Thermal Neutron Tomography Technique Study

Neutron radiography is an important non-destructive testing (inspect) technique.It's application used in military affairs,aviation,space flight,industry,geology,biology,archaeology and so on can not be substituted by other techniques.Neutron tomography is an advanced form of neutron radiography.Using advanced digital technique it can show full inner structure of the objects.This paper aims to study the acquisition of projection images,radiograph preprocessing and tomographic reconstruction.All these serve for the seting up different forms advanced neutron radiography study,experiment,serve platform in our academy.The characteristics of the radiographic images,used as projections for the tomographic reconstruction,set the fundamental limits on the accuracy of the reconstruction.This paper investigates the shielding scheme of CCD(Charge Coupled Device) through experiment,theory analyse,silulation and compare.The shielding scheme reduces the white dot noise resulted from radiation damage.This paper develops MCNP numerical simulation of neutron radiography,as a tool of neutron radiography technique investigation. This paper introduces MCNP simulation method of neutron radiography.The process that Maxwell thermol neutron penetrates the samples is simulated,and clear images are gotten.The results compare of simulation and actual neutron radiography is also given in this paper.The simulation images is very similar to experiment result images.The analyse of effect of scattered neutrons is included in the paper.As the distance between objects and scintillation screen increase,the scattered component decrease.For a distance of double object size,the influence of scattered neutrons to the image can be ignored.The ability that thermol neutrons penetrates Al,Pb,Fe and Cu is discussed.The reason result in difference between simulation and experiment is studied.A conclusion can be drawn that the MCNP simulation method of neutron radiography is credible and can be used to supervise neutron radiography investigation.Before tomographic reconstruction,preprocessing of projection images to correct systematic noise, background noise,white dot noise errors should be done.This paper analyzes the noise of projection images. Combining the experiments carried out on real time neutron radiography facility at SPRR-300,medi-value filter,normalization processing are studied in this paper.Results show that these image processing can decrease noise,improve the images quality.These preprocessing is very useful to tomographic reconstruction.The principle and status of neutron tomography are introduced in the paper.Reconstruction algorithms and preprocessing of radiographs are expatiated in the paper.The first neutron tomography experiment is introduced in the paper.The experiment are carried out on real time neutron radiography facility at SPRR-300.The sample is a aluminum column with holes on it.The first neutron tomography reconstruction image is gotten.Although the view angles is less,the experiment facility is simple, operation is not so precise,and aluminum is not sensitive to neutron,the reconstruction image is better than expected.This indicates that the technique scheme adopted here is reasonable and feasible.It can be a reference for the neutron tomography facility to be built.