A novel laser-collider used to produce monoenergetic 13.3 MeV (7)Li (d, n) neutrons.

Fast neutrons, because of their unique characteristics of electrical neutrality and strong penetration capability in high-Z materials compared with charged particles and X-rays, possess tremendous appliciation value in the fields of materials testing for fusion power plant1, neutron radiography2, neutron therapy3, and others4,5. Intense neutron pulses can be obtained from spallation sources, nuclear reactors, and high-energy particle accelerators. Unfortunately, the enormous size and cost of these devices are preventing their widespread use. The rapid development of high-intensity laser technology offers an alternative approach at relatively low cost, and the ultra-fast nature of laser-driven neutron sources could allow this technology to find further applications in the ultrafast sciences. Because of their cross-sections and Q-values, three nuclear reactions are primarily used for neutron production: Because tritium is radioactive and not readily available, the (d, t) reaction, which is typically applied in inertial confinement fusion experiments, was excluded in the current study. Based on the remaining reactions, there are two main paths for ultra-fast laser-driven-neutron production. One possibility is to use the Coulomb explosion mechanism with a deuterium cluster target6,7. In this regime, the atoms of the clusters are entirely ionized by the laser-cluster interaction, which results in prompt explosion due to Coulomb repulsion and the production of the multi-keV ions required to initiate the fusion reactions. Extensive studies have indicated that 2.45 MeV quasi-monoenergetic neutrons can be produced using deuterium cluster targets through reaction (1)8,9,10,11,12. The measured energy spread, determined primarily based on the thermal velocity of the colliding ions, may be 10% or less13. However, when a cluster medium is used, the kinds of nuclear reactions available are restricted because it is impossible to transform all of the reaction materials (such as lithium or beryllium) into the cluster phase. Therefore, an alternative known as the “pitcher-catcher” approach has emerged14,15. In this method, the laser drives an ion beam (typically of deuterium ions) from a primary pitcher target, usually through target normal sheath acceleration (TNSA)16,17. Then, the ions collide with a secondary catcher target, where the nuclear reactions occur. In this way, high-energy neutrons can be obtained through the 7Li (d, n) and 9Be (d, n) nuclear reactions, as in (2)18,19. The laboratory energy E3 of a neutron produced in this way can be expressed as a function of the incident ion energy E1 and the angle θ of the emitted neutron relative to the incident ion, where m1, m2, m3, and m4 are the masses of the incident ion, the target particle, the neutron, and any other associated particles, respectively20,21. Equation (4) indicates that the energy E3 of neutrons produced in the pitcher-catcher regime strongly depends on the incident ion energy E1 and the Q-value of the nuclear reaction. Because the E1 values that can be achieved through the TNSA mechanism (usually tens of MeV) are on the same order as the Q-value, the neutron beams thus produced are not monoenergetic and therefore are not suitable for detector calibration, neutron-induced cross-section studies, or various other specialized applications22,23,24. A novel method termed the “plasma-collider” technique was first applied by our group to enhance the neutron yields via the collision of high density deuterated plasma generated directly from the laser-plasma interaction25,26. This method has ability to produce numerous multi-keV ions participating in the nuclear reactions, although at a very low cross-section. Therefore, this method has enormous potential to be used to precisely calculate the cross-sections of 7Li (d, n) nuclear reactions because the incident ions are at the multi-keV level. It also has great potential to increase the probabilities of nuclear reactions induced in head-to-head collisions of plasma streams. In addition to these advantages, because E1 is several keV and this is negligible compared with the Q-value (on the order of MeV), equation (4) can be simplied as follows: In this regime, the energy of the neutrons is determined simply by the Q-value of the nuclear reaction, and 13.3 MeV monoenergetic neutrons can be generated via 7Li (d, n) nuclear reactions. These 13.3 MeV neutrons can serve as a new type of laser-driven monoenergetic neutron source, in addition to 2.45 MeV and 14.1 MeV neutrons that can be produced through d (d, n) and d (t, n) nuclear reactions, respectively. In this letter, we present new studies of the production of monoenergetic neutrons from laser-driven K-shaped D-Li target. The “plasma-collider” method was used to significantly increase the numbers of incident d and Li ions at the keV level. Experimental and theoretical methods were used to verify the production of 13.3 MeV monoenergetic neutrons via 7Li (d, n) nuclear reactions.