PNNL

Abstract

Laser-produced plasma (LPP) coupled with optical emission spectroscopy is a promising technique for detecting certain isotopes, and it provides unique capabilities such as standoff and rapid detection with minimal to no sample preparation requirement. The key figures-of-merit for isotopic analysis using optical spectroscopy tools is the linewidth relative to isotope shift. Although the isotopes of hydrogen (1H, 2H, and 3H) possess large isotopic shifts (1H-2H ˜ 180 pm, 1H-3H ˜ 240 pm), being a light element, the H transitions are susceptible to various broadening mechanisms in the plasma environment. One of the critical parameters that influences the linewidth of a transition in an LPP is the incident laser energy. In the present study, we evaluated the role of laser energy on plume expansion dynamics, deuterium emission intensity, and linewidth in a laser-produced Zircaloy-4 plasma. The plasma was generated by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser onto a Zircaloy-4 target. The variation in 2H emission intensity and linewidth were investigated for varying laser fluence and time after the plasma onset. Spatially-resolved and spatially-integrated optical emission spectroscopy were performed and compared to investigate the emission spectral features and linewidth of 2Ha. Monochromatic 2-dimensional time-resolved imaging was also performed to understand the morphology of the deuterium and protium emission relative to all species in the plume. Our results showed that 1Ha, and 2Ha emission predominantly occur closer to the target. Measurements of 2Ha linewidth approached similar values at later times of plasma evolution regardless of the laser energy. The linewidths of the 2Ha transition showed insignificant differences for spatially-resolved and spatially-integrated measurements.