cost,excellent neutron shielding performance,and convenient portability.2)A pumping water shadow cone model was used to establish a correction model for the neutron dose equivalent of a pumping water multi-layer concentric sphere neutron spectrometer,and the correction factor of the spectrometer under the²⁵²Cf neutron field was obtained through this model.3)Using the neutron source spectra of ²⁵²Cf,²⁴¹Am-Be and ²⁴¹Am-B as standard neutron source spectra,the pumped water multilayer concentric neutron spectrometer was used to estimate and correct the high-energy neutron doses of 6 high-energy neutron spectra.factor.