Unexpected observation of ion suppression in a liquid chromatography/atmospheric pressure chemical ionization mass spectrometric bioanalytical method

Ion suppression is a well-known phenomenon in electrospray ionization (ESI) mass spectrometry. These suppression effects have been shown to adversely affect the accuracy and precision of quantitative bioanalytical methods using ion spray. Such suppression effects have not been as well defined in atmospheric pressure chemical ionization (APCI) and there is some debate whether these effects actually occur in the ionization process using APCI. Here an example is described where clear ion suppression was observed during studies on a model compound and three metabolites using APCI liquid chromatography/tandem mass spectrometry (LC/MS/MS).     

Observation of the decay dynamics and instabilities of megagauss field structures in laser-produced plasmas

Monoenergetic proton radiography was used to make the first measurements of the long-time-scale dynamics and evolution of megagauss laser-plasma-generated magnetic field structures. While a 1-ns 10(14) W/cm2 laser beam is on, the field structure expands in tandem with a hemispherical plasma bubble, maintaining a rigorous 2D cylindrical symmetry. With the laser off, the bubble continues to expand as the field decays; however, the outer field structure becomes distinctly asymmetric, indicating instability. Similarly, localized asymmetry growth in the bubble interior indicates another kind of instability. 2D LASNEX hydrosimulations qualitatively match the cylindrically averaged post-laser plasma evolution but even then it underpredicts the field dissipation rate and of course completely misses the 3D asymmetry growth.     

Evidence for stratification of deuterium-tritium fuel in inertial confinement fusion implosions

Measurements of the D(d,p)T (dd) and T(t,2n)(4)He (tt) reaction yields have been compared with those of the D(t,n)(4)He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.     

High-areal-density fuel assembly in direct-drive cryogenic implosions

The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2]. Neutron-averaged areal densities of 202+/-7 mg/cm2 and 182+/-7 mg/cm2 (corresponding to estimated peak fuel densities in excess of 100 g/cm3) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuel adiabat can be accurately controlled under ignition-relevant conditions.     

Radiation chemistry education in Australia

A segment on radiation chemistry should be included in every course on nuclear science because of its unique role and its being relatively far removed from nuclear explosives. Experience of courses at different levels is outlined. Particular attention is given to the use of radiation chemical techniques in the training of postgraduate research students.Honorary AINSE Fellow, formely Post Retirement Fellow, ANSTO Isotope Technology.     

Time-resolved measurements of hot-electron equilibration dynamics in high-intensity laser interactions with thin-foil solid targets

Time-resolved K(α) spectroscopy has been used to infer the hot-electron equilibration dynamics in high-intensity laser interactions with picosecond pulses and thin-foil solid targets. The measured K(α)-emission pulse width increases from ~3 to 6 ps for laser intensities from ~10(18) to 10(19) W/cm(2). Collisional energy-transfer model calculations suggest that hot electrons with mean energies from ~0.8 to 2 MeV are contained inside the target. The inferred mean hot-electron energies are broadly consistent with ponderomotive scaling over the relevant intensity range.     

Applied plasma spectroscopy: Laser-fusion experiments

High-energy-density plasmas created in laser-fusion experiments are diagnosed with X-ray spectroscopy. Hans Griem, considered the father of modern plasma spectroscopy, provided an excellent foundation for this research. He studied the effect of plasma particles, in particular the fast-moving free electrons, on the Stark-broadening of spectral line shapes in plasmas [H. Griem, Phys. Rev. 125 (1962) 177]. Over the last three decades, X-ray spectroscopy has been used to record the remarkable progress made in inertial confinement fusion research. Four areas of X-ray spectroscopy for laser-fusion experiments are highlighted in this paper: Kα emission spectroscopy to diagnose target preheat by suprathermal electrons, Stark-broadened K-shell emissions of mid-Z elements to diagnose compressed densities and temperatures of implosion cores, K- and L-shell absorption spectroscopy to diagnose the relatively cold imploding shell (the “piston”) that does not emit X rays, and multispectral monochromatic imaging of implosions to diagnose core temperature and density profiles. The seminal research leading to the original X-ray spectroscopy experiments in these areas will be discussed and compared to current state-of-the-art measurements.