With the rapid advancement of laser technology, the laser intensity reaches approximately 1022 W/cm2, and charged particles can be accelerated to hundreds of MeV or even several GeV. These energetic particles can trigger nuclear reactions and generate neutrons. Compared with traditional neutron sources, such as reactors, spallation neutrons, and radioactive neutron sources, laser-driven neutron sources (LDNS) have interesting features, such as short duration, which is approximately tens or hundreds of ps, and ultrahigh flux, which is 1018‒1021 /(cm2·s). Moreover, the neutron energy is easy to adjust by manipulating the laser accelerating process. Therefore, studies on LDNS have attracted considerable interest and have shown unique potential for innovative investigations and applications in the past two decades, particularly after the significant progress achieved by Roth et al. in 2013. LDNS is expected to be a powerful alternative to traditional neutron sources and may play an essential role in specific applications, such as the fast neutron resonance radiography and rapid neutron capture. This study briefly reviews the historical development and status of laser-driven neutron sources. Significant attention is given to the recent progress in beam-target neutron sources.
First, this study reviews the technical approaches to increase the yield of laser-driven neutron sources, which mainly include nuclear reaction channels and ion acceleration efficiency. Compared with deuterium-deuterium and proton-lithium reactions, deuterium-lithium nuclear reactions result in larger nuclear reaction cross-sections and, thus, have received special attention in this field. After determining the nuclear reaction channel, the improvement of the neutron yield mainly depends on the optimization of the deuterium acceleration efficiency. Various new schemes for eliminating the contamination layer within the target normal sheath acceleration (TNSA) acceleration process, such as target heating, laser cleaning, and heavy water spraying, have been established. The use of advanced acceleration mechanisms, such as break-out afterburner and collisionless shock acceleration, has also been proposed to increase the cut-off energy and charge of deuterium ions, and the neutron yield eventually reaches as high as 1010 /sr (Fig.2). In addition to yield, neutron directionality is also a critical parameter that influences neutron application. New schemes such as the stripping of D-Li reaction and reverse kinematic effects of heavy ions have also been proposed to generate directional neutron sources. By applying the inverse kinematic effect, the proof-of-principle experiments conducted thus far have achieved a neutron angular distribution with a significant forward impulse and full width at half maximum (FWHM) of 40° (Fig.6), which is nearly half lower than those of the D-D and D-Li reactions. In addition to optimizing the quality of the laser neutron source, the accurate characterization of laser neutron source parameters is also an integral process of the neutron application. This study introduces the experimental diagnostic methods of laser neutron source yield, angular distribution, energy spectrum, and source size. The analysis method of the pulse width is also explained. The wide range of energy spectrum and ultrashort pulse-width characteristics are suitable for fast-neutron resonance analysis applications based on the time-of-flight method. Finally, this study reviews the application status of laser neutron sources. Current applications mainly focus on traditional application scenarios, such as fast neutron photography, fast neutron moderation, and thermal neutron resonance absorption. However, the high flux and short pulse of laser-driven neutron sources also make them valuable in fast-neutron resonance imaging and rapid neutron capture.
Research on laser neutron sources has aroused significant interest and demonstrates unique potential in terms of innovative research and application prospects. However, because of the limited yield, most of the current application experiments mainly focus on the application scenarios of the traditional neutron source, in which the LDNS does not have unique advantages in terms of neutron fluence. However, with the development of high repetition rate and high average-power laser technology, miniaturized laser neutron sources can gain advantages in terms of economy and flexibility to cope with more complex applications. In addition, because of the nonsubstitutable unique advantages of the short pulse width and high flux rate of LDNS, it also has potentials for new applications, such as fast neutron capture, diagnosis of the state of warm dense matter, and fusion material research. Finally, lasers have advantages in generating various particle sources, which can flexibly satisfy the needs of multiple application scenarios. For example, lasers can simultaneously generate multiple radiation sources, such as electrons, ions, γ-rays, and neutrons. The unique effects of combining radiation fields can lead to new applications, such as radiography implemented with thermal neutrons and X-rays. Overall, laser-driven neutron sources are expected to be widely used in scientific and industrial fields and can expand more distinctive application scenarios by adopting more stable and efficient neutron generation methods and more accurate neutron-source parameter characterization techniques.
