Generation of high-energy (>15 MeV) neutrons using short pulse high intensity lasers

Abstract

A roadmap is suggested and demonstrated experimentally for the production of high-energy (>15 MeV) neutrons using short pulse lasers. Investigation with a 3D Monte Carlo model has been employed to quantify the production of energetic neutrons. Numerical simulations have been performed for three nuclear reactions, d(d,n)3He, 7Li(d,n)8Be, and 7Li(p,n)7Be, driven by monoenergetic ion beams. Quantitative estimates for the driver ion beam energy and number have been made and the neutron spectra and yield in the ion propagation direction have been evaluated for various incident ion energies. In order to generate neutron fluence above a detection limit of 106 neutrons/sr, either ∼1010 protons with energy 20–30 MeV or comparable amount of deuterons with energy 5–10 MeV are required. Experimental verification of the concept with deuterons driven by the Titan laser (peak intensity 2 × 1019 W/cm2, pulse duration of 9 ps, wavelength 1.05 μm, and energy of 360 J) is provided with the generation of neutrons with energy of up to 18 MeV from 7Li(d,n)8Be reactions. Future research will focus on optimized schemes for ion acceleration for production of high-energy neutrons, which will involve efficient target design, laser parameter optimization, and converter material.

Generation of high-energy neutrons with the 300-ps-laser system PALS

“…Sorting of the peaks in the scintillation detector signals indicates that the repetitive bursts observed in the emission of fast ions in sub-nanosecond laser-solid experiments [22] may give rise to bursts in emission of fast neutrons generated via the beam-target 7 Li(d, n) 8 Be reaction. Clear evidence is given by the observed well-separated maxima, for example at 52 and 59 ns in the N1 signal, and also at 60 and 78 ns in the N4 signal, that correlate well with the peaks of 200 and 400 keV deuterons appearing in the time dependence of the ion charge density (see Figure 2(b)).…”

“…Only a minority of them can reach ∼16 MeV energy. The maximum neutron yield from both the primary and secondary reactions was 3.5×10 Li(d, n) 8 Be reactions can be estimated from the scintillation detector signal, by taking into account the dependence of the scintillation intensity on the energy deposited by neutrons. If we consider the solid angle of the expanding plasma plume containing the fast deuterons [25] reduced by the solid angle of the laser beam, because the deuterons are emitted from the front target surface, the possible maximum yield could be as high as Y D-Li,max ∼ 2 × 10 [7] .…”

“…The dependence of neutron energy on the energy of deuterons and on the direction of observation is shown in Figure 4. Figure 5 shows the arrival time of neutrons, t N , related to the time of the beam-target interaction, which is the sum of the time of flight TOF D of deuterons to the catcher LiF target and the time of flight N-TOF D-Li of 7 Li(d, n) 8 Be neutrons from the LiF target to the scintillation detectors: Figure 6 shows the scintillation detector signals observed at five different distances and directions N1 to N5 with respect to the mean direction of deuterons impinging on the LiF target (see Figures 1 and 4). Using the dependence of the arrival times of neutrons on the energy of deuterons, E D , we can interpret individual maxima or partial peaks in the scintillation detector signals.…”

“…These beams hitting a secondary target can create high-energy neutrons through, for example, D(d, n) 3 He, 7 Li(p, n) 7 Be, 7 Li(d, xn) 8 Be, 9 Be(p, n) 5 9 B, and 9 Be(d, n) 5 10 B nuclear reactions [2][3][4][5][6][7][8][9][10][11][12][13][14][15] . Fast neutrons with energies in excess of 10 MeV resulting from the 7 Li(d, xn) 8 Be reaction (Q = 15.03 MeV) have been reported by several authors [6][7][8][9][10][11] . Acceleration of deuterons is mostly reported in experiments using lasers with intensities of 10 19 W cm −2 .…”

Enhanced laser absorption from radiation pressure in intense laser plasma interactions

“…2 ). Laser-solid interactions at these intensities have many interesting applications including laser-driven ion acceleration, extreme ultraviolet and x-ray generation, and neutron generation [3][4][5][6][7].…”