Characterizing laser-plasma ion accelerators driving an intense neutron beam via nuclear signatures

A Favalli,D Henzlova,K D Ianakiev,D C Gautier,M T Swinhoe,M Iliev,S Palaniyappan,M Roth,J C Fernandez,S Croft,K Falk,N Guler

doi:10.1038/s41598-019-39054-z

Abstract

Compact, bright neutron sources are opening up several emerging applications including detection of nuclear materials for national security applications. At Los Alamos National Laboratory, we have used a short-pulse laser to accelerate deuterons in the relativistic transparency regime. These deuterons impinge on a beryllium converter to generate neutrons. During the initial experiments where these neutrons were used for active interrogation of uranium and plutonium, we observed β-delayed neutron production from decay of 9Li, formed by the high-energy deuteron bombardment of the beryllium converter. Analysis of the delayed neutrons provides novel evidence of the divergence of the highest energy portion of the deuterons (i.e., above 10 MeV/nucleon) from the laser axis, a documented feature of the breakout afterburner laser-plasma ion acceleration mechanism. These delayed neutrons form the basis of non-intrusive diagnostics for determining the features of deuteron acceleration as well as monitoring neutron production for the next generation of laser-driven neutron sources.

Highlights

Intense laser-driven ion beams have been the subject of considerable study for over a decade[1,2]
We show that in this case, this feature is much more pronounced than previously thought based on limited measurements with ion spectrometers. (3) 9Li β-delayed neutrons have been identified as a source of delayed-neutron background that must be taken into account in the design of the new generation of laser-driven neutron sources for application such as assay of nuclear materials[6,7]
Two 3He thermal neutron coincidence well counters were placed outside the chamber for the detection of β-delayed neutrons, following neutron-induced fission, from active interrogation of nuclear material

Summary

Introduction

Intense laser-driven ion beams have been the subject of considerable study for over a decade[1,2]. By exploiting advanced mechanisms of laser-driven ion acceleration, a new intense and short-duration neutron source with record flux (>1010 n/sr)[3,4] has been demonstrated at the Trident laser facility at Los Alamos National Laboratory (LANL)[5] In these experiments, neutrons are generated from a multistep process starting with the interaction of a short-pulse laser with a deuterated-plastic nanofoil target to make an intense beam of protons and deuterons. Intense neutron burst offers the potential of achieving a high signal-to-noise ratio in difficult environments (e.g., with high neutron background emitted by the interrogated item) and promises a short assay time, which translates to a high interrogated item throughput This application, known as active interrogation, is based on the measurement of induced neutron signatures to identify/assay nuclear materials during (detecting prompt fission neutrons) and after (detecting delayed neutrons from fission products) an interrogation with an external neutron pulse[18,19]. During these groundbreaking experiments at the Trident[5] laser facility, delayed neutron production from 9Li decay

Methods

Results

Conclusion