Research On Fast Neutron Resonance Absorption Continuum Detection Method For Explosives

The method to detect the explosives is based on fast neutron resonance absorption of the low Z element of the explosives,which can be used to identify explosives and calculate nuclide proportion.Recently,most of research work is carried out with single energy neutron beams on the accelerator,these studies have some limitations,it is difficult to achieve portable on-site measurement and the method can't achieve full spectrum data analysis.While the research on the detection of explosives using the continuous neutron energy spectrum of radionuclides in both theoretical and experimental measurements is very few.The difficulties are how to unfold neutron resonance absorption spectrum and measure the continuous fast neutron energy spectrum with high energy resolution.In view of the above two difficulties,the theory and method of resonance neutron detonation detection based on continuous spectrum are first studied.Through the Monte Carlo simulation of fast neutron resonance absorption continuous spectrum,an explosive composition extraction algorithm based on L-M fitting is developed,so a new method for explosive composition detection is established in theory.The nuclide ratio of the four explosives is calculated according to the simulated neutron resonance absorption continuous spectrum with L-M method.The maximum error is less than 10%compared with the theoretical value,which is a fairly accurate result.The energy spectrum is measured based on the time-of-flight method.The effects of time resolution,neutron flight distance,the thickness of the object to be measured,and the statistical fluctuation on the calculation results are taken into account.The results show that the error of energy resolution and the increase of the thickness of the object will cause the increase of the calculation error;the influence of statistical fluctuation makes a certain requirement for the neutron count,and the error is acceptable when the total count is above 106.Secondly,the experimental study of neutron resonance absorption spectrum is carried out.Under the existing neutron source conditions,a new high resolution fast neutron energy spectrum measurement method is explored.The method combines the neutron flight time method,n-gamma discrimination technique and the full digital signal acquisition and analysis technology.Based on the above measurement technology and off-line processing method,the LaBr3 detector,the EJ299 plastic scintillator and DT5730 desktop digital pulse waveform analyzer are used to collect all the neutron and gamma ray information for off-line data processing.The time resolution of experimental neutron time-of-flight spectrum is 1.13ns,so the energy resolution is 23.6keV when the neutron energy is 1MeV,which meet the needs of theoretical design.Finally,the experimental demonstration of the neutron resonance spectra of the simulated samples is finished.The neutron resonance absorption spectra of the urea show obvious resonance absorption peaks,and it conforms to the theoretical resonance absorption peak more than the simulation resultsThe work of this paper not only validates the feasibility of the L-M algorithm fitting the proportion of explosive components,but also provides experimental basis for the research of explosives detection by fast neutron resonance absorption.