Ultrashort Pulsed Neutron Source

We report on a novel compact laser-driven neutron source with an unprecedented short pulse duration ($<50\mathrm{ps}$) and high peak flux ($>{10}^{18}\mathrm{n}/{\mathrm{cm}}^2/\mathrm{s}$), an order of magnitude higher than any existing source. In our experiments, high-energy electron jets are generated from thin ($<3\mu \mathrm{m}$) plastic targets irradiated by a petawatt laser. These intense electron beams are employed to generate neutrons from a metal converter. Our method opens venues for enhancing neutron radiography contrast and for creating astrophysical conditions of heavy element synthesis in the laboratory.

Figure 1

Depiction of the experimental setup. The targets are $0.02–3\mu \mathrm{m}$ thick plastic foils.

Figure 2

Electron spectrum measured at a $\theta =14°$ angle with respect to the laser normal. The measurement was performed with the Cu converter removed.

Figure 3

Simulated particle fluence. The accumulated fluence of electrons (left), photons (center), and neutrons (right) projected on the $y\text{−}z$ plane is shown. The edges of the Cu stack are indicated in orange.

Figure 4

Autography of the Cu plates. (a) The autographs are images of the activation level in each plate. Each autograph corresponds to an area of $5.1\mathrm{cm}\times 5.1\mathrm{cm}$. The autographs of the first 7 plates in the stack are shown in each row. (b) The inferred number of neutrons emitted from each plate by the ${}^{63}\mathrm{Cu}(\gamma ,n){}^{62}\mathrm{Cu}$ reaction.

Figure 5

(a) Target thickness dependence of the total number of neutrons generated per laser shot. Values are interpolated from the neutron dose measured using the Bubble dosimeters. (b) Neutron energy spectrum, measured using time-of-flight technique. The signal is the recorded photomultiplier voltage.

Figure 6

The total absorption cross sections for neutrons in carbon (blue), nitrogen (green), and oxygen (red) are shown. The TOF energy resolution for a flight distance of 3.5 m is shown for three example energy values, for the case of 1 ns (pink) and 100 ps (bright green).