利用气泡探测器测量激光快中子

Laser fast neutron measured by bubble detector

在利用超强激光驱动中子源的研究和应用研究中,中子源的产额及其角分布至关重要.我们在星光III号激光装置上采用气泡探测器对强激光驱动的中子源的产额及其角分布进行了测量.利用超强皮秒激光与碳氘薄膜靶相互作用产生高能氘离子束撞击次级碳氘靶,通过氘-氘核反应产生准单能快中子.实验发现中子束的发射具有一定的方向性,在入射氘离子的传输方向上中子束具有更高的强度,测量得到的中子束最大强度为5.13×10~7n/sr.利用实验测量的氘离子能谱和角分布对中子束角分布进行了理论计算,结果与实验测量基本一致.

Neutron source has broad application prospects in crystallography, neutron irradiation, neutron therapy for cancer,and so on. As a new scheme to produce bright pulsed neutron source, the laser-driven neutron has attracted wide interest. In recent years, laser driven neutron sources have been extensively studied and the great progress has been made.Short pulsed laser driven neutron sources could be a compact and relatively cheap way to produce quasi-monoenergetic neutrons. The yields and the angular distributions of the laser-driven neutron sources are important in the research of laser-driven neutron sources and relevant applications. We conduct experimental investigation of this respect by using the XingGuang-III high intense laser facility, which delivers synchronized picosecond and nanosecond laser pulses. The picosecond laser energy is 100 J, the pulse width is 1 ps, and the focusing spot diameter is 20 μm. At this time, the corresponding laser power density reaches 3 × 10^19 W/cm^2. A high-energy deuterium ion beam is produced by focusing the picosecond laser on a deuterated polyethylene foil, and the deuterium ion beam is incident on a secondary deuterated polyethylene planar target to activate the D-D reaction to obtain the neutron beam. In the experiment, the neutron yield and its angular distribution are measured by the different-sensitivity BD-PND bubble detectors, which are placed in the target chamber around the target. The emission of the neutron beam is found to be non-uniform. A maximum intensity of 5.13 × 10^7 n/sr is observed in the forward direction. The angular distribution of the neutron beam is theoretically calculated by taking into account the energy-angle cross section, the angular and energy distribution of the incident deuterium ion beam. The probability of the neutron energy-angle distribution in the laboratory system is obtained by the coordinate transformation from the probability in the center of mass frame. The results show good agreement with the experimental measurements. This experiment has a certain reference value in the practical application of D-D reaction neutron source.