Film Scintillation Neutron Detector Design And Experimental Studies

There are two obvious characteristics of pulsed radiation field which are the very short duration and the extremely high flux density. It's impossible to detect single particle in the pulse under the modern technology. Thus, the output signal of the detector, the kind of which is called current mode detector, represents the average ionization effect of a large number of particles. The current mode detector used to measure the total number of the fission neutron has three important indexes:neutron sensitivity, the neutron to gamma sensitivity ratio and the flatness lever of the neutron energy response. The film scintillation neutron detector, invented in recent years, is a new current mode detector used to measure the total number of pulsed fission neutrons. This kind of detector has relatively large neutron sensitivity, high ratio of neutron to gamma sensitivity and flat neutron energy response.The paper mainly contains:the structure design of the detector and the sensitivity calibration experiments.The first part analyzes theoretically the scintillator thickness, the window materials, the magnetic induction value of the deflection magnet, and the relative location between the scintillator and photon multiplier tube. The results are concluded as follow:(1) The neutron to gamma sensitivity ratio of the detector can exceed 10 with the scintillating film thickness of less than 0.3mm. (2) Comparing with aluminum window, the iron window produces less Compton electrons while the gamma rays pass through the input window. Thus, the iron was selected as the input window material. (3) The magnetic induction value of 0.1T can totally deflect the Compton electrons,with the highest energy of 1.25MeV, produced by gamma rays passing through the input window. (4) The angle 68 degree between the axis of the PMT and the normal of the scintillator can creat the highest efficiency of fluorescence collecting.Three sensitivity calibration experiments have been done to make research on the performance of the detector. The experiment conclusions are summarized as follow.(1) The shielding effect of gamma sensitivity calibration is very good. The change trend of the gamma sensitivity with the sinctillator thickness agrees with the simulation results. The gamma sensitivity of 0.35mm scintillator is about 1.42×10-14C·cm2. When the distance between the back window and the scintillator is 30cm, there is no need of the back magnet because most of the electrons scattered by the back window can't reach to the scintillator. (2) Since the D-D neutron flux is relatively high and the flight time difference between neutron and gamma makes it much easier for the shielding work, the SNS of all scintillators is bigger than 1.0. The change trend of the D-D neutron sensitivity with the sinctillator thickness agrees with the simulation results. The D-D neutron sensitivity of 0.35mm scintillator is about 6.41×10-14C·cm2. The neutron to gamma sensitivity ratio of 0.35mm scintillator is 4.52, and it can be as big as about 10 when the thickness is 0.1mm.(3) In the D-T neutron sensitivity calibration, since the scattering neutron background is very serious, the SNS of most scintillators is smaller than 1.0. The change trend of the D-T neutron sensitivity with the sinctillator thickness doesn't correspond with the simulation result well.The research shows that the neutron sensitivity of the film scintillation neutron detector can be as big as 10-14C·cm2, the neutron to gamma sensitivity ratio of the 0.35mm scintillator is 4.52 and it can be as high as about 10 when the thickness is 0.1mm. The simulation indicates that the neutron energy response flatness of 0.1mm and 1mm are 0.374 and 0.136 respectively. The flatness of 0.1mm scintillator is about 3 times as large as that of the 1mm one.