Persistence of uranium emission in laser-produced plasmas

Abstract

Detection of uranium and other nuclear materials is of the utmost importance for nuclear safeguards and security. Optical emission spectroscopy of laser-ablated U plasmas has been presented as a stand-off, portable analytical method that can yield accurate qualitative and quantitative elemental analysis of a variety of samples. In this study, optimal laser ablation and ambient conditions are explored, as well as the spatio-temporal evolution of the plasma for spectral analysis of excited U species in a glass matrix. Various Ar pressures were explored to investigate the role that plasma collisional effects and confinement have on spectral line emission enhancement and persistence. The plasma-ambient gas interaction was also investigated using spatially resolved spectra and optical time-of-flight measurements. The results indicate that ambient conditions play a very important role in spectral emission intensity as well as the persistence of excited neutral U emission lines, influencing the appropriate spectral acquisition conditions.

Spatio-temporal evolution of uranium emission in laser-produced plasmas

“…The lack of improvement in S/B ratio could be partly related to the significant rise in background continuum at higher pressures. However, our recent results of U line emission S/B ratios in Ar ambient showed a factor of 4× increase with the addition of Ar ambient gas [13]. This indicates that the nature of…”

“…The persistence data are obtained at a distance 4 mm from the target surface. For the purpose of comparison, the persistence data for U I emission at various Ar ambient pressures are also given, taken from LaHaye et al [13]. Comparing the persistence data obtained in air and Ar ambient environments, it can be seen that the emission persists at significantly longer times in an Ar ambient environment compared to air.…”

“…The persistence data are obtained from OTOF profiles when the intensity drops to 1/e 2 . For comparison purpose, the persistence data for U I emission at various Ar ambient pressures are also given, taken from LaHaye et al [13] According to Eqn. (1), the U emission intensity is determined by both the U atomic number density and the excitation temperature, both of which have strong temporal and spatial variations.…”

“…and environmental factors (nature and pressure of the ambient gas). Recently LaHaye et al [13] reported the emission properties and persistence of U in ambient Ar environment. However, laser ablation plume expansion into inert ambient conditions is less complex compared to their expansion in the presence of a reactive gas like air.…”

“…LA-Laser Absorption Spectroscopy (LA-LAS) is an extremely sensitive method capable of probing elemental as well as isotopic ground and excited state populations [4,5]. LA -Optical Emission Spectroscopy (LA-OES), commonly called Laser Induced Plasma Spectroscopy (LIPS) or Laser Induced Breakdown Spectroscopy (LIBS), provides another dimension to LA-hyphenated techniques in nuclear forensics where light emission from the plasma plume is analyzed [6][7][8][9][10][11][12][13][14].…”