Laser-Driven Neutron Generation Realizing Single-Shot Resonance Spectroscopy

Abstract

Neutrons are powerful tools for investigating the structure and properties of materials used in science and technology. Recently, laser-driven neutron sources (LDNS) have attracted the attention of different communities, from science to industry, in a variety of applications, including radiography, spectroscopy, security, and medicine. However, the laser-driven ion acceleration mechanism for neutron generation and for establishing the scaling law on the neutron yield is essential to improve the feasibility of LDNS. In this paper, we report the mechanism that accelerates ions with spectra suitable for neutron generation. We show that the neutron yield increases with the fourth power of the laser intensity, resulting in the neutron generation of3×1011in4πat a maximum, with1.1×1019Wcm−2, 900 J, 1.5 ps lasers. By installing a “hand-size” moderator, which is specially designed for the LDNS, it is demonstrated that the efficient generation of epithermal (0.1–100 eV) neutrons enables the single-shot analysis of composite materials by neutron resonance transmission analysis (NRTA). We achieve the energy resolution of 2.3% for 5.19-eV neutrons 1.8 m downstream of the LDNS. This leads to the analysis of elements and isotopes within sub-μstimes and allows for high-speed nondestructive inspection.

Alternate abstract:

Plain Language Summary

Neutrons are a powerful tool for investigating the structure and properties of materials. Ultracompact laser-driven neutron sources (LDNS) are attracting interest as the next-generation neutron source after nuclear reactors and accelerator-based facilities. However, understanding the laser-driven ion acceleration mechanism for neutron generation and establishing the scaling law on the neutron yield are essential to improve the feasibility of LDNS. Here, we report on the mechanism that accelerates ions with spectra suitable for the neutron generation and identify how neutron yield changes with laser power.

We focus a laser on a foil of deuterated polystyrene. This generates a plasma that sources and accelerates ions, which in turn bombard a block of beryllium that acts as the neutron source. By measuring the ion spectra, we identify distinct rates of expansion of different ion species, which play a key role in the formation of the ion field. We also find that the neutron yield increases with the fourth power of the laser intensity on the target, which offers a guideline for eventually increasing the neutron flux.

Finally, we demonstrate single-shot analysis of composite materials by neutron resonance transmission analysis. With an energy resolution of 2.3% nearly 2 m from the LDNS, this leads to the analysis of elements and isotopes in less than a microsecond, allowing for high-speed nondestructive inspection.