Development of Neutron Streak Camera Using Recoil Protons

为了应用于惯性约束聚变等离子体的诊断，我们研制了一种新型的利用塑料阴极中的反冲质子的条纹相机。其特点和性能如下：1)计算了14.1 MeV(D-T)中子的探测效率。这种计算是基于蒙特卡罗程序，该程序处理塑料阴极中质子的能量慢化。还考虑了中子氢散射的微分截面和反冲质子的角变能。探测效率随着阴极厚度的增加而增加，当厚度超过前向散射质子的范围(2.2 mm)时，探测效率趋于一个渐近值。最大探测效率为0.4%。2)中子和反冲质子的飞行时间扩散导致了时间分辨率的下降。当阴极厚度为2.2 mm时，二次电子发射的时间分布饱和约为5ps。3)我们搭建了一套阴极直径为25 mm的条纹管探测系统。用紫外短脉冲激光对这种条纹相机进行了检测。在输出荧光屏上以26 mm/ns的扫描速度测量的时间分辨率优于12ps。4)对于阴极狭缝的典型宽度(100-300微米)，该中子条纹相机的时间分辨率估计为14-19ps。5)当总中子产额为(3.5-7)×10^9时，该中子条纹相机可用于激光聚变实验。

For the application to the diagnostics of inertial confinement fusion plasma, we have developed a new type of streak camera which uses recoil protons in a plastic cathode. The distinctive characteristics and performances are as follows ;1) We calculated the detection efficiency for 14.1-MeV (D-T) neutrons. This calculation is based on the Monte-Carlo code which treats the energy slowing-down of protons in the plastic cathode. The differential cross section of neutron scattering by hydrogen and the angular-dependent energy of recoil protons are also taken into account. The detection efficiency increases with increasing the cathode thickness, then saturates to an asymptotic value at the thickness exceeding the range (2.2mm) of forward scattered proton. The maximum detection efficiency was inferred to be 0.4%.2) The time-of-flight spread of neutrons and recoil protons causes the degradation of time resolution. The time spread of the emission of secondary electrons saturates to be about 5ps at the cathode thickness of 2.2mm.3) We have constructed a detection system which has a streak tube of 25-mm cathode diameter. This streak camera was examined using an ultraviolet short pulse laser. The measured time resolution is better than 12ps at a sweep speed of 26mm/ns on the output phosphor screen.4) The time resolution of this neutron streak camera was estimated to be 14-19ps for the typical width (100-300mum) of cathode slit.5) This neutron streak camera can be applicable to the laser fusion experiments if the total neutron yield is (3.5-7) *10^9.