Neutron Energy Spectrum Measurement By Gaseous Scintillator Optical Method

Neutron energy spectrum is one of the most important characteristic parameters in the study and diagnosis of nuclear reaction processes.In this paper,a novel new method for measuring neutron energy spectra is proposed,which is an optical method based on gaseous scintillator and CCD camera.The essence of this method is to determine the energy spectrum according to the charged particle track length.The scintillating luminescence distribution only corresponds to the gaseous scintillator and the particle energy,without the limitation of the source pulse state.This optical method can be applied to the pulse radiation field,and also to the steady state radiation field.It has the advantages of intuitive measurement,good energy resolution,can be suitable for various of charged particle beams,wide energy range,convenient and adjustable.This new method combines with the principle recoil proton measurement for elastic scattering of neutrons and hydrogen nuclei,and converts neutron into recoil proton by converting target,and then obtains the distribution of incident neutron energy spectrum.It is of great academic value and practical significance for the study of neutron spectroscopy and the physical diagnosis of fusion/fission.The purpose of this paper is to establish a set of energy spectrum measurement system based on optical method.The charged particle beam incident into gaseous scintillator,the particle are deposited energy along the track and excited scintillator luminescence.The CCD camera acquires the scintillation image,and then obtains the neutron spectrum according to the scintillation image unfolding.The main research include five parts.1.To establish a model through the theoretical derivation and simulation,research on the correspondence relationship of energy and direction between the incident neutron and recoil proton.The relationship between recoil proton energy and the energy deposition in gas.and the relationship between the energy deposition and scintillator luminescence are also investigated.2.Scintillator luminescence image.The particle incident into gaseous scintillator to excite or partially ionize the gas molecules.And then,the excited molecules produce scintillation luminescence.Through the research and analysis,the composition of the gaseous scintillator is determined to be 90%Ar+10%CF4.The energy response of the detector is very linear,and the energy resolution within 20 keV can be achieved.3.Detector system response.The response process of a series of different energy incident particles in gaseous scintillator is studied,the scintillation intensity along the recoil proton incident direction is extracted as the characteristic quantity.The response matrix of the detection system for different incident energy is obtained.4.Unfolding algorithm.According to the detector response matrix,the accurate distribution of incident neutron is obtained by the unfolding algorithm.A reconstruction algorithm based on the potential reduction interior point has been developed and applied for the first time to neutron energy spetrum unfolding.This algorithm selects the appropriate step length in each iteration process so that the value of the potential function can be decresed,and the iteration direction is the simultaneous solutions of the central path direction and the Newton direction.It can be concluded that this algorithm is sufciently fast and the solution results match the expected results.5.Detecting scheme.For the first time,we put forward a new method called multi-directional weighted scheme which the recoil proton detectors are placed in several directions at the same time.The neutron energy spectrum is reconstructed depend on all several directions recoil proton data with its weighted factor respectively.This method combines the results of multiple dierent directions and in result the results are better.At the same time,the detection efficiency is improved remarkably.The existing energy spectrum measurement methods are limited in some cases,such as the situations of long duration pulse or the real-time measurement.The high energy resolution measurement of these radiation fields is still a remaining problem.This paper aimed at the major requirements for the pulsed neutron energy spectrum measurement,a new method of energy spectrum measurement which has a high energy resolution is developed.The track detector has the features of intuitive and can be applied to pulse radiation field,are combined with the advantages of real-time image information acquisition and processing of modern imaging module.It solves the shortcomings of existing charged particle energy measurement methods,such as complex structure,limited by the intensity of radiation field and so on,and explores a new technical way for the accurate energy spectrum measurement.